soil fumigation and oxamyl drip applications for nematode and insect control in vegetable...

59Ann. appl. Biol. (2004), 145:59-70Printed in UK

*Corresponding Author E-mail: [email protected]

© 2004 Association of Applied Biologists

Soil fumigation and oxamyl drip applications for nematode and insect controlin vegetable plasticulture

By J DESAEGER1*, A CSINOS1, P TIMPER2, G HAMMES3 and K SEEBOLD1

1University of Georgia, Department of Plant Pathology, 2United States Department of Agriculture, CoastalPlain Experiment Station, Tifton, GA 31793-0748, USA

3DuPont Company, Cherrylog, GA 30522, USA

(Accepted 10 December 2003; Received 7 March 2003)

Summary

A series of experiments were conducted to evaluate the effect of oxamyl in combination with the soilfumigants 1,3-D, metam sodium and methyl bromide on nematode damage and fruit yield in vegetables.Experiments were conducted in Tifton, GA, USA over five seasons, between 2000 and 2002, usingfour different vegetables: squash (Cucurbita pepo), cucumber (Cucumis sativus), pepper (Capsicumannuum) and eggplant (Solanum melongena). In the eggplant experiment, insect populations weremonitored. Soil fumigation alone, irrespective of application method or formulation, gave acceptablecontrol of root-knot nematode in all experiments, except in the spring 2001 pepper experiment. Oxamylby itself did not provide control of root-knot nematode (Meloidogyne incognita), but insect populationson eggplant were reduced. Out of three experiments that included oxamyl by itself, root galling causedby Meloidogyne spp. was reduced only on eggplant when nematode pressure was low (five nematodesper 150 cm3 soil). When oxamyl was applied in combination with pre-plant soil fumigation, small butconsistent reductions in root galling were observed. Greatest reductions in galling due to oxamyl werefound when fumigation provided less than optimal nematode control. The timing of application ofoxamyl did not have much impact on nematode infection, but applications early in the season, preferablystarting at planting, appear to be beneficial. Stubby root nematode (Paratrichodorus spp.) populationswere low and variable in most experiments, but neither fumigation nor post-plant nematicide applicationsseemed to have any effect on soil populations at harvest. Crop yields were often significantly greaterwhen oxamyl followed fumigation, as compared to fumigation only, which could be due to a reductionin root-knot nematode damage (and in the case of eggplant also reduced foliar damage by insects),and/or to a carbamate growth stimulant response. These experiments indicate the potential of oxamylto reduce root-knot nematode infection and increase yields of vegetables when combined with soilfumigation by 1,3-D and/or metam sodium. More research is required to understand the effect of croptype, pest pressure, preceding fumigant (1,3-D or metam sodium) and injection timing of oxamyl.

Key words: Soil fumigation, plastic mulch culture, post-plant nematicide, Meloidogyne spp., vegetables

Introduction

Fumigation with methyl bromide has been usedfor over 50 yr to control soilborne diseases, plant-parasitic nematodes and weeds in a wide range offield crops. Since methyl bromide has beencategorised as a Class I ozone-depleting substanceby the Montreal Protocol, production and use ofmethyl bromide will be phased out in the USA bythe year 2005 with scheduled reductions plannedduring the interim (Anon., 1992). The most likelyalternatives to methyl bromide for nematode controlin vegetables are 1,3-dichloropropene (1,3-D) andto a lesser extent metam sodium (active ingredient(a. i.) = methyl isothiocyanate [MIT]) (Locascio etal., 1997; Roberts et al., 1988). However, manyproducers in the USA are concerned that any of the

existing alternatives to methyl bromide will be lesseffective and cause financial losses.

Polyethylene plastic film, first used as mulch inthe late 1950s, accelerates plant growth by increasingsoil temperature and stabilising soil moisture(Granberry et al., 1994). Currently about 20% ofthe total vegetable acreage in Georgia, USA is grownunder plastic mulch (plasticulture) (Doherty &McKissick, 2002) and as a result of theimprovements in crop yield, water, and weedmanagement, this is expected to rise. Currently,plasticulture systems in the US are used primarilyfor field production of tomato, pepper, strawberryand cucurbits. In the sub-tropical climate of theSoutheastern USA, polyethylene film mulched bedsare commonly used for two or three crops beforethey are destroyed. Soilborne pests and diseases

60 J DESAEGER ET AL.

usually become problematic on the second and thirdcrops and practically can only be controlled byapplying pre-plant pesticides through the drip tape.Among the most damaging pests in plastic mulchvegetable culture in the Southeastern USA are theroot-knot nematodes (Meloidogyne incognita(Kofoid & White) Chitwood and M. arenaria (Neal)Chitwood). Root-knot nematodes have a very widehost range. They typically become a problem insandy soils, especially during summer and autumnwhen temperatures are high. For most crop andnematode combinations the damage caused bynematodes has not been accurately determined.

Oxamyl (Vydate) (C7H13N3O3S), first registeredin 1974 by E. I. Du Pont de Nemours and Company,is an oxime carbamate used to control nematodes,mites and insects. As a systemic pesticide, it issuggested for use as a pre-planting, at-planting andpost-planting treatment. Oxamyl is used in a varietyof formulations and is currently one of the onlyavailable post-plant nematicides registered forvegetables in the southeastern USA (Dunn et al.,2001). In the USA, approximately 350 000 kg ofoxamyl are used per year, with cotton accountingfor most of the usage (Anon., 2000).

In vegetable plasticulture, oxamyl has receivedrenewed interest in methyl bromide alternativeprograms as a post-plant drip application followingpre-plant fumigation with 1,3-D and/or metamsodium. Several researchers have observed improvedvigour and fruit quality of tomato and pepper usingsuch combinations (D Dickson, personalcommunication).

