studies of the biology and control of the alfalfa blotch

University of Massachusetts Amherst University of Massachusetts Amherst

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Doctoral Dissertations 1896 - February 2014

1-1-1981

Studies of the biology and control of the alfalfa blotch leafminer, Studies of the biology and control of the alfalfa blotch leafminer,

Agromyza frontella (Rondani) (Diptera: Agromyzidae): a pest of Agromyza frontella (Rondani) (Diptera: Agromyzidae): a pest of

Massachusetts alfalfa. Massachusetts alfalfa.

John Thomas Andaloro University of Massachusetts Amherst

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STUDIES ON THE BIOLOGY AND CONTROL OF THE ALFALFA BLOTCH-

LEAFMINER, AGROMYZA FRONTELLA (RONDANI) (DIPTERA: AGROMY-

ZIDAE): A PEST OF MASSACHUSETTS ALFALFA.

A Dissertation Presented

By

John Thomas Andaloro

Submitted to the Graduate School of the

University of Massachusetts in partial fulfillment

Of the requirements for the degree of

DOCTOR OF PHILOSOPHY

September I981

Department of Entomology

STUDIES ON THE BIOLOGY AND CONTROL OF THE ALFALFA BLOTCH-

LEAFMINER, AGROMYZA FRONTELLA (RONDANI) (DIPTERA: AGRO-

MYZIDAE): A PEST OF MASSACHUSETTS ALFALFA

A Dissertation presented

By

John Thomas Andaloro

Approved as to style and content by:

Dr. David N. Ferro Dept. Head Department of Entomology

ii

John T . Andaloro 1981

All Rights Reserved

DEDICATION

This thesis is dedicated to Bridget VJalsh-Andaloro, my wife of two

and a half years, who unselfishly contributed her time in the

preparation of this manuscript. Her continued assurance, enduring

understanding, and friendship throughout my prolonged graduate ordeal

are proof of exemplary marital and Christian love for which I am

grateful.

This thesis is also dedicated to my parents, Mr. and Mrs. Samuel

and Josephine Andaloro, without whose support, encouragement, and pride

my graduate career would never have been undertaken.

iv

ACKNOWLEDGEMENTS

I wish to express my sincere gratitude to Dr. T. Michael Peters

for his guidance, encouragement, and friendship throughout the research

and preparation of this manuscript. I would like to give special

thanks to Dr.*s James B. Kring, Ronald J. Prokopy, Martin E. Weeks and

Roy Van Driesche for their time, assistance, and suggestions in all

aspects of this research.

In addition, the author extends his gratitude to the following

people:

Ms. Robyn Rufner, Electron Microscopy Lab., Univ. of Mass., for

her assistance in the taking of scanning electron microphotographs, the

Feed, Seed, and Fertilizer Lab., West Exp. Sta., Univ. of Mass., for

supplying protein analyses of alfalfa plant material, Alfred Alicandro

and David Cushing for their help in the collection of field data, and

Misters L. Chromak and E. Tidlund for performing ail the necessary

agronomic practices in the maintenance of the alfalfa test plots.

V

ABSTRACT

STUDIES ON THE BIOLOGY AND CONTROL OF THE

ALFALFA BLOTCH LEAFMINER, AGROMYZA FRONTELLA

(RONDANI): A PEST OF MASSACHUSETTS ALFALFA

(September, 1981)

John T. Andaloro, B.S., Rutgers University

M.S., Rutgers University, Ph.D., University of f^ssachusetts

Directed by: Professor T. Michael Peters

Studies were conducted from 1976-1978 to determine the population

dynamics of Agromyza frontella (Rondani) (Diptera: Agromyzidae) and

evaluate a modified harvest manipulation as a cultural control

technj.qua. Three complete generations and a partial fourth were

observed in v/estern Massachusetts with peak larval densities occurring

in early June, mid-July, mid-August, and late September. An average

U76 heat units (base 6.8^C) v/ere necessary for the development of one

generation. The first two ABL larval generations were synchronized

with the first two alfalfa harvest periods when cutting occurred at 105^

bloom. The later generations were less synchronized with time of

harvest, future larvae were commonly found mining 30 to ^10^ of the

alfalfa leaflets during the first two cuttings. Oven-dried leaflets

with at least one blotch mine weighed 8.2^ less than oven-dried unmined

leaflets. There was also a significant reduction in crude

protein/rained leaflet of 0.18 mg, 13.65^ less than unmined leaflets.

Evidence was obtained that indicated postponement of the first two

vi

harvests until after adult ABL egg deposition can reduce densities of

later ABL life stages. However, this practice resulted in unacceptable

crop quality. Older ABL larvae were observed prematurely evacuating

drying leaves. This indicates that if early harvest is to be utilized

as an effective cultural control then it must precede the development

of the third larval instar (most damaging instar), otherwise the

alfalfa must be immediately removed and not be allowed to dry in the

field.

Another cultural control investigated involved the retention of

uncut borders (perimeters) at harvest to serve as insectaries for

biological control agents of ABL. Fields with uncut "perimeters"

(approximately of crop), achieved 13.6^ fewer ABL late larval mines

during the two year study compared to the totally harvested alfalfa in

the control plots. However, increases in populations of Empoasca fabae

(Harris), Acyrthosiphon pisum (Harris), and mirids resulted in fields

where perimeters were retained compared to total harvest fields.

Reductions in alfalfa stem height, weight, and leaf surface area

occurred in these perimeter fields resulting in a yield loss of 631

kg/h, 18.5^ less than the yield of the total cut fields.

Two treatments of a malathion 5EC (0.84 L/h) plus methoxychlor 2EC

(2.2 L/h) mixture/harvest period reduced these herbivore populations

and increased yield by a mean 536 and 510 kg/h/harvest over the

untreated alfalfa in the perimeter and total cut fields respectively.

Fields with unharvested perimeters required insecticidal treatment to

achieve yields comparable to those of unsprayed totally cut alfalfa

vii

fields. Poor plant growth due to herbivore pressure the initial year

of the study was observed to result in reduced harvest yields on first

cutting the following year when cultural or chemical treatments were

not applied.

Results indicate that chemically treated and totally harvested

alfalfa maintained greater stem densities over the two year period than

did no chemical treatments and retaining uncut field portions.

Vlll

TABLE OF CONTENTS

DEDICATION. iv

ACKNOWLEDGEMENT.v

ABSTRACT.vi

LIST OF TABLES.x

LIST OF FIGURES.xi

LIST OF APPENDICES...xii

Chapter I. .1

Chapter II. POPULATION DYNAMICS OF THE ALFALFA BLOTCH LEAFMINER, AGROMYZA FRONTELLA, (RONDANI) AND ITS INJURY TO ALFALFA.

Introduction. Materials and Methods. 5

Results.. Discussion. 19

Chapter III. RETENTION OF ALFALFA CROP PERIMETERS AS REFUGES: IMPACT ON THE ALFALFA BLOTCH LEAFMINER, AGROMYZA FRONTELLA (RONDANI), OTHER SELECTED INSECTS AND CROP GROWTH.

Introduction.25

Materials and Methods. 27

Results... Discussion..

BIBLIOGRAPHY..

APPENDIX..

ix

LIST OF TABLES

Chapter II.

1. Comparison of protein content and dry weight between paired basal alfalfa leaflets...20

2. Protein loss in alfalfa leaflets due to ABL larval feeding.21

Chapter III.

3. Total number of selected insect species collected from culturally and chemically treated alfalfa. ^1

4. Alfalfa stand densities of experimental research plots.55

Appendix

5. A comparison of oven dried leaf weights and total leaf area among perimeter and total cut plots.94

6. Comparison of leaf weights as a percent of total stem weights am.ong culturally and chemically treated experimental plots. ..95

7. Cost/Benefits of alfalfa perimeter retention and chemical control of insect pests based on optimal stand density. 95

I

X

LIST OF FIGURES

Chapter II,

1, Seasonal occurrence of ^ frontella and crop develop¬ ment under a 4 harvest regime in 1977.

2, Seasonal occurrence of ^ frontella and crop develop¬ ment under a 3 harvest regime in 1977.

3, Seasonal occurrence of ^ frontella and crop develop¬ ment under a ^ harvest regime in Franklin Cty, 1978...15

4, Seasonal occurrence of frontella and crop develop¬ ment under a 4 harvest regime in Hampshire Cty, 1978.17

Chapter III.

5, Experimental plot design for studies on the effect of uncut crop borders upon alfalfa insects.29

6, Comparison of the total number of ABL mines and blotch mines/stem within unsprayed plots between perimeter and total cut fields...35

7, Effect of chemical and cultural control treatments on Empoasca fabae adults, Acyrthosiphon pisum adults and immatures, Lygus spp, adults, and other mirid adults and immatures.38

8, Effect of 1977 chemical and cultural control treatments on total alfalfa dry weight/25 stems,....44

9, Effect of 1978 chemical and cultural treatments of total alfalfa dry weight/25 stems at first harvest.46

10. Effect of 1978 chemical and cultural control treatments on total alfalfa dry weight/25 stems at second, third and fourth harvests. i\Q

11. Differences in net monetary return/h/season due to cultural and chemical control treatments.53

xi

Appendix

12, Seasonal life history of the alfalfa blotch leafminer, Agromyza frontella on harvested alfalfa.....bS

13. Spatial distribution of ^ frontella eggs at specific alfalfa stem heights.71

14. Seasonal occurrence of ^ frontella and crop development under a 4 harvest regime in Deerfield, Ma. 1977.73

15. Dorsolateral view of partially everted female A. frontella postabdominal structure.76

16. Dorsolateral view of ^ frontella ovipositor at early stage of eversion. 78

17. Dorsolateral view of ^ frontella ovipositor at intermediate stage of eversion.80

18. Nearly complete eversion of ^ frontella ovipositor.82

19. Lateral view of completely everted A. frontella ovipositor showing elongated egg laying structure on right.84

20. Oviposit ion puncture on underside of alfalfa leaflet.86

21. Comparison of 1978 peak mean ABL third instars/stem within unsprayed plots between per^imeter and total cut fields just prior to each harvest...88

22. Comparison of mean alfalfa heights from sprayed and unsprayed plots between perimeter and total cut fields at second, third, and fourth harvest periods in 1977.90

23. Comparison of alfalfa heights from sprayed and unsprayed plots between perimeter and total fields at first, second, third, and fourth harvest periods in 1978.

