Monday, June 14, 2010

Late Blight Rears Its Ugly Head Again

Late blight, the disease that wrecked many gardeners’ dreams of a fresh tomato sandwich last year, has been found, wide-spread, in western Pennsylvania. Many horticulturists, me included, were optimistic that we would be spared in 2010 but that hope now appears to be dashed. At this time, late blight has only been confirmed in three western PA counties but all Pennsylvania tomato and potato growers need to be vigilant. For a good discussion of the disease including images, see this site; or this site
To recap…. Late blight is a devastating fungus-like disease of both tomato and potato. Symptoms include rapid blighting of foliage and fruit. Tomato stems exhibit chocolate brown lesions. Leaves have blotchy brown spots and may produce fuzzy, whitish masses on the underside of leaves, especially in the morning when dew is present. Note that this is very different from early blight which results in yellow-brown lesions on lower leaves, containing concentric rings of dead tissue.

What’s a gardener to do? First, be vigilant. Inspect tomatoes and potatoes daily for late blight symptoms. Penn State will be tracking the disease in an attempt to alert commercial growers about the threat of late blight in their vicinity. It’s one thing to miss out on a tomato sandwich…quite another thing to lose a big chunk of your income. Farmers have a lot at stake with a crop of tomatoes or potatoes. Contact your extension office if you think you see late blight. Feel free to bring samples to the office for confirmation of the disease.

How about protecting those plants? Conventional gardeners and farmers can use products containing chlorothalonil, for starters. New foliage needs to be protected as it grows. Organic gardeners have copper fungicides, which will not provide the same level of protection as chlorothalonil but are better than nothing. If you plan to let Mother Nature take its course, and do nothing, at least be prepared to destroy infected plants at the first sign of disease… your neighbors will thank you. Best bet in small gardens is to bag the plants in plastic and cook them in the sun.

Any chance we’ll escape late blight in eastern PA? I was an optimist in the winter because it is known that the organism does not survive without living tissue in the North and Old Man Winter took care of that (except for potato cull piles) . But now that the cat is out of the bag…. I think we’re in for another year of greasy, black fruit in the tomato patch.

Dang… I was feeling good; tying up plants in the rain yesterday. Now I wonder if those raindrops were accompanied by late blight spores. Current conditions are ideal for late blight infection.