Early signs of tomato late blight have been found already in Maryland, and realistically, we can expect to see it again this year. Last year for American gardeners in the east, tomato blight was a disaster. Moreover, for those of us who produce our own calorie crops, the blight on potatoes was at least as serious as the loss of salsa. What can you do to make sure it doesn’t happen again?
The first is obviously make sure you remove all potatoes that may have sprouted again. The second is to plant resistant cultivars – in tomatoes there’s some evidence that Stupice, Juliet and Matt’s Wild Cherry show resistance – and certainly home and professional plant breeders will be starting here to work on blight resistant varieties. If you are planting a late crop of potatoes for fall, consider Defender, Ozette or Jacqueline Lee, which have also shown some resistance.
It helps to stake and prune tomatoes, and allow as much air circulation as possible, and to hill potatoes as fully as possible. There are also copper products certified for organic production that can be used, but they must be applied regularly, beginning *before* infection occurs. If you plan to go this route, begin early. Most of all, watch plants closely and remove all infected plant material as quickly as possible.
There’s more information in this article on Organic Management of Late Blight from Cornell Cooperative Extension.