Cotton seedling diseases are like death and taxes — inevitable. It doesn't matter where on the Texas High Plains you plant cotton, the potential for seedling disease is there in the form of one of 15 different fungi that cause seedling disease. The three major ones on the High Plains are Rhizoctonia solani, Thielaviopsis basicola, and Pythium.
“Crop losses from these diseases are estimated to average about 5 percent annually. For the 2007 cotton crop this would have meant a loss to producers of over $80 million,” said Jason Woodward, plant pathologist, Texas AgriLife Extension Service, Lubbock.
Optimum soil moisture levels and Fahrenheit temperatures for these three pathogens differ: Rhizoctonia, moderate and 75 to 90; Pythium, high and 65 to 70; Thielaviopsis, variable and 60 to 70.
“But with variations in growing conditions on the High Plains in any given spring, all three kinds of seedling diseases can be present at the same time,” Woodward said. “And these pathogens can kill seed and seedlings, significantly reduce the vigor of surviving seedlings and result in poor stands, weakened plants, and yield losses.”
Healthy seedlings have taproots that are relatively long, white, and firm, with numerous white secondary roots. Diseased taproots have dark lesions, may be withered or dead, may have shallow lateral roots, or the entire plant may be dead. “In some cases seedling losses (require) replanting,” Woodward said.
A cotton monoculture, cool and wet soils, high levels of plant residue, poor quality seed, and untreated or inadequately treated seed may increase probability of significant levels of seedling diseases.
“Fortunately, a producer can reduce the likelihood of stand and yield reductions,” Woodward said. “By far the most effective and relatively inexpensive technique is to treat high quality seed with effective fungicides at adequate levels. Also, in cases where disease pressure is high, lint yields can be increased substantially by using additional seed treatments in conjunction with standard or base treatments.
“For example, in 2007 under high seedling disease pressure, net returns per acre for Baytan 30 plus Argent 30 plus Allegiance FL (Base treatment), Base plus Trilex, Base plus Dynasty CST, and untreated check, were $639, $924, $1040, and $339, respectively.”
Other techniques for minimizing seedling disease problems include:
Planting adequately treated seed 2 inches deep on top of beds into moist soil when the 10-day-average minimum soil temperature is at least 65 degrees Fahrenheit at 8-inch depth.
Optimizing soil-fertility levels.
Applying fungicides in the seed furrow while planting if pathogen pressure is high.
“Following the above techniques and recommendations will minimize the probability of stand losses and replanting, and maximize the odds of increased net returns for the producer,” Woodward said.
Additional information on seedling diseases is available at http://lubbock.tamu.edu/. Soil temperatures at the 8-inch depth, as measured by National Weather Service and West Texas Mesonet, are available from Plains Cotton Growers' Web site at http://www.plainscotton.org/weatherdata/. The page pulls the latest information direct from National Weather Service's data storage.