Horticulture
Roger Ort, Horticulture Educator, [email protected]
Late blight: Serious disease of potatoes, tomatoes
Late blight is a plant disease that mainly attacks potatoes and tomatoes, although it can sometimes be found on other crops, weeds and ornamentals in the same botanical family (solanaceae).
Late blight is caused by an oomycete pathogen that survives from one season to the next in infected potato tubers. This organism is well known for its ability to produce millions of spores from infected plants under the wet weather conditions that favor the disease. Early in the season, the disease can be introduced into a field or garden on infected seed potatoes, from volunteer plants growing from diseased potatoes that were not harvested last season, from infected potatoes in cull piles (rejected potatoes), compost piles or infected tomato transplants brought into the area.
Spores produced on infected potatoes and tomatoes can travel through the air, and if the weather is sufficiently wet, can cause new infections. Spores can also be washed through the soil, which may rot before harvest, or in storage. It is very important that everyone who grows potatoes or tomatoes is able to identify late blight and know how to control it, to avoid being a source of spores that infect neighboring gardens and commercial fields.
Preventing late blight
The most effective management strategy for late blight is to avoid sources of early season inoculum (spores). Late blight can only survive on living tissue, so potato tubers or tomatoes are the only source of early season inoculum. Avoid introducing late blight on potatoes by planting healthy certified seed potatoes. Destroy any rejected tubers that you don’t plant. Make sure any potatoes put into compost piles are completely decomposed, and destroy any potato plants that come up from tubers that were left last season.
If the growing season is wet, and late blight is present, fungicides will be necessary to protect your plants from infection. For home gardeners, the only available fungicides that are effective against late blight are protectant materials, which means that they must be on the foliage before spores land on leaves. Therefore, continuous fungicide coverage is necessary to protect plants. Choose a fungicide that has maneb, mancozeb, chlorothalonil or fixed copper as an active ingredient AND has tomato and potato late blight on the label.
Hill up soil around the base of potato plants to provide a barrier to spores that can wash through the soil to tubers. Vines should be dead 2-3 weeks before digging potatoes for storage. To harvest before the vines have died naturally, cut stems just above the surface of the soil 2-3 weeks before harvesting.
— Article produced by the Integrated Pest Management Program, which is funded through Cornell University, Cornell Cooperative Extension, the New York State Department of Agriculture and Markets, the New York State Department of Environmental Conservation, and USDA-CSREES. Written by Abby Seaman, Vegetable IPM, Integrated Pest Management Program, NYSAES, Cornell University; Rosemary Loria, William Fry, and Thomas Zitter, Department of Plant Pathology, Cornell University. Photographs by Meg McGrath and Thomas Zitter, Department of Plant Pathology, Cornell University. Design and layout by Karen English, Integrated Pest Management Program, NYSAES, Cornell University. NYS IPM Publication No. 140.
For more Late Blight infomration please click HERE
http://www.longislandhort.cornell.edu/vegpath/photos/lateblight_tomato.htm