• •

Xll

CHAPTER I

STUDIES ON THE BIOLOGY AND CONTROL OF THE ALFALFA BLOTCH LEAFMINER,

AGROMYZA FRONTELLA (RONDANI) (DIPTERA:AGROMYZIDAE): A

PEST OF MASSACHUSETTS ALFALFA.

The alfalfa blotch leafminer (ABL), Agromyza frontella, was first

detected in Massachusetts in 1968 (Miller and Jensen 1970). It has

since spread westward to Ohio, southward to Virginia, and northward to

the Canadian provinces of Ontario, Quebec, and the Maritimes

(Hendrickson and Barth 1978a; Bereza 1977).

The taxonomy of the insect has been reviewed by both Spencer

(1973) and Steyskal (1972). Biological aspects of A. frontella in

Europe (Durseau and Jeandel 1977) and the United States (Mellors and

Helgesen 1978; Hendrickson and Barth 1978b) have also been studied.

A. frontella is widespread in Europe (Spencer 1973), but at low

population levels with rare localized outbreaks (Bollow 1955). This

has been attributed to the effectiveness of control by natural enemies.

In northeastern U.S. the ABL is considered to be an occasional pest

(Hendrickson and Barth 1978a). Reported economic losses due to larval

feeding have been estimated at $0.2 million in Quebec, in 1975 (Richard

and Gagnon 1976) and at $9/acre in Connecticut 1969-1970 (anonymous

1972).

Plants are damaged by the feeding punctures of adults (pinholing)

(Helgesen and Baxendale 1978; Durseau and Jeandel 1977) and leaf mining

of larvae (Hendrickson and Barth 1978a; Bereza 1977; Bollow 1955).

Byers and Valley (1978) have developed a tentative economic threshold

1

2

for the ABL which indicates that when approximately 22? of all alfalfa

leaflets are infested with at least one blotch mine protein loss

occurs.

Parasitism of ABL in the northeast by native species is minimal,

although season long parasitism rates of up to 36? have been reported

(Hendrickson and Barth 1979). It is believed that these native

parasites have switched over to ABL from native agromyzids, Liriomyza

trifoliearum spencer and L. trifolii. also found on alfalfa. A

possible reason for the occurrence of low levels of parasitization may

be due to the typical alfalfa harvesting practices. Harvesting removes

appreciable numbers of ABL infested leaflets in which immature

parasitoids are developing on the host larvae. Unparasitized third

instar larvae normally escape these harvesting dangers because they

have already abandoned their mines at maturity to pupate in the soil

prior to harvest. Similar occurrences were observed on Liriomyza spp.

leafminers and their parasites in California alfalfa (Jensen and

Koehler 1970),

The alfalfa blotch leafminer has not been studied in Massachusetts

since its presence was originally reported. Information on the extent

of larval mining damage, seasonal occurrence, and control strategies on

Massachusetts alfalfa needed to be collected and analyzed. This thesis

study was, thus, initiated to determine the population dynamics of A.

fronts and the relationship of ABL larval feeding to leaf weight and

protein loss. In addition, a form of modified alfalfa harvesting that

left uncut crop perimeters as a refuge to harbor beneficial-insects and

their hosts was also evaluated. Insect and plant responses to this

cultural control method were compared to conventional insecticidal

control methods.

CHAPTER II

POPULATION DYNAMICS OF THE ALFALFA BLOTCH LEAFMINER,

AGROMYZA FRONTELLA (RONDANI), AND ITS INJURY TO ALFALFA

Introduction

Agromyza frontella, (Rondani), alfalfa blotch leafminer (ABL), was

first recorded in western Massachusetts in 1968 (Miller and Jensen

1970). By 1979, A. frontella adults constituted 63/^ of the insects

swept all season from alfalfa in central and western Massachusetts

(Miller and Shaw 1969). Rapid spread throughout the northeast and

Canada quickly followed (Hendrickson and Barth 1978, Harcourt 1973) and

reached epizootic proportions in many locales.

A. frontella is widespread in Europe (Spencer 1973), but maintains

low population levels and outbreaks are localized and rare (Bollow I

1955). This has been attributed to effective natural control. In

northeastern United States, 14 species of native parasites have been

recovered from A. frontella. They have been reported parasitizing an

average 36^ of the leafminer population throughout the season

(Hendrickson and Barth 1979). It is believed that the native parasites

of the agromyzids Liriomyza trifoliearum Spencer and L. trifolii, also

found on alfalfa, have adapted to the ABL.

A. frontella is considered an occasional economic pest of

northeast alfalfa (Mellors 1979; Hendrickson and Barth 1978). Economic

losses due to larval feeding have been estimated at 0.2 million dollars

in Quebec, Canada in 1975 (Richard and Gagnon 1976) and at 9

dollars/acre in Connecticut 1969-1970 (Anonymous 1972).

A

5

Adults damage plants in the form of punctures, termed pinholing

(Helgesen and Baxendale 1978; Durseau and Jeandel 1977), for the

purpose of feeding on exuded sap. Such adult pinholing and larval

feeding have been described (Hendrickson and Barth 1978; Bereza 1977).

Byers and Valley (1978) have indicated that when approximately 22% of

the alfalfa leaflets are infested with at least one blotch mine,

significant protein loss occurs.

The extent of damage by ABL larval mining and the insect’s

population dynamics in Massachusetts have not been previously examined.

The present study was initiated to determine the seasonal occurrences

and lix’e history of A. frontella’s life stages in western Massachusetts

and to determine the relationship of ABL larval feeding to leaf weight

and protein loss.

Materials And Methods

Experimental plots. Seasonal ABL activity was studied on commercial

and university alfalfa fields in Franklin and Hampshire Counties, MA.

In 1976, 5 commercial fields were sampled weekly from July to

September. In 1977, if commercial fields in Conway (Franklin County),

elevation 500 feet, and 4 university research fields in Deerfield

(Franklin County), elevation 60 feet, were sampled weekly for A.

fVont^ life stages. Commercial fields were in close proximity to

one another and harvested 3-4 times depending on grower preference.

University fields were harvested 4 times. The first 3 harvests of the

6

latter were made when the alfalfa was in approximately 10^ bloom. By

this time many mature ABL larvae had already pupated in the soil,

thereby escaping the hazards of harvest. The fourth harvest occurred

in early to mid-October, after the first killing frost, regardless of

alfalfa height.

In 1978, ABL life stages were monitored approximately weekly in

the same ^ Deerfield plots and every 2-3 days in an Amherst (Hampshire

County) field. The harvesting scheme in both Deerfield and Amherst in

1978 was the same as for the 1977 Deerfield plots. Alfalfa stands at

all sites were 1-3 year old Saranac AR or Saranac varieties.

Sampling adults. Adults preferentially alight on the leaf tips of

alfalfa stems to feed and oviposit (Bremer 1976). When disturbed, they

make short flights to adjacent stems. This makes sweep net sampling

appropriate for estimating relative densities of A. frontella adults

despite limitations reported by other authors for other pests

(Southwood 1966; Cothran and Summers 1972). Samples consisted of 10

sweeps per site with a standard 30.1 cm dia sweep net with a 0.9m long

handle swung in a I80 degree arc through the top 20-25 cm. of alfalfa

growth. Five sites per field were sampled.

Sampling larvae. A fixed sample of 20 stems/field was randomly

selected along a diagonal transect with stems cut at ground level. The

fixed sample size was a compromise between acquiring more accurate

estimates of ABL immature stages in the higher densities and less

accurate estimates for low densities.

7

In the larval census, stems were sampled weekly at all sites,

except Amherst, where stems were taken every other day. For each stem,

the height, number of leaves, and number of mines were recorded. Mines

were divided into specific categories and used to determine specific

age classes of ABL immatures. Mining by the first and second instars

account for linear or early mines. These mines rarely exceed 4.2 mm

and 9 mm respectively in length (Hendrickson and Barth 1978). The

third instar widens the mine into the characteristic comma-shaped

blotch. The category of mature mines was further divided into

abandoned mines and mines still occupied by third instar larvae.

Host Injury Measurement. The "opposite leaflet" technique (Byers and

Valley 1978) was utilized to assess leaf weight and percent protein of

infested and non-infested leaflets. This assay treats the two basal

leaflets of an alfalfa leaf as exact duplicates. Comparative

measurements can then be made when one of the basal leaflets contained

a blotch mine and the other did not. Weight and percent protein

content of uninfested basal leaflets of alfalfa, oultivar Saranac AR,

was acquired by selecting uninfested basal leaflets from field grown

alfalfa. Two samples of 250 paired leaflets each were dried at 22

degrees C for 36h, weighed, and then analyzed for percent crude protein

by the Kjeldahl method (Horwitz 1970). Comparisons between samples

showed little differences in dry weight and only an average 0.17%

difference in crude protein. Therefore, this analysis was used on H

replicates of 250 paired trifoliolates (leaflets) each to determine

protein content and leaf weight. Each leaf had one basal leaflet with

8

at least 1 blotch mine and an opposite leaflet not infested. During

the drying process, those few larvae which still occupied the blotch

mine abandoned it and thus, did not interfere with the protein

analysis.

Results

■Seasonal phenology of A. frontella. During the 3 year period of this

study, ABL completed 3 generations per season in western Massachusetts

(Figs. 1, 3, ^). Adults from overwintering puparia appeared in

mid-May. The first larval generation extended into mid-June and ended

when mature third instar larvae abandoned their mines at the first

harvest (10^5 bloom). First generation adults were present in June and

their progeny began pupation in early to mid-July. Second generation

adults occurred through late-July and August and the ensuing third

generation larvae continued development into September. A partial

fourth generation also occurred, but larval development was protracted

and larvae eventually died due to the cooler fall vreather.

