citrus canker, alternaria and scab diseases of...
TRANSCRIPT
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Citrus Canker, Alternaria and Scab Diseases of Citrus
Megan M. DewdneyAssociate Professor of Plant Pathology and Extension Specialist University of Florida, IFASCitrus Research and Education Center
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CITRUS CANKER
Some slides adapted from E. Johnson
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Fruit size matters!
o Start copper sprays when fruit reach 3/8 in
o Need at least a 21 day interval to protect FRUIT
o Spray volume and tractor speed important for fruit coverage
– Slow down!
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Why a 21-day interval?
oCopper residue is significantly reduced by rain washing
oCopper does not move once dried
oCopper residue is cracked by fruit growth
oCopper model is an alternative if do not want to schedule– Advise when residue is insufficient for control
As the fruit grows, copper must be reapplied to continually cover the fruit as it becomes larger
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Proper Application of Copper
oUse label rate recommended for a disease
oBe cautious in hot weather (> 94°F; 34°C)
–Phytotoxicity can occur more easily in hot weather
oPotential for phytotoxicity can be reduced with greater water volume per acre
oComplex tank mixes, oil applications, and nutritional materials contribute to phytotoxicity
oWith aerial applications get inadequate penetration of canopy for control, best method is with an air blast sprayer
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Field trials and the effect of timing
o Evaluate copper sprays in relation to early season rains for control of fruit infection and drop in young fruiting Hamlins
– In a south central Florida citrus grove
o Compare soluble and fixed copper formulations for efficacy
– 2011, 2014, and 2015
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Fruit canker 2011
Treatment
Kocide 3000 4.0
Kocide 3000 3.0
Kocide 3000 2.5
NuCop 50 W
P 2.0
Nordox 7
5G 3.0
Cupro
fix U
ltra 40 3.0
Kentan D
F 2.62
Badge X2 2.68
Americop 40 D
F 2.5
Magna-B
on 50
Magna-B
on 20
UTC 1
UTC 2
Canke
r le
sio
n incid
ence
(%
)
0
20
40
60
80
100
120 old lesionsyoung lesions
b b b bb b
bb b
a
ab abab
Fruit Drop 2011
Treatment
Kocide 3000 4.0
Kocide 3000 3.0
Kocide 3000 2.5
NuCop 50 W
P 2.0
Nordox 7
5G 3.0
Cupro
fix U
ltra 40 3.0
Kentan D
F 2.62
Badge X2 2.68
Americop 40 D
F 2.5
Magna-B
on 50
Magna-B
on 20
UTC 1
UTC 2
Canke
r fr
uit d
rop
(%
)
0
20
40
60
80
cde de dee
cde
bcde
cde
bcdebcde
abcd
bcde
a
ab
Timing and weather mattersoNeed to watch early season weather forecasts for rainoEffects of being too late
–In 2011, 9 sprays began 15 April (too late) to 27 Sept, attempting to reduce impact of early epidemic
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Dry springo Limited early season infection
– In 2014, rain below average when fruit most susceptible size
Fruit canker 2014
Treatment
Kocide 2
000 4.0
Kocide 3
000 3.0
Nordox 7
5 WG 1
.33
Nordox 7
5 WG 2
.66
ChampIO
N 30 W
DG 3.0
NuCop 5
0HB 2.0
NuCop 3
0HB 3.0
Quimeta
l CO 1
.4
Quimeta
l CH 3
.0
Badge X2 2
.68
Magna-B
on 37
UTC 1
UTC 2
Canke
r le
sio
n incid
ence
0
5
10
15
20
25
30
35
old lesions new lesions
Fruit drop 2014
Treatment
Kocide 2000 4.0
Kocide 3000 3.0
Nordox 7
5 WG 1.33
Nordox 7
5 WG 2.66
ChampIO
N 30 WDG 3.0
NuCop 50HB 2.0
NuCop 30HB 3.0
Quimetal C
O 1.4
Quimetal C
H 3.0
Badge X2 2.68
Magna-B
on 37
UTC 1
UTC 2
No
. canke
r fr
uit d
rop
0
5
10
15
20
25
30
35
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Well timed applicationoWell timed applications can mitigate unfavorable rainfall patterns
