Reduced insecticide rates and strip-harvesting: Effect on arthropod predator abundance in first-growth alfalfa

In 1994, arthropod predator densities were significantly reduced in harvested (swathed and crimped) alfalfa strips (3 m × 9 m) and strips treated with Pounce 3.2 EC® (permethrin) at 0.112 and 0.224 kg (AI)/ha. In 1995, no significant differences in predator densities were observed among management treatments when rainfall occurred on the day of insecticide application and harvested alfalfa was not crimped. Compared with control strips. Lorsban 4E® (chlorpyrofos) applied at 0.140, 0.280, 0.560, and 1.120 kg (AI)/ha did not result in consistent, significant reductions in arthropod predator abundance. Reductions in prey (Acyrthosiphon pisum and Hypera postica larvae) densities after treatment may have contributed to decreased persistence of immigrating predators to areas of low prey density and subsequent lower abundance of predators in treated alfalfa strips. Rates of Lorsban 4E that reduce H. postica larval densities do not consistently reduce arthropod predator abundance when applied in strips. These results indicate that strip applications for H. postica may be the basis for an integrated control program in Iowa.