Palmer Amaranth (Amaranthus palmeri) and Thrips (Thrips sp.) Control with Various Dicamba + Insecticide Tank-Mixes in Cotton (GOSSYPIUM HIRSUTUM)

During the 2018 and 2019 growing seasons, field experiments were conducted in Stoneville and Dundee, Mississippi to evaluate the effect of spray droplet size and carrier volume on the efficacy of dicamba + insecticide tank mixtures to control Palmer amaranth (Amaranthus palmeri) and Thrips (Thrips sp.) in an early season cotton (Gossypium hirsutum) production system.  Experimental plots were planted to a single cotton variety, Delta Pine 1646 B2XF and applications were made when cotton reached the 4-lf growth stage.

Applications were made at 140 and 280 L ha^-1, and at droplet sizes of 200µm and 800µm.  Chemical treatments included: dicamba, acephate, dimethoate, dicamba + acephate, and dicamba + dimethoate.

All applications containing dicamba were made at 800 µm droplet sizes to comply with label restrictions.  Applications containing dicamba + insecticide were made at both 140 and 280 L ha^-1.  Applications containing only an insecticide were made at 200µm and 800µm droplet sizes and both 140 and 280 L ha^-1.  Each replication (4) contained a season-long Pest Free treatment that was maintained weed and insect free and a Non-Treated Control. 

Palmer amaranth visual control ratings were taken at 7, 14, 21, and 28 days after treatment (DAT).  Thrips visual control ratings and thrips counts were taken at 1, 3, and 7 DAT.  Thrips counts consisted of clipping 5 plants per plot at the soil surface, washing with ethanol, and placing in petri dishes for observation under a microscope.

After 28 DAT ratings all plots were maintained weed and insect free throughout the remainder of the growing season.  Twenty-five boll boll-samples were taken and ginned on a laboratory micro-gin for fiber quality analyses, and seed cotton yield was recorded for each plot.