The fortunate lack of early season plant disease in Western cotton is likely a result of cropping techniques and warm weather, but that doesn’t mean producers need not be aware of problems that may arise.
Rainfall in the cotton-growing regions of California, Arizona and New Mexico ranges from three to 14 inches annually. Low moisture and the ability to irrigate only when needed is one of the major factors related to the low impact of plant disease.
The great majority of cotton ground in the West is irrigated prior to plant-ing. Seed is then planted while the ground is still moist but not saturated. Depending on the density of the soil, the new crop may not be irrigated for several weeks. Because the ground is not saturated when the seed is germinating, many of the fungi generally associated with plant disease do not thrive on the seed during the early stages of cotton development.
However, Western cotton is not disease-free.
In all elevations of New Mexico, Arizona and California, cool temperatures and increased moisture influence early fungal development and plant disease. Elevations over 3,000 feet are generally about 12 degrees cooler than lower elevations. Cotton is planted several weeks later in those higher areas.
Lower elevations of Arizona and along the Colorado River where heat units accumulate early are also at risk for fungal plant infection. Lack of crop rotation, cool weather planting, improper seed depth and poor seed bed preparation can influence fungal growth on seedling cotton as well.
“Crop rotation is one of the standard practices to prevent pressure and reduce build up of the inoculum in the soil,” says Randy Norton, regional Extension Specialist with the Univer-sity of Arizona.
Factor In Temperature
He also states that planting in soil 65 degrees and higher, as well as using a seed variety with good seedling vigor, is key to giving the plant an advantage as it emerges.
Bob Hutmacher, Cooperative Extension Service for the University of California, agrees that a cold, wet spring will help facilitate early season plant disease.
“Warmer temperatures without rain and cycles of cold nights will help seedlings power through, in general,” he says.
Rhizoctonia solani is responsible for post emergence damping-off of cotton seedlings. Infected seedlings dry up and die.
Hutmacher sees a few incidents of Rhizoctonia solani infestation in land on which tomatoes were previously grown and relates the disease to rotating cotton into the field too early to get a jump on a long growing season.
Thielaviopsis basicola or black root rot is responsible for a black cortical decay of the tap root. Seedlings can recover from black root rot, but plants will not be as productive as those without the infection.
Best Practices Deliver
Once thought to be a fungi, Pythium, a plant parasite, also can be controlled by best practices used to control fungi. Fungicides are useful against Pythium and usually do a good job unless there is an extended period of “lousy, cold weather,” according to Hutmacher.
California cotton producers and researchers are currently working to prevent further infestation of the fungus, Fusarium Race 4 (FOV 4), another early season seedling pathogen that affects plant growth, often killing the infected plant.
Survey Confirms Fungus Status
At this point, there is no evidence of Race 4 cotton infestation in areas other than the San Joaquin Valley.
A cooperative survey of Arizona cotton by the University of Arizona Cooperative Extension, Arizona Crop Improvement Association, Arizona Cotton Growers Association and Arizona Cotton Research and Protection Council in 2012 indicated that no Arizona cotton ground has been infected with the fungus.
Brent Murphree is the Cotton Board’s Regional Communication Manager for the West. He resides in Maricopa, Ariz.