Protecting your tomatoes from late blight disease

Last year, farmers and gardeners lamented their tomato losses. Late blight disease came early and wiped out about $1.2 million in income for local growers.

Does the same risk exist this year? The pathogen that causes late blight in tomatoes and potatoes usually doesn't overwinter in the Northeast.  But it can survive on last year's potatoes and it can hitchhike in on plants grown at large greenhouses around the country.

"Anyone growing susceptible plants needs to take responsibility to ensure they don't become a 'typhoid Mary,'" says Meg McGrath, plant pathologist at Cornell's Long Island Horticultural Research and Extension Center in Riverhead, N.Y. "We need to treat this like a community disease," she adds. "If infested, even a small garden can have a devastating impact on other plantings."

Experts at Cornell offer these tips to prevent a repeat of last year's devastation:

10 tips to prevent late blight in home gardens

• Kill volunteer potatoes. Dig up, bag and trash any volunteer potato plants that pop up in gardens or compost piles. It may take repeated efforts to get them all.
• Use only certified seed potatoes. Don't use leftovers from last year or table stock from the grocery store.
• Buy healthy tomato plants. Learn what late blight looks like. Report any infected plants while shopping or grow your own plants. (Late blight isn't spread on tomato seeds.)
• Keep plants dry. If plants need watering, water the soil -- not the foliage.
• Inspect plants at least once a week, more often if weather is cool and wet. Immediately remove and bag any foliage you suspect might be infected.
• If symptoms continue despite removing infected foliage, consider removing plants entirely -- sooner rather than later. The longer you wait to remove plants, the more spores will be blown to other gardens and farms.
• Warn neighbors and local Cooperative Extension if you find late blight in your garden.
• Remove infected plants during the middle of a sunny day after leaves have dried. But don't wait for these conditions. Seal plants in garbage bags and leave them in the sun for a few days to kill plants and the pathogen before placing in the trash or burying underground or deep in a compost pile.
• Keep an eye on other tomato-family plants. Some strains of late blight can infect other tomato-family plants, including weeds such as hairy nightshade and bittersweet nightshade. Control them early so that late blight on these plants doesn't go unnoticed. Petunias and tomatillos are also vulnerable to attack.
• Fungicides -- chlorothalonil and copper-based products can control late blight. They require a regular preventive spray schedule and thorough spray coverage. Follow all label directions, including use of respirator, waterproof gloves and protective eyewear.

Ithaca's Food Web articles about late blight from 2009:
Late Blight Hits Local Farms
Protect your tomatoes and potatoes
Watch out: Tomato blight hits Tompkins County
Tracking Tomato Disease Poses Challenges
Huge Tomato Crop Loss Due to Disease