A series of experiments were conducted to evaluatethe effect of oxamyl on populations of nematodesand insects (the latter for eggplant only) and on yieldof vegetables in combination with the soil fumigants1,3-D, metam sodium and methyl bromide.Experiments were conducted over five seasons,between 2000 and 2002, using four differentvegetables: squash (Cucurbita pepo L.), cucumber(Cucumis sativus L.), pepper (Capsicum annuum L.)and eggplant (Solanum melongena L.).

Materials and Methods

Site description and land preparationExperiments were conducted at the University of

Georgia Coastal Plain Experiment Station, Tifton,GA, USA, on a Fuquay loamy sand (88% sand, 8%silt, 4% clay; pH 5.5-6.0; < 2% organic matter;loamy, siliceous thermic Arenic Plinthic Paleudult).The experiment area had a history of vegetable cropsprior to initiation of the studies and was naturallyinfested with southern root-knot nematode(Meloidogyne incognita (Kofoid and White)Chitwood), stubby root nematodes (Paratrichodorusspp. Siddiqi) and ring nematodes (Mesocriconema

spp. Andrassy).Plant beds were formed using a commercial

tractor-drawn bed-former either after rain ormoistened with overhead irrigation to ensure properbed formation. Soil moisture in Expts 4 and 5 wasdetermined with the gravimetric method (Brady,1974) and was measured at 60-80 % of field capacity.Before bed formation, the soil was disc-harrowedand turned 25 to 30 cm deep with a mouldboardplough. Beds were 81 cm wide × 15-18 cm high,with 1.82-m spacing, centre to centre of the bedsand a 3.8-m-wide path between blocks. Bed lengthvaried from 7.6 m to 10.7 m, depending on theexperiment. Beds were covered with black (spring)or white (autumn) plastic mulch (low densitypolyethylene (LDPE), thickness 50 µm) (PlastiTech).Although polyethylene mulch is known to be quitepermeable to methyl bromide and 1,3-D, it still isthe most commonly used agricultural film in theUSA (Wang et al., 1998).

All experiments were done in randomisedcomplete blocks with four or five replicates pertreatment.

General managementIrrigation

A single drip tape was installed 2-4 cm below thesurface in the centre of the beds as the plastic mulchwas applied. All experiments used Aqua-Traxxpremium high-flow drip tape with 30.5-cm spacingbetween emitters and a flow rate of 1.14 litre h-1 at0.69 bar pressure. Drip irrigation was applied everyday or every second day depending on the need.

FertilisationExperimental areas were broadcast fertilised with

various formulations of NPK fertiliser (N-P-K) priorto treatment application. Fertiliser rates ranged from400-700 kg ha-1, depending on soil experimentrecommendations, and fertiliser was incorporatedwith a rototiller approximately 10 cm deep. Expts1, 2 and 4 received a 4-8-24 (N-P-K) formulation,whereas Expts 3 and 5 received a 5-10-15 (N-P-K)formulation of fertiliser. In Expt 1 dolomiticlimestone at a rate of 2240 kg ha-1 was also included.Postplant fertiliser 20-20-20 (N-P-K) at a total rateof 1300 kg ha-1 was applied through the drip systemin equal applications once or twice a week dependingon the need. A 6% Ca-micronutrient solution wasapplied weekly, each time at a rate of 0.19 litre ha-1,via drip beginning at flowering to reduce theincidence of blossom end rot.

Fungicide, insecticide and herbicide applicationsFoliar applied fungicides were sprayed once or

twice a week depending on the need. Copperhydroxide (as Kocide 4.5 LF; 37.5% a.i.; Griffin)was applied at 0.96 litre ha-1, mancozeb (as Dithane

61Oxamyl for nematode control in plasticulture

Drip-applied chemicals were injected through theirrigation system with an injection pump. The drip-applied fumigants, EC35 and metam sodium, wereapplied over a 5-6 hr period, in 150-200 litres ofwater per plot.

Oxamyl (as Vydate C-LV; 45.2% oxamyl a.i.;DuPont) was applied, depending on the test, two orthree times every 2 wk at rates from 0.18 to 0.54 kga.i./ha (0.38 to 1.08 litre ha-1). Injection times foroxamyl varied, depending on the bed coverage thatwas required (Csinos et al., 2002). Since oxamyl isnot volatile, it should be placed in the soil in thetarget area of root development. Unless specifiedotherwise, oxamyl was applied over 2 h for about 1/3 bed coverage at planting (as roots were still limitedto the centre of the bed), over 3 h for about ½ bedcoverage at 2 wk after planting, and over 6 h for fullbed coverage at 4 weeks after planting and later.

Crop managementGreenhouse-grown seedlings were planted 30 or

46 cm apart, depending on the crops, in single rowsusing a hole-puncher combined with a mechanical-hand transplanter and water tank. Planting holes werecut into the centre of the plastic bed adjacent to thedrip tape. Dead or dying seedlings were replacedover the first week.

Soil temperature was measured for eachexperiment and rainfall was recorded within 200 mof the experimental site.

Data collection and analysisNematode population densities in the soil were

determined before fumigation and at harvest fromtwelve soil cores (2.5-cm-diameter × 25-cm-deep)from each plot. Soil cores were mixed, andnematodes were extracted from a 150-cm3 sub-sample by centrifugal flotation (Jenkins, 1964). Rootgalls were assessed at harvest on ten plants per plotand rated on a 1-5 scale: 1 = 0%, 2 = 1% to 25%, 3= 26% to 50%, 4 = 51% to 75%, 5 = 76% to 100%roots galled. In Expts 4 and 5 (spring and autumn2002) root galls were also rated at the flowering stageof the crops (three plants per plot).

Insect populations were monitored on eggplant(Expt 4) at 16 and 23 days after the final oxamylapplication. Insects were identified and counted ineach plot and foliar damage estimated as percentinsect-related defoliation based on five plants perreplicate.

