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POSTERS: Chemical control

Strategies for reducing seed rot and seedling damping-off of alfalfa (Medicago sativa)
Deborah Samac - USDA ARS. Samadangla Ao- Kohima Science College, Melinda Dornbusch- USDA-ARS

Alfalfa seeds are often planted when conditions are ideal for infection by seed rot and damping-off (SRDO) pathogens. Treatment of seed with ApronXL (mefanoxam) does not control all SRDO pathogens and does not protect older plants from root rot caused by these pathogens. The EC50values of eight commercial fungicides registered for use on soybean seeds was determined for SRDO pathogens Pythium sylvaticum, P. ultimumvar. ultimum, P. paroecandrum,Aphanomyces euteiches, Phytophthora medicaginis, Fusarium oxysporum, F. verticillioides, and F. incarnatum-equiseti using agar plate-based assays. Evergol Energy (metalaxyl, penflufen and prothioconazole) had the widest activity against the SRDO pathogens. Fungicides with metalaxyl and ipconazole had low EC50 values for all pathogens except A. euteiches. Ethaboxam had low EC50values for all pathogens except Fusarium species. The strobilurin fungicides had moderate to high EC50 values for all pathogens. Most diseases of alfalfa are managed using resistant cultivars. Selection for resistance to three Pythium strains was done using an agar plate assay. Seedlings with moderate levels of resistance were rescued from the plates and adult plants used for intercrossing. One or two cycles of selection resulted in >50% resistant plants in the three germplasm sources used. Fungicide seed treatments in combination with resistance to pathogens would provide effective disease control for seedlings and adult plants.