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.

Tomato Late Blight: Fall Clean-Up Questions

Can plants with late blight be disposed of by composting?
Theoretically yes, however, plant tissue (including potato tubers) can survive the winter in a warm compost pile. If plant tissue survives, so can the pathogen. Unless you know that you are composting properly, it is recommended that you dispose of infected plants, fruit and tubers in the trash.

Do I need to treat the soil this fall or next spring to prevent late blight from developing next year?
No. Once the tomato plant tissue is dead, the late blight pathogen cannot survive on crop debris. It can, however, survive in potato tubers, so it will be important to destroy any volunteer plants next year.

Can the late blight pathogen survive in or on tomato seed?
No, but there are other pathogens (especially bacterial pathogens) that can survive in or on the seed so there are other reasons to only use seed from healthy plants.

Could the late blight pathogen survive on tomato cages and stakes between seasons?
No. But it is a good idea to disinfect stakes and cages to help control bacterial diseases.

Are there late blight resistant tomato varieties that I should consider planting in the future?
There are some potato varieties with some resistance. These include ‘Elba’, ‘Kennebec’, ‘Allegany’, ‘Sebago’, ‘Rosa’, ‘Defender’, ‘Jacqueline Lee’ and ‘Ozette’. ‘Elba’ is considered the most resistant. There are some new late blight resistant tomato varieties that may be available as soon as 2010.

What can home gardeners and growers do to prevent another late blight epidemic next year?
Make sure that all late blight infected tomato plant and fruit tissue from this season is dead or destroyed. Destroy potato tubers that appear to be infected by late blight and also volunteer potatoes that grow next year.

Next year, make sure to plant healthy disease-free transplants. Examine your plants regularly for symptoms of late blight, especially if conditions are cool and wet. Avoid wet leaves by watering at the base of the plant or by using overhead irrigation during mid-morning so the leaves dry quickly. Improve air circulation by spacing plants farther apart and eliminating weeds.

To see the full article “Tomato Late Blight: Fall Clean-Up” by Beth Gugino, Penn State Plant Pathologist, please visit http://www.ppath.cas.psu.edu/EXTENSION/VEGDIS/Vegetable_Pathology_Home.htm or call your local extension office for a free copy. In Lackawanna County call 963-6842 and ask for the Garden helpline or email LackawannaExt@psu.edu.


Terry Schettini, Extension Educator
Penn State Cooperative Extension in Lackawanna County
Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce