Effect of Prohexadione Calcium Application Timing and Rate on Peanut (Arachis hypogaea) Growth and Yield in Mississippi

Excessive vegetative growth in peanut can lead to decreased harvest efficiency. Peanut vegetative growth is often managed with the plant growth regulator prohexadione calcium. Although application of prohexadione calcium is recommended at 50% and 100% canopy closure (CC) as defined by lateral vines touching, research on the optimal application timing and rate has been minimal. The objective of this research was to evaluate the effect of prohexadione calcium application timing and rate based on percent canopy closure. Experiments were conducted at 6 different sites in Mississippi over 2 years. Treatments in 2020 included prohexadione calcium applied at 50% CC + one application at 100% CC (recommended by product label), two applications in one week at 100% CC, and three applications in one week at 100% CC. In 2020, all prohexadione calcium applications were made at 140 g a.i./ha. Treatments in 2021 included application timings at 50% and 100% CC and multiple application rates at each timing including 70 g a.i./ha, 140 g a.i./ha, and 280 g a.i./ha. Peanut response was evaluated based on pod weight after digging, pod count after digging, dry plant weight, pod loss, and peanut yield. Dry plant weight, pod loss, and pod weight were unaffected by prohexadione calcium application. Peanut yield ranged from 6200 kg/ha to 7300 kg/ha across years, locations, and prohexadione calcium treatments. Yields following all prohexadione calcium application timings and rates were similar to those following applications at the recommended timings and rate. With the exception of two applications in one week at 100% CC, yield response following prohexadione application was similar to that of the untreated check. Therefore, prohexadione calcium application timings and rates are likely more flexible than the labelled recommendation with respect to vegetation management; however, yield enhancement following application was inconsistent.