Pythium root rot (damping off) is one of the most common diseases across the Cotton Belt, especially where soil temperatures at planting are less than 68°F. Roots and stem tissues will appear light tan to dark as they decay and die. Photo courtesy of Dr. Craig Rothrock, University of Arkansas.
Damping off is a collective term that refers to pre-emergence and postemergence symptoms potentially caused by several different soilborne pathogens. Damping off weakens and sometimes kills seedlings before or after germination.
Damping off is most prevalent in wet and cool soil conditions. Seeds typically become infected by soilborne fungi from moisture penetrating the seed coat, or the seed radical is infected at seedling emergence. Common signs of damping off include poor germination, uneven stands and seedlings that look unhealthy after emergence.
Identification and Lifecycle
Although damping off disease symptoms in cotton may result from infection by multiple fungi species, the most common symptoms are part of the Rhizoctonia, Pythium, Thielaviopsis and Fusarium spp. complex. Soilborne diseases can remain viable in the soil for years, even decades.
Cotton seedlings are prone to Rhizoctonia infection when excessive moisture reduces plant growth rate, particularly in early spring. Rhizoctonia can still develop over a wide range of soil moisture conditions and temperatures, however. Symptoms of Rhizoctonia seedling disease appear as reddish-brown sunken lesions below and above the ground. These lesions girdle the stem and eventually cause emerged seedlings to collapse, often referred to as damping off or soreshin.
This is also a soilborne disease that infects seed at the radical – the tip of the seedling – and leads to pre-emergence damping off. The seedling stem may also be infected and result in postemergence damping off. Later in plant development, symptoms may include chlorosis (yellowing) and stunting. Pythium fungi are prevalent in poorly drained soils and produce spores that move in soil water.
Several species of fungal genus Fusarium can be found on diseased seedlings. Seed applied fungicides are an effective management tool.
Also called black root rot, Thielaviopsis disease will weaken young plants during temperatures lower than 68 degrees Fahrenheit, making them more susceptible to other diseases. The fungus is not likely to kill seedlings. When roots are infected, black areas on the outer roots are noticeable, and the root system is underdeveloped. When temperatures climb above 68 degrees Fahrenheit, infected root tissue dissolves, and cotton seedling root growth continues with no sign of infection.
Research shows that high levels of infection from fungi in the cotton seedling disease complex, including Rhizoctonia, Pythium, Thielaviopsis and Fusarium, can slow cotton maturity up to four weeks and reduce annual yield by 5 percent or more, according to North Carolina State University.
Additionally, a recent report published by University of Tennessee Extension shows that common seedling diseases that cause damping off can result in an average annual yield loss of 3 percent.
Managing Cotton Diseases and Damping Off
By following integrated pest management (IPM) practices, growers can control and avoid many yield-robbing cotton diseases while managing disease resistance. A proactive disease management plan that integrates cultural practices with seed selection, seed treatment and at-planting fungicide applications offers the best protection to enhance early cotton growth and make environmental conditions less suitable for diseases to attack.
For cotton-growing areas with a history of disease pressure or conditions that are conducive to seedling disease problems, growers can maximize their stands by planting in optimal soil temperatures and protect their cottonseed investment with a premium fungicide seed treatment such as Trilex® Advanced. It protects against a broad range of cotton seedling diseases, including Fusarium, Rhizoctonia, Pythium and Thielaviopsis basicola and is the preferred fungicide partner for Aeris® insecticide/nematicide seed treatment.
Additionally, Bayer offers cotton growers EverGol® Prime, an innovative seed treatment fungicide that promotes root growth for faster crop establishment. When applied on cotton, EverGol Prime controls soil-borne pathogens including those causing damping off from Rhizoctonia. EverGol Prime is available on all FiberMax® and Stoneville® cotton seed varieties.
View our SeedGrowth section to learn more about cottonseed treatments from Bayer that offer advanced protection against nematodes and early-season insect pests, as well as seed and seedling diseases, or contact your local Bayer representative.