Late blight infected tomatoes threaten potato crop

15 years ago

Industry officials advise home gardeners to check store-bought plants

By Scott Mitchell Johnson
Staff Writer

    The Maine Department of Agriculture and the University of Maine Cooperative Extension are encouraging home gardeners to check tomato and potato plants for symptoms of late blight, a highly destructive disease if left unmanaged.
    “We are urging home gardeners, especially those who may have recently planted tomato seedlings from a big box store, to check for this disease,” said Jim Dwyer, University of Maine crops specialist.
    Symptoms of late blight include irregular-shaped, water-soaked, greasy gray spots surrounded by white mold, which eventually turn into blackened areas on the stems and leaves. These blackened areas dry up, wilt and die.
    “Because the tomato fruits will be ruined by this fungus and the threat of late blight spreading to potatoes, home gardeners that find late blight on their plants should pull, bag and throw out these plants,” said Dwyer. “They should not put them on the compost pile.”
    Early last week, late blight was detected in potatoes in a commercial field and on tomatoes in a home garden in New York. The long stretch of cool, cloudy and rainy weather in June provided classic conditions for the spores of this fungus to spread.
    The disease was also discovered in tomato seedlings stocked in the garden centers of large retailers in Maine including Wal-Mart stores in Bangor, Houlton and Presque Isle, as well as the Presque Isle Lowe’s. The company that produced the seedlings, Bonnie Plants, a large supplier of vegetable, herb and flower transplants based in Alabama, has cooperated fully and pulled its stock from sale and arranged for its destruction.
    Officials with the Maine Potato Board are extremely concerned with the news that late blight has been reported in the region.
    “We’ve spent millions of dollars over the last several years trying to manage that organism and there’s been hundreds of hours of time put in by researchers and industry people trying to get a handle on late blight inoculum sources … everything from cull piles to seed sources to weeds,” said Timothy Hobbs, director of development and grower relations for the Maine Potato Board. “Impact to the potato industry [from late blight] is huge … late blight is what caused the Irish potato famine.
    “If the late blight was confined to just one area, that would be bad enough, but when these tomato plants have been planted all around Aroostook County in peoples’ gardens and there’s late blight on them,” Hobbs said, “they can easily spread to potato fields, and that’s a huge threat to the industry. Late blight will settle on your tomatoes and infect your potatoes, and your potato late blight will go over on your tomatoes. This is going to be a long summer.”
    Hobbs said potato growers have already been advised to implement a five-day spray schedule starting June 25.
    “They’re getting the crop protectant out and getting those plants covered,” he said. “The protectant acts as a blanket on that plant and prevents the spore from infecting it. However, as the plant grows, it outgrows the protectant, so you have to keep going back to recover the new growth and this time of year makes it difficult to keep ahead of the new growth, but that’s what they’re going to attempt to do.”
    Recognizing that it’s more difficult to educate home gardeners who are likely new to the problems of late blight, Hobbs said anyone who has bought a tomato plant this spring or summer should check for symptoms.
    “If they have a question about the symptoms, they could bring a piece of that plant to the University of Maine Cooperative Extension office in Presque Isle and they will ID that for them,” he said.
    “Any plant with those symptoms, we’re recommending they destroy it. There’s no such thing as a late blight hospital … once a plant gets it, it’s got it and it’s going to die from it. There’s no use in trying to limp by with some plants that have late blight in them because it’s not going to work,” said Hobbs. “On those situations where there are no symptoms, they need to be spraying just like the growers are going to be spraying. They need to buy a fungicide product and get their crop covered.”
    Hobbs said growers should be on alert and actively looking for potato late blight.
    “This is as serious as anything that we’ve had in quite a while,” he said. “On a scale of 1-10, we’re at a 10. While there’s not been late blight found on potatoes yet, we’re in a potato production area where 55,000 acres of potatoes are being grown right now. We had somebody bring a tomato plant into the Extension office that bought it two weeks ago that was infected with late blight. We’re already behind the eight ball; that plant’s been out there for two weeks sporulating and we’ve had ideal weather conditions for the spread of late blight, so I’m concerned that we’re just now beginning to learn what the extent of this may be.”
    For more information, call the University of Maine Cooperative Extension, Pest Management Office at 1-800-287-0279, the Cooperative Extension Office in Presque Isle at 1-800-287-1462 or log onto