Residual Large Crabgrass Control In Spring with Fall Indaziflam Applications.

Anecdotal evidence suggests that the new preemergence herbicide indaziflam exhibits long soil residual activity. Preemergence applications are often made in the fall for the control of annual bluegrass in bermudagrass fairways. Long soil residual activity may provide initial annual grass weed control the following spring. Therefore, the objective of our research was to evaluate the residual control of large crabgrass in the spring from preemergence indaziflam applications made the previous fall. Field experiments were conducted at Lake Ridge Country Club in Lubbock, TX on a hybrid bermudagrass fairway (history of large crabgrass pressure) during the fall of 2010. Plots measured 1.5 x 1.5 m and were arranged in a randomized complete block design with four replications of treatments. Treatments were applied using a CO₂ backpack sprayer with XR8004VS nozzle tips and calibrated to deliver 375 L ha^-1 at 221 kPa. Treatments were initiated on 9/6/2010, 3/1/2011, and 5/1/2011; and consisted of single or sequential applications of indaziflam at 35 or 53 g ai ha^-1. Prodiamine at 546.4 g ai ha^-1 was applied on 9/6/2010 or 3/1/2011 for comparison purposes. Percent bermudagrass phytotoxicity was recorded 1, 2, 25, 26, 33, and 34 WAIT. Visual estimates of percent large crabgrass control were recorded 26, 28, 30, 32, 34, 36, and 38 WAIT. Data were subjected to analysis of variance (ANOVA) and means were separated using Fisher’s Protected LSD at the 0.05 significance level. No bermudagrass phytotoxicity was recorded throughout the length of the trial regardless of treatment. Large crabgrass pressure was first recorded on 4/29/2011 (32 WAIT). Untreated check plots exhibited 10 to 20% large crabgrass cover 32 WAIT. Prodiamine applied on 9/6/2010 exhibited 0% control, while all other treatments exhibited 100% control 32 WAIT. All indaziflam treatments still exhibited 100% large crabgrass control 38 WAIT regardless of rate or application timing. Control with prodiamine applied on 9/6/2010 was 0, while control with prodiamine applied on 3/1/2011 remained at 100% 38 WAIT. Indaziflam applied initially on 5/1/2011 controlled existing immature crabgrass plants and provided excellent preemergence control. Large crabgrass pressure was minimal in 2011 due to low soil temperatures in early summer and extended drought conditions. Large crabgrass control with indaziflam may have been less if weed pressure exceeded 15%.