Interactive Effects of Tank-mixed Application of Insecticide, Glyphosate, and Pendimethalin on Growth and Yield of Second-Generation Glyphosate-Resistant Cotton

Research has documented the effects of tank-mixing glyphosate with numerous insecticides on cotton growth and yield; however, no information is available concerning the addition of a residual herbicide such as an aqueous capsule suspension (ACS) formulation of pendimethalin to glyphosate plus an insecticide. Mixtures such as this are important as producers continue to search for costs savings in cotton production and the inclusion of residual herbicides in the planting regimen is needed to mitigate the development and spread of glyphosate-resistant (GR) weeds. Therefore, this research during 2006 and 2007 determined the effects of postemergence (POST) combinations of glyphosate applied alone or plus the ACS formulation of pendimethalin with eight different insecticides on second-generation GR cotton. Glyphosate (Roundup Weathermax) was applied at 1058 g ha-1 alone or tank-mixed with pendimethalin (Prowl H2O) at 1064 g ha-1. The insecticides acephate (Orthene 90 SP) at 560 g ha-1 , beta-cyfluthrin (Baythroid XL) at 37 g ha-1 , dicrotophos (Bidrin 8 E) at 448 g ai ha-1, dimethoate (Dimethoate 4E) at 280 g ha-1, imidacloprid (Trimax) at 53 g ai/ha-1, lambda-cyhalothrin (Karate Z) at 37 g ha-1, oxamyl (Vydate C-LV) at 448 g ha-1, thiamethoxam (Centric 40 WG) at 53 g ha-1, or zeta-cypermethrin (Mustang Max) at 25 g ai/ha were also tank-mixed with glyphosate and pendimethalin. Results indicate that visual crop response in the form of minor malformation and veinal yellowing of contacted leaves can be observed following a POST co-application of pendimethalin with glyphosate (3 to 16%). Addition of insecticides to the glyphosate plus pendimethalin mixture did not affect visual injury. Plant growth and seedcotton yield were not impacted by treatments.