Tobacco growers battle weather, TSWV

Searching for a word to adequately describe this year's Georgia tobacco crop, Extension Agronomist J. Michael Moore finally settles on “ratty.” Growers have seen a little of everything this year, he says, including drought, excessive rain and their No. 1 nemesis, tomato spotted wilt virus.

“We started out with a fairly wet spring and then went into a period of drought,” says Moore. “Then, beginning in June, we received rainfall on an almost daily basis. Since then, while we've been using sucker control chemicals, it has continued to rain almost daily.”

Bad enough

Tomato spotted wilt virus isn't as severe this year as in 2002, when 41 percent of Georgia tobacco plants were lost to the disease, but it's bad enough, he says. “This year, we're estimating that 25 to 30 percent of the tobacco plants in Georgia are infected by the disease.”

Georgia growers still could make 90 percent of their effective quota, or about 51 million pounds, he says.

Growers had somewhat of a forewarning of the problems with tomato spotted wilt virus this year, says Moore. “We made some recommendations to growers about how to avoid tomato spotted wilt losses. We had a damp spring, so we knew the weeds would be growing. And we knew there were numerous thrips out there, because we were trapping them and estimating their numbers into February and March. We also knew from analyzing weeds across the state that the weeds had high levels of the virus,” he says.

Everything, says Moore, pointed to a need for growers to utilize the chemicals Admire and Actigard for the best control of the virus possible.

“Unfortunately, a lot of growers chose to remember 2003 instead of 2002. Some of them scrimped on Admire — they didn't use it or they didn't use enough. And, they chose not to use Actigard because of the cost, and because of the negative publicity associated with the possibility of stunting or damaging plants.

“Where Admire and Actigard were used appropriately, we can see that they did a tremendous job in reducing the amount of tomato spotted wilt virus in the plants. Not only was the virus reduced, but when it showed up later in the season, plants lost only leaves as opposed to the entire plant dying,” he says.

Growers are advised to use Admire at 1.8 ounces per 1,000 plants in the greenhouse prior to transplanting. Or, if they're using bed plants, they can use Admire in the transplant water, says Moore.

“Spraying over-the-top of beds hasn't proven successful. We pretty much leave behind the treated soil before the plants have a chance to take it up and get protection.”

The rate for Actigard is 1 ounce per 100,000 plants, whether on bed plants or in the greenhouse. “We've gotten control at lower rates than that. It's applied prior to transplanting in the greenhouse or in the plant bed.”

There were early reports, says Moore, of growers who had substantial stand losses due to tomato spotted wilt virus. Some growers even plowed up their plants and started over.

“Of course, if you start over and plant again, you start out behind. You start out with plants that are not the preferred age, and it isn't a good situation.”

In a further effort to reduce the incidence of tomato spotted wilt virus, growers have been advised, he says, to wait until after April 7 before transplanting tobacco. Data has shown a reduced incidence of the disease if growers transplant later, he adds.

“So there are several things a grower can do to reduce the incidence of the virus,” says Moore. “Transplanting a little later, making sure the crop gets a good start and grows rapidly and uniformly, using Admire and Actigard prior to transplanting, and general good crop management.

“There are still people who think they can apply a foliar insecticide and kill thrips. They do kill thrips. But, most of the time, thrips already have spread the disease before they're killed. Even if they're killed, others come in and re-infest the field. We know there are hundreds of weeds that can harbor the virus and can transmit the virus to thrips as they hatch and begin to grow on the plants.”

The reality, says Moore, is that tomato spotted wilt virus is endemic, and it's here to stay. “Some may say you should reduce the amount of weed pressure around the fields and in the woods. But if everyone doesn't do it, it's not very useful. You need total decimation in a large area, or it won't work.”

Most Georgia tobacco growers will be harvesting later this year, he says, and black shank is showing up in fields due to frequent rainfall.

“Damage to the root system of the plants is allowing entry for the black shank fungus. Once the fungus is in the plant, it won't live for very long. Part of the problem is that we're seeing this resistant race — Race 1 — and we don't have resistance in the transplants or varieties. We're working towards identifying the areas where this is occurring and making suggestions to growers about using rotations and Ridomil Gold for control.”

Growers haven't had to worry much about black shank in recent years because of dry weather conditions, says Moore. “There are numerous varieties that are touted as having excellent resistance to Race 0 of black shank. Race 1 is a different story, and in some cases, it catches growers off guard.”

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