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Disease knows no season

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A dry fall set up hope for a disease-reduced 2008; a wet winter brings old foes back to the forefront

by David Williams

Plant pathologists may be the only agricultural people that saw any good tidings from the drought of 2007.
While the need for rain hit a lot of growers in the wallet, the only saving grace is that drier conditions provide less of a favorable environment for diseases to develop in tobacco, as well as other crops.
But a wet winter, while recharging the water tables across the Southeast, has reignited the chances for black shank, blue mold and pythium rot to show up in greenhouses and fields this spring.
Paul Denton, professor and Extension burley tobacco specialist at the University of Tennessee, said a dry spring is still a possibility—and that could be a double blessing.
“I am sure that deep groundwater has not recovered, but we get little irrigation water in Tennessee from groundwater,” he said. “Soil moisture has recharged. So we are in pretty good shape. I am not concerned about a dry winter, because even if we get lower than normal rain in winter, our ‘normal’ is such an excess that we will have adequate soil water and surface water going into spring.”
Denton also noted that the dry spring and warmer, drier-than-usual summer prediction gives rise to the belief that disease can be held in check.
“Our main disease problems are black shank and blue mold, with target spot moving up the list,” he said. “All of these are actually inhibited by a dry spring—which is one reason why 75 percent of normal rain in the spring isn't so bad—so we don't expect increased severity as a result of dry weather.”
Kenneth W. Seebold Jr., assistant Extension professor for tobacco and commercial vegetables at the University of Kentucky’s Department of Plant Pathology, sees a wetter winter in Kentucky and a renewed vigilance for the traditional diseases.
“We’ve been really wet and cool here, and it looks like early spring will be the same,” Seebold said. “From a disease standpoint, I expect we’ll be seeing the usual problems on transplants, like pythium and maybe even a touch more of collar rot if the weather stays cool and wet.
“In the field, black shank will likely be the biggest problem that we face in 2008. The long-range forecast is calling for warmer and drier-than-normal conditions this summer, so hopefully that’ll keep blue mold at bay and black shank in check.”
The burley growers have a new weapon in disease resistance this season—a new tobacco strain, KT 206 LC. Denton said the new variety is readily available and well received after testing. It has very high race 0 black shank resistance and moderately high race 1 resistance.
“We expect this variety to have a major impact in reducing losses due to black shank over the next few years, and we highly recommend it to producers with severe black shank problems,” Denton said.
Seebold concurred, saying both KT 204 and KT 206 “can really help in fields with heavy disease pressure.” He added that variety selection cannot be undersold as a tool for managing black shank.