In Expt 3, a soil subsample was used to determinesoil populations of Fusarium spp. (peptone PCNBmedia) (Nash & Snyder, 1962), Pythium spp. (P10ARAgar) (Jeffers & Martin, 1986) and Rhizoctonia spp.(tannic acid benomyl) (Sumner & Bell, 1982).

Vigour ratings were conducted during the first halfof the growing season on a 1-10 scale, 10representing vigorous, healthy plants and 1

DF; 75% a.i.; Rohm and Haas) at 0.69 litre ha-1 andchlorothalonil (as Equus 720; 54% a.i.; Griffin) at0.21 litre ha-1. The insecticides permethrin (asPounce, 38.4% a.i.; FMC) at 0.12 litre ha-1,esfenvalerate (as Asana XL; 8.4% a.i.; DuPont) at0.08 litre ha-1, methomyl (as Lannate LV; 29% a.i.;DuPont) at 0.40 litre ha-1 and spinosad (as Spintor2SC; 22.8% a.i.; Dow AgroSciences) at 0.15 litreha-1 were sprayed with the same frequency in all butthe 2002 experimentss, in which insecticidal activityof oxamyl was monitored. However, the autumn2002 experiment was severely infested withwhiteflies and, starting 2 wk after planting, weeklyinsecticide sprays and drip applications ofimidacloprid (as Admire 2; 21.4% a.i.; Bayer) at 10ml per 100 m bed length were applied to control theinsects. Glyphosate (as Round-Up; 41% a.i.;Monsanto) at 0.50 litre ha-1 was sprayed in betweenbeds to control weeds as required.

Fumigation and oxamyl-applicationsFumigation was done with tractor-drawn injection

applicators (methyl bromide [as Methyl Bromide 98;98% methyl bromide a.i.; Hendrix and Dail] and 1,3-D [as Telone II; 94% 1,3-D a.i.; Dow AgroSciences])and through the drip system (1,3-D + chloropicrin[as InLine; 60.8% 1,3-D a.i. + 33.3% chloropicrina.i.; Dow AgroSciences] and metam sodium [asVapam HL; 42% sodium methyl dithiocarbamatea.i.; Amvac]) (Table 1). Two different injectionapplicators were used. The main injector, referredto as the chisel injector, had chisel shanks spaced 30cm apart for injecting chemicals 20 to 25 cm deepand was equipped with a combination rototiller forspraying chemicals such as metam sodium incombination with injectable products. Methylbromide was always injected using the chiselinjector. 1,3-D was injected with the chisel injectorin all experiments except Expt 3, in autumn 2001,when it was injected with a Yetter Avenger rig. TheYetter rig was designed for deep chemical injection25 to 35 cm deep and was equipped with large 90cm round disks that slice through field debris andtrash. Polyethylene mulch was laid within 1 h afterfumigation, except for 1,3-D in Expt 2, where mulchwas laid 10 days later, following fumigation withmethyl bromide.

Treatment Application method Code

1,3-D Chisel-injection 1,3-D1,3-D (61%) +chloropicrin (33%) Drip-irrigation 1,3-D + C

Metam sodium Drip-irrigation MSMethyl bromide Chisel-injection MBRUntreated control None UTC

Table 1. Key for treatment codes


representing dead plants. In Expts 4 and 5 (springand autumn 2002) fresh root and shoot weights weretaken at the flowering stage of the crop (three plantsper plot). Fruits were hand-harvested, separated intomarketable and cull fruits, counted and weighed.Cull fruits included small-sized, blemished anddiseased fruits.

All data were analysed using ANOVA or GLMprocedures with SAS software (version 8). Thenumbers of nematodes in the soil were transformedto log (x+1) wherever necessary according to anormality test. SED values (standard error ofdifference between means) are given to comparemeans (SED�s for transformed data are inparentheses). Differences between two means wereanalysed using single-degree-of-freedom contrastsand Student�s t-tests (fumigation with oxamyl vsfumigation without oxamyl). A simple binomial(non-parametric) test on the null hypothesis of nodifference between with and without oxamyl wasincluded on the ensemble of tests.

Treatments and datesExpt 1 � Autumn 2000 � Squash

Field plots were established on 30 August 2000and all fumigation treatments (Table 1) were appliedthrough the drip system. Drip fumigation treatmentswere applied as follows: 1,3-D + chloropicrin at 164litre ha-1 on 31 August; 1,3-D + chloropicrin at 164litre ha-1 + metam sodium at 327 litre ha-1 on 1September.

Oxamyl was applied through the drip tape 2 wkbefore planting (6 September, at 0.36 kg a.i. ha-1)and 2 and 4 wk after planting (3 and 17 October at0.09 kg a.i. ha-1 per application). When combinedwith fumigation, oxamyl was applied at 2 and 4 wkafter planting (at 0.09 kg a.i. ha-1 per application)(Table 2).

Twelve days after the last fumigation treatment,on September 12, planting holes were punched toallow aeration. Seven days after holes were made,on 19 September, squash seedlings (cv. Prelude II)were planted. Plots were 10.7 m long and there werefour replicates.

Soil cores were collected on 14 September and 27November and extracted for nematodes. Root gallswere assessed following final harvest on 27November. Vigour ratings were done on 23 Octoberand fruits were harvested on five occasions, 1, 8,14, 17 and 21 November.

Expt 2 � Spring 2001 � PepperThe land was prepared on 25 March 2001 and

chisel-injected treatments were applied on March29 (1,3-D at 168 litre ha-1) and on 9 April (methylbromide at 224 kg ha-1). Both treatments werecovered with plastic on 9 April. Heavy rainfall (40mm) occurred on 29 March. Drip fumigation (1,3-

D + chloropicrin at 164 litre ha-1) was applied on 11April over a 6-h period. Oxamyl was applied throughthe drip tape at 2 and 4 wk after planting (27 Apriland 10 May, at 0.09 kg a.i. ha-1 per application) over6 h of injection time (Table 3). Bell pepper (cv.Capistrano) seedlings were transplanted on 19 April.Plots were 10.7 m long and there were fourreplicates.

