SUSCEPTIBILITY OF SELECTED COTTON CULTIVARS TO SEEDLING DISEASE PATHOGENS AND BENEFITS OF CHEMICAL SEED TREATMENTS

The susceptibility of 12 Upland cotton cultivars to three soilborne fu ngi, Pythium ultimum, Rhizoctonia solani, and Thielaviopsis basicola, was evaluated in greenhouse experiments. Based on symptom development and seedling survival, cultivars highly resistant to P. ultimum includ ed Delta Pine (DP) 6166, Prema, DP 6100, and Maxxa. A relatively low i ncidence of pre-emergence damping-off caused by R. solani occurred in ChemBred 7, DP 6100, and Royale, although all cultivars subsequently s uffered significant post-emergence damping-off. All cultivars were equ ally susceptible to T. basicola. In both greenhouse and field evaluati ons, there were no benefits of metalaxyl seed treatment in Pythium-res istant cultivars. Seed treatment with carboxin-pentachloronitrobenzene for the control of Rhizoctonia-induced damping-off resulted in stand increases in all 12 cultivars in greenhouse tests and in 3 of 6 cultiv ars in field trials.