Harvesting regimes and population dynamics. The comparative effects of

different alfalfa harvest regimes on ABL larval population dynamics are

depicted in Figs. 1 and 2. First harvest of Conway I alfalfa (Fig. 1)

in early June, interfered with the majority of third instar larvae

completing development. At first harvest, an average of 5 abandoned

mines/stem was recorded. At Conway II (Fig. 2), a delay in harvest of

9

Fig. 1. Seasonal occurrence of A. frontella and crop development

under a 4 harvest regime. Conway, Franklin Co., MA, 1977. For sample

means, n=20.

Mea

n N

o. M

ines

/Ste

m

10

15 30 MAY

11

Fig. 2. Seasonal occurrence of A. frontella and crop

under a 3 harvest regime. Conway, Franklin Co., MA, 1977.

means, n=20.

development

For sample

80-

60

O) X

E a>

*^'g40l-

1-20

40-

E (U

Co «/) <D

C

O Z c o 0) 5

30-

20

10

Conway 11-1977 j p pearly mines (1,2 inst.) j

r A:—-Alate mines (3 inst.)

0— abandoned mines

I i

15 30 MAY

HA

RV

EST

2

13

two weeks resulted in a seven fold increase in abandoned mines over

that of Conway I. Initiation of first generation adult emergence

occurred in both fields the third week of June. At this time, regrowth

of alfalfa in Conway I had already achieved an average height of 20 cm,

due to the early cutting, whereas the later cut Conway II field was

still in stubble. The number of abandoned raines/stem that occurred in

Conway I during the second, third, and fourth harvest periods, despite

an early first harvest, was 22, 15, and 7 respectively. The timing of

the second and third harvests were favorable for larval development and

mine abandonment. Post harvest alfalfa in Conv^ay I was in the stubble

stage as the majority of leafminers pupated in the soil. Subsequent

fly emergence and oviposition then occurred in synchrony with new

growth of alfalfa. Conversely, in Conway II, second generation flies

oviposited on mature alfalfa which was harvested late in mid-August.

This late harvest terminated a large number of developing third

generation larvae resulting in insignificant levels of fourth

generation larvae on the third cutting. When fields are harvested in a

timely manner, third generation larvae are found in third cutting

alfalfa.

^^glglilI£,.^^equenGy and population dynamics. In 1978, the population

tr ends of both ABL adults and immatures were observed in Deerfield

(Fig. 3) and in Amherst (Fig. 4). Sampling of ABL life stages occurred

weekly in Deerfield and every 2-3 days in Amherst. Both fields were

harvested four times on approximately the same dates.

Sampling ABL lifestages every 2-3 days resulted in highly detailed

14

Fig. 3. Seasonal occurrence of A frontella and crop development

undsr a. 4 harvast ragiina. Deerfield, Franklin Co., MA, 197B. For

sample means, n=20.

Mea

n N

o.

Min

es/S

tem

Mea

n S

tem

Hgt

. (c

m)

15

/

100

80

60

40

20

40

30

Deerfield -1978

O early mines (1,2 inst.)

.‘A late mines (3 inst.) •-• abandoned mines A-A adults

B i 300

200

100 1

\ 1

CN CO

to Uj

\ •

K- »—

>

< a:

\ % \ QC

< X

1 A Uj > Q£ < X

1

Mean

N

o.

16

Fig. 4. Seasonal occurrence of A. fronted and crop developmen

under a 4 harvest regime. Amherst, Hampshire Co., MA, 1978. For

sample means n=20.

SEP

Mean N

o.

Adu

18

data (Fig. 4), but involved four times as many samples during the first

harvest period and approximately three times as many in the second and

third periods compared to a weekly sampling scheme. Small changes in

ABL density were more noticeable in the Amherst field where more

frequent samples were taken. At Deerfield (Fig. 3), initial emergence

of adults may have been missed by weekly sampling during the first

three harvest periods. Consequently, peak adult occurrences in both

harvest periods 1 and 2 are questionable since the level prior to the

first sampling date is unknown. The same situation arose while

sampling for early mines in Deerfield, during the first harvest.

Regardless, weekly sampling of adults and immatures in Deerfield gave

accurate indications of population trends within each harvest period

compared to similar trends achieved by more frequent sampling at

Amherst. Sampling frequency has little effect on the accuracy of the

number of abandoned mines detected since they essentially remain

unchanged, or may slightly decrease due to dehiscence of leaves, and

thus, are accumulative once larval evacuation occurs.

Developmental heat units. Heat units (base 6.8^ C) (Hendrickson and

Barth 1978) were accumulated throughout 1977 and 1978 according to

Arnold (I960) and correlated to the developmental time of the first 3

ABL generations. In 1977, a generation was determined as time between

first appearance of first larval instars of 1 generation to first

appearance of first larval instars of the next generation.

Approximately ^59 heat units accumulated for completion of the first

generation, and 525 and 500 for the second and third respectively. In

19

1978, heat units were totaled for each generation starting at first

appearance of eggs until first appearance of adults. The thermal units

accumulated during development of first, second, and third generations

in 1978 were 468, 450, and 455 respectively.

Effects of larval feeding. Mean comparisons of weight and percent

protein content of paired basal leaflets, one containing a blotch mine

and one unmined are presented in Table 1. Unmined leaflets weighed

8.2^ more than mined leaflets. A significantly lower percentage of

protein was found in mined leaflets (27.2) than in unmined leaves

(30.7), giving a 3.55^ loss. To find the actual crude protein

CP/leaflet in rag, the mean dry weight/leaflet was multipled by the

percent protein content. Table 2 lists the average CP/leaflet and the

difference in CP between unmined and rained leaflets per replicate. The

average CP loss for four replicates was O.I8 mg/leaflet or 13.8^.

Discussion

The data from this three year study indicate that the generations

of j^fomyza frontella appear synchronous with the growth periods of

alfalfa under a four harvest regime. This may be attributed to the

normal developmental time of an ABL generation of 36, 31, and 27 days

at 20, 23, and 26 C respectively (Hendrickson and Barth 1978) which

closely relates to the time temperature requirements for an alfalfa

harvest period. The lack of overlap between generations may also be

due to the harmful effects of harvesting on ABL life stages. Removal

TABLE 1

Comparison of protein content and dry weight between paired basal alfalfa leaflets.^

Mean^ Dry Wt/leaflet (mg) Protein Content (%)

Unmined A.40± 0.

Mined^ 3a 4.04± 0.4a

Uninined 30.7± 3.4a

Mined^ 27.2± 0.9b

Means followed by different letters indicate a significant difference at the P = 0.01 level.

Average of four replicates; one replicate = 250 pairs of basal leaflet.

Blotch Mine either complete (abandoned) or near complete (containing mature larvae) .

TABLE 2

Protein loss in alfalfa leaflets due to ABL feeding.

Crude Protein/Leaflet

Unmined Mined Difference Crude Protein Loss/Leaflet (%)

1.3±0.05a 1.12+0.08b 0.18±0.04 13.8%

Crude Protein/Leaflet = dry wt/leaflet x protein content (%).

Means followed by different letters indicate a significant difference at the P = 0.01 level.

22

of alfalfa canopy exposes the soil to direct ■mlight and results in

increased soil temperatures with decreases in soil moisture (Pinter et

al 1975). These conditions speed pupal development beyond the rate

which occurs under a canopy cover (Bremer 1976) and may also reduce

pupal survival due to harsh conditions.

Reduction of A. frontella populations appears to be an attainable

goal for alfalfa producers. Insecticidal control of ABL has proven to

be effective, but unacceptable for economic and environmental reasons

particularly because of the interference with the natural enemies which

exists between the alfalfa weevil Hypera postica (Gyllenhal) and its

natural enemies. However, the use of cultural controls would be less

costly, more advantageous to the stability of other alfalfa insect

complexes, and more acceptable to the grower. An effective cultural

control of ABL involves early harvest of alfalfa (Bremer 1976) which

removes large numbers of immatures from the field along witn the plant

matter. In this study, the first harvest of Conway I (Fig. 1) was

assumed to be too la.te to reduce the subsequent second larval

generation. Observations in the laboratory on the ability of older

larvae to evacuate their mines and form puparia either because of loss

of turgor or temperature change indicate that many nearly mature larvae

may escape the adverse effects of harvest. This phenomenon probably

also occurs in the field after alfalfa is cut and left to dry. Thus,

early harvest of alfalfa for leafminer control is not only to achieve

maximum yield of crop, but may be ineffective unless it is implemented

prior to the appearance of third instars (blotch mines), particularly

since it is this stage which causes the majority of damage.

23

Conversely, delaying first and second harvests as occurred at Conway II

(Fig. 2) results in minimal shelter for emerging first generation flies

and in the removal of newly laid eggs and young larvae of the third

generation. Late harvest is a less acceptable method of cultural

control due to the reduction of alfalfa quality and the loss of

dehisced lower leaves during post bloom.

Predicting the general time of ABL occurrence through v;eather

measurements could aid in the optimal sampling of ABL adults. The

average number of ambient thermal units, base 6.8^ C, accumulated from

the field in 1977-78 was found to be similar to the 484 heat units

reported by Hendrickson and Barth (1978) for laboratory reared flies.

Such consistency indicates the use of thermal unit accumulations as an

adequate tool for use in forecasting ABL generations. Since the

immature ABL spends approximately two-thirds of its time pupating in

the soil, acquiring thermal units based on soil temperatures may be

more accurate in predicting adult emergence.

