Potato charcoal rot is unmistakable. The disease also hits several other crops where it decimates the harvest. Only certain conditions cause activity of the fungus responsible, which lives in soil. Cultural changes and careful selection of seed can limit the damage of this fatal disease. Read on for some tricks to protect your potato crop.
About Charcoal Rot of Potatoes
Potatoes are an important economic crop and one which is prey to several insect and disease problems. Charcoal rot is one that affects the tubers and the lower stems. It is a fungal disease that also affects over 500 other plants: beans, corn, and cabbage among them. In potatoes, charcoal rot causes tubers that are inedible and can't even be used for seed. In many crops, charcoal rot will diminish yield and cause evident damage to stems. In potatoes, the first signs are in the leaves, which wilt and turn yellow. Next infected are the roots and then the tubers. By the time the stem develops tiny, black, ashy fungal structures, the plant is too diseased to save. Potatoes with charcoal rot will show signs at harvest. Tubers are infected first at the eyes. Water-soaked gray lesions appear that slowly turn black. Interior potato flesh gets mushy and turns pink, finally darkening to black. Sometimes only a few plants in a crop are affected but the fungus does spread easily.
Control of Charcoal Rot of Potatoes
Charcoal rot in potato plants develops from Macrophomia phaseolina. This is a soil-borne fungus that overwinters in soil and in plant debris. It is most prevalent in periods of hot, dry weather. Soil types that favor development of potato charcoal rot are sandy or gritty on hills or compacted zones. These sites tend to dry out quickly and encourage development of the disease. The fungus also can be spread through infected seed. There are no resistant cultivars, so certified disease-free seed potatoes are essential to controlling charcoal rot in potato plants. Stress also encourages disease formation. Often, plants will show no signs until the end of the season when temperatures are getting hotter and after flowering. It is not only important to select disease free seed potatoes or plants but to rotate the crop every two years to a non-favored plant such as wheat. Allow plenty of circulation between plants to prevent crowding and the stress associated with such growing conditions. Maintain average soil moisture. Avoid tilling and use an organic mulch around potatoes to conserve moisture. Provide adequate phosphorus and potassium as well as nitrogen to encourage plant growth and overall health. Since there are no fungicides registered for use against potatoes with charcoal rot, never save tubers from an infected crop for next year's seed.
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Bonnie Grant is a professional landscaper with a Certification in Urban Gardening. She has been gardening and writing for 15 years. A former professional chef, she has a passion for edible landscaping.
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