Monitor For Late Blight

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Growers must be vigilant scouting for late blight in their tomato and potato fields, even in September, says Margaret McGrath, a professor in the plant pathology department at Cornell University. The recent late blight outbreak in the Northeast has been nothing short of devastating, and the dollar figure attached to the devastation has yet to be determined, she adds.

Overall, she says tomatoes seemed to be more susceptible than potatoes, but until researchers sit down and do studies, McGrath says she can’t come to any definite conclusions.

Nevertheless, growers still have to be wary of the pathogen in their fields. “We get hot, dry weather [in the fall] and growers will be lulled into thinking that they don’t have to worry about late blight anymore,” she says. “It’s not
going to go away if it is in your field.”

Control Tips

To help growers keep late blight from taking over their fields, McGrath offers a few tips:

1. Whether or not you have late blight, maintain diligent scouting. “If you have it in your field, you must stay on a good management program,” she says. “You may be able to extend your spray interval, but realize that if you extend too much, there could be big problems.”

2. Talking potatoes. “You have to manage tubers, and get rid of cull piles,” she says. “If any tubers are left in an infected field, make sure you destroy them promptly when they sprout next year.”

3. If you abandon a field, don’t just leave it. “Don’t be a source of inoculum for other people,” says McGrath. “Destroy the field. The fastest way to do that is with an herbicide like diquat.”

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