Although A. frontella is considered an occasional economic pest of

alfalfa, studies comparing yields of alfalfa treated with insecticides

have shown no significant yield increases (MacCollom et al 1980, Byers

and Valley 1978), The results of our experiment indicated that oven

dried leaflets infested with one or more blotch mines weighed 8.2?^ less

than uninfested leaflets. We also found an average 13.8^ reduction in

protein content/infested leaflet which concurs with the results of

Byers and Valley (1978). This may represent potential economic loss,

if many leaves have mines, assuming supplemental protein is.required to

replace the protein lost to the leafminer.

24

Reduction in plant weight and digestable dry matter may be of

greater significance than indicted in this study dependent upon the

extent of larval infestation. Chronic leafmining damage may also

adversely affect the plant's susceptibility to crown rot, its ability

to overwinter, and stand longevity.

CHAPTER III

RETENTION OF ALFALFA CROP PERIMETERS AS REFUGES:

IMPACT ON THE ALFALFA BLOTCH LEAFMINER, AGROMYZA

FRONTELLA (RONDANI), OTHER SELECTED INSECTS AND CROP PRODUCTION

Introduotion

The alfalfa blotch leafminer (ABL) Agromyza frontella (Rondani) is

a European agromyzid species recently introduced into the United States

(Miller and Jensen 1970). It has since spread to Ohio, V/est Virginia,

Ontario, Quebec, and the Maritimes (Hendrickson and Barth 1978, Bereza

1977). Large adult (Kim 1975) and larval (Andaloro et al 1978)

populations occur in the northeast, with occasional reportings of

economic losses in alfalfa yield and quality (Byers and Valley 1978,

Richard and Gagnon 1976). In Europe A, frontella is of little economic

importance (Bollow 1955); a condition attributed to the high percentage

of parasitization (70-90^) by a complex of parasitoids (Durseau and

Jeandel 1977). In the northeastern U. S,, a complex of parasitoids

exists and is believed to have adapted to ABL from native agromyzids

found on alfalfa (Hendrickson and Barth 1979). This parasitoid complex

was responsible for a season long average parasitism rate of 36% in

Delaware, where 5 host generations occur. The average parasitization

rate for the first two ABL larval generations was ^3%, whereas, during

the remaining 3 generations average parasitization was 55^. Low levels

of parasitism early in the season were attributed to poor parasite-host

synchrony and too few parasitoids. Conventional alfalfa harvesting

practices which remove the leafminer host and drastically alter the

25

26

physical environment may prevent the buildup or rebound of the ABL

parasitoid complex early in the season. Such harvesting also removes

appreciable numbers of ABL-infested leaflets in which immature

parasitoids are developing on the host larvae. Many mature ABL larvae

normally escape these harvesting dangers because they have already

abandoned their mines to pupate in the soil. Such harvesting appears

to be less harmful to the leafminers than to their parasites. Similar

phenomena were observed on Liriomyza leafminers and their

parasites in California alfalfa (Jensen and Koehler 1970).

A variety of harvest modifications have been employed in alfalfa

insect pest rnamagement. Certain of these innovative harvest practices

were designed to reduce environmental instability (VanDen Bosch and

Stern 1969) and allow for maximum natural enemy conservation while

others either suppressed pest numbers by early removal of hay (Bremer

1976) or reduced pest emmigration into adjacent high cash crops (Stern

et al 1964). The objective of this study was to evaluate a form of

modified alfalfa harvesting that left uncut crop perimeters as a refuge

to harbor beneficial insects and their hosts. The effects of retained

crop perimeters on other alfalfa pests and the subsequent impact that

their population levels had on alfalfa crop production were also

monitored. Insect and plant responses to this cultural control method

were compared with responses to conventional insecticidal control

methods.

27

Materials And Methods

Experimental plot design. A two year old stand of Saranac AR variety

alfalfa in Deerfield, Franklin County, MA was divided into H 30m by 15ra

fields (Fig. 5). At each harvest, 2 of these designated "total cut"

fields (C), were completely harvested. Starting with the first cutting

the other 2, specified as "perimeter" fields (P), were left with an

uncut crop border or perimeter of 0.6m width (10-12^ of total area

represented by dotted lines in (Fig. 5). At the second harvest, an

uncut crop border of similar size was established inside the original

border which was then cut and removed with the rest of the crop. At

the third harvest, the outermost portion of alfalfa was again retained

as the uncut refuge. There was no fourth harvest either year,

although, data collected post 3rd harvest are referred to as occurring

in the fourth harvest period.

Each of the 4 fields was further subdivided into 4, 8m by 15m

plots. Two plots (labeled S) in each field were sprayed 1-3 times per

harvest with a malathion (5EC) plus methoxychlor (2EC) mixture (0.84L +

2.2L/ha) after the initial harvest. The remaining two plots (labeled

U) in each field were left unsprayed. The uncut crop borders in the

perimeter fields were not sprayed.

In an attempt to minimize movement of insects between experimental

areas, 4m wide strips of field corn (1977) and Balboa rye (1978) were

planted between and around the fields.

28

Fig. 5. Experimental plot design for 1977-1978 studies on the

effect of uncut crop borders upon alfalfa insects. Unsprayed (U) and

sprayed (S) plots are located within the perimeter (P) and total cut

(C) fields. (The dashed line within the P fields indicates position of

the originally retained border. Dashed line between fields indicates

sites of 2m high tobacco net fence). Due North points directly to the

upper right hand corner, Franklin Co., MA.

30

Sweep samples. A sweep net was chosen as the sampling tool to

determine the relative densities of the alfalfa pests and predators

included in the study. It*s use for sampling alfalfa insects has been

well documented (Pruess et al 1977, Cothran et al 1975, and Callahan et

al 1966).

A sweep sample consisted of three 180° sweeps with a standard 30.1

cm diameter insect net through the top 20-25 cm of alfalfa. Two random

samples/week were taken from each plot except v/hen alfalfa was in the

stubble stage. No samples were taken directly from the uncut crop

borders in the perimeter fields.

Insects swept in 1977 were identified and separated into 7

categories: adults of 1) A. frontella, 2) Empoasca fabae (Harris)

(potato leafhopper), and 3) Lygus spp.; all life stages of

Acyrthosiphon pisum (Harris) (pea aphid), 5) nabids,

6) coccinellids, and 7) plant bugs other than Lygus. In 1978, the

only changes in tallying insect taxa included the separation of plant

bug adults from their nymphs and the addition of potato leafhopper

nymphs and Therioaphis maculata (Buckton) (spotted alfalfa aphid)

adults and nymphs.

Stem sampling. Stem samples were collected for stem height, weight,

and leaf area and to document the ABL stages. Each sample consisted of

35 random main alfalfa stems collected at 2-3 step intervals along a

diagonal transect and cut at ground level. Samples did not-include

stems from the uncut border nor from the area where borders had been

31

during the previous harvest.

Plant height was determined for 25 stems from each sample. Stems

were then defoliated and both leaves and stems were oven dried at

75° C for approximately 30 h. Immediately after drying, weights of the

25 stems and also of the leaflets were recorded. Population densities

of the 3 ABL larval instars were determined on the remaining 5 stems.

Mines were used to determine specific age classes of immature ABL*s.

Mining by the first and second ABL larval instars in linear or early

mines. These mines rarely exceed 4.2mm and 9mm respectively in length

(Hendrickson and Barth 1978). Third (final) instar larvae widen the

^ine into the characteristic comma—shaped blotch. This category was

further divided into mines already "abandoned” by mature larvae which

had.dropped to the soil to pupate and mines still occupied by either

live or dead third instar larvae. Any leaflet which exhibited any of

the ABL type mines was categorized as a mined leaflet.

Results

Response of A. frontella to control treatments. Sampling A. frontella

adults during first harvest period, prior to initiation of the

experiment, indicated homogeneity among the plots. During the

remaining three harvest periods in 1977, there was no overall

significant difference (P=0.45) betv/een total number of flies swept

from the perimeter (P) and total out (C) fields. Analysis was based on

the variance of the fly populations observed over the 11 sampling

32

dates, A significant difference (P=0.06) occurred in 1978, as a

greater number of ABL adults were collected from the P fields over all

sampling dates. Statistical comparison tests performed on

individual sampling dates in 1978 revealed no significant differences

in overwintering fly numbers between the P and C fields during the

first alfalfa growth before the initial retention of borders.

Significant differences in number of first generation adults did occur

between the P and C fields in 1978 after the establishment of borders.

Uncut alfalfa borders accumulated adults which had emerged when the cut

alfalfa was at minimal growth. Over a prolonged period the uncut

alfalfa vjithin the retained perimeter became rank and harbored fewer

flies.

‘ Methoxychlor plus malathion treatments applied 1~2 days prior to

sampling in 1977 significantly (P=0.01) reduced A. frontella

populations in the S (sprayed) plots. Insecticidal treatments applied

5 to 7 days prior to sampling in 1978 resulted in no significant

differences in fly numbers between the U (unsprayed) and S plots. This

may have been due to the intense fly populaton pressure in 1978, short

residual of malathion and methoxychlor, and taller more lush alfalfa in

the S plots causing fly dispersal from the unsprayed plots. During one

particular sampling date during first generation in 1978, significantly

more flies were collected from the S plots of both the P and C fields.

The numbers of ABL mines/stem, particularly blotch mines, v^ere

used to assess jft, frontella larval populations and the extent of plant

damage. Differences in numbers of blotch and abandoned mine numbers

within the plots were also used as a comparative measure of successful

33

larval development and, thus, an indication of the cumulative effect of

natural enemies. Fig. 6 shows a comparison of the number of blotch

mines (either abandoned or still occupied by live third instars)/stem

and the total number of mines (formed by first, second, third or

abandoned third instars)/stem found within the PU and CU plots in 1977

and 1978. Since insecticidal treatments reduced the larval populations

to such low levels in all the S plots, the data from the PS and CS

plots are not presented.

In 1977, mine populations in all unsprayed plots were similar. In

1978 significantly fewer mines were found in the perimeter plots.

There were more total mines at first and third harvest and a greater

number of blotch mines at first and second harvest in the CU plots than

in the PU plots. This is the reverse of A. frontella adult response

where greater fly numbers were swept from the PU plots in 1978.

