P-308 - Efficacy of in-furrow application of Phytophthora sojae inoculum and fungicide treatments under field conditions

Phytophthora sojae is a common oomycete responsible for damping-off, root rot, and stem rot in soybean. Field trials play a crucial role in evaluating host resistance and fungicide combinations for disease management. Achieving consistent disease pressure is challenging due to factors including inoculum viability and adverse environmental conditions. Many seedling and root pathogens are grown on grain which is dried and applied in furrow at planting. P. sojae loses viability when dried, greatly reducing the efficacy of this technique. This study evaluated an alternative P. sojae inoculum with two seed treatments in field conditions with irrigation in Piatt County, IL, in 2024. The experiment consisted of four replicates applied to two 20 ft rows. Blended agar plates infested with P. sojae were applied as a slurry in furrow at planting. The treatments consisted of (1) a non-inoculated check treated with conventional seed treatments containing the active ingredients Fludioxonil, Sedaxane, and Thiamethoxam; (2) the same seed treatment inoculated; (3) the same seed treatment plus Mefenoxam inoculated. The field was irrigated twice daily until 7 days after emergence. Plant count, vigor, and other physiological data was recorded. Results show a significant (p < 0.05) reduction in these variables in the inoculated treatment without Mefenoxam compared to the non-inoculated and inoculated with Mefenoxam treatments. These results demonstrate a promising approach for enhancing disease pressure in P. sojea field trials. The experiment will be repeated in 2025 for further validation.