Late blight threatens tomatoes

A healthy tomato flower

Tomatoes may be even more precious this summer than in previous years.  Yesterday, the state of Massachusetts released a pathogen alert about the Late Blight, the disease responsible for the Irish Potato Famine of the 1840s.  Conditions are perfect for late blight, and crops across New England are suffering. 

Late blight is caused by a persistent fungus that lives on potato tubers.  It can survive the winter on them, and is easily spread to other potato and tomato plants by infected potatoes left in the ground from the previous season. It can also be transmitted by farm or garden equipment that has come into contact with the mold, and can be washed into the soil by rain, where it spreads to other plants. 

A blighted potato

The hot, wet weather we've had all summer is ideal for this devastating disease, which has been known to wipe out an entire crop not just in gardens or at individual farms, but across huge swaths of land.  It can be difficult to spot early on, when infected plants could be destroyed to prevent the spread of the blight, and is so contagious and fast-spreading that often, by the time it is discovered, it's too late to save any of the crop.

No matter where you get your tomatoes, this year you may find less of them, and at a higher price, than you're accustomed to.  Even if you're growing your own tomatoes at home, you're not necessarily safe.  Many big-box stores, including Home Depot, Wal-Mart, Kmart, and Lowe's, unknowingly sold infected plants to consumers.  Some are offering refunds to those whose plants were killed by the fungus, but that won't save your supper.

Unripe tomatoes with late blight

While there are fungicides that can be sprayed on plants to prevent blight, they are not used by organic growers, and there is no good treatment for the disease once plants are infected,

The best defense against late blight is to recognize the early symptoms and dispose of infected plants as quickly as possible.  According to the Washington Post, "The initial symptoms are small, watery, gray or brown lesions on the leaf that quickly spread to the entire leaf. The fungus causes dark-brown lesions on the stems. The tomatoes turn brown and rot."  Click here for a gallery of images showing the symptoms of late blight.

Late blight is so tough and contagious that the only way to get rid of it is to burn or deeply bury infected plants, or seal them in plastic bags and throw them in the garbage.  Do not add blighted plants to your compost, as blight can easily survive in the warm, moist environment of a compost heap and re-infect plants next season.