Recognizing Recognizing Diseases of Diseases of
PecanPecanJason BrockJason Brock
Dept. of Plant PathologyDept. of Plant PathologyUniversity of GeorgiaUniversity of Georgia
Tifton, GATifton, GA
Benefits to Disease Benefits to Disease RecognitionRecognition
Better disease managementBetter disease management Proper fungicide selectionProper fungicide selection Make adjustments for certain Make adjustments for certain
diseasesdiseases Need to be proactive for disease Need to be proactive for disease
controlcontrol Better insect managementBetter insect management
Elimination of unneeded Elimination of unneeded insecticide applicationsinsecticide applications
Diseases to be Diseases to be CoveredCovered
Pecan ScabPecan Scab Downy SpotDowny Spot AnthracnoseAnthracnose Leaf ScorchLeaf Scorch Zonate Leaf SpotZonate Leaf Spot Powdery MildewPowdery Mildew Phytophthora Shuck and Kernel Phytophthora Shuck and Kernel
RotRot
PECAN SCABPECAN SCABPECAN SCABPECAN SCAB
Pecan ScabPecan Scab The most wide-spread and The most wide-spread and
destructive disease of pecan.destructive disease of pecan. The disease that drives management The disease that drives management
programs.programs. Favored by prolonged periods of Favored by prolonged periods of
wetness (12 hours)wetness (12 hours) Symptoms develop Symptoms develop immatureimmature tissue – tissue –
including leaves, twigs, and shucks.including leaves, twigs, and shucks.
Pecan Scab Pecan Scab SymptomsSymptoms
Small, dark spots (1-5 mm)Small, dark spots (1-5 mm) Lesions might coalesce.Lesions might coalesce. On leaves, older lesions stop growing, dry On leaves, older lesions stop growing, dry
out, & crack (might have ‘shot holes’).out, & crack (might have ‘shot holes’). More common on lower leaf surfaceMore common on lower leaf surface Upper & lower lesions do not always Upper & lower lesions do not always
match.match. When pathogen is sporulating, lesions When pathogen is sporulating, lesions
look ‘velvety’ (green to black).look ‘velvety’ (green to black).
Pecan ScabPecan Scab
Pecan Scab on Pecan Scab on TwigsTwigs
Lesions are Lesions are elongated elongated and run and run parallel to parallel to the twig the twig axis.axis.
Pecan Nut ScabPecan Nut Scab
Pecan Scab DamagePecan Scab Damage Leaf ScabLeaf Scab
Reduced photosynthesisReduced photosynthesis Defoliation (when scab is severe)Defoliation (when scab is severe) Source of inoculumSource of inoculum
Nut ScabNut Scab Reduced sizeReduced size Nut dropNut drop Reduced % kernelReduced % kernel
SCAB DAMAGESCAB DAMAGESCAB DAMAGESCAB DAMAGE
REDUCED NUT SIZEREDUCED NUT SIZE EARLY NUT DROPEARLY NUT DROP
LOWER %KERNELLOWER %KERNEL
LEAF DROPLEAF DROP
TWIG DEATHTWIG DEATH
REDUCED NUT SIZEREDUCED NUT SIZE EARLY NUT DROPEARLY NUT DROP
LOWER %KERNELLOWER %KERNEL
LEAF DROPLEAF DROP
TWIG DEATHTWIG DEATH
Control of Pecan Control of Pecan ScabScab
Resistance (?)Resistance (?) Fungicide applicationsFungicide applications
Typically 7-10 spraysTypically 7-10 sprays Bud break through shell hardeningBud break through shell hardening Most critical time is between nut Most critical time is between nut
set to shell hardening.set to shell hardening. Post-pollination periodPost-pollination period June/July spraysJune/July sprays
Most susceptible cultivars were oncethought to be scab resistant.Pathogen is cultivar specific.This complicates screening.
