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How to Manage Pests
UC Pest Management Guidelines
Potato
Sclerotium Stem Rot
Pathogen: Sclerotium rolfsii
(Reviewed 8/07,
updated 8/07)
In this Guideline:
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Affected stems on plants
with sclerotium stem rot first show a moist decay at or slightly below the soil
surface where infection is initiated. Stem lesions expand up and down the stem,
and all plant parts can be infected. Stem infection leads to wilting and
yellowing of the foliage. Tubers are typically infected by way of stolons. The
fungus quickly grows over the tuber surface and invades, resulting in a moist
cheesy decay. Portions of infected plant parts and nearby soil often are covered
with the white, radiating mycelium of S.
rolfsii. The mycelium generates small spherical sclerotia (about 1–2 mm in diameter) that are white when young and brown when
mature.
S. rolfsii attacks many
field and vegetable crops in warm regions. The fungus persists in soil between
crops. Germination and infection by the sclerotia are favored by hot
temperatures (80° to 90°F) and moist soil surfaces. Sclerotium stem rot is considered
to be a problem only in hot climate growing areas. Losses typically occur at
the end of the season. The fungus can invade dead vines as well as living ones.
Extensive tuber losses can be initiated within a few days of harvest if the
fungus is present, and rot can continue in transit. Potato cultivars vary in
their degree of susceptibility but current cultivars have not been well
classified.
Relatively early planting
minimizes stem and tuber rot by avoiding the late season high temperatures that
favor disease. Plant fields infested with S. rolfsii before
noninfested fields. Do not store tubers in the ground unnecessarily before
harvest; this allows more time for infection at favorable warm temperatures.
Rotate to crops that are less susceptible (e.g., nonfleshy, root or tuber
crops).
Preplant chemigation with
metam sodium is recommended for fields known to be infested with S. rolfsii; the
treatment has afforded good control for at least one season. Applications of
the soil amendment ammonium bicarbonate made just before harvest will kill mycelium,
but not the sclerotia, of the fungus, thus preventing tuber infection for about
3 to 5 days.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
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| When choosing a
pesticide, consider information relating to the impact on environmental
quality Not all registered pesticides are listed. Always read label of product being used.
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| A. |
METAM SODIUM* |
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(Vapam, Sectagon) |
37.5–75 gal |
48 |
0 |
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(Metam Sodium) |
50–100 gal |
48 |
0 |
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COMMENTS: Follow
manufacturer recommendations on waiting interval between treatment and planting.
Fumigants such as metam sodium
are a source of volatile organic compounds (VOCs), which are a major
air quality issue. Fumigate only as a last resort when other management strategies
have not been successful or are not available. |
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UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
Diseases
R. M. Davis, Plant Pathology, UC Davis
J. Nuñez, UC Cooperative Extension, Kern Co.
B. J. Aegerter, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the disease section:
C. Smart, Plant Pathology, UC Davis
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