D3456: Influence of nitrogen fertilization, sorghum cultivar, and insecticide applications on infestations of Melanaphis sorghi and grain sorghum yield

Melanaphis sorghi is a serious economically damaging pest of sorghum, Sorghum bicolor (L.), across the southern USA. This experiment investigated the impacts of nitrogen (N) fertilization, sorghum cultivar and insecticide applications on M. sorghi and grain sorghum yield at Tifton, Georgia. Field trials with three insecticide treatments (untreated, 8 oz flupyradifurone as in-furrow application or 5 oz flupyradifurone as foliar application), three N fertilization levels (high, medium or low) and two sorghum cultivars (resistant: DKS37-07 and susceptible: DKS53-53) were conducted on grain sorghum the spring/summer of 2022. The number of sorghum aphids on sorghum leaves and plant condition was rated weekly. Irrespective of insecticide treatments and fertilization levels, aphid populations peaked on July 13^th and declined sharply by late-July before experiencing a second peak (with fewer aphid numbers) in early August. Low and high N fertilization supported higher aphid density and severity of infestation (cumulative insect days [CID]) on both the susceptible and resistant cultivars. Aphid density and severity of infestation on the susceptible sorghum cultivar (DKS53-53) were 3.4- to 4.8-fold greater than on the resistant cultivar (DKS37-07). Nitrogen fertilization was associated with improved yield as the high N fertilization plots preserved yield for both sorghum cultivars. Compared to untreated plots, in-furrow and foliar insecticide applications supported greater grain sorghum yield. The study suggests that manipulating N fertilization, sorghum cultivars and in-furrow (IF) and foliar insecticide application can help suppress aphid infestations and improve grain yield in sorghum production in southern USA.