DOWNYDOWNYSPOTSPOT
DOWNYDOWNYSPOTSPOT
Downy Spot Downy Spot SymptomsSymptoms
Typically starts in lower part Typically starts in lower part of treeof tree
First appear on lower surface First appear on lower surface (late spring to early summer)(late spring to early summer)
Circular, yellowish spots (2-5 Circular, yellowish spots (2-5 mm)mm)
Downy Spot Downy Spot SymptomsSymptoms
During wet periods, lesions During wet periods, lesions might look ‘frosty’ or white might look ‘frosty’ or white due to fuzzy fungal growth.due to fuzzy fungal growth.
Lesions become visible on Lesions become visible on upper surface 6-8 weeks laterupper surface 6-8 weeks later
Lesions turn golden brown Lesions turn golden brown on lower surfaceon lower surface
Downy Spot DamageDowny Spot Damage
Reduced photosynthesisReduced photosynthesis Early leaf drop, which can Early leaf drop, which can
lead tolead toReduced nut qualityReduced nut qualityLate season growth flushesLate season growth flushes
Results in fewer flowers for the Results in fewer flowers for the next yearnext year
Downy SpotDowny Spot
Source: Compendium of Nut Crop Diseases in Temperate Zones
Control of Downy Control of Downy SpotSpot
Pre-pollination is the critical Pre-pollination is the critical time for management.time for management.
Stick to the scab control Stick to the scab control program.program.
ANTHRACNOSEANTHRACNOSEANTHRACNOSEANTHRACNOSE
?
AnthracnoseAnthracnose Favored by rainy weather and Favored by rainy weather and
temperatures in the mid to upper temperatures in the mid to upper 80s ºF.80s ºF.
Damage: reduced yield and qualityDamage: reduced yield and quality Reduced kernel sizeReduced kernel size Nut dropNut drop Nuts stick tightNuts stick tight
Stick to scab control programStick to scab control program
Symptoms on shuckSymptoms on shuck Shiny, dark brown Shiny, dark brown
sunken lesions sunken lesions usually near usually near proximal end or proximal end or along shuck suturesalong shuck sutures
Lesions can enlarge Lesions can enlarge and cover entire and cover entire shuckshuck
Salmon-colored Salmon-colored spores within sunken spores within sunken lesionslesions
Source: Compendium of Nut Crop Diseases in Temperate Zones
LEAF LEAF SCORCHSCORCH
LEAF LEAF SCORCHSCORCH
Leaf Scorch – Similar Leaf Scorch – Similar symptomssymptoms
Scorch due to nutrient imbalance Scorch due to nutrient imbalance (Desirable)(Desirable)
High [N] & low [K]High [N] & low [K] Fungal leaf scorchFungal leaf scorch
PhomopsisPhomopsis sp. sp. Anthracnose (Anthracnose (Glomerella cingulataGlomerella cingulata))
Bacterial leaf scorch (Bacterial leaf scorch (Xylella Xylella fastidiosafastidiosa))
MitesMites
Leaf Scorch Leaf Scorch SymptomsSymptoms
Brown to tan lesions on the Brown to tan lesions on the margin or at the apex of the leaf.margin or at the apex of the leaf.
Lesions progress inward.Lesions progress inward. Lesions have a distinct margin Lesions have a distinct margin
separating healthy and necrotic separating healthy and necrotic tissue.tissue.
Can be confined to limbs or Can be confined to limbs or throughout the treethroughout the tree
Source: Compendium of Nut Crop Diseases in Temperate Zones
Nutrient relatedNutrient related
Source: Pecan Pest Management in the Southeast, CAES
Distinct Margin
Xylella Leaf ScorchXylella Leaf Scorch
Source: Compendium of Nut Crop Diseases in Temperate Zones
ZONATE ZONATE LEAF SPOTLEAF SPOTZONATE ZONATE
LEAF SPOTLEAF SPOT
Zonate Leaf SpotZonate Leaf Spot
More sever in over-crowded More sever in over-crowded orchardsorchards
Erratic distributionErratic distribution Favored by prolong wet Favored by prolong wet
periodsperiods
Zonate Leaf SpotZonate Leaf Spot SymptomsSymptoms
Leaf spots (15-20 mm) with concentric ringsLeaf spots (15-20 mm) with concentric rings More obvious on the lower leaf surfaceMore obvious on the lower leaf surface Lesions appear light brown to tan on the Lesions appear light brown to tan on the
lower leaf surface and grayish white on the lower leaf surface and grayish white on the surface.surface.
