AMHERST - For Brookfield Farm, the loss of 3,000 tomato plants to late blight has been like a death in the family.

"Just when the time had come to harvest the fruits of our labor, it is now time to say goodbye," the farm's newsletter said last week. "We were hanging on many hopes and prayers, but alas, it is now time to admit the inevitable and say farewell."

A lot of farmers and backyard gardeners have been grieving for their tomato plants. The cool, rainy June and July, combined with starter plants that were infected with late blight in the South and distributed in the Northeast, have caused yields to plummet. The prices of the surviving tomatoes will increase.

On Sunday, a team of experts came to the University of Massachusetts to analyze the problem, look at effective strategies for preventing late blight, and suggest ways to avoid it next year. The "emergency meeting" came at the end of the annual conference of the Northeast Organic Farming Association.

Late blight is a fungus that is similar to the one that caused the potato famine in Ireland in the 1840s, said Abby Seaman of the New York Extension Service. It is distinguished by dead areas on leaves and dark spots on stems, and it can wipe out a tomato field in a week, she said. It can also affect potatoes.

Once late blight is present, it can produce billions of spores that are carried by the wind and can infect tomato plants in a 30-mile radius, she said. That's why gardeners are urged to uproot and bury any blighted plants.

"But I don't want everyone to be freaked out by every spot on their tomatoes," she said. More common tomato diseases like septoria leaf spot and fusarium wilt can be misdiagnosed as late blight, she said.

For organic growers, the best defense seems to be sprays containing copper, said Ruth Hazzard, UMass Extension vegetable specialist.

These must be sprayed at intervals of seven to 10 days, five when the weather is wet, she said. Gardeners should cover their skin and eyes while using these sprays, she said.

The copper will not accumulate in the soil in toxic quantities, and some of the mineral is essential to plant growth, Hazzard said.

"But when you see lesions all over, it's time to call it a day and stop letting your crop be a generator of spores that your neighbors might not appreciate," she said.

Besides copper sprays, gardeners and farmers can avoid late blight by preventive maintenance, said Dan Kittredge, a farmer and director of the Real Food Campaign, which provides education on the role of minerals in soil biology.

"When someone has the flu, 10 people can walk into a room and only five get sick," he said. "Just because fungal spores are in the atmosphere doesn't mean they'll all get sick."

All the rain of June and July leached minerals out of the soil, and the lack of sun shut down photosynthesis and deprived the soil of food, he said. Restocking the soil with minerals will help plants survive, he said.

Soils with low pH levels are more vulnerable to fungal disease, he said.

It's important to not plant just tomatoes or just potatoes, as diversity makes it harder for diseases to spread, said Michael Glos, a farmer from Richford, N.Y.

Next year, farmers and gardeners should consider starting tomatoes from seed rather than buying existing plants, he said. Early plantings may produce crops before the diseases come in, and increasing the space between plants to promote air circulation could help, he said.

"The likelihood of a major outbreak next year is highly likely," said Paul Stamets, a fungus expert from Olympia, Wash.

Beneficial fungi are being developed that could help fight late blight, which will probably survive in the ecosystem for three to five years, he said. Coating seeds at the point of germination could be valuable, he said.

Some tomato varieties are being developed with resistance to late blight. They bear the names Legend, Mountain Magic, Plum Regal, Juliet and Stupice.

Another piece of good news is that late blight apparently does not survive in soil, Hazzard said.

Gardeners may be mourning their dead tomato plants now, but there's always next year. The knowledge they've gained about late blight this year may help prevent an infestation next year, and the odds are against a third consecutive rainy June and July in 2010.

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