Cottony rot is caused by the fungus Sclerotinia sclerotiorum. Infection by S. sclerotiorum occurs when 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 infect carrot. Sclerotia can survive in soil up 8 to 10 years. White mold affects many plants and crops, including lettuce, sunflower, bean, and potato, among over 400 other plant species.
Initial symptoms appear as small, water-soaked, lesions on crowns and roots. A 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 as great as 70% are not uncommon.
Contans is a commercial formulation of a fungus pathogenic to S. sclerotium sclerotia, and may reduce white mold incidence and/or severity when applied to soil for many years.
Avoid excessive irrigation and fertilization that leads to dense, lush canopies favorable for white mold. Promote air movement within the canopy by planting cultivars with smaller, upright 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.
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 Cottony Rot (White Mold):
Pesticide |
Product per acre |
Application Frequency (days) |
Remarks |
Boscalid |
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Endura |
4.5 oz |
7-14 days |
Max of 5 applications (22.5 oz) per season; do not make more than 2 sequential applications before rotating to a fungicide with a different mode of action; 0 day PHI |
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Strobilurin and Strobilurin/Boscalid |
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Pristine |
8-10.5 oz |
7-14 days |
Maximum of 6 applications or 63 oz per season; do not make more than two sequential applications of Pristine; 0 day PHI |
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Quadris |
9.2-15.4 fl oz |
7-14 days |
Maximum of 4 applications or 3.75 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 |
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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: Carrot, Disease, Cottony Rot (White Mold)
Date: 04/01/2007