Late summer, infected leaflets begin to Late summer, infected leaflets begin to dropdrop. .
Signs of the pathogenSigns of the pathogen Sporulation might be observed on the Sporulation might be observed on the
lower leaf surface within the lesionslower leaf surface within the lesions
Source: Compendium of Nut CropDiseases in Temperate Zones
Source: Illustrated Genera ofImperfect Fungi, 4th Ed.
POWDERYPOWDERYMILDEWMILDEW
POWDERYPOWDERYMILDEWMILDEW
Powdery MildewPowdery Mildew Only grows on living tissueOnly grows on living tissue Appears midseason to lateAppears midseason to late Reduces kernel weight (up to Reduces kernel weight (up to
20%)20%)
Powdery Mildew - Powdery Mildew - LeavesLeaves
Initial lesions are circular, but Initial lesions are circular, but become irregular.become irregular.
Large irregular faded areas Large irregular faded areas develop.develop.
Little fungal growthLittle fungal growth Early infections may lead to Early infections may lead to
misshapen leaflets.misshapen leaflets.
Powdery MildewPowdery Mildew
Powdery Mildew - Powdery Mildew - ShucksShucks
More common on fruit than leavesMore common on fruit than leaves Dusty white spots (3-6 mm)Dusty white spots (3-6 mm) Shucks might become completely Shucks might become completely
covered with dusty white growthcovered with dusty white growth Older lesions might not have the Older lesions might not have the
“powdery mildew’, but will appear “powdery mildew’, but will appear russeted.russeted.
Powdery MildewPowdery Mildew
Source: Illustrated Genera ofImperfect Fungi, 4th Ed.
Source: Pecan Pest Management in the Southeast, CAES
Control of Powdery Control of Powdery MildewMildew
The critical time is during rapid nut The critical time is during rapid nut expansion (June-July)expansion (June-July)
Not all ‘scab fungicides’ work.Not all ‘scab fungicides’ work. When powdery mildew is a When powdery mildew is a
concern:concern:► ► Enable/AgriTin/ co-packEnable/AgriTin/ co-pack ►► Stratego Stratego►► Orbit/SuperTin co-packOrbit/SuperTin co-pack ►► Sulfur Sulfur►► Elast/Enable tank mixElast/Enable tank mix
PHYTOPHTHORAPHYTOPHTHORASHUCK ROTSHUCK ROT
PHYTOPHTHORAPHYTOPHTHORASHUCK ROTSHUCK ROT
Phytophthora Shuck Phytophthora Shuck RotRot
Occurs after prolonged wet Occurs after prolonged wet periods and air temperature periods and air temperature less than 87 F for daily highless than 87 F for daily high
Appears mid to late August, Appears mid to late August, early Septemberearly September
Sporadic occurrence; not Sporadic occurrence; not found every year.found every year.
Phytophthora Shuck Rot Phytophthora Shuck Rot DamageDamage
Nuts lost as stick tights (up to Nuts lost as stick tights (up to 50%).50%).
Kernels totally rotted.Kernels totally rotted. Late season infections - rancid Late season infections - rancid
kernels.kernels. Not able to separate infected from Not able to separate infected from
healthy nuts.healthy nuts. Mix with healthy kernels during Mix with healthy kernels during
shelling, quality reduced.shelling, quality reduced.