Third instar ABL mortality V7as measured in 1978. The number of

mines containing dead third instars was counted separately from the

number of blotch mines containing live third instars and abandoned

mines in Fig. 6. There was an overall significant (P=0.01) difference

in the total number of dead third instars between the PU and CU plots

in 1978. The most pronounced difference occurred during second harvest

period where more dead third instar larvae/stem were found in the PU

plots (8) than in CU plots (4.8).

Msponse of selected insects to control treatments. The effect of the

2 control regimes upon the more important alfalfa insect pest

populations present during the experiment are sho\m in Fig. 7.

34

Fig. 6. Comparison of the total number of ABL mines (formed by

first, second, and third abandoned third instars) and blotch nines

(formed by third and abandoned third instars)/stem within upsprayed (U)

plots between perimeter (P) and total out (C) fields in Franklin Co.,

MA. If means differ significantly at a particular sampling date they

are indicated by 95? confidence limits according to Scheffe’s multiple

comparison test. For each sample mean, n=20.

35

SA

MP

LIN

G

DA

TE

S

36

Response of some insect populations to the treatments during post

treatment may be misleading. Close proximity of sprayed plots to

unsprayed plots created a situation where insects dispersed from

unsprayed (U) plots of high densities to the sprayed (S) plots of low

densities. This insect movement masked the total effectiveness of the

chemical treatment due to rapid recolonization of the S plots, but

concurrently reduced insect numbers in the U plots.

E, fabae was first collected in Massachusetts within the first 2

weeks of June, just after first harvest in both 1977 and 1978.

Economically injurious populations (Edwards et al 1978) occurred during

second harvest in 1977 and during second and third harvest in 1978

(Fig. 7). Insecticidal treatments significantly reduced PLH numbers in

the'S plots during second and third alfalfa growth periods both years.

However, in 1978 chemical control measures did not adequately suppress

—• ^^^ae populations belov; the economic threshold level of 1 to 2

adults and or nymphs/sweep. A significantly greater number of

leafhoppers occurred in the PU plots than in the CU plots only on

August 30, 1978. Sampling within the 0.6m wide uncut perimeter in 1978

revealed a 10-20 fold increase in PLH*s compared to numbers found in

the cut portion of the P plots. Large numbers of PLH persisted within

the border even as the alfalfa aged.

Pea aphid populations were greatest during second harvest in July

1977 and 1978 (Fig. 7). Applications of methoxychlor plus malathion

significantly reduced aphid numbers in the S plots compared to those in

the U plots. In 1978, despite application of 2 sprays during second

harvest period, pea aphids were still numerous in the S plots.

37

Fig. 7. Effect of chemical (sprayed, S; unsprayed, U) and

cultural (perimeter, P; total cut, C) control treatments on Empoasca

fabae adults, Acyrthosiphon pisum adults plus imraatures, Lygus spp.

adults, and other mirid adults plus immatures in Franklin Co., MA. * ,

Least significant differences (LSD) represent significance to the P=.05

level for each sample mean, n=8.

i

NU

MB

ER

OF IN

SE

CT

S/3 S

WE

EP

S

38

39

Significantly greater aphid numbers were found in the perimeter U and S

plots compared to the total cut U and S plots at time of peak

population. Pea aphid numbers were observed to build up faster in the

PS plots than in the CS plots following pesticide applications in the

second harvest period.

Fluctuations in the densities of specific mirids under the two

treatment regimes are presented in Fig. 7- Response of adult Lygus

spp. populations, predominately Lygus lineolaris Palisot de Beauvois,

varied considerably from that of other mirid spp. and are, thus,

depicted separately. The prevalent mirid species other than Lygus spp.

were Adelphocorus lineatus (Goeze), A. rapidus (Say), Plagiognathus

politus Uhler, P. cuneatus Knight, Poecilocapsus lineatus (F), and

Reuterscopus ornatus (Reuter).

Lygus bugs and other mirids vjere present in high numbers

throughout 1977 and 1978. Lygus bug adult numbers were greater than

all other mirid adults and nymphs together at all harvest periods

except third harvest in 1978. Insecticide sprays had a lesser effect

on adult Lygus spp. than on remaining plant bugs. Lygus adults were

one of the first insects to recolonize sprayed plots and when left

uncontrolled (Sept. - Oct. 1977), rapidly reach high density levels.

Significantly greater numbers of adult Lygus bugs were present in

the PU plots than in the CU plots at 5 sampling dates throughout the

study. The reverse occurred only once in 1977. Populations of mirid

spp. other than I^gus responded to perimeter retention, in the same

manner as adult Lygus. Differences in mirid numbers between the PU and

CU plots were most pronounced at third harvest in 1978 when highest

40

populations were present. Significantly more bugs were found at this

time in the PU and PS plots compared to the CU and CS plots.

Nabis alternatus (Parshley) and N. americoferus (Carayon) were the

only representatives of the nabid taxa found in the research plots,

Nabids were the most abundant insect predators sampled, with adult plus

nymphal populations reaching up to 10/sweep in the unsprayed plots.

Nabid population levels within unsprayed plots varied little from that

of the sprayed plots both years. The retention of uncut borders had

little impact on nabid numbers. There was little variation in

population levels between perimeter and total cut unsprayed fields.

Peak populations of coccinellid adults plus immatures never

exceeded 1 and 1,25/sweep in 1977 and 1978 respectively. The

predominant coccinellid species collected were Coleomegilla maculata

Timberlake, Coccinella trifasciata Mulsant, and Coccinella

transversoguttata Brown. These predator species were detrimentally

affected by insecticidal treatment, with populations suppressed to near

zero in 1977 and at second and fourth harvests in 1978. There were no

significant differences in coccinellid numbers between the PU and CU

plots either year, nor was there a significant correlation between

coccinellid and aphid numbers.

Summary of treatment effects on insect population densities. The total

number of individuals of the selected taxa that were collected from

each field at the 25 sampling dates is listed in Table 3. Of the

72,621 herbivorous individuals (excluding ABL life stages) swept from

the U plots, 42,921 were captured in the P fields, 1.5 times the number

TABLE 3 41

Total number of selected insect species collected from culturally (PU, CU) and chemically (PS, CS) treated alfalfa on 25 sampling

dates in 1977 and 1978. Franklin Co., MA.

Number (and percent) of insects swept from:

_Perimeter(P)_ Total Cut(C) Unsprayed(U) Sprayed(S) Taxa

Therioaphis maculata4 (A + N)~

Agromyza frontella Adult 3rd instar Abandoned mines Leaves with mines

Nabis spp. (A + N)

Unsprayed(U)

747 (44)

29,274 (27) 1,673 (30)

2,354 (31)

5,500 (28)

539 (26)

Sprayed(S)

351 (16)

903 (23)

282 (10)

305 (18)

16,848 (18)

169 (10)

27,065 (25) 799 (14)

1,164 (16)

3,792 (19)

397 (19)

88 (16)

687 (31)

1,010 (25)

1,049 (36)

487 (29)

25,824 (28)

593 (35)

26,521 (25) 2,286 (40)

2,532 (34)

6,497 (33)

706 (34)

170 (31)

360 (16)

743 (19)

200 ( 7)

210 (12)

10,768 (12)

194 (12)

24,484 (23) 902 (16)

1,416 (19)

4,065 (20)

459 (22)

76 (14) Coccinelli- 205 (38) dae (A + L)

Empoasca Fabae (A)^ 802 (36)

Lygus spp.(A)1,318 (33)

Miridae^(A) 1,379 (47)

Miridae^’^ 693 (41) (N)l

Acyrthosi- 38,032 (42) phon pisum (A + N)

A Adults, N—Nymphs, L=Larvae

2 Other than Lygus spp.

3 Tallied separately in 1978.

4 Collected only in 1978 (July, Aug. and Sept.).

from the CU plots. Perimeter retention in the PS plots resulted in a

34it increase of herbivorous insects over the number collected in the CS

plots.

Seventy percent of all herbivores (including ABL) collected from

the sprayed and unsprayed plots were from the unsprayed plots. The use

of rnalathion plus methoxychlor reduced pest numbers by a factor of 2.3.

Insecticidal use reduced the 2 predator complex populations by a factor

of 1.6.

Mature ABL larvae (third instar), abandoned mines, and leaves with

mines were distributed unevenly with a greater percentage in the total

cut fields. This is the reverse of the trend in overall response of

other herbivorous insects to the cultural treatment.

Effect of control treatments on stem height, weight, and total lea_f_

area. Plant growth differed greatly in the experimental plots in 1977

and 1978. Alfalfa treated with insecticides was significantly taller

than unsprayed alfalfa within the perimeter and total cut fields in

1977 and 1978. Alfalfa height was significantly reduced within both U

and S plots of the P fields. In 1978, at first and third harvests, the

CS plots produced significantly taller alfalfa than the PS plots. In 4

of the harvest periods during the 2 years, the CU plots yielded alfalfa

of a mean height statistically the same or greater than that of the PS

plots.

Differences in oven dried stem weights from the various treatments

were consistent with their respective height differences and are shown

in figs. 8, 9, and 10. However, statistical differences in stem height

43

Fig, 8, Effect of 1977 chemical (sprayed,S; unsprayed, U) and

cultural (perimeter, P; total cut, C) control treatments on total (stem

+ leaf) alfalfa dry weight/25 stems at second, third and fourth

harvests in Franklin Co., MA. At each harvest date means accompanied

by different letters indicate a significant difference at P=.05

according to Duncans New Multiple Range test. For each sample mean,

n=4.

44

r 1 IS

(0

o JD u

D o

“D (D >.“D

o D ®

5 £ ^ >.

a o lim in !>-

O o C Q. a. D in

It ii II II u O. 3 LO

h-

O)

(D

bD

f“n I I r I i I I 1."I'” r I I I lO O lO o csj CM

SUJ9JS SZ/(S)mSi3M X

CU

LT

UR

AL

TR

T.

