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How to Manage Pests
UC Pest Management Guidelines
Tomato
Damping-Off
Pathogens: Phytophthora, Pythium, and Rhizoctonia spp.
(Reviewed 1/07,
updated 1/07)
In this Guideline:
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Seedlings affected by damping-off fail to emerge or fall over and
die soon after emergence. Stems usually have a dark, shriveled portion at the
soil line. Damping-off is generally limited to areas where drainage is poor or
where soil is compacted, but whole fields can be affected, especially in early
plantings exposed to rain.
"Damping-off" is a general term for the death of
seedlings, either before or after emergence, under damp conditions. It is
mainly an early season problem, causing the greatest losses in cool, wet soils.
Fungi that cause damping-off occur in all soils where tomatoes are
grown, and they infect tomatoes when the soil is wet. Infection is most common
under cool conditions, although both Phytophthora and Rhizoctonia can also infect seedlings in warmer soils. Once
tomato seedlings reach the 2- or 3-leaf stage, they are no longer susceptible
to infection by Pythium or Rhizoctonia; however, Phytophthora can infect tomato plants at any stage. Damping-off
due to Pythium may increase where green manures such as volunteer grain are worked
into the soil just before planting. Damping-off does not necessarily carry over
from one season to another in the same places but appears only when and where
conditions favor infection.
Proper field and seedbed preparation and good water management
significantly reduce losses from damping-off. By using sprinklers for germination,
you keep better control of water and lessen the chance of infection. If
possible, avoid planting when the soil is cool; seeds germinate faster and seedlings
are more vigorous when the soil is warm, so they are less likely to be damaged.
The use of fungicide seed treatments can help prevent damping-off. When
seedling loss is extensive, replanting may be necessary.
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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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