Use of Cultural Practices to Enhance Spring Dead Spot Fungicide Efficacy.

Efficacy of fungicides for the control of root-infecting fungi may be limited by fungicide penetration into the soil profile. Cultivation practices aimed at reducing the thatch layer may also increase fungicide infiltration. Therefore, field experiments were conducted at Hillcrest Country Club in Lubbock, TX during the fall of 2010 to evaluate the effect of cultural practices on fungicide efficacy for the chemical control of spring dead spot (SDS) disease in a bermudagrass fairway. Plots measuring 1.5 m² were arranged in a randomized complete block design with four replications of treatments. Cultural treatments were conducted prior to fungicide application and consisted of no cultivation, verticutting, hollow-tine aerification, or aerification + verticutting. Fungicide treatments were applied on 8/15/2010 with a CO₂ backpack sprayer equipped with XR8008VS nozzles calibrated to deliver 757 L ha^-1 at 221 kPa and consisted of fenarimol at 2.29 kg ai ha^-1 or tebuconazole at 0.87 kg ai ha^-1. All treatments received a sequential application 30 days after initial treatment (DAIT). SDS control ratings were recorded the following spring (2011) when symptoms appeared following bermudagrass green-up. Visual ratings of % SDS disease cover were recorded every two weeks until bermudagrass recovered in the summer. Data were subjected to analysis of variance (ANOVA) and means were separated using Fisher’s Protected LSD at the 0.05 significance level. SDS pressure without cultivation was 15 to 16% on 4/25/2011, regardless of fungicide treatment. Verticutting did not increase the efficacy of fenarimol, but did decrease % SDS pressure 2% when conducted in conjunction with tebuconazole. The combination of either fungicide with aerification or aerification + verticutting greatly reduced % SDS pressure on 4/25/2011. Fenarimol and tebuconazole treatments exhibited 8 to 9% and 2 to 3% SDS pressure, respectively, when used in conjunction with aerification or aerification + verticutting. This trial will be replicated over time.