Soil cores were collected on 26 March, 20 Apriland 3 August and extracted for nematodes. Root gallswere assessed following final harvest on 1 August.Vigour ratings were done on 1 June and fruits wereharvested on six occasions: 26 June, 5, 11, 18 and24 July and 1 August.

Expt 3 � Autumn 2001 � CucumberField plots were established on 8 August 2001 and

chisel-injected treatments were applied the followingday. All pre-plant fumigant applications were chisel-injected on 9 August, methyl bromide at 224 kg ha-1

with the chisel injector and 1,3-D at 168 litre ha-1

with the Yetter rig. Oxamyl was applied through thedrip tape at a rate of 0.09 kg a.i. ha-1 per application.Applications were done at 0, 2, 4 wk after planting(WAP) (starting on 6 September), at 2, 4, 6 wk WAPand at 4, 6 and 8 WAP (Table 4). Cucumber seedlings(cv. Thunder) were planted 27 days after fumigationon 5 September. Plots were 7.6 m long and therewere five replicates.

Soil cores were collected on 5 September and 15November and extracted for nematodes. Root gallswere assessed following final harvest on 14November. Vigour ratings were done on 27September and fruits were harvested on fouroccasions, 15, 24 and 31 October and 7 November.

Expt 4 � Spring 2002 � EggplantField plots were established on 18 March 2002

and all chemicals were injected through the drip tapeon 19 and 20 March. 1,3-D + chloropicrin wasapplied at 243 litre ha-1 and at 122 litre ha-1 (whencombined with metam sodium). Metam sodium wasapplied at 701 litre ha-1 and at 351 litre ha-1 (whencombined with 1,3-D + chloropicrin). Oxamyl wasapplied at planting (15 April) and at 2 and 4 wk afterplanting at 0.18 kg a.i. ha-1 per application (Table5). Eggplant (cv. Black Beauty) seedlings weretransplanted on 15 April. Plots were 9.1 m long andthere were five replicates.

Soil cores were collected on 17 March, 15 Apriland 5 July and extracted for nematodes. Root gallswere assessed at the flowering stage (4 June) andfollowing final harvest on 5 July. Stand counts weredone on 9 and 22 April. Vigour ratings were doneon April 30 and fruits were harvested on threeoccasions, on 13, 20 and 26 June.


Expt 5 � Autumn 2002 � SquashField plots were established on 18 August 2002

and the following day methyl bromide was chiselinjected at 224 kg ha-1. All other experiment plotswere shaped and covered with plastic the same day.The following day (20 August), the drip-appliedfumigants, 1,3-D + chloropicrin at 122 litre ha-1,metam sodium at 351 litre ha-1, and the combinationof 1,3-D + chloropicrin and metam sodium (samerates) were applied. Oxamyl was applied starting atplanting (10 September) and at 2 and 4 wk afterplanting at 0.18 kg a.i. ha-1 per application (Table

6). Squash seedlings (cv. Prelude II) were planted30 cm apart on 10 September. Plots were 9.1 m longand there were five replicates.

Soil cores were collected on 18 August, 5September and 28 October and extracted fornematodes. Root galls were assessed at the floweringstage (8 October) and following final harvest on 17October. Stand counts were done on 11 and 16September. Vigour ratings were done on 23September and 14 October, plant weights wererecorded on 5 October, and fruits were harvested onthree occasions, 7, 10 and 14 October.

Table 2. Nematode infection at final harvest, plant vigour and total marketable yield of squash, autumn 2000,Tifton, GA

Initial nematode counts per 150 cm3 soil were 175 for root-knot and 76 for stubby root nematode.All treatments were applied through the drip tape.Oxamyl rates are total rates for different applications; a oxamyl was applied at 2 wk before planting (0.36 kg a.i. ha-1) and at two and4 wk after planting (0.09 kg a.i. ha-1 per application); boxamyl was applied at two and 4 wk after planting (0.09 kg a.i. ha-1 perapplication); c F probability based on log (x+1) transformed data (in parentheses); zero values were excluded from analysis

Marketable fruit yieldGall index Nematodes per 150 cm3 soil Plant vigour Number Weight

Treatment Rate ha-1 (1-5) Root-knot Stubby root (1-10) (× 103) ha-1 (t ha-1)

1,3-D + C 164 litre 1.7 10(1.96)

18(2.82)

6.5 16.09 3.99

Oxamyla 0.54 kg a.i. 3.6 115(4.62)

5(1.20)

4.8 13.77 3.63

1,3-D + C + oxamylb 164 litre + 0.18 kg a.i. 1.4 8(1.36)

0(0)

5.8 12.89 3.25

1,3-D + C + MS 164 litre + 327 l 1.7 0(0)

10(1.96)

6.8 15.10 4.04

NTC 4.1 73(3.67)

10(1.52)

3.8 11.15 3.21

SED (df = 12) 1.1 - (0.81) - (0.74) 1.1 2.95 0.85F probability < 0.01 < 0.01c 0.08 0.09 0.52 0.78

Table 3. Nematode infection at final harvest, plant vigour and total marketable yield of pepper, spring 2001,Tifton, GA

Initial nematode counts per 150 cm3 soil were 18 for root-knot and 0 for ring nematode.MBR and 1,3-D were chisel-injected to a depth of 20 cm inches; 1,3-D + C and oxamyl were applied through the drip tape.a Oxamyl rate is total rate for two different applications; oxamyl was applied at 2 and 4 wk after planting (0.09 kg a.i. ha-1 perapplication).b F probability based on log (x+1) transformed data (in parentheses)


Treatment Rate ha-1 (1-5) Root-knot Ring (1-10) (× 103) ha-1 (t ha-1)

MBR 224 kg 3.5 1147(6.63)

