D3258: Impact of planting date and insecticide application methods on Melanaphis sorghi

Melanaphis sorghi is a serious pest of sorghum production across the southern USA. We investigated the impact of planting date and insecticide application method including in-furrow (IF) vs. foliar insecticide applications on M. sorghi infestation and grain sorghum yield. Field trials with four treatments (untreated, 4 oz Sivanto HL IF, 5 oz Sivanto HL IF, 5 oz Sivanto Prime foliar) and two planting dates (mid-April to early May; late May to early June) were conducted on grain in Tifton, Georgia and Florence, South Carolina in 2020. Number of sugarcane aphids on sorghum leaves and plant condition was rated weekly. Sugarcane aphids first appeared in the early planted plots in early June in Tifton and early July in Florence and exceeded the treatment threshold (50 per leaf) within two weeks. Late planted plots received aphid detections in late June in Tifton and late July in Florence and exceeded the treatment threshold within 1 week. A single foliar application to selected plots immediately brought the infestation below threshold. Aphid counts never exceeded the treatment threshold in either of the IF treatments in both locations. Generally speaking, early planting dates combined with IF insecticide treatment resulted in maximum grain yield. Foliar insecticide applications suppressed aphids but were inconsistent compared to IF applications. Our study suggests that planting early and using an in-furrow (IF) insecticide is the most consistent way to suppressed aphid infestations and improve grain yield in sorghum production in southern USA.