– 2015, April rain greater than average when fruit at most susceptible stage
Fruit canker 2015
Treatment
Nordox 7
5 WG 1.33
ChampIO
N 30 WDG
NuCop 30HB 2.5
NuCop 30HB 1.75
NuCop 30HB 1.0
Quimetal C
O 1.4
Quimetal C
H 3.0
Kocide 3000 3.0
UTC 1
UTC 2
Canke
r le
sio
n incid
ence
(%
)
0
10
20
30
40
50
60
70
old lesions new lesions
bc bc bc
bc bc
bc
c
bc
ab
a
Fruit drop 2015
Treatment
Nordox 7
5 WG 1.33
ChampIO
N 30 WDG
NuCop 30HB 2.5
NuCop 30HB 1.75
NuCop 30HB 1.0
Quimetal C
O 1.4
Quimetal C
H 3.0
Kocide 3000 3.0
UTC 1
UTC 2
No
. canke
r fr
uit d
rop
0
20
40
60
80
100
120
140
160
180
200
cbc
c c
bcbc
bc
bc
a
ab
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Effect of inoculum carry overoApril rains induced early season fruit drop – Not canker inoculum carry over from previous season
oEarly bloom this season–Initiate program once fruit reach 3/8 in. dia.–May be in mid- to late-March
Month
April May June July Aug Sept Oct Nov
Rain
fall
(mm
)
0
100
200
300
400
20142015
Treatment
Cu treated Untreated Cu treated UntreatedF
ruit d
rop
pe
d/tre
e d
ue
to
canke
r
0
10
20
30
40
50
60
2014 2015
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How has Michael changed things?
oOn all trees, hurricane force winds push bacteria past any barriers
– Where inoculum present, considerable mature leaf infection and stem lesions
– Particularly bad in young blocks, especially if high canker in surrounding blocks
oStem lesions found on twigs
– Will contribute years of inoculum;
– Leaves only supply significant inoculum for a few months post-infection
oFor non-bearing and young blocks, Blockade recommended
– Copper does not control stem or leaf lesions
– Will help to suppress inoculum
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Conclusions on Application Timing
o Spray timing before spring rains critical for fruit protection once 3/8 in. dia
o Inoculum from infected leaves and stems from previous season always present in spring
– Stem lesions more problematic
– Michael has amplified and spread inoculum in the area
o Early fruit infection leading to fruit drop depends on spring rains coinciding with most susceptible fruit stage
o In June-July, infections of fruit > 1.5 in. result in smaller lesions that do not induce premature drop
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CITRUS SCAB
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Citrus Scab
oCausal fungus: Elsinoë fawcettii
oFound in most humid citrus production regions
o Important for fresh fruit production
–Economic damage restricted to peel
o Infects young leaves, twigs, and fruit
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Symptoms
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Citrus Scab Disease Cycle Caused by Elsinoëfawcettii
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Infection
oOptimal temperature range –74.3 to 80.6°F (23.5 to 27°C)
oOptimal leaf wetness–Between 12 and 24 hrs
–Can infect in as little as 4 hrs
oTend to see more disease with low lying areas where there is more dew and longer dew periods
Agostini et al., 2003
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Host Range and Tissue Susceptibility
oYoung leaves and fruit are susceptible
–Leaves immune to infection until half expanded
–Fruit remain susceptible up to two months post petal-fall
o Summer flush can be especially badly affected
oThe host range of E. fawcettii is complicated
oMatter of considerable phylogenic research
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Host RangeDisease Pathogen Pathotype Hosts
Citrus scab Elsinoëfawcettii
FBHR Lemon, grapefruit, Temples, sour orange, sweet orange, Satsuma, many tangerines
FNHR Lemon, grapefruit, Satsuma
Tyron’s Lemon, Cleopatra
Lemon Lemon