0 8.0 32.18 6.54

1,3-D 168 litre 2.9 137(3.13)

0 8.0 32.45 5.72

1,3-D + oxamyla 168 litre + 0.18 kg a.i. 1.6 15(1.69)

0 7.3 32.06 6.68

1,3-D + C + oxamyla 164 litre + 0.18 kg a.i. 1.1 18(2.38)

0 8.3 29.89 6.23

NTC 2.9 375(5.93)

8 6.5 25.09 4.72

SED (df = 12) 0.6 - (1.41) - 0.7 5.31 1.20F probability 0.04 0.06b - 0.40 0.60 0.66


Table 4. Nematode infection at final harvest and total marketable yield of cucumber, autumn 2001, Tifton, GA

Initial nematode counts per 150 cm3 soil were 80 for root-knot, six for stubby root, and 27 for ring nematodes (the latter was nolonger recovered at the end of the experiment).MBR was chisel-injected to a depth of 20 cm; 1,3-D was chisel-injected with a Yetter rig to a depth of 30 cm; oxamyl was appliedthrough the drip tape.a Oxamyl rate is total rate for three different applications; a oxamyl was applied at 0, 2 and 4 wk after planting; b Oxamyl was appliedat 2, 4 and 6 wk after planting; c Oxamyl was applied at 4, 6 and 8 wk after planting (0.09 kg a.i. ha-1 per application).d F probability based on log (x+1) transformed data (in parentheses); zero values were excluded from analysis



MBR 224 kg 1. 0(0)

2 9.4 56.27 34.20

1,3-D 168 litre 1.7 10(0.78)

6 7.8 43.71 25.47

1,3-D + oxamyl a 168 litre + 0.27 kg a.i. 1.4 6(0.69)

2 8.4 49.05 30.37

1,3-D + oxamyl b 168 litre + 0.27 kg a.i. 1.3 0(0)

2 9.0 54.77 33.34

1,3-D + oxamyl c 168 litre + 0.27 kg a.i. 1.6 4(0.61)

6 9.4 48.46 29.54

Oxamyl a 0.27 kg a.i. 3.7 140(3.90)

2 8.4 38.25 23.68

Oxamyl b 0.27 kg a.i. 4.7 160(4.14)

4 7.0 28.10 18.76

NTC 4.4 132(4.40)

8 8.4 39.29 25.10

SED (df = 28) 0.6 - (1.28) - 1.0 5.96 3.55F probability < 0.01 < 0.01d 0.93 0.14 < 0.01 < 0.01



Oxamyl a 0.54 kg a.i. 1.7 1324(6.99)

28(2.69)

6.8 11.55 10.93

MS 701 litre 1.6 3031(5.66)

42(3.33)

7.0 12.09 12.08

1,3-D + C 243 litre 1.3 112(4.58)

19(2.91)

4.8 8.51 9.17

MS + oxamyl a 701 litre + 0.54 kg a.i. 1.0 5(1.27)

27(3.12)

6.8 15.61 17.16

1,3-D + C + oxamyl a 243 litre + 0.54 kg a.i. 1.1 7(1.37)

84(4.30)

5.4 9.87 10.13

MS + 1,3-D + C 351 litre + 122 l 1.3 5(1.55)

19(2.50)

6.2 10.03 9.97

MS + 1,3-D + C+ oxamyl a

351 litre + 122 l+ 0.54 kg a.i.

1.1 7(1.45)

33(3.24)

7.2 14.96 14.02

NTC 2.6 3008(7.80)

41(3.43)

8.6 11.98 11.96

SED (df = 28) 0.3 - (1.56) - (0.65) 0.8 2.21 1.93F probability 0.01 < 0.01b 0.18 b 0.01 0.04 0.01

Table 5. Nematode infection at final harvest and total marketable yield of eggplant, spring 2002, Tifton, GA

Initial nematode counts per 150 cm3 soil were five for root-knot and 10 for stubby root nematode.All treatments were applied through the drip tape.a Oxamyl rate is total rate for three different applications; oxamyl was applied at 0, 2 and 4 wk after planting (0.18 kg a.i ha-1 perapplication); b F probability based on log (x+1) transformed data (in parentheses)


Results

Plant-parasitic nematodes in the experiment areawere predominantly Meloidogyne incognita(southern root-knot nematode), mixed with lowpopulations of Paratrichodorus spp. (stubby rootnematode). Mesocriconema spp. (ring nematodes)were found erratically and will not be furtherdiscussed. Initial nematode populations variedconsiderably among the different experiments andthey were consistently higher in autumn experimentsas compared to spring experiments. Root-knotnematode counts (per 150 cm3 soil) were 175 inautumn 2000, 18 in spring 2001, 80 in autumn 2001,five in spring 2002 and 546 in autumn 2002.

Expt 1� Autumn 2000Oxamyl alone did not reduce root-knot nematode

infection over the untreated control (Table 2). Rootgall index was significantly reduced after fumigationwith 1,3-D + chloropicrin, and no further reductionin root galling was noted when fumigation wasfollowed by oxamyl. Root-knot nematode damageto the squash was confounded by severe incidenceof airborne fungal and viral diseases. Squash yieldswere similarly low for all treatments, and notsignificantly different.

Expt 2� Spring 2001Nematode galls and soil populations were lowest

with drip-applied 1,3-D + chloropicrin, and highestwith the chisel-applied fumigants, 1,3-D andespecially methyl bromide (Table 3). Root gallingwas reduced when chisel-injected 1,3-D wasfollowed by oxamyl (P = 0.07 for the single-degree-

of-freedom contrast). Pepper yields were notdifferent among treatments. Observed yields in 1,3-D-fumigated plots were 21% greater than in theuntreated control; additional oxamyl resulted inanother 17% increase. Yields of plots treated withmethyl bromide were similar to yields of plots treatedwith 1,3-D + oxamyl.

