In wet conditions, the lesion can extend upwards several centimeters from the soil line. Excessive soil moisture predisposes cotton seedling to infection by reducing their rate of growth. Infection occurs over a wide range of soil moisture levels. Root Rot Pythium infects the seed and radical, causing seed rot and pre-emergence damping off. At later stages of plant development, Pythium may cause stunting and chlorosis.
Pythium is most damaging to cotton seedlings at low temperatures and high soil moisture content.
Degree of infestation is also impacted by soil texture and organic matter. Black Root Thielaviopsis is most prevalent in Texas, Mississippi, New Mexico, and the San Joaquin Valley area of California. Infection occurs at the seedling stage with roots and the portion of the hypocotyl below soil line rotting and turning black. When older plants are infected by Thielaviopsis the result is collar rot. All rights reserved.