Disease Management for

Organic Strawberries:

1. Foliar and Fruit Problems

Steven T. Koike

University of California

Cooperative Extension

Monterey County

Foliar Fruit

• Angular leaf spot

• Anthracnose

• Common lf spot

• Phomopsis lf bl.

• Leaf blotch

• Powdery mildew

• Gray mold

• Anthracnose

• Rhizopus rot

• Mucor rot

• Leather rot

• Powdery mildew

• Gray mold

• (Anthracnose)

• Rhizopus rot

• Mucor rot

• Leather rot

• Powdery mildew

• Angular leaf spot

• Anthracnose

• Common lf spot

• Phomopsis lf bl.

• Leaf blotch

• Powdery mildew

Foliar Fruit

Limited Management Choices

• Resistant cultivars: lacking

• Exclusion: helps with a few diseases

• Spray materials: most partially

effective (exception: sulfur for pm)

• Cultural practices: helpful

Resistance

• True genetic resistance: lacking

• Differential susceptibility

• Simulated resistance/tolerance

– Environmental factors

– Plant architecture

Relative susceptibility of strawberry

cvs. to powdery mildew

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9 10 11 12

% leaf areainfected

(Nelson et al. 1996)

Exclusion

• Exclusion = do not bring the problem

into the field.

– Plant “disease free” transplants

– Plant “pathogen free” transplants

– Avoid bringing in infested soil

Spray Materials

• Inorganics

– Sulfur, copper, bicarbonates

• Organics

– Oils, plant extracts, compost extracts

• Microbials

– Biocontrol agents, antagonists

Cultural Practices

• Crop rotation

• Site selection (microclimate)

• Sanitation

• Drip irrigation

• Plant density considerations

• Other

Disease Management for

Organic Strawberries:

2. Soilborne Problems

Steven T. Koike

University of California

Cooperative Extension

Monterey County

Soilborne Pathogens

• Major pathogens

– Verticillium

– Phytophthora

– Colletotrichum

• Minor pathogens

– Rhizoctonia

– Cylindrocarpon

– Macrophomina *

– others

Verticillium

wilt

Phytophthora

root and crown

rot / fruit rot

Macrophomina

phaseolina

Strawberry as a Host

• Perennials: slow growing and

exposed to pathogens for a long time

• Transplants: exposed at trans. stage

• Undergoes prolonged physiological

stress during fruiting

• No completely resistant cultivars

• Some differences in susceptibility

Soilborne Pathogens

• Persistent, long term residents in soil

• Survive without a strawberry host

• Populations slowly decline in

absence of host

• Different strains may exist

• Live in complex ecological systems

Managing Soilborne Problems

• Site selection: avoid problems

• Exclusion: transplants, infested soil

• Crop rotation

• Use less susceptible cultivars

• Proper cultural practices

• Biofumigation: broccoli rotation

Verticillium Host Ranges

V. source lettuce strawb pepper cauliflower

lettuce ++++ +++ + 0

strawberry +++ ++++ + +

pepper + + ++++ +

pepper* +++ +++ ++++ +

cauliflower 0 + + ++++

+++/++++ = very good host

+ = not a very good host

0 = not a host

* = unusual pepper isolate

Field Context Case Study

Pepp

yes

Straw

yes

Spin

no

Straw

yes

Lett

yes

Straw

no

Straw

yesStraw

no

Straw

no

Caul

noA

Brocc

no

Brocc

no

Pepp

no

Lett

no

Caul

yes

Caul

yes

Previous

Vert y/n?

B

Field Context Case Study

Pepp

yes

Straw

yes

Spin

no

Straw

yes

Lett

yes

Straw

no

Straw

yesStraw

no

Straw

no

Caul

noA

Brocc

no

Brocc

no

Pepp

no

Lett

no

Caul

yes

Caul

yes

Previous

Vert y/n?

B

0

2

4

6

8

10

12

14

16

18

20

V V V V S S S S V V V S S S

Mic

ros

lero

tia

g-1

so

il

BRL BSP LET

4/22/97 1/22/98 8/8/00

BRL= Broccoli, BSP=Brussels sprouts, LET=Lettuce

Soil samples taken during the course of the study in different rotation

treatments

V=Vegetable, S=Strawberry

Means with same letter are not significantly different at P<0.05, n=30

a

a

a

a

b

c

Crop rotation effects on Verticillium in soil

0

0.5

1

1.5

2

2.5

3

3.5

4-Ju

n

11-J

un

18-J

un

25-J

un

2-Ju

l

9-Ju

l

16-J

ul

23-J

ul

30-J

ul

6-Aug

Dates of disease rating

Wil

t severi

ty

Broccoli

Lettuce

Organic

Crop rotation effects on Verticillium wilt

severity of strawberry

USDA