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

In 2018, 2019, and 2020, a field experiment was conducted to evaluate the effect of carrier volume and spray droplet size on the efficacy of dicamba + insecticide tank mixtures to control both Palmer amaranth (Amaranthus palmeri) and thrips (Thrips sp.) in cotton (Gossypium hirsutum). This experiment consisted of two field locations: the Delta Research and Extension Center in Stoneville, Mississippi, and Hood Farms in Dundee, Mississippi.  Four-row plots were planted with a single cotton variety: DP 1646 B2XF, and plot dimensions were 3.9m x 14.2m (Stoneville, MS) and 3.8m x 9.1m (Dundee, MS).  Applications were initiated when cotton reached the 4-leaf growth stage.

Applications were made with a Capstan Pinpoint Pulse-Width Modulation (PWM) sprayer on a high-clearance Bowman Mudmaster at a ground speed of 14.5 km hour^-1.  A single formulation of dicamba: (XtendiMAX®) applied at 1.5 kg ha^-1, and two insecticides: acephate (Acephate 97UP) applied at 0.2 kg ha^-1, and dimethoate (Dimethoate 4EC) applied at 0.4 kg ha^-1 were chosen. This experiment utilized two carrier volumes: 140 and 280 L ha^-1 and two droplet sizes: 200µm and 800µm.

Visual thrips damage ratings (1-5) and thrips counts (adults and nymphs) were taken at 1, 3, and 7 days after treatment (DAT).  Visual Palmer amaranth control (0-100) was evaluated at 7, 14, 21, and 28 DAT, and visual cotton injury (0-100) was rated at 7, 14, and 21 DAT.  Seedcotton yield was collected using a spindle picker modified for plot research.