Disease threatens local tomato, potato plants

Vermont's early summer cloud cover and wet weather is killing local crops. If you grow tomatoes or potatoes for farmers markets or for personal consumption, take heed. This is shaping up to be one of the worst years for Late Blight, the fungal disease made famous as the cause of the Irish potato famine of the mid-1800s.

Today, this disease doesn't pose the threat of famine, since we don't depend on one or two local crops for our food, but it could ruin potato and tomato crops for local farmers and gardeners unless they are alert and take appropriate action. Note that this disease poses no threat to people--except for the loss of these crops.

Late blight is caused by the fungus called Phytophthora infestans, and it's actually not uncommon in the northeast, since it thrives in cool summer temperatures and frequent rains. But usually its occurrence is limited to later in the growing season and only certain areas of the region, typically in a few farm fields.

This year, the plant disease has shown up early and is widespread. Worse, it's been identified on tomato plants for sale at a number of Vermont home garden centers, suggesting that large numbers of home gardeners have already purchased infected plants, which may serve as a source of inoculum (spores) that can spread the disease.

Late blight inoculum is easily carried long distances by wind currents, so anyone growing tomatoes or potatoes should be on the lookout for signs of the disease, even in the most remote areas in our region. Currently all varieties of tomato and potato plants grown in home gardens and in commercial fields are susceptible to late blight. If your plants have late blight, be prepared to destroy them in order to limit spread of the disease.

The Late Blight organism is not seedborne (however, it is tuberborne in potato), so that tomato plants started from seed locally should be free of the disease, at least initially.

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