Expt 3 � Autumn 2001The chisel-injected fumigants, methyl bromide and

1,3-D, suppressed root galling and soil densities ofroot-knot nematode (Table 4). No significantimprovement was noted when oxamyl followed 1,3-D. Oxamyl by itself, irrespective of timing ofapplication, did not reduce nematode infection overthe untreated control

Yields of cucumber were greatest followingmethyl bromide and the combination of chisel-applied 1,3-D with oxamyl applied through the driptape. Yields were low for untreated and oxamyl-only-treated plots. 1,3-D by itself increased yields overthe control by 12%, and oxamyl following 1,3-Dgave an additional increase of 4-15%, depending onthe application timing of oxamyl (P = 0.06). Thegreatest yield increase was noted when oxamyl wasapplied at 2, 4 and 6 wk after planting.

Fungal populations in the soil were predominantlyFusarium spp. and some Pythium and Rhizoctoniaspp. MBR was the only treatment that reducedpopulations of Fusarium spp. in samples taken priorto transplanting (data not presented). No treatmenteffects were noted on any of the soil fungi by harvest.

Expt 4 � Spring 2002Oxamyl by itself reduced root galling compared

Table 6. Nematode infection at final harvest and total marketable yield of squash, autumn 2002, Tifton, GA



MBR 224 kg 1.3 3(0.84)

14(1.43)

8.0 11.49 3.75

MBR + oxamyl a 224 kg + 0.54 kg a.i. 1.0 0(0)

0(0)

7.4 12.25 3.98

MS + oxamyl a 351 litre + 0.54 kg a.i. 1.5 1(0.36)

0(0)

5.9 9.97 2.56

1,3-D + C + oxamyl a 122 litre + 0.54 kg a.i. 1.0 4(0.61)

22(0.94)

7.2 9.00 3.02

MS + 1,3-D + C 351 litre + 122 l 2.2 13(1.72)

41(2.96)

5.4 7.16 2.09

NTC 3.5 61(2.31)

29(3.04)

4.9 2.49 0.99

SED (df = 20) 0.6 - (1.51) - (1.28) 1.1 1.89 0.76F probability < 0.01 0.21 b 0.01 b 0.06 < 0.01 0.01

Initial nematode counts per 150 cm3 soil were 546 for root-knot and 10 for stubby root nematode.MBR was chisel-injected at a depth of 20 cm; 1,3-D + C, MS, and oxamyl were applied through the drip tape.a Oxamyl rate is total rate for three different applications; oxamyl was applied at 0, 2 and 4 wk after planting (0.18 kg a.i. perapplication); b F probability based on log (x+1) transformed data (in parentheses); zero values were excluded from analysis


to the control, but M. incognita soil populations weresimilarly high in the two treatments (Table 5).Equally high M. incognita soil populations in metamsodium-treated plots were largely due to very highpopulations in two out of five replicates. Fumigationcombined with oxamyl reduced root-knot nematodeinfection compared to fumigation with 1,3-D +chloropicrin or metam sodium only, althoughdifferences were small. Differences were highlysignificant for the soil population of root-knotnematode (P = 0.01 when comparing either metamsodium or 1,3-D + chloropicrin with and withoutoxamyl) and slightly significant for root galling (P= 0.08 when comparing metam sodium with andwithout oxamyl). At flowering stage, few root gallswere observed in the non-treated control and nodifferences were noted in shoot and root weights(data not given).

Overall, root-knot infection was minimal and didnot negatively affect eggplant yields. Compared tofumigation alone, eggplant yields were 10% higherwhen oxamyl was combined with 1,3-D +chloropicrin, and 30 % when it was combined withmetam sodium and metam sodium + 1,3-D +chloropicrin (P = 0.06 for total number of fruitsharvested). Eggplant yields were higher in plotstreated with metam sodium than with 1,3-D +chloropicrin (P = 0.05).

Foliar insect damage to eggplant was significantlyreduced following oxamyl applications (on average14.8% of foliage affected without oxamyl, and 7.2%with oxamyl, P < 0.01; Fig. 1). The most commoninsects were eggplant flea beetles (Epitrix fuscula(Crotch)) and leaf-footed bugs (Leptoglossus spp.),averaging 25 and 20 individuals per 10 m bed lengthin non-treated beds, respectively (data not given).When oxamyl was applied, populations of bothinsects were consistently lower at five or lessindividuals per 10 m bed length (P < 0.01).Fumigation with metam sodium and/or 1,3-D +chloropicrin reduced populations of Epitrix fusculaon average by half. Leptoglossus spp. were reducedonly when beds were fumigated with metam sodium.Other insects that were observed on eggplant weretarnished plant bugs (Lygus lineolaris (Palisot deBeauvois)) and garden fleahoppers (Halticusbractatus (Say)), but populations were too low todraw any meaningful conclusions.

Expt 5 � Autumn 2002Few or no nematode galls were found with methyl

bromide, with or without oxamyl (Table 6). No directcomparisons with regard to efficacy with and withoutoxamyl were possible for any of the other fumigants.However, oxamyl in combination with metamsodium and/or 1,3-D + chloropicrin showed less rootgalling compared to fumigation with 1,3-D + metamsodium without oxamyl (P = 0.02), and yields were

respectively 17% and 30% greater with oxamyl (P= 0.04 for fruit weight and P = 0.01 for fruit number).

Root-knot nematode caused severe stunting ofsquash in 60% of non-treated plots during the firstweeks after planting and these plots had near zeroyield. The mean fresh shoot weight at 25 days afterplanting was 0.72 kg per plant in non-treated plotsand 1.17 kg per plant in fumigated plots (P < 0.01,data not given). Later in the season, the wholeexperiment suffered wilting, due to melonworm(Diaphania hyalinata L.) infesting the stem, andairborne fungal pathogens, such as gummy stemblight (Didymella bryoniae (Auersw.) Rehm) anddowny mildew (Pseudoperonospora cubensis (Berk.and Curt.) Rostow) affecting the foliage. Highpopulations of whitefly (Bemisia argentifolii(Bellows and Perring)) resulted in �silverleaf� andpapaya ringspot virus, transmitted by aphids, causeddiscoloration and tumours on the fruits. Airbornediseases affected the experiment uniformly (P >0.10).

