Late Blight Information
Late blight update: Late blight has been found in the Northeast. Be vigilant!
Contributors: Elizabeth Dyck, Organic Consultant and John Mishanec, IPM Vegetable Program
Given the severe outbreak of late blight last year, it is highly likely that late blight inoculum is present around New York State. Moreover, confirmed cases of late blight have been reported in 2010 in Long Island, Ohio, Pennsylvania, and Ontario. It isn’t time to panic, but it is important to take several steps.
1. Re-familiarize yourself with the conditions that favor late blight, how it spreads, its symptoms on tomato and potato, and how to manage it.
For more information, see these useful websites:
Map detecting late blight risk due to weather conditions
Long Island CCE late blight webpage
UMass late blight webpage
Webinar for organic growers
2. Minimize the risk of the disease.
- Immediately dig up any volunteer potato plants (tubers and all) and destroy them or place them in an airtight container in the trash. For those that haven’t planted potatoes yet, be sure to check each tuber for disease symptoms before planting.
- Plant potatoes and tomatoes for adequate airflow during the season.
- When purchasing transplants, buy from a local, reputable grower and inspect plants carefully at time of purchase and before actually transplanting.
3. Begin scouting for the disease.
Check tomato and potato plantings at least weekly and more frequently in periods of weather that favor the disease (rainy conditions or mornings with heavy dew).
Examine the field before you enter and look for areas that may harbor humidity, for example - low spots, shady areas or rows along tree lines. These are where you will likely find late blight first. Look for large black spots on leaves the size of a quarter. Also look for black spots on the stems. In the morning, you will see a white halo around the spot. On the stems, the black area will be about a half inch above and below where a leaflet comes off the stem where a spore germinated.
4. If you suspect late blight, immediately contact your local CCE office to confirm whether the disease is actually present.
Click here for contact information.
5. If you chose to spray your organic potatoes and tomatoes, remember to contact your certifying agency to confirm approved products.
John Mishanec, IPM Vegetable Program, recommends the following: Organic growers should start applying an approved copper product. The recommended rate of copper for tomatoes and potatoes is 2 lbs./Acre. You must thoroughly cover the crop. Many organic farmers do not have sufficient spray equipment to sufficiently cover the crop, so you may want to take this into account when deciding if spraying will work on your farm.
NOFA-NY Certified Organic, LLC Approved Copper Products
Tips for Spraying with a Backpack Sprayer
Copper Toxicity: There has been some concern from organic growers about copper toxicity in the soils by using too much copper. There is not a lot of information about copper toxicity, but in Florida, they use a lot of copper on their crops. They also use higher rates and make many, many applications. They have seen very little copper toxicity, if any, in Florida and if they don’t have it, we here in NY probably will not have a problem with the limited amounts we will use on our crops and good rotation practices. However, this is a concern for many growers and many choose to pull and destroy plants rather than spray copper.
6. Educate farmers and gardeners! We must all work together to prevent another late blight outbreak. Remind your neighbors to be vigilant.
It will take good weather and a certain amount of luck to escape late blight this year. But by becoming vigilant now and instituting good, preventative management practices, we can lessen the risk of another outbreak.
