P-101 - Evaluation of Demethylation Inhibitors, Strobilurin and Benzamidazole fungicide sensitivity in Colletotrichum orbiculare from Virginia watermelon

Anthracnose, caused by Colletotrichum orbiculare, threatens watermelon (Citrullus lanatus) production in Virginia, reducing yield and post-harvest fruit quality. Control failures in the field suggest potential fungicide resistance. This study aims to assess local C. orbiculare isolates for fungicide sensitivity. In 2024, a total of 102 C. orbiculare isolates were collected from six watermelon fields across Virginia. Isolates were identified, single-spored, and placed into long-term storage. Field trials were conducted in 2024 to determine key fungicides for sensitivity testing. The strobilurins tested, pyraclostrobin alone and a premix of azoxystrobin and the triazole difenoconazole, significantly reduced disease compared to nontreated plots. There was no significant difference in final foliar disease severity between the strobilurin treatments but the azoxystrobin/difenoconazole premix reduced the area under the disease progress curve compared to pyraclostrobin alone. The triazoles (flutriafol, mefentrifluconazole, tebuconazole) failed to control disease, but the triazolinthione (prothioconazole) reduced disease symptoms by 50% compared to the nontreated control. The benzamidazole thiophanate-methyl is commonly used by growers against anthracnose and significantly reduced disease compared to nontreated plots but was not as effective as some of the other fungicides. Based on field trial results, azoxystrobin, difenoconazole, prothioconazole and thiophanate-methyl were selected for in-vitro EC50 testing. Results from in-vitro assessments will be presented.