BRATTLEBORO — It's been a dry and hot summer so far in Windham County, which is good news if you're a tomato, but bad news if you're a fungus.
The damp and cool conditions of last summer fueled an outbreak of late blight, a fungal disease that wiped out many tomato and potato crops in Vermont and New Hampshire.
This summer, things appear to be OK, according to Vern Grubinger, a vegetable and berry specialist in the University of Vermont Extension's Brattleboro office.
“The word on late blight right now is vigilance,” Grubinger said. “Growers and gardeners need to scout their plants regularly for symptoms of this disease.”
Late blight flourishes in wet weather and 65- to 75-degree temperatures. It causes brown spots - often with a dark green, water-soaked edge - on leaves or stems of tomato and potato plants.
Under the right conditions, such as last summer's unseasonably wet weather, late blight can kill plant in a matter of days. And one late-blight lesion can produce 100,000 to 300,000 spores per day.
There have been reports of late blight spotted in Maine and western Massachusetts, but Grubinger said the fungal disease has not appeared in Windham County.
“It may or may not arrive here,” Grubinger said, “depending on weather and whether inoculum [the spores that spread the disease] is present - either in place from last year's potato tubers that sprout, or on the wind from the southern places where it has been confirmed.”
Wendy Sue Harper, vegetable and fruit technical advisor for the Northeast Organic Farmers Association, said that in the past, the strains of late blight in New England were intolerant of hot weather.
“However, the strain we saw last year in Vermont seems to tolerate warmer conditions,” she said, adding that pathologists suspect this warmer weather strain is the one reappearing this season.
Grubinger also advised gardeners that other diseases can be found on tomatoes in Vermont - diseases that may be confused with late blight.
“Early blight is a disease of tomatoes and potatoes starting usually on lower leaves with yellowing and brown spots,” he said. “It is pretty common in most gardens and farms - its spores are in the soil and it over-winters. So does Septoria leaf spot, which shows up as small, dark spots on the leaves and can coalesce into a large, dead area on leaves.”
Grubinger said mulch often helps slow the progress of early blight - as well as Septoria leaf spot - because it keeps soil from splashing up onto foliage. Promoting good drying of plants by regular pruning of excess suckers, staking, and watering the ground without wetting the foliage are also helpful ways to prevent blight.
If gardeners or farmers think they might have plants with late blight, Grubinger said they can send a sample to the UVM Plant Diagnostic Clinic, Jeffords Hall, 63 Carrigan Drive, Burlington, VT 05405. He said the normal $15 fee for gardeners has been waived to help UVM Extension keep track what is going on in the state.
Grubinger said that if late blight does show up, “the good news it is already a month later than it arrived last year, so many potatoes and tomatoes are well on their way to harvest. The more time that goes by, the less the risk of loss.”
Commercial farmers are more likely to consider protective spraying to be worthwhile than gardeners, Grubinger said, because their income is at risk.
“Such sprays need to be repeated every week or so to keep new growth covered,” Grubinger said. “Organic farmers can use some forms of copper hydroxide, but it turns plants and fruit blue, so that makes work washing fruit before sale. If and when late blight is confirmed in the area, then more people may consider protective spraying to be worthwhile.”
Harper said if late blight is confirmed on plants, “destroy them immediately.”
“Late blight can only survive on living tissue,” he said. “Once the plant is dead, late blight dies, too.”