Rainfall amounts were well above average and heat units were considerably below average for the first several months of the cotton-growing season in 2007.
“As a consequence, levels of Verticillium and Fusarium wilt are much higher on the Texas High Plains in 2007 than in 2006,” said Terry Wheeler, plant pathologist with the Texas Agricultural Experiment Station at Lubbock. These wilts can be mistaken for each other, since the leaves turn yellow or brown and the vascular system is discolored with both diseases, but there are also distinct differences between them.
This disease is found mostly in the sandier soils southwest of Lubbock (Gaines, Dawson, and Terry counties), and requires root-knot nematode to be present.
Symptoms may begin at the late seedling stage through mid-July, when plants begin to die. Plants will typically have a loss of turgidity in an upper leaf, even before yellow color in the leaves occurs. Young plants die rapidly, while older ones may linger for a while.
The only options available for ameliorating Fusarium wilt-damage are controlling root-knot nematodes and using the best Fusarium wilt-tolerant varieties.
“Yield increases of up to 25 percent can be obtained when nematodes are controlled by 5 lbs of Temik 15G in the furrow at planting,” said Wheeler.
“In general, stripper varieties have more tolerance to Fusarium wilt than picker varieties, but picker varieties can often tolerate more stand loss and still yield,” said Wheeler. “We conduct variety testing to determine the best varieties for Fusarium wilt fields.”
This disease is widely spread over the Texas High Plains and is not substantially affected by root-knot nematode. Symptoms of this disease typically occur over a wide time range, usually from flowering and later. Disease severity is highly dependent on weather, and is much worse in years when cool, wet conditions occur from mid-July to mid-August.
“The best way to minimize Verticillium wilt is with variety selection and reduced levels of irrigation. Yield can be reduced by 70% between the most tolerant and most susceptible varieties. Also, in wet summers, we encourage producers with a history of Verticillium wilt to water lightly, but we don't know yet what to recommend in terms of irrigation in drier summers.”
If fields have wilt symptoms, producers should have symptomatic plants identified as to which type (Fusarium or Verticillium). “We can do that at the Lubbock research and extension center if there is some question.”
“Around February, we post the results from our Verticillium and Fusarium wilt variety tests online at http://lubbock.tamu.edu. This work, which is funded by the cotton growers through Plains Cotton Improvement Program and Cotton State Support, is the best guide I can recommend to manage these diseases,” Wheeler said.