The control of potato earlyblight:forecasting models and cultivar

resistance

Isaac Kwesi Abuley Department of Agroecology, Aarhus University

What is early blight?

A. solani

A. alternata

2

Five planting dates and three varieties

• Agata: Verysusceptible/very earlymaturing.

• Sava: Moderately slowblighing/medium maturing

• Kuras: Slow blightingand late-matuing potatocultivar.

3

Resistance to to EB is age-dependent

Maturity-based model (Physiological days)

5

0

250

500

750

jun jul aug sep oktDate

Phys

iolo

gica

l day

s (P

days

)

Flakkebjerg 2017

TOMCAST model

6

Integrating age-dependent resistance and weaather-based model

• Age < 300 Pdays• No spray regardless of the weather

• Age 300-500 Pdays• Spray ½ or 2/3 dose:• 20 DSV

• Age 300-500 Pdays• Spray full dose:• 20 DSV

Integrating age-dependent susceptibility (cv. Kardal)

8

Critical days model

5

10

15

20

25

0 10 20 30 40Temperature (C)

Min

imum

wet

ness

(h)

9

Magarey et al. (2005) Phytopathology95:92-100.

Critical days model with cv. Kuras

0

25

50

75

100

jul 15 aug 01 aug 15 sep 01 sep 15Assessment date

Early

blig

ht se

verity

(%)

TreatmentsUntreatedMaximum protection72-Risk hours120-Risk hoursCritical days

a

0

20

40

60

80

aug 01 aug 15 sep 01 sep 15 okt 01Assessment date

Early

blig

ht se

verity

(%)

TreatmentsUntreatedMaximum protection72-Risk hours120-Risk hoursCritical days

b

10

Four groups of resistance

0

25

50

75

100

40 60 80 100 120DAE

Early

Blig

ht S

ever

ity (%

Group AAgataSolist

SSBintje

a

0

25

50

75

100

40 60 80 100 120DAE

Early

Blig

ht S

ever

ity (%

SSBintje

Group BExcellencyFontane

b

0

25

50

75

100

40 60 80 100 120DAE

Early

Blig

ht S

ever

ity (%

)

SSBintje

Group CCarolusEnergieKubaOlev aPL 08-4007PL 08-4010Roy alSaturnaSav aSeresta

c

0

25

50

75

100

40 60 80 100 120DAE

Early

Blig

ht S

ever

ity (%

)

SSBintje

Group DAv arnaAv entraAv enueEurograndeFestienKardalKurasNorv anoNov arnoSignumStratosWotan

d

11Abuley et al. (2018). Plant Pathology, 67(2), 315-326.

Epidemiological data

• Disease assessment (0-100%)• Infection rate (rate). • The mid-time (T50).• Duration of epidemic (Yt). • Mid-severity (Y50). • rAUDPC. • Daily Defoliation (DD).

Abuley, Isaac Kwesi 12

Univariate analysis of Epidemiologal parameter

Variety T50 (DAS) DD (%day-1) Y50(%) Yt (days) rAUDPC rate (day-1)

Bintje 32.08j 2.06b 63.94b 48.8g 0.36b 0.23d

Carolus 41.07hi 1.78c-f 13.15cd 57f 0.27cd 0.23dEnergie 38.93ij 1.86b-e 17.94c 56f 0.27cd 0.22deFontane 31.78j 2.02bc 59.58b 49.8g 0.36b 0.25c

13

Cluster analysis

• 2015

1 4 2 3

0.01.0

2.03.0

Hierarchical Clustering

inertia gain

Solis

tAg

ataFe

stien

Norv

arno

Wota

nKa

rdal

Aven

traAll

star

Signu

mAv

enue

Euro

gran

deSt

ratos

Kura

sAv

arna

Exell

ency

Fonta

neBin

tjeCa

rolus

Satur

naEn

ergie

Roya

lOl

eva

Sava

PL 08

-400

7Se

resta

Kuba

PL 08

-401

0

0.00.5

1.01.5

2.02.5

3.0

Click to cut the tree

14

Cultivar resistance to EB depends on foliagematurity

Integrating cultivar resistanceCultivar Resistance level

Agata Very susceptible

Sava and Oleva Moderately slow blighting

Kuras Slow blighting

Spray schedule Description

Untreated No spray fungicide application

Standard spray Fungicide application started from 50% row closure @ 14 days interval.

TOMCAST 15 1st spray at 330 P-days and subsequent spray at 15 TOMCAST DSV

TOMCAST 20 1st spray at 330 P-days and subsequent spray at 20 TOMCAST DSV

Abuley, Isaac Kwesi 16

Integrating cultivar resistance

17

Oleva Sava

Agata Kuras

aug 01 aug 15 sep 01 sep 15 aug 01 aug 15 sep 01 sep 15

0

25

50

75

100

0

25

50

75

100

Assessment date

Dis

ease

sev

erity

(%)

Fungicide schedule Standard treatment TOMCAST-15 TOMCAST-20 TOMCAST-25 Untreated

Integrating other components to control EB

18

Timing N application affects early blight

19

0

25

50

75

100

jul aug sepAssessment date

Dis

ease

sev

erity

(%)

Treatment

Untreated

Standard appl

Late applicatio

Split applicatio

Split applicatio

Split applicatio

0

2500

5000

7500

aug sep oktAssessment date

Nitr

ate

cont

ent (

ppm

)

Treatment

Untreated

Standard app

Late applicati

Split applicatio

Split applicatio

Split applicatio

A minimum of 2 years rotation

20

General conclusions• Resistance to early blight depends on foliage maturity.

• Susceptiblity of potatoes to early blight increases with plant age.

• Fungicides can be adjusted based on the plant age.

• Varietal resistance does not affect the onset of early blight.

• 2 years between subsequent potato cultivation is sufficient.

• Higher TOMCAST thresholds could be used on cultivars with higherlevel of resistance.

• Potatoes that recieve N at emergence or as split application are lesssusceptible than potatoes that recieve N before planting.

Abuley, Isaac Kwesi 21

Papers

• Abuley, I.K. & Nielsen, B.J. (2019). Integrating cultivar resistance into the TOMCAST model to control early blight, caused by Alternaria solani. Crop Protection, 117:69-96.

• Abuley I.K., Nielsen B.J. and Hansen H.H. (2019). The influence of crop rotation on the onset of early blight (Alternaria solani). Journal of Phytopathology, 167:35–40.

• Abuley, I.K., Nielsen, B.J., Hansen, H.H. (2018). The influence of timing the application of nitrogen on early blight (Alternaria solani). Pest Management Science. https://doi.org/10.1002/ps.5236.

• Abuley, I. K., Nielsen, B. J., & Labouriau, R. (2018). Resistance status of cultivated potatoes to early blight (Alternaria solani) in Denmark. Plant Pathology, 67(2), 315-326.

• Abuley, I. K. & Nielsen, B.J. (2017). Evaluation of models to control potato early blight (Alternaria solani) in Denmark. Crop Protection 102: 118-128.

Thanks for your attention