A cool, wet spring has created ideal conditions in Pennsylvania, New Jersey, and more than a dozen other states, most in the Northeast, for late blight, a devastating disease that threatens tomatoes and potatoes grown by farmers and home gardeners alike.
Best known for causing the Irish potato famine in 1845, late blight is spread from plant-to-plant over 30 to 40 miles by millions of fungal spores sent airborne by wind and rain. Once infected, plants must be destroyed.
It's a frightening thought in Pennsylvania and New Jersey, where farms produce potato and tomato crops worth about $85 million annually, according to the U.S. Department of Agriculture.
But so far, the impact in the Philadelphia-South Jersey region has been relatively light - six confirmed cases - and if warm, dry weather continues, officials believe damage could be contained. They warn, however, that if sustained wet weather returns, the potential for significant destruction remains.
"Growers have been preparing for it by spraying preventive fungicides, but sprays don't cause an immunity in the plant. So, even with the preventive sprays, commercial growers are very vulnerable," said Karen Snover-Clift, director of Cornell University's plant-disease diagnostic clinic, which is tracking the outbreak.
Late blight, a worldwide scourge thought to have originated in Central America and debuted in Europe and North America around 1830, is caused by a fungus called Phytophthora infestans. A handful of cases typically surface in this area in September or October, at season's end, and thus aren't much of a problem.
In any event, sophisticated weather- and disease-forecasting usually give growers and farmers plenty of time to apply protective fungicides.
A wet spring
"But we had a funky spring, 20 days and 20 nights of rain, making this the first time in decades we've had late blight this early," said Carl Schulze, who oversees plant-health issues for the New Jersey Department of Agriculture.
Reports began surfacing in late June after tomato seedlings bought at big-box stores were found to be contaminated with the fungus. Within 24 hours, Bonnie Plants of Union Springs, Ala., the nation's largest tomato supplier, pulled its remaining plants from the stores at a loss of more than $1 million.
So far, late blight has been confirmed in 19 counties in Pennsylvania, including a commercial potato field in Chester County and a large home garden in Montgomery County. Five counties in New Jersey are affected - a home garden and tomato field on the same road in Cumberland County; a commercial potato field in Salem; and tomato fields in Gloucester, Hunterdon and Sussex Counties.
Officials are not identifying homeowners or farmers, and they warn that the fungus sometimes affects eggplant and petunias, too. It is not harmful to humans.
No one knows how many tomato seedlings were sold before Bonnie's recall, but, undoubtedly, it was a lot. Ever popular, home gardening is now enjoying a surge because of the economy and a growing interest in local, organic produce. And tomatoes are the most popular fruit - technically, it's a fruit - in those gardens.
Ripping out tomatoes
They're certainly Warren Jacobs' favorite.
The 53-year-old consulting arborist has been growing tomatoes since he was a kid. These days, he mostly cultivates heirloom varieties from seed in his Perkiomenville garden - 80 in all, which he and his wife, Jodie, enjoy all summer, then strain and freeze for winter.
In the spring, Jacobs impulsively bought one cherry tomato plant for his deck at a local Home Depot. He soon realized "it had some kind of fungus disease. I thought, 'Well, this plant's no good,' and I put it aside."
Then, he saw a Rutgers University e-mail warning about late blight. "I walked out to the garden, saw the symptoms on some of my other tomato plants, and I freaked out," Jacobs recalled. "I ripped them out . . . great big giant plants loaded with tomatoes."
After the Pennsylvania State University Cooperative Extension in Montgomery County confirmed his late blight suspicions, he raced out to buy fungicide for the remaining 40 or so plants.
But Jacobs is fully cognizant it's probably too late to save them. "I'm not happy at all," he said.
Nor is Bonnie, which supplies 50-million hybrid-tomato seedlings a year to stores in 49 states, including most big boxes. "This has put a real, real, real, real wet damper on a great year for us," said Dennis Thomas, Bonnie's general manager.
Thomas said Bonnie had not shipped plants from Alabama; the company relies on a network of 61 "growing stations" around the country to distribute its product.
"We're not the only ones that take tomatoes up there. We've been blamed unfairly," he said, citing clean inspections at company greenhouses in 38 states, including Pennsylvania and New Jersey.
Plants can get infected at any point - in a greenhouse or field, in a store, or in a backyard. But thus far, Gary Stecker of G&G Stecker Farm in Swedesboro, who grows early tomatoes on eight acres and late tomatoes on six acres, has been lucky.
"We haven't seen late blight, thank God," he said. "We've been spraying."
Only one remedy
Once symptoms appear - greenish-brown, greasy-looking spots or lesions on top of the leaves and white fuzz underneath - there's only one remedy.
"The only thing you can do is destroy the plant. There's no product that can be sprayed after you have it," said Beth K. Gugino, assistant professor of vegetable-crop pathology at Penn State.
Veteran gardeners call this "roguing" a plant: You carefully pull it out so as not to liberate any spores, seal it in a plastic bag, put the bag in the sun to kill the spores, then throw the bag in the trash. Do not compost.
For healthy-looking plants, experts recommend spraying a fungicide with the active ingredient chlorothalonil, which is classified as "moderately toxic" by the U.S. Environmental Protection Agency. There are few effective organic options.
Just as weather got us into this, weather will get us out.
"As long as we have this hot, dry weather stick around, the threat of late blight will disappear," said C. Andrew Wyenandt, vegetable pathologist at Rutgers, "but if it kicks back into cool and rainy, like June, the threat would kick back in."
Contact staff writer Virginia A. Smith at 215-854-5720 or firstname.lastname@example.org.