Role of Pythium spp. in the seedling disease complex on cotton; results from the National Cottonseed Treatment Trials

Fungicides are universally sold on cottonseed to control a number of seed-borne and soilborne pathogens that affect the germination of seed and emergence, survival and vigor of seedlings. The National Cottonseed Treatment Program evaluates seed treatment combinations in 15 to 20 trials annually. The importance of Pythium species in the seedling disease complex on cotton in these trials was examined with the fungicide treatment metalaxyl, disease ratings, and pathogen isolations from seedlings and soil populations from the non-treated control plots at each location. Fungicides improved stand over the non-treated control in 120 of the 214 trials conducted by cooperators, 56% of the trials. For the 120 trials with a fungicide response, metalaxyl alone gave a significant response in 40 trials indicating the importance of Pythium spp. in these trials. Based on seedling stand response for the metalaxyl treatment compared to seed not treated, responses were found more frequently and stand responses were greater as minimal soil temperatures at planting decreased from 20 to 12 C and total rainfall increased the first three days after planting. Isolation frequency from seedlings and soil populations of Pythium spp. were poorly correlated with disease symptoms and stand response suggesting these data have a limited role in characterizing the importance of Pythium spp. in the seedling disease complex on cotton.