Insecticides in field pea benefit grain yield and protein concentration

Abstract Pea leaf weevil ( Sinoa lineatus L.) (PLW) has established robust populations throughout the Northern Great Plains as field pea ( Pisum sativum L.) has become a popular legume species in cropping systems across the region and has established itself as a major economic insect of concern for pea growers. Adult PLW feeds on leaflet margins after plant emergence, reducing yield potential. Following oviposition, PLW larvae utilize rhizobium nodules as their main food source, decreasing N fixation, N availability, and grain protein concentration. Chemical controls are available to control PLW infestations via seed coat or foliar insecticide. Previous research has shown the potential for reducing plant damage and increasing yield with chemical tools; however, little research has been conducted on the benefit that these chemical controls have on improving yield and protein. An experiment was established in Bozeman, MT, for 3 years to evaluate three rates (control, low, and high) of seed‐coat‐applied thiamethoxam and three application timings (control, early, and late) of foliar‐applied lambda‐cyhalothrin on pea grain yield, grain protein concentration, and protein yield. Spraying lambda‐cyhalothrin increased grain yield by 162 (early) and 128 (late) kg ha −1 , resulting in a mean net profit increase of $68.68 ha −1 . Applying seed coat thiamethoxam resulted in elevated grain protein ( p = 0.098) and protein yield levels ( p = 0.072), with a $14 ha −1 net profit increase at the high rate via protein premiums. This study shows the agronomic benefits to pea producers of using seed‐applied and foliar insecticides to mitigate PLW, thereby increasing yield and grain protein concentration.