If you’re a gardener, you may already know the bad news: late blight is here.

It’s very likely spores were blown in during Tropical Storm Irene and symptoms began showing up last week. If you haven’t looked at the garden in a few days, do so now, according to Paul Hetzler, horticulture and natural resources educator with Cornell Cooperative Extension of St. Lawrence County.

While other diseases weaken plants to varying degrees, late blight is unique in its complete destruction of affected crops. Spores, easily killed by sunlight, can travel miles in cloudy conditions. Even a small amount of moisture on tomato or potato leaves will allow this fungus to penetrate into the plant, Hetzler says.

Once watery lesions on tomato leaves and firm, brown greasy-looking spots on the fruit appear it’s too late to save the plants but you can still harvest unblemished tomatoes to ripen indoors. Check them daily for signs of decay. Vines should be either piled and securely covered with a tarp, preferably in a sunny location, or bagged and sealed until all green plant material has blackened, he said.

Affected potato plants should be cut off at the base and treated as above. The potatoes can be left a week or two to harden up and then harvested as usual, being extra careful not to damage them.

At this point, if your plants don’t have symptoms you can apply a protectant fungicide containing chlorothalonil. Complete coverage is essential, as is regular inspection of the plants. It’s fortunate that late blight is in fact late this year, unlike the 2009 season, and most growers will have gotten a significant crop.

For more information, call Cooperative Extension at 379-9192 or email at ph59@cornell.edu