Gray mold is a disease of potato foliage and tubers caused by the fungus Botrytis cinerea. The fungus has a very broad host range that includes many other vegetables, including tomato, pepper, dry bean, and onion. The disease cycle begins when wind or water deposits spores (ascospores or conidia) onto a leaf, where the fungus directly penetrates host tissue and infects the plant. Cool, wet weather and lush crop canopies greatly increase infection, especially on senescing or previously diseased plant parts. Heavy dew, fog, and frequent rain or irrigation increase gray mold severity. The pathogen may survive between potato crops in crop debris and soil as spores (conidia) or dormant resting structures (sclerotia), pathogenically on other plants, or saprophytically on organic matter.
Gray mold is most severe when temperatures are mild to moderate and moisture is abundant; warm, dry weather suppresses disease development. Disease symptoms are generally first observed on flowers as gray, fuzzy growth. As flowers drop into the foliage, lesion may develop on leaves, appearing as tan, wedge-shaped lesions largely confined by plant veins. Stems often develop a brown, slimy rot when leaf infections progress through petioles. Tuber infections are rare, but can occur when tubers are wounded during harvest and handling operations. Affected tubers have a wrinkled skin with a soft, wet rot that can extend deep into tubers. A dry rot can develop with tuber infections, but other tuber rotting fungi and bacteria can also invade gray mold lesions and cause a soft rot. The disease is generally not economically important in the High Plains, but can mask other diseases and make accurate disease diagnosis difficult.
No biological control practices have been developed for gray mold of potato, but biological control of the gray mold pathogen on other crops has been successful with various bacteria, yeast, and beneficial fungi.
Avoid excessive irrigation and fertilization that can lead to dense, lush canopies favorable for gray mold development. Avoid irrigation during rainy weather that can prolong periods of leaf wetness.
Fungicides effectively suppress gray mold, but resistance to several fungicides has been reported in B. cinerea strains from other vegetables.
Common/Trade Name |
Product per Acre |
Application Frequency
|
Remarks |
Chlorothalonil |
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|
Agronil 500 |
1-2 1/8 pt |
7-10 days |
May be applied through sprinkler irrigation with 10-day application interval. |
|
Agronil 720 |
0.75- 1.5 pt |
7-10 days |
May be applied through sprinkler irrigation with 10-day application interval. |
|
Bravo 500 |
1 - 2 1/8 pt |
7-10 days |
Maximum of 23 pints per acre; May be applied through sprinkler irrigation with 10 day application interval. |
|
Bravo 720 |
0.75-1.5 pt |
7-10 days |
Maximum of 16 pints per acre; May be applied through sprinkler irrigation with 10 day application interval. |
|
Bravo S |
3-4 pt |
7-10 days |
|
|
Bravo Ultrex |
0.7 –1.4 lb |
7-10 days |
Maximum of 14.5 pounds per acre |
|
Bravo Weather Stik |
0.75-1.5 pt |
7-10 days |
Maximum of 16 pints per acre |
|
Bravo Zn |
1 –2 1/8 pt |
7-10 days |
Maximum of 23 pints per acre |
|
Chlorothalonil 4L |
1 -2 1/8 pt |
7-10 days |
|
|
Manicure T/O Flowable |
1 ½ tsp/gal to cover 200 sq ft of crop |
7-10 days |
|
|
Terranil 6L |
0.75-1.5 pt |
7-10 days |
Maximum of 16 pints per acre; 7 day PHI |
|
Terranil Cu |
1.7-3.4 pt |
7-10 days |
Maximum of 36 pints per acre; 7 day PHI |
|
Terranil S |
3-4 pt |
7-10 days |
|
|
Terranil Zn |
1-2 1/8 pt |
7-10 days |
Maximum of 21 pints per acre; 7 day PHI |
Nitroaniline |
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|
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. |
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Categories: Potato, Disease, Botrytis Vine Rot, Gray Mold
Date: 03/29/05