Plant experts recommend farmers, gardeners take steps to avoid another tomato blight outbreak

Tomato growers told to take steps against blight

CLAVERACK, N.Y. — As farmers and home gardeners set out their tomatoes this spring, plant experts offered suggestions for preventing another outbreak of late blight, which destroyed millions of dollars worth of tomatoes in the eastern U.S. last year.

Chris Cashen said the tomato plants on his organic farm in the Hudson River Valley were taller than him last July when he discovered some collapsed on their trellises. Within weeks, 80 percent of his crop, which included more than a dozen varieties of cherry, plum, heirloom and hybrid slicer tomatoes, had died.

Late blight, best known for causing the Irish potato famine of the 1850s, infected tomato plants in at least 23 states and Canada last year, causing millions of dollars in damage and extra labor and pesticide costs. With the outbreak extending from New England to Florida and as far west as North Dakota, farmers had to spend much time and money spraying expensive pesticides to prevent infection or risk losing entire fields.

Cornell University plant pathologist Meg McGrath said another outbreak is likely this year. Late blight has already hit gardens in Florida and Louisiana, but farmers and gardeners can cut their losses by isolating plots, removing remnants of last year’s plants and inspecting for signs of disease.

Agriculture experts also recommend buying plants from local nurseries to avoid the spread of disease over long distances.

“Most other diseases, we can live with,” McGrath said. “With late blight, you lose everything, and it’s very contagious, with spores carried on the wind.”

Late blight is caused by a fungus-like organism called an oomycete that’s spread by airborne spores. It flourishes in cool, wet conditions and can survive during the winter in living tissue, such as potatoes buried underground.

Last year was unusual in that late blight arrived early in the season rather than the fall, when it typically shows up, and it thrived throughout the unusually cool, wet summer, McGrath said.

The U.S. Department of Agriculture didn’t investigate the cause of the outbreak. But pathologists suspect mass-produced tomato plants shipped to big box stores from the South were the source because blight was found on tomato seedlings at garden centers for the first time and the same strain was found in 23 states, McGrath said.

This year, big nurseries are being aggressive in spraying and taking other steps to prevent infection, and the outbreak shouldn’t be as bad, she said.

Alabama-based Bonnie Plants, which grows 125 million tomato plants a year for sale at big box stores, pulled all its tomato plants from Home Depot, Lowe’s, Kmart and Walmart stores in New York and New England when the blight appeared. The company said the plants had likely been infected after shipment.

Bonnie Plants uses a strict spray program to prevent infection and since last year’s outbreak, it has added three new fungicides for late blight to its regimen, president Stan Cope said.

Still, Cashen said he fears there could be another outbreak linked to plants from big box stores because their employees aren’t trained to spot infections as farm workers are. He doesn’t spray, but plants tomatoes from his own greenhouses in numerous, separate plots on his farm in Claverack so it’s harder for any disease to infect all of them.

John Mishanec, a cooperative extension agent in eastern New York, advised home gardeners to buy tomatoes and other plants from local growers, not only to support the farms, but to avoid infections that might be carried from afar.

Because the blight can survive over the winter in potatoes left in the field, McGrath advised growers to throw out any potatoes left from last summer and destroy any potato plants that sprout from last year’s tubers. The disease doesn’t survive over the winter in soil, she said.

“The blight strain we had last year really liked tomatoes, but it also was able to infect potatoes,” McGrath said. “We’ll see it again this year if we don’t get rid of all the potatoes that were infected.”

Amy Hepworth, an organic grower whose customers include Whole Foods and co-ops in the New York City metropolitan area, fought off late blight with fierce tenacity on her 25 acres in Milton. As an organic farmer, she could not use fungicides but could spray with copper, which leaves a protective blue residue but must be reapplied after each rain.

“Sometimes when it was really bad, we’d be spraying three to five times a week,” Hepworth said. “It was unprecedented. I’ve grown tomatoes for 20 years and never seen that kind of pressure.”

When she found signs of blight, Hepworth burned the plants with propane torches and carried the remains out of the field. The effort paid off.

“We sold tomatoes up until the first week of December,” Hepworth said.

Cornell University in recent years has developed tomato varieties resistant to late blight, including Mountain Magic and Plum Regal, but the seeds aren’t expected to be widely available until next year, McGrath said.

The best advice for tomato growers, whether they are gardeners or commercial farmers, is to be vigilant, watching for black patches on stems, leaves and fruit, and catch any sign of disease early, McGrath said. Growers who suspect blight should have it confirmed by a cooperative extension agent who will alert other growers.

“This is a community disease,” McGrath said. “If you’ve got it, you have to tell everybody. We have to know where it’s occurring to protect farms.”

Blight-infected plants must be pulled up, bagged and disposed of in the trash.

On the Net:

www.hort.cornell.edu/lateblight