Systemic Insecticides as Lygus Bug Controls Compatible with Bee Pollination on Alfalfa1

Abstract

Two low-bee-hazard methods of control, the use of granular insecticides and application of insecticides through a sprinkler irrigation system, were tested against Lygus Hesperus Knight and L. elisus Van Duzee in alfalfa grown for seed. Only dimethoate provided control of lygus bugs when applied through irrigation sprinklers. However, such applications at higher than normal dosage rates to blooming alfalfa apparently caused a low mortality to alfalfa leafcutting bees, Megachile rolundala (F.), by nectar contamination. Dimethoate applied after hay cutting and before development of seed crop blooms was non-hazardous to bees. Temik® (2-methyl-2- (methylthio)-propionaldehyde O-(methylcarbamoyl)oxime), Baygon® ( 0 -isopropoxyphenyl methylcarbamate), and NIA-I0242 (Furadan® (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) granules provided nearly 7 weeks control of lygus bugs at 2 to 3 lb per acre in both aerial broadcast and ground side-dressed applications. Temik at 5 lb per acre gave from nearly 7 weeks to more than 3 months control of lygus bugs and also controlled pea aphids Acyrtho siphon pisum (Harris). Granular systemic insecticides were not effective until irrigation was applied, but either sprinkler or rill irrigation sufficed. Beneficial predators either were not seriously reduced or were able to recover in time to keep aphids below economic levels. Trichlorfon performance was improved by timing the second application about 10 days after the first, killing the early lygus instars winch had hatched out in the meantime, Abate®( O,O -dimethyl phosphorothioate O,O diester with 4,4'-thiodip.henol) provided 3 weeks control of lygus bugs, but was highly toxic to the alfalfa leafcutting bee and moderately toxic to the alkali bee, Nomia melanderi Cockerell.