Rain damage and TSWV seen on
Georgia tobacco tour

by Jennifer Whittaker, Editor

Pictured from left, Ware County tobacco grower A.J. “Cotton” Bennett and David Jones, a retired UGA Extension entomologist, discuss the impact the insecticide Admire® has had on controlling tomato spotted wilt virus. The two have worked since the mid-90s to determine the best mixture and application rates of insecticides for controlling TSWV.

Signs of excess rain and tomato spotted wilt virus (TSWV) were evident in many of the fields where the 2005 Georgia Tobacco Tour stopped during the three-day tour held June 6-8.

Drooping plants and sunscalded yellow leaves indicated plants suffering water damage and infected with TSWV.

“What’s making diseased plants show up worse is the excessive rainfall the farmers have had,” Dr. J. Michael Moore, UGA Extension tobacco specialist, explained. “Tobacco roots need oxygen to survive. The plants are drowning and are oxygen deprived. As the plants suffocate, the roots rot. They have to regenerate a new root system.”

Moore said the best thing growers can do for a crop that has received excess rain is to wait and let the water evaporate out of the soil and allow the plant to regenerate new roots.

“Often growers try to add fertilizer to fields that have received excessive rainfall and plants are showing damage,” Moore said. “That’s not what the plants need. They just need a chance to recover.”

Farmers in southeast Georgia hosting stops on the tour said they had received between five to eight inches of rain in the week before the tour. Several of the farms received rain the night before the tour came to their farm. In July, farmers received more rain from Tropical Storms Cindy and Dennis.

Bacon County tobacco grower David H. Lee, who is participating in the UGA Extension Tobacco Team’s variety trials, said farmers need varieties that can standup to adverse weather and produce a crop that cigarette companies want. Lee’s farm is one of several sites where the tobacco team is studying how well tobacco varieties perform and resist various diseases. Other farm stops on the tour spotlighted research to control disease and insect damage and ways to improve yield through production techniques.

Bacon County tobacco grower David Lee is pictured checking his crop for signs of TSWV and TMV. Lee participates in UGA variety trials in hopes researchers can develop a variety that can withstand adverse weather and disease pressure.

In June, the incidence of TSWV was running as high as 55% in fields where plants were not treated for the disease, Moore said. This compares with an incidence rate of 42% in untreated fields in mid-June last year. TSWV is spread by thrips and causes plants to deteriorate or die when infected. Because virus diseases can’t be controlled once a plant is infected, growers are encouraged to treat transplants with insecticides before they are planted.

“It just seems like tomato spotted wilt virus is worse than usual because of weather and insect pressure,” Ware County grower A.J. “Cotton” Bennett said. “By using Admire® we have been cutting our tomato spotted wilt losses fifty percent. In plots where we didn’t use Admire losses would be twice as great. If the people who say Admire doesn’t work just left four to eight rows untreated they would see a difference. I would rather take a thirty percent loss than a sixty percent loss any day.”

David Jones, a retired UGA Extension entomologist who has worked with Bennett since the mid-1990s to determine the best mixture and application rates of insecticides for controlling TSWV, says it’s essential for tobacco plants to be treated before they are transplanted.

“Thrips land on tobacco plants within just a few hours of transplanting them,” Jones explained. “Tomato spotted wilt symptoms start to appear fourteen to twenty-one days after a plant is infected. Once plants are in the field there’s really nothing to do.”

Growers are also having to contend with another tobacco disease, tobacco mosaic virus (TMV) which can be detected by the presence of dark and light green patches that appear on tobacco