Phytophthora Shuck Rot Phytophthora Shuck Rot SymptomsSymptoms
Rot begins at the proximal end.Rot begins at the proximal end. Entire shuck will become rotted Entire shuck will become rotted
(within 4 days).(within 4 days). Necrotic tissue is dark brown, but Necrotic tissue is dark brown, but
does not collapse.does not collapse. Infected in late Aug/early Sept: Infected in late Aug/early Sept:
dry and stick tightdry and stick tight Infected in late Sept/Oct: open Infected in late Sept/Oct: open
before drying; nuts have bitter before drying; nuts have bitter tastetaste
Source: Compendium of Nut Crop Diseases in Temperate Zones
Inoculated young clusterInoculated young cluster
M. Hotchkiss and C. Reilly, SE Fruit and Tree Nut Research Laboratory, USDA –ARS, Byron, GA
Phytophthora Shuck Rot Phytophthora Shuck Rot ControlControl
Key QuestionsKey Questions1.1. Has this been a problem in the past?Has this been a problem in the past?2.2. Has the weather been conducive for Has the weather been conducive for
disease development?disease development? YES -YES - Look for symptoms.Look for symptoms. Apply fungicide before a rain Apply fungicide before a rain
and make all applications prior and make all applications prior to shuck split.to shuck split.
TPTH (AgriTin or SuperTin) 7.5 oz/ATPTH (AgriTin or SuperTin) 7.5 oz/A
Disease Disease ManagementManagement
Cultivar Cultivar RecommendationsRecommendations**
* Patrick J. Conner, Horticulture Department, UGA -Tifton.
Resistance Resistance LevelLevel
RecommendeRecommendedd
RecommendeRecommended for Triald for Trial
Not Not RecommendeRecommende
dd
ExcellentExcellent ElliotElliot
Kanza (in Kanza (in north)north)
GaffordGafford
Syrup MillSyrup Mill
JenkinsJenkins
CarterCarter
ExcelExcel
Gloria GrandeGloria Grande
CurtisCurtis
BartonBarton
GoodGood SumnerSumner McMillanMcMillan CandyCandy
MediocreMediocre OconeeOconee
CaddoCaddo
PawneePawnee
ForkertForkert
StuartStuart
MorelandMoreland
Cape FearCape Fear
KiowaKiowa
PoorPoor SiouxSioux
DesirableDesirable
Know Your OrchardKnow Your Orchard CultivarsCultivars History of scab pressureHistory of scab pressure History of other diseasesHistory of other diseases
e.g. downy spot; zonate leaf spot, powdery mildew; e.g. downy spot; zonate leaf spot, powdery mildew; Phytophthora shuck & kernel rotPhytophthora shuck & kernel rot
How long to complete applicationHow long to complete application
When your schedule is tight, hit When your schedule is tight, hit trouble areas first.trouble areas first.
Fungicide GroupsFungicide Groups
• AgriTin• Super Tin
• EnableEnable• OrbitOrbit• Propimaropimaxx
• AboundAbound• HeadlineHeadline
• StrategoStratego• ElastElast
Risk of ResistanceRisk of Resistance
LowLow ModerateModerate HighHigh
Three Part SeasonThree Part Season1)1) Pre-pollinationPre-pollination
Bud break through nut set (mid-Bud break through nut set (mid-May or casebearer time)May or casebearer time)
10-14 day intervals10-14 day intervals
2)2) Post-pollinationPost-pollination Nut set to shell hardeningNut set to shell hardening 10-21 day intervals10-21 day intervals
3)3) After shell hardeningAfter shell hardening
Rules to FollowRules to Follow If you use If you use EnableEnable or or PropimaxPropimax alone, alone,
then DO NOT use then DO NOT use EnableEnable/AgriTin; /AgriTin; OrbitOrbit/SuperTin; Elast+/SuperTin; Elast+EnableEnable; or ; or StrategoStratego later in season. later in season.
Do NOT make more than 3 Do NOT make more than 3 applications of Headline and/or applications of Headline and/or Stratego.Stratego.
DO NOT use Elast full season.DO NOT use Elast full season.
Fungicide Fungicide ApplicationApplication
ChoiceChoiceWhat to use?What to use?
TimingTimingWhen to apply?When to apply?
CoverageCoverageHow to apply?How to apply?
What to spray for What to spray for nut scab?nut scab?
Post-pollination is the critical Post-pollination is the critical period for protection.period for protection.
