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How to Manage Pests
UC Pest Management Guidelines
Tomato
Powdery Mildew on Field-grown Tomatoes
Pathogens: Leveillula taurica (Oidiopsis taurica)
(Reviewed 1/08,
updated 1/08)
In this Guideline:
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Leaves on infected tomato plants develop irregular, bright yellow
blotches; severely affected
leaves die but seldom drop. Spots of dead tissue, sometimes surrounded by a yellow
halo, eventually appear in the blotches. There are no lesions on stems or
fruit. Rarely, a gray mycelium develops
on the lower leaf surface of infected leaves. Severe infections kill leaves and
result in sunburn fruit and weakened plants.
Powdery mildew occurs in most tomato-growing areas of California.
The fungus infects weeds and crops in the solanaceous family; spores are
carried by wind to tomato plants. The disease usually occurs late in the
season. High relative humidity favors disease development. Mild temperatures
favor infection while higher temperatures hasten the death of infected leaves.
When
conditions are conducive to disease development, fungicide applications may be
necessary to control powdery mildew.
Organically Acceptable
Methods
Sulfur sprays are acceptable for use on organically certified produce.
Monitoring and Treatment
Decisions
A weather-based,
forecasting model is available
online. The model predicts the occurrence of powdery mildew based on
temperature, relative humidity, and leaf wetness. Growers can use the model to
accurately time fungicide applications.
Fungicides are not needed
for control unless the disease becomes extensive. If you see early symptoms,
check weekly to monitor the progression of the disease. Multiple, early
applications of sulfur are likely to provide control. An application of
azoxystrobin may be more effective than sulfur if it is well timed. There are
no immune tomato varieties in California.
| Common name |
Amount/Acre** |
R.E.I+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
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| The following
materials are listed in order of usefulness in an IPM program, taking into
account efficacy. When choosing a pesticide, also consider information
relating to environmental impact. |
| |
| A. |
PYRACLOSTROBIN |
| |
(Cabrio) EG |
8–12 oz |
12 |
0 |
| |
MODE OF ACTION GROUP
NAME (NUMBER1): Quinone outside inhibitor (11)
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COMMENTS: Do not apply more than 2 sequential applications or more than 96 oz/acre/season. |
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| B. |
MYCLOBUTANIL |
| |
(Rally) 40 WSP |
2.5–4 oz |
24 |
0 |
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MODE
OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
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| C. |
TRIFLOXYSTROBIN |
| |
(Flint) |
Label rates |
12 |
3 |
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MODE OF ACTION GROUP
NAME (NUMBER1): Quinone outside inhibitor (11)
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| D. |
SULFUR# |
Label rates |
24 |
0 |
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MODE OF ACTION GROUP
NAME (NUMBER1): Multi-site contact (M2)
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| E. |
AZOXYSTROBIN |
| |
(Quadris) F |
5–6 fl oz |
4 |
0 |
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MODE OF ACTION GROUP
NAME (NUMBER1): Quinone outside inhibitor (11)
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COMMENTS: Apply on a
7- to 14-day interval; make no more than three sequential applications before
alternating with a fungicide that has a different mode of action. Do not
alternate or tank mix with fungicides to which resistance has developed in the pathogen population. |
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![[Precautions]](/IMAGES/btn-precautions_bul.gif)
![[UC Peer Reviewed]](/IMAGES/logo-ucpeerreviewed.jpg)
UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
Diseases
R. M. Davis, Plant Pathology, UC Davis
G. Miyao, UC Cooperative Extension, Solano/Yolo counties
K. Subbarao, USDA Agricultural Research Station, Salinas
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the disease section:
B. W. Falk, Plant Pathology, UC Davis
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