Sclerotinia sclerotiorum is the casual organism of white mold of cucurbits and over 400 other plant species. White mold is a minor disease of cucurbits, but this disease can be economically important in cucumber, squash, and pumpkin under certain conditions. Little is known about the disease cycle in cucurbits, but it is probably initiated by dormant resting structures (sclerotia) and airborne ascospores. Infection appears to occur on dead and dying flowers, tendrils, and petioles. The fungus can also colonize stem wounds. S. sclerotiorum grows through vines quickly and form sclerotia within diseased tissues. The pathogen can be disseminated within and among fields as sclerotia on equipment, wind- and waterborne ascospores, and by the movement of diseased plant materials. S. sclerotiorum survives between cucurbit crops as a pathogen on numerous weeds and crops, and in the soil as dormant sclerotia.
White mold symptoms on fruit vary from none to water-soaked lesions at the infection point. A fluffy, cotton-white mycelium and numerous dull black, irregularly shaped sclerotia may appear on fruit where they contact the soil. Sometimes diseased fruit can become dry and mummified. Internally, fruit are soft and watery; numerous sclerotia form within diseased fruits. White mold is a fairly minor disease of most cucurbits, but can be quite severe when it occurs. The disease renders fruit unmarketable.
Contans is a commercial formulation of a fungus pathogenic to S. sclerotium sclerotia, and may reduce white mold incidence and/or severity if applied to soil over many years.
Since white mold is a relatively minor disease of cucurbits, few management strategies have been developed. White mold is most severe when the soil surface is kept continuously moist for two or more weeks. Therefore, promoting air movement within the plant canopy can significantly reduce disease incidence and severity. Avoid dense planting, narrow row spacing, and excess and overhead irrigation. Orientating rows parallel to the prevailing wind direction can also help reduce periods of leaf wetness in semi-arid environments. Long crop rotations to nonhosts such as small grains, corn, or onion can help reduce the number of sclerotia in the soil.
Chemical controls do not provide consistent disease control because it is difficult to obtain thorough coverage of foliage, vines, and fruit.
Product List for White Mold:
Pesticide |
Product per acre |
ApplicationFrequency
|
Remarks |
Nitroaniline |
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Botran 75-W |
1.33 lb/100 gal |
14 days |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Cucurbits, Disease, White Mold, Cucumber, Squash, Pumpkin
Date: 04/01/2007