Whether for commercial growers or backyard gardeners, conditions are, unfortunately, ripe this summer for late blight.
Last week, Cornell University pathologists confirmed a case of the disease — which can devastate tomato crops — on a sample from Indiana County, according to Bob Pollock, the county’s Penn State Extension director.
“We know it’s in the area and usually, if it’s in one place, then it’s in some other areas also,” Pollock said.
The disease has been confirmed or suspected in Lancaster, Somerset and Chester counties, too, based on information from USABlight, a USDA project that monitors the disease.
Late blight can spread from state to state through storm fronts, often progressing south to north or west to east, according to Pollock. It can also develop from affected seeds or spread to tomatoes from diseased plants nearby.
While it’s not uncommon to see a few cases each year, weather conditions conducive to late blight development are giving gardeners good reason to be on the lookout this month.
“If they have tomatoes, they need to be looking at those plants, if not on a daily basis, at least a couple of times a week, especially a day or two after we have a storm come through,” Pollock said. “Really, it’s best to regularly check them for signs and symptoms of the disease.”
Late blight is characterized by light green to dark brown spots on plant leaves, as well as brown or black stem lesions and greasy greenish brown spots on tomato fruit.
The blight can kill not only leaves, but entire plants, and in as little as a week.
Caused by a pathogen called phytophthora infestans, late blight started the Irish potato famine of 1845 and 1846.
In 2008 and 2009, late blight crippled tomato plants throughout the Northeast, when, in what Pollock calls a “perfect storm” situation, diseased plants were sold throughout the U.S. and weather conditions were ideal for late blight to spread.
“By the time people started to put the pieces of the puzzle together,” Pollock said, “it was all over the place.”
Farmer Dan Yarnick, of Yarnick’s Farm and Yarnick’s Farm Market, was contacted a week or so ago by the Penn State Extension about the presence of a case in the county.
“The weather’s definitely perfect for the late blight to appear,” he said. “It thrives on weather like we’re having now.”
Rainy days and a stretch of nights with temperatures in the mid-60s and low 70s have made it easy for the pathogen to spread.
Watering plants late in the day when nights are cool, as well as long-lasting dew, can create the right conditions for blight to thrive, Pollock said.
Yarnick hasn’t seen signs of late blight on his farm, but Tuesday afternoon, he was out on his tractor scouting for late blight and applying fungicide to tomatoes as a preventive measure.
“It can devastate a field or a garden in just a few days,” he said. “It’s definitely a problem.”
Older plants, he said, are more susceptible. But so are plants that are producing or just about ready to produce tomatoes.
Left untreated, late blight can spread quickly.
“The home gardeners really have to be on the lookout for it,” Yarnick said. “They should be applying a fungicide at least once a week if they want good tomato plants.”
Products are available that may help home growers fight late blight. The most effective, according to Pollock, are those containing chlorophalonil. For organic gardeners, copper is an option.
Rain works against efforts to treat crops by washing the fungicide away. That’s why Yarnick advises applying products every seven to 10 days.
If blight is suspected, Pollock encourages gardeners to bring plants to Indiana’s Penn State Extension office.
Getting rid of affected plants is often the best way to handle an outbreak. Plants must be disposed of properly to prevent the spread of late blight.
Pollock suggests leaving diseased plants tied in a garbage bag and sitting in the sun until they turn brown.
“What we shouldn’t do is just yank them out and throw them on a pile,” he said. “As long as the plant has some life in it, the disease will live in it, then it will still spread around.”
Center Township resident Jim Bernard remembers his encounter with late blight from about 30 years ago.
Bernard, a Penn State Master Gardener, went away for two weeks as part of his National Guard duties.
When he returned, his 30-foot by 30-foot tomato garden was overtaken by late blight.
“The tomatoes were all practically dead; any fruits left were rotten,” he said. “It really set me back considerably. We didn’t have too many tomatoes that year.”
To prevent blight, Bernard suggests seeking late blight-resistant varieties of tomatoes. But some gardeners still want to grow their personal favorites. In the past 10 years or so, gardeners have come up with a solution. They graft preferred tomato varieties onto root stalks of blight-resistant ones such as Maxifort or Mountain Magic.
“Since it’s the root stock that governs most everything, it will be resistant to the late blight,” Bernard said.
He is already making plans to do some grafting next year.
“There are some tomato plants that I really like, but they aren’t resistant to late blight,” he said.
PHOTO: Joey Yarnick sprayed tomato plants to prevent blight recently at his family’s vegetable farm in Armstrong Township. (JAMIE EMPFIELD/Gazette)
TIPS TO AVOID LATE BLIGHT
• Eating infected tomatoes, whether fresh or frozen, is advised against, as is using them for canning.
• While not dangerous for human consumption, tissue damage and increased pH levels resulting from late blight make it easier for harmful micro-organisms to grow on tomato fruit.
• If infected, green tomatoes picked early can still develop symptoms, regardless of whether plants show early signs of disease.
• If late blight is confirmed in your garden, destroy infected plants and notify any neighbors growing tomatoes or potatoes.
• Leave any infected plants that you remove in a bag and set out in the sun until they are brown; large amounts of diseased plants can be put under a tarp.
• Inspect plants weekly; remove symptomatic leaves, stems and fruits — or entire plants — quickly and regularly.
• To prevent late blight, select late blight-resistant tomatoes and certified potato seeds.
Prevention is not guaranteed, but they are less susceptible.
Sources: USABlight: www.usablight.org, Penn State Extension: www.extension.psu.edu.
More information about late blight is available through the Indiana County Penn State Extension office at 827 Water St., Indiana, at (724) 465-3880.