SRCG Satsuma, Rough lemon, Clementine, grapefruit
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Cultural Controls
o Disease-free nursery trees
– Start clean and problems are unlikely
o Hedge and top badly-affected plantings
– Does not move far into canopy
o No vigorous rootstocks
o No overhead irrigation
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Citrus Scab Control
o Common control products– Enable
– Strobilurin fungicides (Abound, Gem, Headline)• Good for first application
because kills fungus in last year’s lesions
– Ferbam
– Copper - All formulations• Use later in the season as it is
not as effective as other products
Feb Mar Apr May Jun Jul Aug Sept Oct
Tangerines
Grapefruit
o If infestation is light, disease can be pruned out
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Spray Timing
o Sprays are mainly for groves with a recent history of scab
oKey to good scab control is timing
o1st application at ¼ flush expansion
–Enable, ferbam or strobilurin fungicide
o2nd application at petal fall
–Different chemistry from 1st application
o3rd application 3 weeks post-petal fall
–Copper can fit well in this application
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Grapefruit Spray Trial 2004Date March 6-7 April 4-5 May 3
Program 1 Untreated control (UTC) Untreated control Untreated control
Program 2 Pristine 38WG (16 oz) Pristine 38WG (16 oz) Pristine 38WG (16 oz)
Program 3 Abound 2.08EC (12.4 fl oz) Enable 2F (8.0 fl oz) Kocide 2000 (4.5 lb)
Program 4 Gem F (2 fl oz) Ferbam Granuflo (5.0 lb) Gem F (2 fl oz)
Program 5 Endura 70WG (4.5 oz) Headline 2.09EC (9.2 fl oz) NuCop 50DF (4.0 lb)
Program 6 Abound 2.08EC (12.4 fl oz) Ferbam Granuflo (7.5 lb) Abound 2.08EC (12.4 fl oz)
Program 7 Abound 2.08EC (12.4 fl oz) Ferbam Granuflo (7.5 lb) Kocide 2000 (4.5 lb)
Program 8 Abound 2.08EC (12.4 fl oz) Enable 2F (8.0 fl oz) Abound 2.08EC (12.4 fl oz)
Program 9 Kocide 2000 (2 lb) Kocide 2000 (2 lb) Kocide 2000 (2 lb)
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Severity Rating
0
0.5
1
1.5
2
2.5
UTC Kocide Abound,Enable,Kocide
Abound,Ferbam,Abound
Abound,Enable,Abound
Abound,Ferbam,Kocide
Endura,Headline,
NuCop
Gem,Ferbam,
Gem
Pristine
a
b
c
d d dde
de e
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% Marketable Fruit
0
20
40
60
80
100
Pristine Gem,Ferbam,
Gem
Endura,Headline,
NuCop
Abound,Ferbam,Kocide
Abound,Ferbam,Abound
Abound,Enable,Abound
Abound,Enable,Kocide
Kocide UTC
a ab ab ab ab bcc
dd
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ALTERNARIA BROWN SPOT
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Symptoms
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Symptoms
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Alternaria Brown Spot Disease Cycle Caused by Alternaria alternata
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Alternaria Brown Spot Control
oCommon control products
–Copper - All formulations at a high rate
–Strobilurin-containing fungicides (Abound, Gem, Headline, Amistar Top and Pristine)
• Bolded products are premixes with alternate modes of action
• If severity high, useful for early sprays but also when hot
–Ferbam
Mar Apr May Jun Jul Aug Sept Oct
Tangerines
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Cultural Controls
o Start with clean trees
o Increase air drainage in grove when planting
oAvoid excessive growth promotion
–Too much nitrogen
–Overwatering
–Severe hedging
–High vigour rootstocks
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2018 Trial Details – Rates Program April 2 April 17 May 4 May 23 June 6 June 26
1 Priaxor(9 oz)
Priaxor(9 oz)
Priaxor(9 oz)
Priaxor(9 oz)
Priaxor(9 oz)
Priaxor(9 oz)
2 Amistar Top (15.4 fl oz)
Amistar Top (15.4 fl oz)
