w. r. stevenson university of wisconsin - madison, department of plant pathology

W. R. StevensonW. R. Stevenson

University of Wisconsin - Madison, University of Wisconsin - Madison, Department of Plant PathologyDepartment of Plant Pathology

Potato Late BlightPotato Late Blight

W. R. Stevenson, UW-Madison

Why Do We Worry About Late Blight In A Seed Area ?


Seed potatoes are generally grown in cooler climates Seed potatoes are generally grown in cooler climates more favorable for late blight developmentmore favorable for late blight development

Late blight pathogen is wind borne, long distancesLate blight pathogen is wind borne, long distances

Late blight pathogen is tuber-borneLate blight pathogen is tuber-borne

Late blight is a community diseaseLate blight is a community disease

Seed potatoes are generally grown in cooler climates Seed potatoes are generally grown in cooler climates more favorable for late blight developmentmore favorable for late blight development

Late blight pathogen is wind borne, long distancesLate blight pathogen is wind borne, long distances

Late blight pathogen is tuber-borneLate blight pathogen is tuber-borne

Late blight is a community diseaseLate blight is a community disease


Concerned customer baseConcerned customer base

Possible loss of crop certificationPossible loss of crop certification

Cost of disease controlCost of disease control

• $50 per acre $50 per acre $250 per acre $250 per acre

"Triple bottom line" "Triple bottom line"

• financial viability financial viability

• environmental responsibility environmental responsibility

• responsibility to society responsibility to society

Concerned customer baseConcerned customer base

Possible loss of crop certificationPossible loss of crop certification

Cost of disease controlCost of disease control

• $50 per acre $50 per acre $250 per acre $250 per acre

"Triple bottom line" "Triple bottom line"

• financial viability financial viability

• environmental responsibility environmental responsibility

• responsibility to society responsibility to society




Pathogen arrives in seed area via wind or seedPathogen arrives in seed area via wind or seed Infection of susceptible, unprotected plantsInfection of susceptible, unprotected plants

• Before adequate fungicide programsBefore adequate fungicide programs

• Poor or no fungicide coveragePoor or no fungicide coverage Long wet and cool periodLong wet and cool period Disease spreads rapidlyDisease spreads rapidly Control costs escalateControl costs escalate Tuber infectionTuber infection Pathogen survives winter on tubersPathogen survives winter on tubers Repeat the cycleRepeat the cycle

Pathogen arrives in seed area via wind or seedPathogen arrives in seed area via wind or seed Infection of susceptible, unprotected plantsInfection of susceptible, unprotected plants

• Before adequate fungicide programsBefore adequate fungicide programs

• Poor or no fungicide coveragePoor or no fungicide coverage Long wet and cool periodLong wet and cool period Disease spreads rapidlyDisease spreads rapidly Control costs escalateControl costs escalate Tuber infectionTuber infection Pathogen survives winter on tubersPathogen survives winter on tubers Repeat the cycleRepeat the cycle

The Late Blight CycleThe Late Blight Cycle


Tougher seed standardsTougher seed standardsCurrently allow 1% seed infection Currently allow 1% seed infection Some states force growers to plant only certified Some states force growers to plant only certified

seedseedRejection of seed lots when late blight on foliageRejection of seed lots when late blight on foliageWould a field be rejected for 1? 10? 100? 1000? Would a field be rejected for 1? 10? 100? 1000?

lesions per field??lesions per field??Can we predict tuber infection on basis of foliage Can we predict tuber infection on basis of foliage

infection??infection??





Breaking The CycleBreaking The Cycle


• 1% seedpiece infection1% seedpiece infection

• 10 ft-diameter area killed from 1 infected 10 ft-diameter area killed from 1 infected seedpieceseedpiece

10 foot diameter10 foot diameter

Potato Late BlightA Little Inoculum Goes a Long Way





• 1% seedpiece infection1% seedpiece infection• 10 ft-diameter area killed from 1 infected seedpiece10 ft-diameter area killed from 1 infected seedpiece• = 25% of the area of the field= 25% of the area of the field


Rules regarding cull pilesRules regarding cull piles

WI – mandatory cull pile destruction by May 20WI – mandatory cull pile destruction by May 20

