Late blight affects nightshade plants, which include tomatoes, potatoes, eggplant, tomatillos, and peppers. It can also attack petunias, which are closely related. Though the fungus responsible for the blight is common, this summer it is unusually early and extremely severe.
Late blight spreads more quickly than any other plant disease. Three days is enough time to wipe out an entire field of tomatoes. Once blight has infected a plant, there is no cure. Organic gardeners can apply copper-based sprays, and non-organic growers have the option of using synthetic fungicides, but any spray works only to suppress, not erase fungus. None have been effective this summer.
Brown spots on stems are one of the first symptoms. Cornell University’s College of Agriculture Web site provides helpful photos and descriptions of the disease. Since airborne spores can travel up to 40 miles, to prevent spreading home gardeners should pull plants out at the first sign of late blight. Place plants in plastic bags, seal, and send out with the trash. Do not compost infected plants. This FAQ page is a regularly updated source of information from Cornell.
If you find your tomato crop infected, here’s a bit of consolation. The fungus is not dangerous to humans. Green tomatoes that appear unaffected by the blight may be picked and brought indoors. Once inside, if they develop brown spots as they ripen, simply cut away the affected area. The fruit is safe for eating.
Plant pathologists report that home gardeners, by planting infected tomato starts purchased at large retailers, inadvertently transferred the disease across the Northeast states. The increase of neighborhood gardens and favorable conditions for fungal growth contributed to what will be the worst tomato harvest in memory.
Next year, gardeners can take the following steps to help keep late blight away. Buy plants from locally based nurseries, where disease is monitored more closely than at big box stores. Or even better, start plants yourself from seeds, since seeds do not carry the disease. Home gardeners are likely to pay close attention to their foods sources, and as Dan Barber wrote in the Times, a plant that travels 2000 miles to your garden is no different from a tomato that travels 2000 miles to your plate. Pay attention, too, to the connections between the plants you care for and the wider agricultural world. This season’s late blight disaster provides a vivid example of the close link between garden and farm. Finally, continue to support local farmers, whose income will be diminished if their crops include tomatoes.