recognizing diseases of pecan jason brock dept. of plant pathology university of georgia tifton, ga

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


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


Nutrient relatedNutrient related

Source: Pecan Pest Management in the Southeast, CAES

Distinct Margin

Xylella Leaf ScorchXylella Leaf Scorch

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

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



ElastElast



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





StraStrategotego

EnableEnable

PropimaxPropimax

HeadlineHeadline

USE DO NOT USE

POST: Co-packsPOST: Co-packs





StraStrategotego

HeadlineHeadline

EnableEnable

PropimaxPropimax

USE DO NOT USE

POST: Elast or Elast + POST: Elast or Elast + TinTin



StraStrategotego

EnableEnable

PropimaxPropimax

HeadlineHeadline



USE DO NOT USE

POST: Elast + EnablePOST: Elast + Enable



StraStrategotego

HeadlineHeadline



EnableEnable

PropimaxPropimax

USE DO NOT USE

POST: StrategoPOST: Stratego





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.

recognizing diseases of pecan jason brock dept. of plant pathology university of georgia tifton, ga

Documents

pecan nut scab slide

pecan scab slide

kernel slide

size reduced size nut

pecan scab symptoms

kernel rot slide

kernel lower

downy spot slide