HPIPM:Potato White Mold
From Bugwoodwiki
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Author: Howard F. Schwartz and David H. Gent
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Contents |
Identification and Life Cycle
White mold is caused by the fungus Sclerotinia sclerotium. The pathogen has a very broad host range, attacking over 400 plant species including dry bean, carrot, lettuce, melons, sunflower, and several weeds. The fungus produces a dormant resting structures called sclerotia that can survive for 3 to 5 years in the soil. These sclerotia may germinate under cool, moist conditions and directly infect stems and leaves in contact with the soil, or produce a mushroom like structure called an apothecium. Apothecia release up to 8 million windblown ascospores that are spread within the field. The ascospores land on and colonize senescing tissues such as flowers and leaves, and later invade healthy tissues. New sclerotia are formed on the diseased tissues and are returned to the soil.
Plant Response and Damage
White mold symptoms initially appear as soft, watery lesions on stems on or near the soil, but become bleached or tan when dry. Under wet, humid conditions lesions can expand and girdle stems, causing wilting of foliage above the lesion. White, fuzzy growth and black sclerotia are generally apparent on lesions. Tuber infections are rare, but have been observed. Lesions are initially small and depressed near eyes, but enlarge, become blackened, and cause a soft rot. Infected tubers are often filled with fungal mycelium and sclerotia. Yield losses from white mold are difficult to assess in potato, but probably cause little loss even when disease is severe.
Management Approaches
Biological Control
Contans is a commercial formulation of a fungus pathogenic to S. sclerotium sclerotia, and may reduce white mold incidence and/or severity with repeated applications over several years.
Cultural Control
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, schedule irrigations to prevent continuous leaf wetness throughout the evening.
Chemical Control
Fungicides may be economical in fields with a history of severe white mold. The number of fungicide applications necessary for effective disease control varies depending on when and how long apothecia are produced. A single fungicide application directed at the base of plants at row closure is often sufficient for effective disease suppression.
| Common/Trade Name | Product per Acre | Application Frequency (days) | Remarks |
|---|---|---|---|
| Boscalid | |||
| Endura | 5.5-10 oz | 7-14 days | Maximum of 2 applications (20 oz) per season; Rotate with fungicides with a different mode of action; 30 day PHI |
| Fluazinam | |||
| Omega | 5.5-8 fl oz | 7-10 days | Maximum of 3.5 pts per season; 14 day PHI |
| Iprodione—not all formulations listed | |||
| Rovral | 1-2 lb | 7-10 days | Do not irrigate within 24 hours of application; Maximum of 4 applications per season; 14 day PHI |
| Rovral 4 Flowable | 1-2 pt | 7-10 days | Do not irrigate within 24 hours of application; Maximum of 4 applications per season; 14 day PHI |
| Nitroaniline | |||
| Botran 75-W | 2 lb | 10- 14 days | 14 day PHI |
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.