Discussion

Soil fumigation gave acceptable control of root-knot nematode in all but one experiment. Lack ofnematode control with chisel-applied fumigants, 1,3-D and methyl bromide, in Expt 2 was probably dueto insufficient diffusion of the chemicals because ofextreme wet conditions at the time of application(Knavel et al., 1965; Lembright, 1990). Due to heavyrainfall at the time of application in Expt 2, soilmoisture was probably close to 100% of fieldcapacity. Optimum soil moisture for fumigation withmethyl bromide and 1,3-D is between 30% and 70%of field capacity (Lembright, 1990). Efficacy of 1,3-D in Expt 2 may also have been reduced because ofhigh volatilisation as beds were left uncovered for10 days. In all other experiments polyethylene mulchwas applied immediately following fumigation.

Otherwise, any of the application methods of 1,3-D, shallow injection with the chisel injector or deepinjection with the Yetter rig, or application throughthe irrigation system, performed well and providednematode control similar to methyl bromide. Thesame was true for the different formulations of 1,3-D, the 94% 1,3-D soil fumigant, or the emulsifiableconcentrate having 61% 1,3-D and 33%chloropicrin, or the combined application of the latterwith metam sodium. The nematicidal potential of1,3-D has been sufficiently demonstrated in fieldexperiments ever since its introduction in 1956 (Starket al., 1944; Noling & Becker, 1994). No conclusionscould be drawn on the efficacy of metam sodium byitself, as the product was only experimented in spring2002 when nematode pressure was low (< five root-knot nematodes per 150 cm3 soil before fumigation).However, variable results have been produced


worldwide with regard to control of nematodes withmetam sodium (Munnecke et al., 1967; Noling &Becker, 1994). In general, in the southeastern UnitedStates, the capacity of metam sodium to control root-knot nematodes has been poor (Locascio & Dickson,1998). In spite of poorer nematode control withmetam sodium, eggplant yields in spring 2002 weregreater than with 1,3-D + chloropicrin, probably dueto phytotoxicity problems with the latter (personalobservation).

Oxamyl by itself did not provide control of root-knot nematode. Out of three experiments thatincluded oxamyl by itself, root galling was reducedonly on eggplant during autumn 2002 whennematode pressure was very low. When nematodedamage was more severe, no difference was notedbetween oxamyl and non-treated plots. This confirmsthe current understanding that oxamyl by itself, atleast at the current application rates for vegetables,cannot be a substitute for soil fumigation. It may atbest slow the early progression of the diseasesymptoms but cannot provide season-long nematodecontrol. Earlier drip studies in Florida showed goodcontrol of M. incognita when oxamyl was appliedover a 9-wk period, but no control when it wasapplied over a 2-wk period (Overman, 1975). Non-fumigant nematicides have often failed to controlthe intended pests or to achieve consistent economicreturns for the grower, particularly when comparedwith conventional preplant mulched fumigation withmethyl bromide or other broadspectrum fumigants(Noling, 2001). Nematode management must beviewed as a preplant consideration because once rootinfection occurs and plant damage becomes visible,it is generally not possible to control the nematodeseffectively and avoid significant yield losses.

When oxamyl was applied in combination withpre-plant soil fumigation, small but consistentreductions in root galling were observed (Fig. 2,

Folia

r dam

age

(%)

25

20

15

10

5

0Control Metam

sodium1,3-D +

chloropicrinMetam

sodium +1,3-D +

chloropicrin

SED (df = 28)

Fig. 1. Effect of soil fumigation with metam sodiumand/or 1,3-D + chloropicrin and oxamyl dripapplications on foliar insect damage on eggplant,spring 2002, Tifton, GA. White bars = fumigant only;black bars = fumigant + oxamyl.

student�s t-test = 0.01, seven comparisons, n = 32;binomial test P = 0.02 (two-tail test), n = 7). Thescope for additional nematode control when oxamylfollowed methyl bromide was limited, as methylbromide gave almost complete control of root-knotnematode. However, whenever fumigation providedless than optimal nematode control, as with 1,3-Din Expt 2 and with metam sodium in Expt 4, oxamylwas able to cause greater reductions in root-knotnematode infection. The most direct comparisonson the effect of oxamyl were conducted incombination with 1,3-D. 1,3-D alone is a goodnematicide and generally gave acceptable controlof root-knot nematode in our experiments. However,

Frui

t yie

ld (t

ha-1

)

35

30

25

20

15

5

10

0

Roo

t gal

l ind

ex (1

-5)

5

4

3

2

1

0

= SED

1,3-

D (6

1%) +

chlo

ropi

crin

(33

%)

1,3-

D

1,3-

D (6

1%) +

chlo

ropi

crin

(33

%)

1,3-

D

Met

am s

odiu

m

Met

hyl b

rom

ide

Squa

shA

UTU

MN

�00

Pepp

erSP

RIN

G �0

1

Cuc

umbe

rA

UTU

MN

�01

Squa

shA

UTU

MN

�02Eggplant

SPRING �02

Fig. 2. Effect of soil fumigation and oxamyl dripapplications on nematode root gall index and fruit yieldof vegetables (squash, cucumber, bell pepper andeggplant) during five cropping seasons from autumn2000 till autumn 2002, Tifton, GA. White bars =untreated; black bars = fumigant; grey bars = fumigant+ oxamyl.

1,3-

D (6

1%) +

chlo

ropi

crin

(33%

) +m

etam

sod

ium


temperatures and greater initial nematode inoculumin autumn.