45

Fig. 9. Effect of 1978 chemical (sprayed, S; unsprayed, U) and


+ leaf) alfalfa dry weight/25 stems at first harvest in Franklin Co.,

MA. Means accompanied by different letters indicate a significant

difference at P=.05 according to Duncans New Multiple Range test. For

each sample mean, n=4.

Iyii

ei2

,i9

78

46

Q> "a

© s

O Ss^ ■3 rs e>

^_ E a» >» fS CL ra

Lm

© Q c o. 3 (f)

II II II II

CD

.T’T I I ' i If) o U) If)

If)

Cu

ltu

ral

Trt

.

47

Fig, 10. Effect of 1978 chemical (sprayed, S; unsprayed, U) and


+ leaf) alfalfa dry weight/25 stems at second, third, and fourth

harvests in Franklin Co., MA, At each harvest date means accompanied

by different letters indicate a significant difference at P=.05

according to Duncans New Multiple Range test. For each sample mean,

n=4.

T3 o 0>

>»t3 3 o m 0) O E La

cx ra ra La (/) b o O s a.

& II J» li II

O d. =>

CO CU

LT

UR

AL

TR

T.

49

did not always indicate a significant difference in stem weight. In

1977, stem weights were statistically greater in the C fields than in

the P fields at third (August 16) and fourth (October 11) harvest

periods (Fig. 8). Stem weights also were greater in the S fields than

in the U fields at second (July 14) and fourth harvest periods. The

first alfalfa crop in 1978 achieved the greatest stem weights (Fig. 9).

Although the alfalfa had not yet been subjected to either cultural or

chemical treatments for the 1978 season, the weight differential/25

stems between alfalfa in P and C labeled fields was the greatest of any

harvest period. There was a total dry stem weight increase of 11

grams/25 stems from alfalfa in CU plots compared to that in PU plots.

This weight difference was mainly due to stem rather than leaf weight.

No significant differences in total stem weights existed between S and

U plots within either P fields or C fields at this time. During the

third and fourth harvest periods in 1978, (Fig. 10) PU alfalfa weight

was significantly less than CU alfalfa weight. During the final three

harvests in 1978 the sprayed alfalfa weighed more than the unsprayed

alfalfa within each cultural treatment.

Leaf area is proportional to leaf weight and the factor 331.5cm^/g

oven dried leaf has been calculated by Robinson and Massengale (1967)

for Moapa variety alfalfa. The total leaf area (TLA) is twice the

measured leaf area value since entomophagous insets search both the

upper and lower sides of leaves. In this study, the two year overall

average of TLA at harvest for PU, PS, CU, and CS plots were 64.4, 75.5,

77.1, and 87.6 sq. m/sq. m of ground surface. Leaf area was greater in

the insecticide treated fields compared to the unsprayed fields and in

50

the total cut fields compared to the perimeter fields.

The effect of treatments on alfalfa yield and crop value. Optimal

yield was derived by correcting mean oven dry alfalfa weight/25 stem

sample to optimal stand density of 350 stems/sq. m and converting to

kg/ha. The overall mean for all harvests in 1977 and 1978 for PU, PS,

CU, and CS plots are 2782, 3318, 3^13, and 3923 kg/ha respectively.

Malathion plus methoxychlor treatments significantly increased the mean

yield of treated plots over untreated plots at harvest by approximately

536 kg/ha or 16^ in P fields and 509 kg/ha or 13^ in C fields.

Retention of uncut perimeters at each harvest had a statistically

significant negative effect on forage yield: unsprayed P plots yielded

a mean deficit of 631 kg/ha/harvest or 18.5^ less than that of

unsprayed C plots. Sprayed P plots yielded a mean reduction of 604

kg/ha/harvest or ^5% less than sprayed C plots. Percent differences in

yield between P and C fields do not reflect unharvested crop perimeters

which were retained. Yield differences are only those of the harvested

areas.

Differences in yield do not accurately indicate what the monetary

return per treatment is since the final yield does not reflect

accumulated treatment costs. Thus, a cost/benefit analysis on the

chemical and cultural control treatments was obtained to acquire a more

realistic view of the results of the treatment. Chemical

cost/treatment was valued at $7.95/ha. There were 6 insecticidal

treatments in 1977 and 5 in 1978. Costs for labor, machine, use, and

depreciation relative only to chemical application were evaluated and

51

combined with chemical cost to equal a total of $16.05/ha/treatment.

Retention of a border left approximately of the crop unharvested

aiid, thus, comprised a ^0% loss in yield/season. Alfalfa was valued

both years at $88,14/I000kg of dried alfalfa (Lyford 1979). All other

expenses such as harvesting, fertilizer use, and labor costs which were

similarly performed on all the plots were not included in the

cost/benefit analysis. For the purposes of this study no additional

cost was subtracted to compensate for possible reduced quality of

alfalfa which made up the perimeter.

The annual monetary net return/ha for alfalfa harvested from the

research plots after chemical and cultural treatment costs were

subtracted, are depicted graphically in Fig. 11. The monetary mean

return/ha of the unsprayed total cut plots (CU) was chosen as a base

line or check from which all comparisons were made.

The PU and PS plots in 1977 similarly netted an approximate $165

loss/ha/yr compared to the CU control plots. The disparity in monetary

net return between the PS and CU plots is due vjholly to chemical and

cultural treatment costs because the alfalfa yields of the 2 plots were

similar. Although the PS plots out-yielded the PU plots by

approximately 1300kg/ha for the 1977 season, the monetary return did

not significantly offset the chemical costs necessary to achieve that

difference.

The 1978 CS and PS plots netted approximately $ 100/ha more than

their respective unsprayed counterpart plots. Retention of a perimeter

in the 1978 PU plots resulted in a loss of about $390/ha/yr .due to the

combination of reduced yields and the 10? hay loss for border use.

52

Fig. 11. Difference in net monetary return/h/season due to

cultural and chemical control treatments using the total cut unsprayed

(CU) plots as a baseline. Franklin Co., MA. P=perimeter; C=total cut

S=spraysd; U-unsprayed.

54

Chemical treatments'on perimeter plots (PS) did not increase yields to

the extent where the net return/h i-ias comparable to that of PU.

.<;tand density. The differential decline in alfalfa stand during this

study is depicted in Table 4. Stand densities taken in October 1978 at

termination of the project were greatly reduced from those taken at the

beginning of the study in July 1977. Stem densities followed the

pattern previously defined for alfalfa stem height, weight, and yield

namely CS>PS>CU>PU.

Discussion

The results of this study indicate that the retention of uncut

alfalfa perimeters as a refuge for natural enemy conservation and

buildup suppressed ABL larval populations, but promoted a significant

increase in the numbers of other alfalfa insect pests and an overall

deleterious effect on yield and stand quality.

Uncut alfalfa perimeters seemed to attract insect migrants and ABL

adults which had begun to emerge V7hen the cut alfalfa was at minimal

growth. This may partly explain why there were significantly more ABL

flies in the perimeter unsprayed plots than in the total cut unsprayed

plots in 1978. Conversely, a significantly greater number of blotch

mines were recorded in CU plots than in the PU plots in 1978. This may

be attributed to the occurrence of greater rates of ABL larval

mortality caused by parasitism and predation as was found with 3rd

instar larvae in the P fields in 1978. The existence of a large ABL

55

TABLE 4

Alfalfa stand dansitias of axparlinental research plots. Franklin

Co., MA. P=perimeter; C=total cut; S=sprayed; U=unsprayed.

Treatment Number of stems/sq. m

July 1977

Oct. 1973

PU 318 96

PS 315 184

CU 349 152

CS 334 215

56

parasitoid complex (Hendrickson and Barth 1979) may be a factor in the

reduction of ABL populations, particularly since the most abundant

parasite, Diglyphus intermedius (Girault), kills additional larvae by

probing without oviposition.

Studies on Liriomyza spp. leafminers in California showed that

infestations were less severe in strip cut fields than in completely

cut ones (Jensen and Koehler 1979). Predation was indicated as a key

factor in reducing leafminer infestations. The high correlation of

Lygus spp. with third instar larvae in this experiment may lend support

to the possible role mature plant bugs play as falcultative predators

of inactive leafminers (Wheeler 1976; 1977). Other factors may be

involved in explaining the difference in ABL larval numbers.

The proliferation of plant growth and significant (P=.001)

increases in TLA in the total cut fields may have hindered the

searching effectiveness of predators. This could result in the greater

survival of ABL larvae, thus, more blotch mines in the CU plots.

Unless the retention of perimeters was specific to the buildup of

natural enemies of A. frontella it would seem that the other herbivores

would also have been subjected to more intensive predation and

parasitization. However, this did not appear to have occurred in this

study and it can only be speculated that crop border retention

maintained and promoted pest populations to levels such that natural

enemy action could not inhibit them. This agrees with earlier reports

by authors on the effects of modified harvesting practices. Summers

(1976) reported 62^ more Lygus spp. collected from fields where 3.1ra

wide uncut strips every 50m were left compared to a solid cut field.

57

In addition, Schlinger and Dietrick (1960) found 79.5^ of the captured

insects from alternate strip cut and solid cut fields v/ere from the

strip cut fields. Simonet and Pienkowski (1979) found that when leafy

material or uncut stems remained in poorly harvested fields, field

survival of potato leafhopper nymphs was higher and contributed to the

insect*s increase during alfalfa re-growth. These authors did not

define the detrimental effects increased pest populations had on

alfalfa hay production.

The PU plots which maintained significantly higher populations of

herbivores in this study produced significantly shorter alfalfa which

weighed less than the alfalfa in the CU plots. The same difference in

crop quality was also observed between the PS and CS plots despite

insecticidal applications. Crop growth parameters measured at first

harvest, 1978, indicate that insect feeding on alfalfa, one year may

affect alfalfa re-growth the next year. The response of alfalfa growth

at first harvest, 1978, prior to any treatments for that year, was

similar to the response of alfalfa growth in 1977 which was subjected

to different insect damage levels due to the different treatements.