• BuryBury

• Grind and spreadGrind and spread

• LandfillLandfill

• Feed to livestockFeed to livestock

Rules regarding cull pilesRules regarding cull piles

WI – mandatory cull pile destruction by May 20WI – mandatory cull pile destruction by May 20

• BuryBury

• Grind and spreadGrind and spread

• LandfillLandfill

• Feed to livestockFeed to livestock



Volunteer potatoesVolunteer potatoes

Mild winters or heavy early fall snowsMild winters or heavy early fall snows

Early season planting of row crops – peas, beans, Early season planting of row crops – peas, beans,

corncorn

Lack of effective herbicidesLack of effective herbicides

Are volunteers a public nuisance?Are volunteers a public nuisance?

Volunteer potatoesVolunteer potatoes

Mild winters or heavy early fall snowsMild winters or heavy early fall snows

Early season planting of row crops – peas, beans, Early season planting of row crops – peas, beans,

corncorn

Lack of effective herbicidesLack of effective herbicides

Are volunteers a public nuisance?Are volunteers a public nuisance?



Seed purchase and handlingSeed purchase and handling

Know the seed growerKnow the seed grower

• Visit the grower, walk the fields, view the Visit the grower, walk the fields, view the storagesstorages

Ask for field records – Ask for field records –

• IPM scoutsIPM scouts

• Certification inspectorsCertification inspectors

• Shipping point inspection Shipping point inspection

Seed purchase and handlingSeed purchase and handling

Know the seed growerKnow the seed grower

• Visit the grower, walk the fields, view the Visit the grower, walk the fields, view the storagesstorages

Ask for field records – Ask for field records –

• IPM scoutsIPM scouts

• Certification inspectorsCertification inspectors

• Shipping point inspection Shipping point inspection



If late blight If late blight riskrisk associated with seed - associated with seed - Consider treating seed with Tops/MZ/Curzate = Consider treating seed with Tops/MZ/Curzate =

EvolveEvolveConsider treating field with protectant fungicide at Consider treating field with protectant fungicide at

emergence emergence

If late blight pathogen If late blight pathogen confirmedconfirmed on seed - on seed - Consider the consequences of planting infected seedConsider the consequences of planting infected seed

• Increased management costsIncreased management costs

• Risk to crop in field and storageRisk to crop in field and storage

• Community source of late blightCommunity source of late blight

If late blight If late blight riskrisk associated with seed - associated with seed - Consider treating seed with Tops/MZ/Curzate = Consider treating seed with Tops/MZ/Curzate =

EvolveEvolveConsider treating field with protectant fungicide at Consider treating field with protectant fungicide at

emergence emergence

If late blight pathogen If late blight pathogen confirmedconfirmed on seed - on seed - Consider the consequences of planting infected seedConsider the consequences of planting infected seed

• Increased management costsIncreased management costs

• Risk to crop in field and storageRisk to crop in field and storage

• Community source of late blightCommunity source of late blight



At emergence (risk of late blight in seed, volunteers or cull At emergence (risk of late blight in seed, volunteers or cull pile)pile)

Consider treatment with protectant fungicideConsider treatment with protectant fungicide

At row close or at 18 severity valuesAt row close or at 18 severity values

If no late blight, but risk high (18 severity values)If no late blight, but risk high (18 severity values)

• Protectant spray with chlorothalonil, mancozeb, Protectant spray with chlorothalonil, mancozeb, metiram…metiram…

• Repeat at 5-7 day interval depending on crop Repeat at 5-7 day interval depending on crop growth and weathergrowth and weather

At emergence (risk of late blight in seed, volunteers or cull At emergence (risk of late blight in seed, volunteers or cull pile)pile)

Consider treatment with protectant fungicideConsider treatment with protectant fungicide

At row close or at 18 severity valuesAt row close or at 18 severity values

If no late blight, but risk high (18 severity values)If no late blight, but risk high (18 severity values)

• Protectant spray with chlorothalonil, mancozeb, Protectant spray with chlorothalonil, mancozeb, metiram…metiram…

• Repeat at 5-7 day interval depending on crop Repeat at 5-7 day interval depending on crop growth and weathergrowth and weather



