Blight

Here we are in the midst of summer. Perfect for picnics, all sorts of outside activities, and enjoying the freedom this season brings. We will be celebrating Independence Day and the weather forecast is great. The summer, so far, has been much better than last. Remember? Lots of rain, lower than average temperatures, and a disappointing growing season for the home gardener. Even worse, this time last year, we were plagued by late blight. While weather does play a part in the development of the disease, the pathogen, Phytophtora infestans, has to be present in order for late blight to develop.

In parts of Pennsylvania there have been confirmed cases of late blight. Late blight is a disease that can kill plants and wipe out crops in a few days if conditions favor disease growth. Those conditions described the 2009 growing season – cool to moderate temperatures with wet weather. Once you have seen late blight wipe out a garden or field, you begin to understand how important preventative measures are to protecting your home garden.

Late blight affects primarily potatoes and tomatoes, not other garden crops. Spores can blow for many miles, land on a wet tomato or potato leaf and start a new infection. So the disease can quickly spread from one garden to another. Infections can be prevented by regular spraying with fungicides containing chlorothalonil or mancozeb, but applications must begin before the disease gets started and continue through the growing season every 7 days to protect new growth. If weather is dry, you can stretch this interval; but if we have heavy rains, you may have to shorten it.

Gardeners should be spraying fungicides on their tomato and potato plants to prevent infection. Keep in mind that fungicides prevent infection they do not cure it. All plant surfaces should be covered with fungicide before conditions favor infection. Do not wait until after the rain stops to apply fungicides – they should be sprayed and dry before rain starts. Thorough coverage of all plant surfaces is needed for good control.

Remember, fungicides are to be used and handled according to labeled instructions. For more information on late blight, please contact the Penn State Master Gardener Helpline at 570-963-6842 or email: LackawannaMG@psu.edu


Steve Ward
Master Gardener Coordinator
Penn State Cooperative Extension in Lackawanna County
Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.