Courtesy Purdue University/Ray Martyn Take steps this year to prevent potato and tomato crops from being damaged by late blight.

Along with this year’s cool, damp weather came the threat of late blight in potatoes and tomatoes, especially in the Northeast and Midwest. Because of the fungal disease’s quick-moving and potentially fatal nature, it can reappear in next year’s crop, and small farmers should take necessary precautions.

“Late blight is a significant problem in cool, wet environments,” says Martin Draper, the program leader in plant pathology at the USDA’s National Institute of Food and Agriculture, noting that the risk of next year’s crop being affected depends on weather factors. “If the weather is hot and dry, it is possible no late blight will develop. If it is cool and wet again, the disease could be worse.” 

Because of the widespread problem of late blight outbreaks in 2009 crops, the spores are likely to be more abundant than they have been in the past decade, Draper says.

The 2009 outbreak in the northeastern states was derived from a mixture of weather conditions and the transportation of late blight spores into the area, conditions that are not likely to happen again, says Dan Egel, extension plant pathologist at Purdue University.

However, Egel recommends small farmers take four steps to prevent late blight in their 2010 crops:

1. Throw away seeds saved from this year’s crop. Late blight can overwinter and spread again next year. 

2. Plow under the crop and all vines. Plowing starts the decay process. The more a crop decays, the more likely the late blight will die with it. 

3. Plan for next year’s crop rotation now. Rotating the crops keeps the soil full of nutrients, but also prevents live spores from infecting new plants. For small farmers and home owners who don’t have room to rotate crops, Draper recommends removing as many of the plants as possible and throwing them away. Composting infected matter is not recommended, but can be done with the proper precautions.

4. Pull next year’s early volunteer crop. “Next year, go back to where potatoes were grown and pull those up,” Egel says. Although it might be overly cautious, it beats having another year of infected crop.

Small farmers can identify late blight by carefully inspecting potato and tomato plants. A lot of dead leaves on an infected fruit is the first red flag, Egel says. An olive-green lesion appears under the leaf and the edges of the leaf turn white. This can then spread to the stems and fruit.

Read more about the 2009 late blight outbreak here.