Effect of Nozzle Selection on Weed Control and Yield in Mississippi Cotton

A field study was conducted at the Blackbelt Research Station in Brooksville, MS to understand the effect of nozzle type and herbicide application timing on weed control in cotton.  For the tractor study, five nozzle types: Ultra-Low Drift (ULD) 12004, Guardian Air (GA) 11004, Guardian Air Twin (GAT) 11004, 3D 10004, and High Flow (HF) 14008 were compared. For the backpack study, four nozzle types: Ultra-Low Drift (ULD) 12002, Guardian Air (GA) 11002, Guardian Air Twin (GAT) 11002, 3D 10002 were assessed.  Applications were made at 140 L ha^-1 (15 gal ac^-1). Spray pressure for the 04 nozzles was 276 kPa (40 psi) and 138 kPa (20 psi) for the HF 08 nozzle. Herbicide applications were made at four different timings: preemergence (PRE), early post (EPost), early-mid post (EMpost), and late post (LPost) corresponding to the preemergent, 2-3 leaf, 5-6 leaf, and match head square stages respectively. Programs selected were: PRE fb EPost fb LPost; EM Post only; EPost fb LPost. Results showed no difference between sprayer type or nozzle type for weed control, where all programs resulted in control at or above 90%. For yield results, neither nozzle type nor sprayer type was significant so data were pooled across those factors. Yield results showed that the EMpost program resulted in the best yield (2600 lbs seed cotton / acre) compared to the other two programs respectively (2312 and 2340 lbs seed cotton / acre). The results are less indicative of pursuing a one-time application only, but rather reflects a need to further examine glufosinate tolerance among cotton varieties. Given that weed control results were all optimal, the difference in yield appears to be more a factor of cotton sensitivity to a late season glufosinate application than due to yield loss from weed control.