Diagnosis and Prevention of Vegetable
Diseases in Organic systems
Daniel S. Egel
Department of Botany and Plant Pathology
Purdue University
4369 N. Purdue Rd.
Vincennes, IN 47591
(812) 886-0198 egel@purdue.edu
Learn about what diseases
are important for your
crop/location
Tomato Diseases
Anthracnose
Bacterial spot
Canker
Early blight
Fusarium crown rot
Fusarium wilt
Gray mold
Late blight
Leaf mold
Root knot
Septoria
Speck
Timber rot
TMV
Verticillium
Residue borne tomato diseases-rotations of
2-4 years and fall tillage critical
Disease
Maybe
Seed
borne
Resistance Comments
Anthracnose Yes
No
Bacterial
spot/speck
Yes
Speck
Canker
Yes
No
Stake & mulch
Early blight/
No
Septoria
No
Late blight
Yes
Unusual in Indiana
No
Primarily greenhouse
diseases
Leaf mold/
gray mold
No
No
Soil borne tomato diseases-rotations of
more than 4 years and fall tillage critical
Disease
Maybe
seed
borne
Resistance Comments
Fusarium
crown rot
No
No
Fusarium
wilt
Yes
Yes
3 races exist
Phytopthora
diseases
No
No
Includes buckeye rot and
root rot
Root knot
No
Yes
White mold
(timber rot)
No
No
Wide host range. Causal
agent survives many
years in soil.
Verticillium
wilt
No
Yes
Wide host range.
Pumpkin Diseases
Black rot
Fusarium
fruit rot
Powdery
mildew
Bacterial fruit spot
Downy mildew
Phytophthora blight
Plectosporium
blight
Virus diseases
Residue borne pumpkin diseases-rotations of
2-4 years and fall tillage critical
Disease
Maybe
seed
borne
Resistance Comments
Bacterial
fruit spot
Yes
No
Also affects squash
Black rot
Yes
No
aka, gummy stem
blight
Plectosporium
blight
No
No
Powdery
mildew
No
Partial
Readily windborne
Soil borne pumpkin diseases-rotations of
more than 4 years and fall tillage critical
Disease
Fusarium
fruit rot
Phytophthora
blight
Maybe
Seed
Borne
Resistance
Yes
No
No
No
Comments
Water management
critical. Avoid
rotations with
solanaceous crops.
Pumpkin diseases that are neither
soil or residue borne
Disease
Maybe
seed
borne
Resistance Comments
Downy
mildew
No
No
Overwinters in SE US
Virus
diseases
No
No
Overwinters in SE US
or on weed hosts
Post Planting Disease Management
•Fungicides/bactericides
•Apply materials preventatively
•Importance of the latent period
Latent periodthe time between infection and symptom production.
Septoria leaf spot of tomato-latent period about 6 days.
Downy mildew of pumpkin-latent period 4-12 days.
1. The latent period means that there are normally
more infections present than the eye can see.
2. Even the best fungicide/bactericide
merely slows the production of symptoms.
3. Therefore, it is best to apply a pesticide in a
preventative manner.
Hypothetical Fungicide Trial
High Disease 1000
Low Disease
900
800
700
600
500
400
300
200
100
0
No fungicide
Brand X
Brand Y
Brand Z
Fungicide Trial
Biofungicides on snap beans 1
White Mold
Product
OMRI*
Ballad + Biotune
A, x
Ballad + Champion + Biotune
Contans
A, R, x
A
Oxidate + Trilogy + Kaligreen + Cohere
Trilogy + Kaligreen
R, R, A, x
R, A
% control
91
80
43
102
60
140
77
32
170
A=allowed, R=restricted, x=not listed
*Organic Materials Review Institute
Biofungicides on snap beans 2
Gray Mold
Product
OMRI
Ballad + Biotune
A, x
Ballad + Champion + Biotune
Contans
A
Oxidate + Trilogy + Kaligreen + Cohere
Trilogy + Kaligreen
A, R, x
R, R, A, x
R, A
% control
65
0
78
49
160
62
69
106
22
A=allowed, R=restricted, x=not listed
Scout for diseases
Why scout?
Identify disease problems during the season
•To change practices this year
•For next year
How to scout:
A=Healthy leaf; B=infectious pattern;
C=non-infectious pattern (nutrition?);
D=non-infectious pattern (stress?)
Old leaf chlorosis-muskmelon
Interveinal chlorosis-muskmelon
Alternaria leaf blight of muskmelon
Septoria leaf spot-tomato
Septoria leaf spot-tomato
Contact herbicide damage-watermelon
Contact herbicide damage-watermelon
Downy mildew-pumpkin
Downy mildew-pumpkin
Downy mildew-pumpkin
Powdery mildew of pumpkin
Pumpkin virus
Pumpkin virus
Pumpkin virus
Fusarium wilt-watermelon
Healthy roots
Vascular discoloration
Fusarium wilt-watermelon
Diseased roots
Using a Diagnostic Lab
1.
2.
3.
4.
5.
6.
7.
Collect fresh, don’t send over weekend.
Send several examples
Crush proof container
Provide lots of information
Don’t pull plants-do bag roots
Press leaves
Contact lab