White mold is caused by the fungus Sclerotinia sclerotiorum. Infection by S. sclerotiorum occurs when soilborne sclerotia (dormant resting structures) germinate when the soil surface is continuously wet for at least two weeks. The germinating sclerotia form small, tan, cup-shaped structures called apothecia, which release millions of airborne ascospores that colonize dead plant parts (such as senescent flowers) and infect pea tissues. Sclerotia can survive in soil for up 8 to 10 years. The disease is most destructive during cool, wet weather in dense plant stands. White mold affects many plants and crops, including lettuce, sunflower, dry bean, and potato, among over 400 other plant species.
Initial symptoms appear as the plant canopy closes over rows during flowering and pod development. Lodged stems in contact with the soil develop watery lesions, with snowy white mycelium and black, irregularly shaped sclerotia become apparent as disease progresses. Disease losses vary depending on cropping history and weather conditions, but disease losses of 70% or more are possible.
Contans is a commercial formulation of a fungus (Coniothyrium minitans) pathogenic to S. sclerotorium sclerotia, and may reduce white mold incidence and/or severity when applied to soil over multiple years.
Practice a four-year or longer rotation to non-hosts such as corn or small grains. Plant high quality seed free from white mold sclerotia. Avoid excessive irrigation and fertilization that leads to dense, lush canopies favorable for white mold. Promote air movement within the canopy by planting varieties with open architecture, planting rows parallel to prevailing wind direction, and planting on wider row spacing. These practices will reduce the duration of leaf and soil wetness, and may help reduce white mold in semi-arid production areas. If possible, use drip irrigation or schedule irrigations to prevent continuous leaf and soil wetness. Deeply incorporate crop debris to bury sclerotia and hasten their breakdown.
Chemical controls are most effective when combined with cultural control strategies, and are generally not necessary if sound cultural practices are followed.
Product List for Sclerotinia Stem Rot (White Mold):
Pesticide |
Product per Acre |
Application Frequency
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Remarks |
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Azoxystrobin |
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Quadris |
6.2-15.4 fl oz |
7-14 days |
Maximum of 3 applications or 2.88 quarts per season; Do not make more than 1 application of Quadris before rotating to a fungicide with a different mode of action; 0 day PHI |
|
Boscalid |
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Endura |
6 oz |
7-10 days |
Begin at 20-50% flowering; Maximum of 2 applications or 22 ounces per season; 21 day PHI |
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Neem |
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Trilogy |
1% solution |
7-14 days |
Apply in 25 to 200 gallons |
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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: Canola and Mustard, Disease, Sclerotinia Stem Rot, White Mold
Date: 04/10/2007