Stubby root nematode populations were low andvariable in most experiments, but neither fumigationnor post-plant nematicide applications seemed tohave any effect on soil populations at harvest. Somespecies of Paratrichodorus are known to migratevertically in the soil to escape unfavorable conditions(Ingham et al., 2000). Stubby root nematodes maybe pathogenic to vegetables, but only at much greaterlevels than observed in this experiment.

Both autumn squash crops (2000 and 2002) facedsevere airborne pest and disease pressure and yieldswere poor throughout the entire experiment.Therefore, no meaningful conclusions regardingyields could be drawn in squash experiments.

In the other experiments, crop yields showed someincrease when oxamyl followed fumigation, ascompared to fumigation only, although differenceswere mostly not significant. However, there was atrend in all five experiments towards greater yieldswhen oxamyl was applied (Fig. 2, student�s t-test =0.01, 7 comparisons, n = 32; binomial test P = 0.06(one-tail test), n = 7). These yield increases couldbe due to root-knot nematode control or, in the caseof eggplant, may have been associated with reducedfoliar damage and insect control. The latter was thecase with pepper in Puerto Rico, where oxamyl didnot affect root-knot nematode galling, but decreasedweevil infestation and increased pepper yields(Acosta et al., 1987). No suppressive action ofoxamyl, however, was noted against whiteflies,aphids and melonworm, which ravaged the autumn2002 experiment. Although oxamyl has showneffectiveness against whiteflies and aphids in thegreenhouse, this was at much higher dosages (4 litreha-1 at weekly or biweekly intervals) than in ourexperiments (Cabello et al., 1997).

Greater yields could also be a function of theoxamyl treatment itself interacting with thevegetables and promoting growth. Oxamyl is knownto have a growth stimulant response, referred to as a�carbamate kick�, with certain crops (Rethwisch &Kruse, 1998). Improved vigour and fruit quality oftomato and pepper with oxamyl following metamsodium or 1,3-D have also been observed in Florida(D Dickson, personal communication). In ourexperiments, yield increments were generally greaterfor solanaceous (10-30% increment) as comparedto cucurbit crops (0-15% increment), indicating thatoxamyl may act differently according to crop type.As far as we know, there are no reports of beneficialeffects of oxamyl on cucurbits. However, thedifferent response could also be related to seasonaleffects, as solanaceous crops were grown in springand cucurbits were grown in autumn. Ourexperiments were unable to establish whether cropspecies/family or the greater pest and disease

the combination with oxamyl reduced root gallscompared to the fumigant by itself (Fig. 2, student�st-test = 0.05 for 1,3-D-based fumigants (1,3-D and1,3-D + chloropicrin), five comparisons, n = 17). Acombination of 1,3-D and oxamyl was the mostprofitable treatment for the control of potato cystnematodes (Globodera pallida) in potatoes (Barkeret al., 1998).

Oxamyl, like other carbamate pesticides, probablyacts through impairment of nematode nervoustransmission by inhibition of acetylcholinesterase,as it is the case in insects and vertebrates (Bunt, 1975;Wright et al. 1980). Oxamyl concentrations inirrigation water in our tests varied from 0.5-10 mglitre-1 depending on application concentration andirrigation time. Soil concentrations of oxamyl withinthis range have been found to cause inhibition ofhatching (5-10 mg litre-1), inhibition of movement(2-5 mg litre-1) and inhibition of feeding (0.5-2 mglitre-1) (Anon., 2003a). As oxamyl has shortpersistence and its poisoning effects are reversible,the chemical is considered nematostatic rather thannematicidal (Bunt, 1975).

Application timing of oxamyl followingfumigation with 1,3-D did not seem to have muchimpact on nematode infection. Although applicationslate in the season (6 and 8 WAP) may be beneficial,applications early in the season, preferably startingat planting, seem advisable, especially if climaticconditions during fumigation were unfavourable, asin Expt 2. Stephan & Trudgill (1983) observed thatthe longer oxamyl treatment was delayed after root-knot nematode infection, the fewer nematodes werekilled. This was ascribed to the fact that nematicidalactivity of oxamyl, although it is systemic, is greatestnear the root surface or the immediate rhizosphere(Potter & Marks, 1976; Wright et al. 1980). Thus,the primary action against endoparasitic nematodesis in the soil phase of the life cycle, preventing thenematodes from attempting to penetrate the roots(Hague, 1979). Several studies have indicated thatonce in the plant, nematodes are less sensitive topesticides (Whitehead et al., 1973; Bunt, 1975). Thecurrent recommendation is to apply oxamyl at thetime of transplanting and sequentially on a 10 to 14day interval for three total applications (Anon.,2003b). This would ensure continuous disruption ofthe root-knot nematode life cycle during the crop�sfirst one to two months of growth. The life cycle ofMeloidogyne incognita on tomato may take from63 days (at 16°C) to minimum 20 days (at 30°C) tobe completed (Ploeg & Maris, 1999).

Very low squash yields in non-treated plots duringautumn 2002 were due to severe root-knot nematodeinfection immediately after transplanting, resultingin stunted plants and total yield loss in three out offive replicates. Root-knot nematode pressure wasalways greater in autumn than in spring due to higher


pressure in autumn were responsible for the differentgrowth responses among plant families.

The results of this study indicate the potential ofoxamyl to reduce root-knot nematode infection andincrease yields of vegetables when combined withsoil fumigation with 1,3-D and/or metam sodium.More research is required to understand the effectof crop type, pest pressure, preceding fumigant (1,3-D or metam sodium) and injection timing of oxamyl.

Acknowledgements

The authors thank the DuPont and DowAgrosciences Companies for financial assistance,and Jimmy Laska, Lewis Mullis, Unessee Hargett,Don Hickey, Tonya Jo Cravens, Thomas Hilton,William Wilson, David Clements, Adam K Montfortand Chris Williamson for technical assistance. Wealso wish to acknowledge the valuable input of threeanonymous reviewers.

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