Caused by: Thielaviopsis basicola Diagnostic Note: Early scouting is crucial because initial infection of the cortical root tissue by T. basicola can occur 10-14 days after planting. Whereas, symptoms of black root rot have been observed in seedlings as early as 3 weeks after planting. Levels of disease incidence and severity increase in fields that contain Root-Knot nematode (Meloidogyne incognita) and Reniform nematodes (Rotylenchulus reiformis). Therefore, soil sampling for nematodes prior to planting season should highly be considered. Yield Loss Estimate: Rhizoctonia solani is 1 of 4 cotton seedling pathogens known to cause cotton yield losses in Tennessee. Often, there is not just one disease that is causing the yield loss. Therefore, when totaling yield losses due to cotton seedling disease, all 4 pathogens are considered. In 2018 alone, it is estimated that 162,000 bales of cotton were lost to seedling disease in the United States. This is the equivalence of 48.6 million dollars lost. Table 1 demonstrates where seedling disease has ranked over the past 5 years for disease loss estimates in cotton across the U.S. In Tennessee, cotton seedling diseases can be great cause of concern. Together, these diseases compose the biggest disease problem Tennessee cotton producers encounter during a growing season. Since 1995, seedling diseases have caused from 3%-22% within the state. Yield losses were typically higher in years with cool and wet conditions present early on in the season.
Symptoms: Characteristic symptoms of black root rot include initial delay in seedling growth, as well as, darkening of the tap root/ lateral roots. The darkening of the roots is the visual representation of the outer root cortex decaying. In severe cases, all of the lateral roots may be lost.
Seedling exhibiting loss of lateral root due to black root rot