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How to Manage Pests
UC Pest Management Guidelines
Cucurbits
Monosporascus Root Rot
Pathogen: Monosporascus cannonballus
(Reviewed 11/05,
updated 6/08)
In this Guideline:
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Aboveground symptoms of monosporascus root rot appear as wilting,
yellowing, and wedge-shaped necrotic areas on crown leaves extending to
petiole. When temperatures are high and the crop is within 3 weeks of
harvest, entire vines may collapse Infected roots exhibit firm,
brownish to reddish lesions, and a general rot of secondary and smaller
roots. Wilt may occur without pronounced root symptoms. After the
roots die, black, round structures (perithecia), which contain spores, are
produced on the roots. Symptoms are most severe on watermelons, mixed
melons, and muskmelons but also occur on squash. Decline is generally
more severe on cantaloupe than honeydew melon.
Monosporascus vine decline is favored by high temperatures.
Optimum temperatures for M. cannonballus vegetative (hyphal) growth are from 77° to 95°F,
and from 77°to 86°F
for spore (ascospore) production. Plant stress caused by high
temperatures, too little or too much water, heavy fruit load, insect
infestations, or a combination of these factors may favor vine collapse.
In desert production areas, entire fields may collapse before fruit are mature.
Apply metam sodium or uproot plants shortly after harvest.
Ascospores are not affected by metam sodium or by desiccation. However,
before ascospore production, the fungus is vulnerable. If ascospores have
not yet been produced, an application of metam sodium, or uprooting the plants
and allowing the roots to dry on the soil surface will kill the fungus.
Because most of the spores are produced 1 to 3 weeks after the crop is
harvested, the use of either of these techniques soon after harvest could help
prevent the buildup of spore concentrations in soil to levels that are likely
to cause economic damage to the next melon crop planted in the same field.
Preplant fumigation with label rates of chloropicrin is effective
under some soil conditions.
| Common name |
Amount/Acre |
R.E.I.+ |
| (trade name) |
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(hours) |
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| A. |
METAM SODIUM* |
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(Vapam, Sectagon) |
Label rates |
48 |
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COMMENTS: Fumigants such as metam sodium are a source of
volatile organic compounds (VOCs) but are minimally reactive with other air
contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available. |
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| B. |
CHLOROPICRIN* |
Label rates |
48 |
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UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Diseases
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
W. D. Gubler, Plant Pathology, UC Davis
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
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