Investigating the rain‐free period of mepiquat chloride as affected by surfactant, rate, and interval between application and simulated rainfall

Abstract

AbstractSporadic and unpredictable rain events can reduce agrichemical efficacy if a sufficient rain‐free period is not reached following application. Mepiquat chloride (MC) is used to regulate vegetative growth in cotton (Gossypium spp.), and the rain‐free period, according to the label, is 8 h or reduced to 4 h when applied with a surfactant. Experiments were conducted in 2021–2022 to evaluate the effect of MC treatment and dry time between application and a simulated rainfall event on cotton growth following application. The MC treatments were applied during the second week of squaring and were washed from the surface of the leaves 0, 2, 4, and 8 h after application using a center pivot irrigation system that delivered 0.4–0.6 inches of simulated rainfall. All MC treatments, averaged across dry time, slowed cotton growth regardless of surfactant or rate applied. Dry time demonstrated similar results, with dry times ≥2 h slowing growth. However, when cotton growth over time was evaluated, it was determined that in situations where cotton growth is more aggressive, reapplication of MC was necessary sooner where the initial application was removed from the surface of the leaf 0–2 h after application compared to 4–8 h after application. Adding a surfactant to MC applications did not reduce the rain‐free period, and when at least 4 h of dry time was achieved, MC applications were just as effective as an 8 h dry time, even when cotton growth was aggressive.