University Park, Pa. -- Last year an epidemic of late blight disease on tomatoes not only forced many home gardeners to throw out their plants, but also threatened the crops of thousands of growers throughout the state. Along with cool, wet weather, the distribution of infected plants through big-box stores spurred along the widespread outbreak.
Led by Beth Gugino, Penn State assistant professor of plant pathology, the University responded with targeted, timely information to Extension educators, growers, master gardeners and the media. Among the advice was to throw out the plants and move on -- eating a tomato from an infected plant is generally discouraged, and canning carries the risk of botulism.
With springtime approaching, Gugino offers some tips that home gardeners can start thinking about now.
-- Kill the Potatoes. The disease hits spuds, too, and while the winter will kill off any infected tomato plants, potato tubers can survive the cold and therefore, so can the pathogen. Make sure potato plants are pulled up and thrown out in the trash (if composted improperly, the potatoes can be a source of the disease this year).
-- Rotate crops. Arrange your garden so that you rotate out of a plant family for two to three years. For example, the nightshade plants include eggplants, tomatoes and peppers. "The idea behind rotation is that many pathogens tend to be problems on multiple members in a given plant family, not just individual crops," said Gugino.
-- Avoid Overhead irrigation. It's best to water from below to keep leaves as dry as possible. This helps prevent the spread of the fungus as well as other common tomato diseases. If you only have access to overhead irrigation, water by mid-morning so leaves dry quickly.
-- Plant healthy transplants. There was a gardening boom last year (seed companies reported an increase in sales) and infected transplants were sold. Look at transplants for unhealthy characteristics such as pale green or brown lesions.