If late blight present in area, but not in fieldIf late blight present in area, but not in field

• Treat with cymoxanil plus chlorothalonil, Treat with cymoxanil plus chlorothalonil,

mancozeb, metiram immediatelymancozeb, metiram immediately

• Continue at tight interval for three sprays then Continue at tight interval for three sprays then

protectant aloneprotectant alone

If late blight present in area, but not in fieldIf late blight present in area, but not in field

• Treat with cymoxanil plus chlorothalonil, Treat with cymoxanil plus chlorothalonil,

mancozeb, metiram immediatelymancozeb, metiram immediately

• Continue at tight interval for three sprays then Continue at tight interval for three sprays then

protectant aloneprotectant alone



If late blight present in field in pocketsIf late blight present in field in pockets

• Disk hot spots with perimeterDisk hot spots with perimeter

• Treat rest of field and adjacent fields with Treat rest of field and adjacent fields with

cymoxanil immediately, and again in 5 dayscymoxanil immediately, and again in 5 days

• Then continue with protectant programThen continue with protectant program

If late blight present in field in pocketsIf late blight present in field in pockets

• Disk hot spots with perimeterDisk hot spots with perimeter

• Treat rest of field and adjacent fields with Treat rest of field and adjacent fields with

cymoxanil immediately, and again in 5 dayscymoxanil immediately, and again in 5 days

• Then continue with protectant programThen continue with protectant program



Late blight throughout fieldLate blight throughout field

• Destroy field immediately and treat adjacent Destroy field immediately and treat adjacent

fields with famoxate/cymoxanil immediately and fields with famoxate/cymoxanil immediately and

again in 5 daysagain in 5 days

• Continue with protectant programContinue with protectant program

Late blight throughout fieldLate blight throughout field

• Destroy field immediately and treat adjacent Destroy field immediately and treat adjacent

fields with famoxate/cymoxanil immediately and fields with famoxate/cymoxanil immediately and

again in 5 daysagain in 5 days

• Continue with protectant programContinue with protectant program



Mid SeasonMid Season

Focus on protectant program that may include Focus on protectant program that may include

Curzate, Acrobat or TattooCurzate, Acrobat or Tattoo

Scout fields weekly or even more oftenScout fields weekly or even more often

Careful irrigation to avoid excessCareful irrigation to avoid excess

Mid SeasonMid Season


Curzate, Acrobat or TattooCurzate, Acrobat or Tattoo

Scout fields weekly or even more oftenScout fields weekly or even more often




Late SeasonLate Season


Acrobat, TattooAcrobat, Tattoo

Apply vine desiccant to protect size of seed potatoes Apply vine desiccant to protect size of seed potatoes

and to allow at least 3 weeks of dead vines before and to allow at least 3 weeks of dead vines before

harvestharvest


Late SeasonLate Season


Acrobat, TattooAcrobat, Tattoo

Apply vine desiccant to protect size of seed potatoes Apply vine desiccant to protect size of seed potatoes

and to allow at least 3 weeks of dead vines before and to allow at least 3 weeks of dead vines before

harvestharvest




Effective late blight strategy focuses on:Effective late blight strategy focuses on:

Keeping the fungal pathogen out of the planting areaKeeping the fungal pathogen out of the planting area

Intensive monitoring of every fieldIntensive monitoring of every field

Careful monitoring of weather conditionsCareful monitoring of weather conditions

Careful application of fungicideCareful application of fungicide

Partnership between each and every growerPartnership between each and every grower

Prompt response to local outbreaksPrompt response to local outbreaks

Effective late blight strategy focuses on:Effective late blight strategy focuses on:

Keeping the fungal pathogen out of the planting areaKeeping the fungal pathogen out of the planting area

Intensive monitoring of every fieldIntensive monitoring of every field

Careful monitoring of weather conditionsCareful monitoring of weather conditions

Careful application of fungicideCareful application of fungicide

Partnership between each and every growerPartnership between each and every grower

Prompt response to local outbreaksPrompt response to local outbreaks

Summary

Questions ?

Questions?

and comments . . .

and comments . . .

w. r. stevenson university of wisconsin - madison, department of plant pathology

Documents