Spring Dead Spot Recovery In Response to Preemergence Herbicide Applications.

Turfgrass managers often make preemergence herbicide applications in early spring for annual grass and broadleaf weed control in bermudagrass fairways. This may coincide with the appearance of spring dead spot (SDS) disease. Utilization of certain preemergence herbicides may delay bermudagrass recovery from SDS and further contribute to a weakened turfgrass system. Therefore, field trials were conducted at Hillcrest Country Club in Lubbock, TX during the fall of 2010 to examine SDS recovery of a bermudagrass fairway in response to preemergence herbicide applications. Plots measuring 1.5 m² were arranged in a randomized complete block design with four replications of treatments. Preemergence herbicides were applied on 3/15/2011 to a bermudagrass fairway exhibiting symptoms of SDS disease. Treatments were applied with a CO₂ backpack sprayer equipped with XR8003VS nozzles calibrated to deliver 304 L ha^-1 at 276 kPa and consisted of prodiamine at 0.73 kg ai ha^-1, pendimethalin at 2.5 kg ai ha^-1, oryzalin at 1.68 kg ai ha^-1, dithiopyr at 0.56 kg ai ha^-1, oxadiazon at 3.4 kg ai ha^-1, indaziflam at 0.053 kg ai ha^-1, and dimethenamid at 1.68 kg ai ha^-1. An untreated check was included for comparison. All treatments received a sequential application on 6/15/2011. Visual ratings of % SDS disease cover were recorded every two weeks until bermudagrass recovered completely in the untreated check plots. SDS cover was converted to % SDS recovery by comparing back to initial ratings. Data were subjected to analysis of variance (ANOVA) and means were separated using Fisher’s Protected LSD at the 0.05 significance level. All treatments exhibited less SDS recovery compared to the untreated check except oxadiazon 14 weeks after initial treatment (WAIT). On 6/21/2011 (14 WAIT) the untreated check exhibited 46% SDS recovery while oxadiazon exhibited 55% SDS recovery. SDS recovery was 33% for pendimethalin, 25% for dimethenamid, 23% for prodiamine, 21% for oryzalin, 19% for dithiopyr, and 15% for indaziflam 14 WAIT. This trial will be replicated over time.