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Late blight confirmed in Allegany and Steuben Counties

September 12, 2012
Westfield Republican / Mayville Sentinel News

BELMONT - Allegany County has had late blight confirmed in two locations and it has also been confirmed in Steuben County.

This is a disease that affects potatoes, tomatoes, peppers and even some weed species. This has the potential to travel long distances from an initial outbreak via spores dispersed on the wind. If an outbreak is not managed, it can lead to a major late blight epidemic. This can affect both home gardeners and commercial farms and could cause crop failure and large economic losses.

Both late blight outbreaks in Allegany County have been managed by killing the plant tops by breaking them off at the soil line and applying fungicides labeled for late blight until the foliage is dead and dry. However, there could be more unconfirmed outbreaks which should be taken care of whether commercial scale or small garden plots.

Article Photos

Submitted photo
Plants in Allegany County were confirmed to be infected with late blight recently. Late blight has also been confirmed in Steuben County.

How can gardeners know if they have late blight? Cornell University's Horticultural Research and Extension Center suggests the first step in diagnosis is to examine affected plants thoroughly for symptoms. Don't stop at the first symptom. Look at other plant parts too. Early in the day when there is dew is best. At that time, late blight lesions seen from the undersides of the leaves look dark with very fine, white fuzz on the margin of the lesion. The fuzz is late blight spores. There is a noticeable margin around the dark lesions that often looks light green to yellow green.

Late blight can affect all parts of the plant - leaves, stems, flowers and fruits - whereas some of the late blight imitators do not. Characteristic leaf symptoms are very large spots, which look water-soaked at first and then turn brown, often with a border of light green wilted tissue. The best place to look for the white fuzzy growth of spores is on the underside of leaf lesions. Large, dark brown lesions develop on stems and petioles, and sometimes the pathogen sporulates on these, too. When petioles are affected, the whole leaf can collapse. Affected fruit develop large, brown, firm areas.

If anyone notices spots on leaves, but aren't sure it is late blight, Cornell University has a great website with photos of late blight and its imitators to help with the diagnosis. Go to

If anyone thinks they have late blight after reviewing the Cornell University research website, promptly:

submit a sample to the Cornell University Lab, so it can confirm and identify the pathogen strain. Visit for complete details on how to send a sample and overnight shipping;

bag, bury or destroy affected plant tissue;

do not compost plants with late blight;

notify neighbors; and

continue applying fungicides weekly if plants are kept.

Understand symptoms cannot be cured, plus this disease can develop rapidly, so late blight is harder to manage when fungicides are applied starting after symptoms are seen then before. For those who prefer not to use any fungicides, understand late blight cannot be left unmanaged because of the potential impact on others' plants. Destroying affected plants as soon as the disease is identified is the best option to prevent widespread outbreaks. Copper is a good choice for organically produced plants; chlorothalonil is the most effective conventional fungicide ingredient available to gardeners. Before using any fungicide, read entire label and understand the safety information.



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