Photo courtesy of North Carolina State University

Photo courtesy of Colorado State University

The reason, as well as a number of other questions surrounding this disease, remains unanswered. Le Strange, along with fellow farm advisers Tom Turini in Fresno County and Scott Stoddard in Merced County, are working with a team led by UC Davis plant pathology professor Bob Gilbertson to solve some of those mysteries.

Immature flower thrips pick up the virus by feeding on infected plants. More than 900 plants, including peppers, tomatoes, lettuce, ornamentals and numerous weeds, are tomato spotted wilt virus hosts.

The virus remains viable in the immatures, but they cannot infect plants, Gilbertson says. Only adult thrips can spread the virus, although females do not pass it along in their eggs.

Adult thrips live 30 to 45 days, and they can spread the virus their entire lives.

If plants are infected early in their growth, they'll have upcurled leaves, bronzing, leaf necrosis and stunted growth. They typically won't bear fruit.

Plants infected later may have upcurled leaves, bronzing, leaf necrosis and a wilted appearance. Ripe and immature fruit may be mottled, misshapen, bumpy and have the classic darker ringspots.

Tomato spotted wilt has appeared sporadically for several years in California's Central Valley, but didn't cause enough economic damage to draw growers' attention, Le Strange says. In 2003, however, a widespread outbreak in Merced County decimated several fields and sounded as a wake-up call.

Since then, it has shown up more frequently.

"Where tomato spotted wilt virus is in epidemic proportions, it never seems to go away — it's always in the background," Le Strange says.

Lettuce is one of the host crops, and the researchers say they suspect the crop may help carry over the virus from one tomato season to another. Radicchio also is a host, and tomato fields planted next to an already harvested but infected radicchio field were quickly infected.

Some growers also have pointed to the state's increased almond acreage as a possible source of thrips and virus. This spring the researchers attempted to collected 25 thrips from each of four corners of almond orchards adjacent to previously infected crops.

They only managed to collect six thrips, and none was infected with spotted wilt virus.

The researchers also surveyed and trapped greenhouses where tomato transplants were grown. Although they noted that thrip populations increased over the duration, no thrip every tested positive for the virus.

Based on surveys, Gilbertson says they think thrips don't carry a lot of the spotted wilt virus early in the season.

"That tells us they have to get charged up with the virus from other sources," he says.

By late June and early July, Gilbertson says they detect more virus in the thrips, telling him that they pick up the virus from plants infected earlier in the season.

"That's why we are really pushing for thrip management once we see the thrip population growing early in the season," Gilbertson says. "Thrips are reproducing on tomato flowers. That means those tomatoes can be a source of virulent thrips."

Even an aggressive management program doesn't always mean "no disease," Turini says, citing two severely infested fields in his area as examples.

In one field, the grower used a soil-applied neonicotinoid at planting but no foliar thrips material later in the season.

In another field, the grower used the soil-applied neonicotinoid at planting followed by a foliar dimethoate treatment. The field still had 23 percent spotted wilt symptoms.

"We really don't know how bad this field would have been if he didn't have this program," Turini says. "Thrips can increase very rapidly and can build [insecticide] resistance easily. But a specifically timed insecticide may reduce virus spread."

Of the several thrips material Turini tested in a field trial, the best ones reduced thrips populations by only 40 percent.

Follow these steps to fight tomato spotted wilt virus, thrips Monitor for thrips with yellow sticky cards and sentinel plants, such as petunias. Treat for thrips at the first signs of virus. Plant resistant tomato varieties that have the Sw-5 gene. No commercial pepper varieties carry the Sw-5 gene. Control weeds in and around fields, since more than 900 plants can harbor the virus and act as disease reservoirs. Practice good field sanitation by plowing under crops as soon as they are harvested. If you suspect you have spotted wilt in a field, you can test for it using Immunostrips from Agdia of Elkhart, Ind. The easy-to-do assay takes about five minutes to perform.

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Environmental benefits of local foods may not be clear-cut

Matt Mariola and his wife, Debora, enjoy selling their home-grown vegetables every Saturday morning at the Wooster, Ohio, Farmers Market. They like buying locally, too.

Occasionally they even sell food to Mariola's brother, Mike, who owns the South Market Bistro and is a big proponent of local foods.

But are the Mariolas reducing environmental impacts by selling and buying locally? The answer isn't black and white, according to a paper that Mariola wrote and was published recently in the journal Agricultural and Human Values.

Most people assume that the fewer miles a food travels to market, the less fossil fuel it uses, he says. With the average piece of domestically grown produce traveling 1,500 miles to reach its destination, the popularity of purchasing locally grown foods has taken off. But the environmental advantages of purchasing locally grown food aren't clear.

"There are so many variables to look at — to be honest, we just don't know whether buying locally is or is not the best choice environmentally, especially when you look at both sides of the process," Mariola says. That means examining energy expended for both delivering food to the market as well as that used by consumers traveling to the food they purchase.

For the first part of the process, Mariola says it's important to take into account economies of scale. A fully loaded semi trailer, for example, can haul more than 38,000 items.

While hauling a bushel of tomatoes across country from its California home to an Ohio grocery store would be prohibitively expensive, dividing that cost — and the energy used during transport — among 38,000 tomatoes is less daunting.

If the long-distance food is transported on rail instead of highways, energy costs are even less. And global shipping can even be less energy-intensive on a per-item basis: a typical ocean-going cargo vessel can carry about 7 million items of produce on board, he says.

Compare those numbers to dozens of growers each using individual pickup trucks to haul their tomatoes to neighborhood farmer's markets, Mariola says. While the energy impact is likely still less for the locally grown food, the difference may not be as much as people assume.

The equation gets even more interesting when examining the energy consumers use to travel to purchase food. One-stop shopping at a major grocery store can offer real energy savings over driving to farmers' markets that may be out of a family's normal travel pattern.

But the energy balance away from local foods usually completely tips when consumers travel directly to farms to purchase specific food items, he says.

"More people are going directly to farms to purchase food," Mariola says. "In fact, I do so myself — I like buying milk, grapes, blackberries and other items from particular farms, and we enjoy the interaction we have with the growers. But the fact that I'm traveling a good distance, individually, to purchase one food item completely removes any environmental advantage to purchasing locally produced food."

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