Decide what you want to spray Decide what you want to spray during this time, and work from during this time, and work from there.there.
Resistance management dictates Resistance management dictates certain uses of fungicides.certain uses of fungicides.
PRE PRE POSTPOST
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
Elast + Elast + EnableEnable
Elast + TinElast + Tin
StraStrategotego
EnableEnable
PropimaxPropimax
HeadlineHeadline
Agri-TinAgri-Tin
Super TinSuper Tin
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
ElastElast
Elast + TinElast + Tin
Elast + Elast + EnableEnable
StraStrategotego
Not all ‘scab Not all ‘scab fungicides’ are fungicides’ are suitable for suitable for powdery mildew powdery mildew or zonate leaf or zonate leaf spot.spot.
POST: Agri-Tin or Super POST: Agri-Tin or Super TinTin
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
Elast + Elast + EnableEnable
Elast + TinElast + Tin
StraStrategotego
EnableEnable
PropimaxPropimax
HeadlineHeadline
USE DO NOT USE
POST: Co-packsPOST: Co-packs
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
Elast + Elast + EnableEnable
Elast + TinElast + Tin
StraStrategotego
HeadlineHeadline
EnableEnable
PropimaxPropimax
USE DO NOT USE
POST: Elast or Elast + POST: Elast or Elast + TinTin
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
StraStrategotego
EnableEnable
PropimaxPropimax
HeadlineHeadline
Elast + Elast + EnableEnable
Elast + TinElast + Tin
USE DO NOT USE
POST: Elast + EnablePOST: Elast + Enable
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
StraStrategotego
HeadlineHeadline
Elast + Elast + EnableEnable
Elast + TinElast + Tin
EnableEnable
PropimaxPropimax
USE DO NOT USE
POST: StrategoPOST: Stratego
OrbitOrbit/SuperTin co-/SuperTin co-packpack
EnableEnable/AgriTin co-/AgriTin co-packpack
Elast + Elast + EnableEnable
Elast + TinElast + Tin
StraStrategotego
EnableEnable
PropimaxPropimax
HeadlineHeadline
USE DO NOT USE
TinTin**
Co-packsCo-packs ElastElastElastElast
+ Tin+ Tin * Elast* Elast
+ Enable+ Enable**
StrategoStratego
Co-packsCo-packs
ElastElast
+ Tin+ Tin
ElastElast
+ Enable+ Enable
HeadlineHeadline
StrategoStratego
EnableEnable
PropimaPropimaxx
Pre-pollination Pre-pollination PeriodPeriod
Leaf Scab and Downy SpotLeaf Scab and Downy Spot
Orbit/SuperTin co-packOrbit/SuperTin co-packElast+TinElast+Tin
Enable/AgriTin co-packEnable/AgriTin co-packElast+EnableElast+Enable
HeadlineHeadline Propimax Propimax
StrategoStratego EnableEnable
After Shell After Shell HardeningHardening
Scab and other leaf diseases can Scab and other leaf diseases can occur in August and September – occur in August and September – Protect next year’s crop.Protect next year’s crop. Enable/Super Tin co-packEnable/Super Tin co-pack Orbit/Super Tin co-packOrbit/Super Tin co-pack
Phytophthora shuck & kernel rotPhytophthora shuck & kernel rot Agri-TinAgri-Tin Super TinSuper Tin
Fungicide TimingFungicide Timing
Set ScheduleSet Schedule In south GA ‘Desirable’ is In south GA ‘Desirable’ is
sprayed about every 14 dayssprayed about every 14 daysPre-pollination: 10-14 daysPre-pollination: 10-14 daysPost-pollination: 10-21 daysPost-pollination: 10-21 days
Weather Based – AUPecanWeather Based – AUPecan CombinationCombination
Fungicide CoverageFungicide CoverageGood coverage might be Good coverage might be as important as as important as fungicide selection.fungicide selection.
Pay attention to Paul Pay attention to Paul Sumner’s talk at Sumner’s talk at 11:00.11:00.