Leath and Byers (1977) reported potato leafhopper and aphid feeding one

year affected alfalfa production the next.

Position effect was partly precluded when the findings of soil

analyses was similar for all test plots. However, other unmeasured

soil and environmental factors specific to location, i.e. soil

moisture, may have had a favorable impact on alfalfa production in the

C fields.

The application of malathion plus methoxychlor proved to be

58

effective against non-mobile pests. Indirectly, through herbivore

control, spraying was believed to have improved alfalfa crop growth in

the S plots compared to the U plots within the P and C treated fields.

Myers et al (1974) similarly reported increased alfalfa growth through

the use of specific insecticides in the field. Effect of chemicals

directly or indirectly on the physiological growth of alfalfa (Leigh

1963, Chapman and Allen 1948) is a lesser, but possible factor for

increased stem growth. Insecticidal applications on alfalfa in the

perimeter field (PS) was required to produce alfalfa of comparable

height and yield to that of unsprayed alfalfa in the total cut field.

Spraying was economical only in 1978 (fig. 10), but the results also

indicate that insectical applications in the P plots were not

sufficient to overcome the deleterious effects and cost of the retained

perimeter

The differential decline in alfalfa stand during the study

suggests insects play a major role both directly and indirectly in the

longevity of alfalfa in addition to diseases and climate. Reports of

the effects of insect feeding on decreasing cold hardiness of alfalfa

(Harper and Freyman 1979; Hower and Muka 1976), and predisposing plants

to root rots (Leath and Byers 1977) comply with our results. Such

typical stand reductions which growers normally attribute to winterkill

may actually be the result of cumulative insect and pathogen stress

factors. Our stand density data indicate that insecticidal treatments

and complete cutting of fields may not only produce superior yielding

alfalfa, but may also maintain a denser alfalfa stand compared to no

chemical treatment and retaining unharvested field portions.

Bibliography

Andaloro, J. T., T. M. Peters, and A. J. Alicandro. 1978. Correlation of common plant taxa phenologies to development of Agromyza frontella (Rondani) (Diptera: Agromyzidae). J. N. Y. Entomol. Soc. 86:276.

Anon. 1972. Alfalfa blotch leafminer situation in eastern United States. Coop. Econ. Insect Report. 22:132.

Arnold, C. Y. I960. Maximum-minimum temperatures as a basis for computing heat units. Am. Soc. Hort. Science. 76:682-92.

Bereza, K. 1977. Alfalfa blotch leafminer. Ontario (Canada) Factsheet No. 77-067. 2pp.

Bollow, H. 1955. Ein Massenauftreten der minierfliege Agromyza frontella (Rondani) an Luzerne. Pflanzenschutz. 7:141-43.

Byers, R. A. and K. Valley. slf3-lfa blotch leafminer. Insects Conf., Purdue Univ p40-43.

1978. An economic injury level for the Proc. 15th Ann. N. E. Inv. Alfalfa

., W. Lafayette, IN, Oct 17-18, 1978.

59

Callahan, R. A., F. R. Holbrook, and F. R. Shaw. 1966. A comparison of sweeping and vacuum collecting certain insects affecting forage crops. J. Econ. Entomol. 59:478-81.

Chapman, R. K. and T. C. Allen. 1948. Stimulation and suppression of some vegetable plant by DDT. J. Econ. Entomol. 4l;6l6-23.

Cothran, W. R. and C. G. Summers. 1972. Sampling for the Egyptian alfalfa weevil: a comment on the sweep net method. J. Econ Entomol. 65:689-91.

Cothran, W. R., C. G. Summers, and C. E. Franti. 1975. the Egyptian alfalfa weevil: Comparison of 2 standard techniques. J. Econ. Entomol. 68:563-4.

Sampling for sweep net

Durseau, L-. Jr. and D. Jeandel. 1977. Alfalfa blotch leafminer (Diptera: Agromyzidae) laboratory studies of biology in Europe Proc. Entomol. Soc. Wash. 79:259-65. urope.

Edwards, C. R., R. i. Abrams, and P. Sutton. 1978, Extension

1 T prog.„ 1,

Lafayette, IN. Oct! 17-^8,^197r p?9-22.^“'’‘^"®

Harcourt, D. G. 1973. Agromyza frontella (Rnndanil (Diptera: Entomol. Soc.

61

Harper, A. M. and S. Freyman. 1979. Effect of the pea aphid Acyrthosiphon pisum (Homoptera: Aphididae) on cold-hardiness of alfalfa. Can. Entomol. 111:635-36.

Helgesen, R. G. and F. Baxendale. 1978. Feeding activity of the alfalfa blotch leafminer, Agromyza frontella (Rondani) (Diptera: Agromyzidae). J. N. Y. Entomol. Soc. 86:274. Abstract.

Hendrickson, R. M. and S. E. Barth. 1978a. Notes on the biology of ^^Slyphus intermedius (Hymenoptera: Eulophidae), a parasite of the alfalfa blotch leafminer, Agromyza frontella. Proc. Entomol. Soc. Wash. 80:210-15.

Hendrickson, R. M., Jr., and S. E. Barth. 1978b. Biology of the Blotch Leafminer. Ann. Entomology. Soc. Am. 71 :295-8.

Hendrickson, R. M., Jr., and S. E. Barth. 1979. Effectiveness of the native parasites against Agromyza frontella (Rondani) (Diptera-

87^85-S!^^^’ P®st of alfalfa. J. N. Y. Entomol.’ Soc.

Horwitz, W. (ed.). 1970. Official Methods of Analysis of the AssociatioOpOf Agricultural Chemists. 11th ed. p. 16. Washington,

“°a?f;cung’at?fif; as factors affecting alfalfa stand persistence. Rep. 25th Alfalfa Improvement Conference. ARS-NC-52. p88-95. J-mprovernent

62

Jensen, G. L. and C. S. Koehler. 1970. Seasonal and distribution abundance and parasites of leafminers of alfalfa in California. J. Econ. Entomol. 63:1623-28.

Kim, K. C. 1975. Annual summary. Alfalfa blotch leafminer. Penn. Coop. Econ. Insect Rep. 22:132.

Lyford, S. J. 1979. Corn silage versus alfalfa. Dairy Digest, Publication No. USPS 915-480, Coop. Ext. Serv., University of Massachusetts.

Death, K. T. and R. A. Byers. 1977. Interaction of Fusarium root rot with pea aphid and potato leafhopper feeding on forage legumes. Phytopath. 67:226-29.

Leigh, T. F. 1963. The influence of two systemic organophosphates on growth, fruiting and yield of cotton in Calif. J. Econ. Entomol. 56:517-22.

MacCollom, G. B., G. Baumann, and J. G. Welch. I98O. Effect of Agromyza frontella (Rondani) (Diptera: Agromyzidae) on alfalfa Q^^^lity and yield. J. N. Y. Entomol. Soc. 88:56—7. Abstract.

Mellors, W. K. 1979. User’s Manual For: MINERSIM, A computer Simulation Model For The Alfalfa Blotch Leafminer. Cornell Univ Ithaca, N. Y. 28pp.

63

Mellors, W. K. and R. G. Helgesen. 1978. Developmental rates for the alfalfa blotch leafminer Agromyza frontella, at constant temperatures. Ann. Entomol. Soc. Am. 711886-88.

Miller, D. E. and G. L. Jensen. 1970. Agromyzid alfalfa leafminer and their parasites in Massachusetts. J. Econ. Entomol. 63:1337-38.

Miller, D. E. and F. R. Shaw. 1969. Forage crop insects in Massachsuetts. Coop. Econ. Insect Report. 19:849-50.

Pinter, P. J., Jr., N. F. Hadley, and J. H. Lindsay. 1975. Alfalfa crop micrometeorology and it*s relation to insect pest biology and control. Env. Entomol. 4:153-62.

Pruess, K. P., K. M. Lai Saxena, and S. Koinzan. 1977. Quantitative estimation of alfalfa insect populations by removal sweeping. Environ. Entomol. 6:705-8.

Richard, C. and C. Gagnon. 1976. Pertes dues aux maladies chez la luzerne au Quebec en 1975. Canadian plant disease survey. 56:82-4.

Robinson, C. D. and M. A. Massengale. 1967. Use of area weight relationship to estimate leaf area in alfalfa. Crop Sci. 7:394-5.

64

Schlinger, E. I. and E. J. Dietrick. I960. Biological control of insect pest aided by strip-farming alfalfa in experimental program. Calif. Agr. 14:8-9.

Simonet, D. E. and R. L. Pienkowski. 1979. Impact of alfalfa harvest on potato leafhopper populations with emphasis on nymphal survival. J. Econ. Entomol. 72:428-31.

Southwood, T. R. E. 1966. Ecological Methods With Particular Reference To The Study Of Insect Populations. Methuen and Co. London. 39 Ip.

Spencer, K. A. 1973. Agromyzidae (Diptera) of Economic Importance In Series Entomologica, vol. 9, E. Schimitschek (ed.), W. Junk, The Hague, 418pp.

Stern, V. M., R. Vanden Bosch, and T. F. Leigh. 1964. Strip cutting alfalfa for Lygus bug control. Calif. Ag. 18:4-6.

Steyskal, G. C. 1972. The taxonomy of the alfalfa blotch leafminer, Agromyza frontella (Rondani). USDA Coop. Econ. Insect Rep. 222:134-7.

Summers, C. G. 1976. Population fluctuations of selected arthropods in alfalfa: Influence of two harvesting practices. Environ. Entomol. 5:103-110.

65

Vanden Bosch, R., and V. M. Stern. 1969. The effect of harvesting practices on insect populations in alfalfa. Proc. Tall Timbers Conf. Ecol. Anim. Control by Habitat Manage. 1:47-51.