Amistar Top (15.4 fl oz)
Amistar Top (15.4 fl oz)
Amistar Top (15.4 fl oz)
Amistar Top (15.4 fl oz)
3 Luna Sensation(6.5 fl oz)
Luna Sensation(6.5 fl oz)
Kocide 3000(3.5 lbs)
Luna Sensation(6.5 fl oz)
Kocide 3000(3.5 lbs)
Luna Sensation(6.5 fl oz)
4 Luna Sensation(6.5 fl oz)
Velum(6.0 lbs)
Kocide 3000(3.5 lbs)
Luna Sensation(6.5 fl oz)
Kocide 3000(3.5 lbs)
Luna Sensation(6.5 fl oz)
5 Pristine(18.5 oz)
Kocide 3000(3.5 lbs)
Pristine(18.5 oz)
Kocide 3000(3.5 lbs)
Pristine(18.5 oz)
Kocide 3000(3.5 lbs)
6 Endura(6.5 oz)
Kocide 3000(3.5 lbs)
Endura(6.5 oz)
Kocide 3000(3.5 lbs)
Endura(6.5 oz)
Kocide 3000(3.5 lbs)
7 Kocide 3000(3.5 lbs)
Kocide 3000(3.5 lbs)
Kocide 3000(3.5 lbs)
Kocide 3000(3.5 lbs)
Kocide 3000(3.5 lbs)
Kocide 3000(3.5 lbs)
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Disease severity
0
0.1
0.2
0.3
0.4
Amistar Top Luna S. +Velum
Luna S. +Kocide
Priaxor Kocide 3000 Endura +Kocide
Pristine +Kocide
a
b
cc
d d d
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Marketable Fruit
80
85
90
95
100
Kocide 3000 Pristine +Kocide
Endura +Kocide
Priaxor Luna S. +Kocide
Luna S. +Velum
Amistar Top
a a
a aab
b
c
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Proportion of Population Sampled
o 2008 - 2012 n = 817
Resistant57.6%
Susceptible
42.4%
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Manage Tangerines As If Resistance Presento Should use mixture fungicides with alternative modes of
action (in Pest Management Guide)
oFrequent rotation with copper or other multisite fungicides like ferbam
o So far no sign of resistance
o Sample spray programQuadrisTop or Pristine
Copper Opposite premix
Ferbam Copper QuadrisTop or Pristine
11/3 or 11/7
M1 11/7 or 11/3
M3 M1 11/3 or 11/7
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QUESTIONS?
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Newer product: Blockade (formerly Actigard)
oNot a traditional pesticide
– Plant activator that triggers natural defense mechanism called systemic acquired resistance (SAR)
oNo direct effect against pathogens
oIntended to supplement copper applications for fruit protection
– Some foliar activity on non-bearing trees
oActivates plant defense system prior to disease
oActive ingredient: Acibenzolar‐S‐methyl
– Group 21 fungicide mode of action• Not a reference to efficacy against bacteria
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Chemical versus natural induction
o SAR can be naturally or chemically induced
– Natural induction is caused by a low level of plant pathogen attack
– Systemic throughout the plant
o Disease can develop before natural induction becomes effective
o High inoculum levels can overcome activation
o Chemical induction can occur before disease onset
– Apply in anticipation of disease
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Blockade use recommendations
o New plantings (0-3 year-old trees)
– Start as first growth beginning and continue non-bearing cycle
– Soil applied neonicotinoid insecticides can induce SAR and can be alternated with Blockade
– Use other canker management methods too
– Maintain SAR throughout season
o Objective to limit the establishment of canker during juvenile phase
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Blockade use recommendations
o Young bearing plantings (4-5 year-old trees)
– Initiate post-bloom, prior to conditions favorable to canker
– Use other canker management methods too
– Continue throughout spring, summer, and fall on 30-60 day intervals depending on tree size and planting density
o Mature plantings (6+ year-old trees)
– Continue throughout summer on 30-45 day intervals depending on tree size and planting density
o Can limit foliar lesion development and reduces inoculum potential