Cornell Cooperative Extension

July 30, 2012

Late blight has arrived

Late blight is a devastating fungus disease that wipes out tomato and potato crops with breathtaking speed. 

Now home gardeners and commercial growers need to watch their plants more carefully than ever because late blight was just confirmed on tomatoes in a West Chazy home garden last week.

Anyone who grew tomatoes or potatoes in 2009 knows all too well what late blight does to these crops.

There are only two good things I can think of about this disease: It affects only tomatoes and potatoes, and it does not overwinter in soil or plant debris.

The only way the strains we currently have of this disease can survive from one year to the next is on potato tubers. 

Late blight is of serious concern because it can wipe out entire plantings of tomatoes or potatoes in a matter of days and it spreads rapidly from one garden or planting to the next. 

It usually arrives when spores from infected plants to our south are blown into our area on storm fronts. Because of all the turbulent, stormy weather we’ve had across the eastern United States already this year, pathologists at Cornell are assuming that spores have been spread over most of the state already. But the hot dry weather we’ve experienced discourages those spores from growing. We’ll just have to wait and see if the rainy weather late last week created better conditions for those spores to flourish. Let’s hope not.

Anyone growing tomatoes or potatoes should check their plants daily.

As soon as you see anything suspicious, clip off a few leaves or branches, drop them in a plastic bag, and bring it to any Cornell Cooperative Extension office. There are two common diseases — early blight and septoria leaf spot — that we see every year, and we want to rule those out first. If we suspect late blight, we’ll send it off to the lab at Cornell for verification at no charge.

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