Wheeler, A. G., Jr. 1976. Lygus bugs as falcultative predators. Proc. Lygus Bug: Host plant interaction workshop. Aug. 21, 1976. Univ. Press of Idaho, Moscow.

Wheeler, A. G., Jr. 1977. Studies on the arthropod fauna of alfalfa. VII Predaceous insects. Can. Entomol. 109:423-27.

• 4 ^

1H< i,*

:vr

APPENDIX

r^'*'

67.

Fig. 12. Seasonal life history of the alfalfa blotch leafminer,

Agromyza frontella on harvested alfalfa in Hampshire and Franklin

counties, Massachusetts 1976-1978. (P=pupae, A=Adults, E=eggs,

L=larvae)

68

overwintering P j

GEN I

GEN II

GEN III

GEN IV

A E L

P partial diapause? A L HZL.

P porfiol diapause?

1 L

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

I

69

distribution of A» frontella. Gggs. In 1976 observations were

made on ^ frontella*s propensity to lay eggs vertically along the

alfalfa stem. In Fig. 13 are egg counts/third of stem taken during the

third harvest period in Hampshire and Franklin county alfalfa fields.

They indicate that a larger percentage of the eggs were consistently

deposited within the top two thirds of the plant with a special

preference to the top third. A large number of eggs were laid into new

unfolded leaflets located near the apical meristem. This behavior

supports the appearance of large numbers of flies in the upper canopy.

In Northfield and Amherst fields egg populations were increasing

in the middle third plant section while decreasing or remaining the

same in the top third section toward the end of the growing period.

This may be due to the fact that after formation of terminal flower bud

later in the harvest period more growth is from lateral buds, and thus

these may be more attractive to gravid females.

Oviposition in new leaves appears to be an adaptive survival trait

evolved by the leafminer to insure optimal nutrition for the larva and

liklihood of the leaf staying intact long enough for larval

ae,.lop.,„t. Old loodted od th. botlo. ihlrd of the pi.„t

senesce and fall from the plant prior to larval completion. In

addition, suboptimal nutrient levels in the old leaflets may prolong

time to larval maturity thus increasing risk of larva

leaflet at time of its abcission from the leaf.

s presence in the

70

Fig. 13. Spatial distribution of frontella eggs at specific

alfalfa stem heights in Hampshire (Amherst) and Franklin (Northfield,

Deerfield) counties, Massachusetts commercial fields in 1976 during

third harvest periods. For each sample mean n=10.

Mea

n N

o.

Eggs/

3rd o

f S

tem

71

I

I

72

Fig, 14. Seasonal occurrence of A. frontella and crop ^"development

under a 4 harvest regime. Conway, Franklin Co., Mass., 1977. For

sample means n=20.

Mea

n N

o. M

ines

/Ste

m

73

-190

> Q. C

(/>

CO

(D <0

TD

I

Mean N

o.

74

Figs. 15-19- Scanning electron microscopy. The Agromyza

frontella female utilizes her ovipositor for the dual purposes of

oviposition and production of feeding punctures, (pinholing). The

latter are special holes bored into the underside of the leaflet that

produces an exuded sap which the female laps up for nourishment.

Rarely does the hole break the epidermis of the upper side of the

leaflet. Fig. 15 depicts a dorsolateral view of the female’s

post-abdominal structure in the stage believed to be utilized in the

production of feeding punctures. The ovipositor has numerous small

chitinous rasping teeth x^hich aid in lacerating the side of the hole

produced in the leaflet tissue thus allowing for maximal juice flow.

The sculptured sheath also gives the ovipositor rigidity.

The ovipositor is normally held telescoped inside the abdomen

(Fig. 16). During the preceding oviposition and pinholing the tube is

everted (Figs. 17> 18), until at full expansion, the egg laying

apparatus comes into view. Bollow (1955) observed that during

oviposition the ovipositor is placed vertically on the leaf and bores

with turning movements into the epidermis and underlying parenchyma.

As the ovipositor reaches the parenchyma, it is bent over at a right

angle, and the hols is lengthened horizontally so that the egg can be

laid into the parenchymal layer of the leaf as depicted in Fig. I9.

The female is able to remove her ovipositor keeping the membraneous

leaf epidermis intact thus preventing dessication. This is probably

accomplished by the female turning her ovipositor sideways. The

lateral surfaces of the ovipositor have few chitinous teeth* (Figure 16)

which enable it to brush against the top of the epidermis without

breaking it.

75

Fig. 15. Dorsolateral view of (240x) partially everted female

Agromyza frontella (Rondani) post abdominal structure. This stage of

ovipositor expansion is utilized by the female for producing feeding

punctures (pinholing) in alfalfa leaflets.

- niW

;

77

Fig. 16. Dorsolateral view (590x) of A. frontella overpositor at

early stage of eversion.

79'

Fig. 17. Dorsolateral view (570x) of A. frontella ovipositor at

intermediate stage of eversion.

81

Fig

(470x).

18. Nearly complete eversion of A. frontella ovipositor

Egg laying structure with receptors are becoming visible.

83

Fig. 19. Lateral view (480x) of completely everted A.

ovipositor showing elongated egg laying structure on right.

)

frontella

Fig. 20. Oviposition puncture on underside of alfalfa leaflet.

Separation of the leaf cuticle from the lower epidermis occurs during

egg placement in the spongy mesophyll. Egg (not visible) is in upper

left hand corner of picture obscured by the lower epidermal cell layer.

87

Fig. 21. Comparison of 1978 peak mean (+/- standard deviation)

dead ABL third instars/stem within unsprayed (U) plots between

perimeter (P) and total cut (C) fields just prior to each harvest in

Franklin Co., Massachusetts. For each sample mean n=20.

89

Fig. 22. Comparison of mean alfalfa heights from sprayed (S) and

unsprayed (U) plots between perimeter (P) and total cut (C) fields at

second, third, and fourth harvest periods in 1977 in Franklin Co.,

Massachusetts.

If means differ significantly from each other at a particularly

date they are indicated by 95^ confidence intervals (according to

Scheffe’s multiple comparison test). S above arrow indicates

insecticide application. For each sample mean, N=100.

90

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Jun

e

July

Au

g.

Sept.

Oct.

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91

Fig. 23. Comparison of alfalfa heights from sprayed (S) and

unsprayed (U) plots between perimeter (P) and total cut (C) fields at

first, second, third, and fourth harvest periods in 1978 in Franklin

Co., Massachusetts.

If means differ significantly from each other at a particular date

they are indicated by 95^ confidence intervals (according to Scheffe’s

multiple comparison test). S above arrow indicated insecticide

application. For each sample mean, N=100.

/

93

Alfalfa leaf weight. Oven dried leaf weights/25 stems were obtained

from stems in Figs, 8, 9, and 10, (Chapter 3), at all sampling dates.

Leaf samples were taken to measure canopy growth parameters and

approximate leaf area. Leaf weights averaged over all 7 harvests

indicate relationships similar to those that existed among the

previously mentioned stem heights and weights. The 2 year overall

average leaf weights/25 stems were 6.95, 8.13, 8.30 and 9.^1 grams from

the PU, PS, CU, and CS plots respectively.

Alfalfa leaves constituted an overall average of 41 percent of the

total stem dry weight at harvest Table 6. Variation in percent leaf

weight at different harvests ranged from 26 percent (June 1978) when

alfalfa v/as approximately 90cm tall to 52 percent (Oct 1978) when

alfalfa was approximately 17cm tall. Leaf weight/stem weight ratio was

found to be inversely proportionate to stem height which supports

similar findings by Bula and Hintz (1978). Therefore, taller alfalfa

will yield a greater percentage of stem weight rather than leaf weight.

This is of importance for nutritional purposes since 75^ of the

^^^^l^ble protein in the alfalfa plant is present in the leaves. Late

cutting of first harvest alfalfa, when it achieves great heights, would

result in high yields of plant matter but a proportionally lower yield

in protein content than that which would have been attained at an

earlier cutting.

94

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TABLE 6

Comparison of leaf weights as a percent of total stem weights among culturally and chemically treated experimental plots in

Franklin Co.,

Harvest Dates

Perimeter(P) Unsprayed(U) Sprayed(S)

Total Cut(C) Unsprayed(U) Sprayed(S)

VII-14-77 40 39 40 39

VIII-16-77 46 43 45 44

VI-12-78 27 28 25 26

VII-17-78 37 36 39 37

VIII-29-78 47 43 47 40

X-13-78 56 51 50 51

Mean 42 40 41 40

Each number is the mean % leaf weight of 4 replicates.

% leaf weight = leaf weight(g) ^ total stem weight (g) .

TABLE 7

Cost/Benefits of alfalfa perimeter retention and chemical control of insect pests based on optimal stand density.

Perimeter(P) Total Cut(C) Unsprayed(U) Sprayed(S) Unsprayed(U) Sprayed(S)

Seasonal Yield kg/ha I977I 6633 7952 7885 9217

$ Value of Hay (3 $88.14/1000kg 584.69 700.98 695.06 812.43

$ Cost/ha for Chem Trt/yr^ — -96.33 — -96.33

Yield Loss/ha/yr Due to Perimeter Retention^ -58.46 -70.09

Actual $ Return/ ha/yr 526.23 534.56 695.06 716.10

Seasonal Yield (kg/ha) 1978'^ 12845 15275 16007 18243

$ Value of Hay @ $88.14/1000kg 1132.24 1346.44 1410.96 1608.07

$ Cost/ha for Chem Trt/yr^ — -80.27 -80.27

Yield Loss/ha/yr Due to Perimeter Retention^ -113.22 -134.64

Actual $ Return/ ha/yr 1019.02 1131.53 1410.96 . 1527.80

Total of 2nd, 3rd, and 4th harvest.

Cost includes labor, machine use and chemicals for 6 insecticide applications.

Equals 10% of total yield/harvest.

Total of all 4 harvests.

Cost includes labor, machine use and chemicals for 5 insecticide applications.

studies of the biology and control of the alfalfa blotch

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