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July 08, 2009

Tomato Blight: 'It's Bad News'



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Nothing says summer like a ripe, red tomato. Gourmets and gardeners wait impatiently each summer for the tasty orbs to ripen and during those few weeks when the crop is harvested, food lovers revel in the juicy delight.

But this year may be different. Cornell Cooperative Extension in Riverhead has issued a blight alert, warning commercial and residential growers alike to beware of late blight.

Dr. Meg McGrath, professor of plant pathology from Cornell University called late blight "worse than the Bubonic Plague for plants." Caused by Phytophthora infestans, late blight means "certain death" for tomato plants, she said.

Late blight was responsible for the Irish Potato famine in the 1840s, and according to Cornell's website, has indeed been identified at a commercial potato farm in Riverhead.

What makes late blight particularly deadly is the ease with which spores travel on the wind, infecting other plants rapidly. The disease thrives in cool, cloudy and rainy weather, when cloud cover protects spores from the sun.

According to Thomas A. Zitter, of the Department of Plant Pathology, Cornell University, the occurrence of late blight in 2009 is different from previous outbreaks in two ways. This is the earliest late blight has been reported across a wide area – it's been found across the Northeast and New York state, not to mention states to the south and west of Long Island.

Zitter reported that several years ago an occurrence of the disease originating in one source in upstate New York spread to 14 counties by the end of the summer, "destroying tomatoes in the entire region."

The second difference from traditional outbreaks, and "more tragic for the Northeast," is that infected plants were distributed to large local retail stores from Ohio to Maine. "Never before has such an extensive distribution of infected plants occurred," Zitter said. Worse, infected plants can easily contaminate healthy plants on the store shelves. Experts believe the disease originated with, or was at least exacerbated by, one supplier that distributes to the four major big box stores.

"What we know is that diseased plants have been found at garden centers in big box stores by extension specialists and pathologists from Ohio to Maine. There are many more stores than people looking; we are assuming affected plants are widespread based on the high frequency of finds," McGrath said.

"There is one large company that produces a lot of the vegetable and herb plants. Its headquarters are in Alabama," McGrath continued. "There have been situations in the past where diseases and insect pests were brought into northern production areas on vegetable transplants produced in southern areas, and late blight is a disease that can occur in the south during their winter production season, thus the immediate conclusion that this was another case of plants produced in the south where they were exposed to a pathogen occurring there."

Although the Associated Press reported tomato plants have been removed from Home Depot, Wal-Mart, Lowe's and Kmart stores in all six New England states and New York, an associate in the garden center at the Riverhead Wal-Mart said he'd received no directive to remove plants. They were available at the Home Depot in Riverhead last week as well. "We've known they had a problem in Riverhead for a while," McGrath told The Independent Monday morning. "I was in there last Thursday."

Since box store garden centers often sell plants on consignment, store managers may feel they lack the authority to remove the plants from shelves, McGrath said.

Each state has responded differently to the crisis, she explained. New Jersey and Maine directed stores to stop sales completely. In New Hampshire, front-page news stories alerted growers and during a trip to Massachusetts over the weekend, McGrath noted there were no tomato plants to be found. On Long Island, she first noted residential cases of late blight in gardens where plants had been purchased at the Home Depot stores in Middle Island and Riverhead.

Based in Ithaca, Zitter checked local stores in the area and saw plants had been removed as of June 27. But the disease had already spread to healthy plants, which were still available for sale. "I know this same event is being repeated in multiple garden centers around the region," Zitter said. "The major question is, how many homeowners bought the plants {at box stores]," McGrath said.

Zitter checked small garden centers around Ithaca and found no evidence of late blight. While the Cornell expert is adamant about the need to warn against an "impending disaster," it appears so far late blight hasn't made it to the South Fork.

It could be a case of buying local combined with weather conditions. Elaine Jones at Vicki's Veggies in Amagansett said she gets her tomatoes from Helen's greenhouse in Riverhead, which has been blight free to date. Purchasing plants from such self-contained sites as Helen's could help. Jones reported that her family grows local tomatoes for sale, too, but the weather has been so poor, the plants didn't get into the ground until just under two weeks ago.

Tony Giannini and Mark Lewis, working their plot at the East End Community Organic Farm in East Hampton, reported they get their tomato plants from EECO Farm, where they're greenhouse-raised from seed. Although they're puny, the plants looked healthy.

Timing – when plants were purchased – may be a factor. Avid home tomato gardener Bob Wooding purchased plants at both Wal-Mart and Home Depot in early May. He kept them indoors for several weeks before planting and so far, his plants are flourishing. Wooding may have gotten his plants before the infection started, McGrath theorized. Still, she said, "he needs to monitor them."

Homeowners "cannot control" the spread of the disease, McGrath informed. "It's like trying to control the Bubonic Plague with over the counter medication, rather than prescription drugs," she said. Commercial growers have access to treatments that individual gardeners don't. She fears organic farms will get hit the worst.

The biggest concern, said McGrath, is that homeowners' plants may already have late blight. "If they don't realize it, it will multiply and spread." Diseased plants have to be removed and contained in garbage bags for disposal, as opposed to added to compost piles.

So, what's a gardener to look for? Classic symptoms of late blight are nickel-sized or larger olive green to brown spots on leaves, with a grayish white, fuzzy growth on the undersides. Leaf lesions begin as tiny, irregularly shaped brown spots. Brown to blackish spots develop on upper stems, and firm brown spots develop on the actual tomato. According to the CCE alert, symptoms are "quite dramatic and very obvious to the naked eye."

Because late blight is so contagious, McGrath seemed confident the disease would spread rapidly and extensively across Long Island, even to places it hasn't been seen yet. Experts are seeing outbreaks in new areas continually. The only thing that might slow the spread, she said, is the onset of extremely hot and dry weather.

Without the weather's cooperation, late blight may also spread to certain weeds, like bittersweet nightshade. "Then it could really take off," McGrath said. Homeowners are unlikely to monitor ailing weeds, or remove them before blight can spread. "People think if their weeds are dying, that's great," the pathologist observed. Petunias may also become infected.

McGrath has been the resident vegetable pathologist for Cornell University on Long Island for 21 years. She's seen late blight outbreaks five times in those years. Every other time the disease hit in late August, September and October. "It's not a big deal then," she said, noting that tomato season generally winds down by summer's end. This is the first time she's seen late blight so early in the growing season. "This has never happened before," McGrath concluded. "It's bad news."

kmerrill@indyeastend.com

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