It is likely in Michigan with such a wide crop range for other crops to serve as sources of the pathogen. cinerea can be seed-borne and develop from mycelium on the mother tuber. The fungus overwinters as sclerotia or mycelium in plant debris. Stem lesion on potato, occurring all the way up the stem. The gray appearance of the lesion is a result of the gray/black conidia on long-stalked conidiophores on the leaf surface. The disease initially appears as a tan lesion (Photo 1) at the leaf margin and eventually the entire leaflet, the compound leaf, becomes necrotic. Stem lesions may partially girdle the stem, but under hot conditions (greater than 85 degrees Fahrenheit) the whole stem can break down, especially in the presence of secondary bacteria. Stem lesions are common during senescence and may become infected at leaf scar sites or any form of stem damage, in particular from corn stem borers (Photo 4). Stem lesions on potatoes can occur all the way up the stem (Photos 3 and 4). Petiole lesions from leaflet infection.Īs the disease spreads along the petiole to the main stem, a lesion can form at that junction. Petiole lesions develop from leaflet infection and colonization and often constrict the conducting function of the compound leaf, limiting transport of photosynthates to the tubers (Photo 2). Leaflet lesions are readily seen on senescent tissue or tissue that has been damaged by mechanical, meteorological or chemical damage such as fertilizer application (Photos 1 and 2). The pathogen can overwinter as sclerotia, which germinate in the spring and early summer to produce clusters of “grape-like” conidia that are readily spread in air currents. Botrytis blight can also cause postharvest symptoms on potato tubers that are similar to Fusarium dry rot. Standard fungicide protection programs offer some suppression, but when conditions are wet the disease can develop quickly and enhance defoliation. Tuber infection can occur if the inoculum levels are high and the storage facility is very humid.
Botrytis blight drivers#
In recent years, Botrytis blight has posed a large threat to the potato crop even in drier years like 2012, as one of the major drivers of gray mold is excessive irrigation with high fertilizer inputs, which leads to a dense canopy that remains wet for a longer period of time. The disease is usually the result of excessive humidity and other stress factors that may include presence of potato early die, excessive rates of evapotranspiration and nitrogen deficiency. The pathogen has an extremely wide host range with well over 200 reported hosts including snap beans, other edible beans and soybeans, lettuce, tomatoes, various soft fruits, peas, peppers and many herbaceous perennials, and is found wherever potatoes are grown. The fungus Botrytis cinerea causes Botrytis blight, also known as tan spot or gray mold. Botrytis blight is causing problems in potatoes throughout Michigan this season.
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