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News Release
RI Department of Environmental Management
235 Promenade Street, Providence, RI 02908
(401) 222-2771 TDD/(401) 222-4462
For Release: July 3, 2009
Contact: Gail Mastrati 222-4700 ext. 2402

DEM ADVISES HOME GARDENERS, FARMERS AND COMMERCIAL GROWERS TO BE ALERT FOR SYMPTOMS OF LATE BLIGHT IN TOMATO AND POTATO PLANTS

PROVIDENCE - The Department of Environmental Management's Division of Agriculture is advising home gardeners, farmers and commercial growers that an outbreak of Late Blight has been identified in some tomato and potato plants in Rhode Island. Therefore, all tomato and potato crops — those grown commercially as well as those grown in home gardens — should be viewed as potentially suspect for the disease and measures taken to monitor for and if necessary control the disease. DEM views the disease as a serious threat to agriculture and declares it to be a public nuisance. The Department will determine if additional regulations or quarantine are necessary.

Late Blight is a very destructive and infectious disease that is spreading among tomato and potato plants in gardens and commercial farms in the eastern US, in part due to the rainy and humid weather. Uncontrolled, Late Blight rapidly produces spores that are carried by air currents to other plants and from one garden or field to others.

The most common early symptoms on tomato transplants are brown lesions on stems, with white fungal growth developing under moist conditions. Classic symptoms are large (at least nickel-sized) olive-green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain). Sometimes the lesion border is yellow or has a water-soaked appearance. Leaf lesions begin as tiny, irregularly shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. If the lesion has a yellow border and is occurring on the bottom of the plant, it is likely due to infection of either Early Blight or Septoria leaf spot, two common diseases found in home gardens.

Commercial growers are advised by URI Cooperative Extension to apply fungicides and take other cultural practices to protect their crop and prevent spread of the disease, which otherwise would mean certain death of their crops.

Home gardeners are also advised by URI Cooperative Extension need to act quickly to protect garden-grown tomato and potato plants and to make sure that your plants don't become a source of spores that could infect commercial farms, as Late Blight spores are easily dispersed by wind.

According to the Cooperative Extension, here are the steps home gardeners should take:
  1. Please inspect your tomato plants daily. If symptoms are already appearing on plants in your garden, these plants should be removed. Plants should be placed in a plastic bag, secured and discarded in the trash or completely buried 2 feet underground so plants decompose and will not re-sprout. Plants should not be composted, put on a cull pile, or left outside.


  2. If you want to try to control late blight with fungicides, you need to begin spraying fungicide now — even before you see symptoms — and you need to continue spraying regularly. Use a product that contains chlorothalonil. These products are only effective if used before the disease appears and should be reapplied every 5-7 days if wet weather persists. Chlorothalonil is a protectant fungicide, with no systemic movement in the plant, so thorough coverage is necessary. For organic farmers and gardeners, the options are very limited, since only copper fungicides can be used, and copper is not very effective on late blight. It is easily washed off by rainfall.


  3. Most other vegetables are not affected, such as lettuce, eggplant, peppers, squash, carrots, green beans and broccoli.
For further information, commercial growers can contact Heather Faubert at the URI Cooperative Extension at 874-2967. Homeowners should contact the URI Master Gardener Hotline at 1-800-448-1011.

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