The Effect of Fungicide Timing On Spring Dead Spot Control In Bermudagrass.

Field experiments were conducted at Hillcrest Country Club in Lubbock, TX during the fall of 2010 to evaluate the effect of fungicide application timings for the chemical control of spring dead spot (SDS) in a bermudagrass fairway. Plots measuring 1.5 m² were arranged in a randomized complete block design with four treatment replications. Treatments were applied using a CO₂ backpack sprayer equipped with XR8008VS nozzles calibrated to deliver 757 L/ha at 221 kPa. Initial applications were made on 7/22/2010 or 8/15/2010 and consisted of fenarimol (2.29 kg ai ha^-1), thiophanate-methyl (7.62 kg ai ha^-1), fenarimol (2.29 kg ai ha^-1) + thiophanate-methyl (7.62 kg ai ha^-1), fluoxastrobin (0.43 kg ai ha^-1), tebuconazole (0.87 kg ai ha^-1), azoxystrobin (0.12 kg ai ha^-1), and azoxystrobin + propiconazole (0.99 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. Earlier fungicide applications [7/22/2010 followed by (fb) 8/15/2010] exhibited less SDS pressure on 4/25/2011 than later applications (8/15/2010 fb 9/12/2010). Untreated check plots exhibited 68% SDS pressure. Earlier applications of tebuconazole, fenarimol, azoxystrobin + propiconazole, and fenarimol + thiophanate-methyl exhibited the least amount of SDS pressure (9, 11, 12, and 13%, respectively), on 4/25/2011. All other earlier application treatments exhibited ≥ 20% SDS cover on 4/25/2011. Later fungicide application treatments exhibited ≥ 23% SDS cover regardless of treatment on 4/25/2011. This trial will be replicated in time.