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POSTERS: Chemical control

Comparative analysis of two fungicide sensitivity tests for Helminthosporium solani
Sommer Desotell - Michigan State University. Paige Pline- Michigan State University, Noah Rosenzweig- Michigan State University, Gilberto Olaya- Syngenta Crop Protection

Helminthosporium solani is a pathogenic fungus which causes silver scurf (SS), a potato-specific disease often found in temperate regions. SS causes cosmetic defects in potato seed tubers which negatively impact the crop’s marketability and storability. MI growers must implement strategies to manage the long-term storage of their product and mitigate this persistent disease. Thus, effective fungicides may control SS and extend the storage period for potatoes. This study had two main goals. First, determine the in vitro sensitivity of H. solani to three classes of fungicides: DMI fungicides [difenoconazole (DFZ)], SDHI fungicides [Solatenol (STL) and sedaxane (SDX)], and phenylpyrrole fungicides [fludioxonil (FDL)]. Second, compare the accuracy and precision of the spiral gradient dilution method to a standard tenfold agar plate dilution method. Tubers with symptoms of SS were sampled from potato storages from the United States. A total of 32 isolates have been collected. The relative growth and germination of spores for all mono-conidial H. solani isolates are being recorded to determine isolates sensitivity to the fungicides listed above. Preliminary results from screening of a limited number of isolates (n=8) collected from ID, WI and MI indicted that EC50 values ranged from 0.2 to 2.6 for STL and 1.6 to 3.5 for SDX. Spiral gradient and agar plate dilution to estimate the effective fungicide concentration at which 50% of the fungal growth is inhibited (EC50) in vitro for all isolates are ongoing.