BENTAZON SPRAY RETENTION, ACTIVITY, AND FOLIAR WASHOFF IN WEED SPECIES

Greenhouse studies were conducted to investigate the effects of adjuva nt and rainfall on bentazon spray retention, efficacy, and foliar wash off in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Benta zon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil con centrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blen d (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk af ter treatment was similar with either adjuvant on velvetleaf and smoot h pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklep od as compared to COC. Rainfall at 1 h after application generally red uced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application a s compared to COC. Overall, bentazon spray retention on plants was 9 t o 550% higher with OSB as compared to COC among the species at 1 h aft er application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adj uvants except in smooth pigweed and ranged from 39 to 98% among the fo ur weed species at 1 h after application. OSB exhibited specificity fo r certain weed species and the potential to minimize bentazon spray re aching the soil by increasing deposition.