Increasing spray volume and ozone spray of tetraconazole improve control against strawberry powdery mildew

Powdery mildew caused by Podosphaera aphanis is a serious disease in strawberry production, particularly under protection. The use of synthetic fungicides is the main strategy to control strawberry powdery mildew (SPM). However, resistance development to traditional fungicides including triadimefon and carbendazim has led to failure to manage this crucial disease. It is pivotal for the growers and the strawberry industry to develop new fungicides and application technologies that can achieve proper control in an environmentally friendly way. In this study, in vitro toxicity assays and field trials were conducted to screen highly efficacious fungicides and application technologies were optimized to improve the control of SPM. In the P. aphanis spore germination assay, the results showed that the median effective concentration (EC50) of tetraconazole, bupirimate, pyraclostrobin, and flusilazole was 3.90, 4.85, 5.46, and 6.03 mg/L, respectively. Results from field trials showed that the highest control was recorded in the treatment of tetraconazole at 56.25 mL/ha. Tetraconazole treatment was then selected in the application technology tests. In spray volume tests, the results demonstrated that increased the spray volume from 900 L/ha to 1050 and 1200 L/ha significantly improved the control of SPM. Moreover, results from the spray instrument tests showed that the index of SPM in the ozone spray (18.52 %) was significantly reduced compared to the conventional spray (22.96 %), which was better than that of electrostatic spray (21.48 %). Taken together, these results indicated that tetraconazole could effectively control SPM both in in vitro assays and field trials. Increase in the spray volume and the use of ozone spray significantly improved the control of SPM.