The purpose of this study was to assess the susceptibility of the bollworm, Helicoverpa zea (Boddie), to the pyrethroid cypermethrin in the primary crop production areas of Texas. Pyrethroid insecticides are widely used in cotton and in other production systems, such as grain sorghum and corn. The statewide monitoring program that evaluated resistance in male H. zea was conducted from April to September 2005, surveying nine Texas counties with a total of 5,041 moths from all areas used for analysis. Data from all areas were sent to Texas A&M University Toxicology Laboratory for analysis. Considerable variability in response to cypermethrin was detected in H. zea across the state. Based on LC50 data, the most resistant populations were from Nueces, Uvalde, and Williamson counties while the most susceptible populations were from Ellis, Fisher and Mitchell, Hockley, and Swisher counties. Accepted for publication 2 October 2006. Published 19 July 2007.
Forage sorghum (Sorghum bicolor L.) grown for silage production is frequently infested by the sugarcane aphid (SCA; Melanaphis sacchari [Zehntner] [Hemiptera: Aphididae]). The objective of this study was to establish first-time action thresholds for SCA infestation, leaf feeding, honeydew, and/or dead leaves. In this 2-yr Texas High Plains study, we quantified the impact of varying densities of SCA and subsequent damage beginning at boot stage to yields and silage nutritive value of a susceptible forage sorghum hybrid (Pioneer 841F) by using untreated controls and different insecticide treatments (lambda cyhalothrin, chlorpyrifos, malathion, and flupyradifurone). Aphid damage occurred from boot to flowering growth stages. Damaging infestations continued until harvest in 2017, but SCA densities declined sharply after peaking at the beginning milk growth stage (BMS) in 2019. Damage levels were significantly correlated to increases in aphid densities at BMS (R 2 = .91) in 2017 and at 50% bloom (R 2 = .83) and BMS (R 2 = .86) in 2019. Yield losses increased with increasing damage at the BMS in 2017 (R 2 = .82) and 2019 (R 2 = .42). Reductions in nutritive value were correlated to yield reductions. Results indicate that SCA infestations should be controlled when ≥20% of the leaf area is infested and damaged at BMS to prevent yield and nutritive value losses in the fresh and ensiled forage.Based on this work, an action threshold for forage sorghums to minimize losses to yield, nutritive value, and economic returns is presented.
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