Late blight threatens potatoes and tomatoes

ADDISON COUNTY — In Whiting, Karen LeRoy is on the lookout for a culprit that could wreak havoc in her garden this year. And this summer, it’s not the usual critters, like deer or rabbits or pesky insects, that pose the greatest threat — it’s the late blight, a fungal disease that horticulturists say could wipe out tomato and potato crops in Vermont.
It’s a watch that many other gardeners — hobbyists and professional farmers alike — took up this week, after word got out that tomato plants sold at some large garden centers in neighboring states may have been infected with the late blight.
In the world of fungal diseases, this blight is a heavy hitter: the disease was made famous as the cause of the Irish potato famine in the mid-1800s.
Specialists today say the disease doesn’t pose the same threat of famine, given the wider diversity of crops that now make up the typical American’s diet. But for commercial growers and backyard gardeners alike, the late blight could ruin tomato and potato crops if it spreads.
Late blight is caused by the fungus Phytophthora infestans, and according to vegetable and berry specialist Vern Grubinger at the University of Vermont Extension, the blight isn’t actually that uncommon in the Northeast, where cool summer temperatures and frequent rains help the blight thrive.
But typically the blight doesn’t crop up until later in the growing season, and it’s usually limited to a few farm fields or small regions.
This year, though, the blight has shown up early, and appears to be more widespread than it has been in the past, Grubinger said. The blight has also been identified on tomato plants for sale at a number of chain store garden centers, which means that home gardeners may have purchased infected plants.
The plants have been traced back to a supplier in the South — and now those plants might serve as a source of spores that can spread the disease.
“We’re trying to be proactive to keep this thing down to a dull roar,” said Grubinger. “It can be managed, but for most homeowners, that will mean keeping a close eye on your plants.”
At Popoma Farm in Whiting, LeRoy said the blight is definitely on her radar. A report on Vermont Public Radio on Tuesday about the possible disease tipped her off, and she did some research online to find out just what the late blight would look like, should it hit her garden.
Because she and her daughter have grown all their own tomato plants, LeRoy isn’t worried about possible contamination from commercial supplier. But she’s not taking any chances — she’s throwing out the two tomato plants that were given to her by a friend.
“I’m going to rip them out of the ground and put them in the garbage,” LeRoy said.
During wet summers, LeRoy said her tomato plants typically start to look a little sickly. Some years, it’s worse than others. But LeRoy said that in more than 30 years of gardening, she’s never heard such a serious warning about a possible blight this early in the season.
She and her daughter are trying to take as many preventative steps as they can to keep their tomato plants — and, by extension, their potatoes — healthy. That includes using a biodegradable brown paper mulch, a new system for staking the plants, and an organic copper fungicide she plans to spread in her gardens.
But so far, the weather isn’t cooperating: this summer’s wet weather encourages fungal diseases like the late blight.
The late blight spores can be easily carried long distances by winds, so Grubinger advises anyone growing tomatoes or potatoes to be on the lookout for signs of the disease. Those signs are typically obvious to the eye, he said. Infected areas on tomato leaves, stems and fruit appear to be water-soaked spots (varying in size from a nickel up to a quarter). The infected areas often start at leaf tips or edges, and if they dry out quickly, they may appear lime-green or beige in color.
The edges of those infected, water-soaked areas may also be covered with white fungal growth, and brown or almost black lesions typically appear on infected stems.
If a gardener finds signs of the late blight on a plant, they should pull it up, wrap it in a plastic bag, and put the plant in the garbage — not, Grubinger said, on a compost pile where spores will still be able to spread. Another option is to turn large plantings underground, where the plant will decompose.
For LeRoy, whose foray into gardening in the 1970s blossomed into a farm and community-supported agriculture business, the blight’s potential to wipe out both her tomatoes and potatoes is troubling. She’s a history buff, too, which means she’s well aware of the havoc the blight once wreaked.
“We are very conscious and aware of the fact that blights and insects and diseases can easily affect your food crops,” LeRoy said. “Now we have the advantage of being forewarned.”
LeRoy, her husband Charles, and her daughter Hannah are all on the look out for signs of the disease, though LeRoy hopes that the buffer of forests around her farm will keep spores — should they become windborne — at bay.
“We’re just going to be really vigilant,” she said. “Gosh, it’s alarming, especially when you’re trying to make a living from your garden and farm.”

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