REDUCED INSECTICIDE RATES AND STRIP-HARVESTING - EFFECT ON ARTHROPOD PREDATOR ABUNDANCE IN FIRST-GROWTH ALFALFA

In 1994, arthropod predator densities were significantly reduced in ha rvested (swathed and crimped) alfalfa strips (3 m x 9 m) and strips tr eated with Pounce 3.2 EC(R) (permethrin) at 0.112 and 0.224 kg (AI)/ha . In 1995, no significant differences in predator densities were obser ved among management treatments when rainfall occurred on the day of i nsecticide application and harvested alfalfa was not crimped. Compared with control strips, Lorsban 4E(R) (chlorpyrofos) applied at 0.140, 0 .280, 0.560, and 1.120 kg (AI)/ha did not result in consistent, signif icant reductions in arthropod predator abundance. Reductions in prey ( Acyrthosiphon pisum and Hypera postica larvae) densities after treatme nt may have contributed to decreased persistence of immigrating predat ors to areas of low prey density and subsequent lower abundance of pre dators in treated alfalfa strips. Rates of Lorsban 4E that reduce N. p ostica larval densities do not consistently reduce arthropod predator abundance when applied in strips. These results indicate that strip ap plications for H. postica may be the basis for an integrated control p rogram in Iowa.