A comparison of recommended and reduced insecticide regimes in alfalfa

The objective of this study was to evaluate the effects of the recommended rates of insecticides applied at two different population levels of the alfalfa weevil, Hypera variabilis Hbst. (Coleoptera: Curculionidae) and the reduced levels of insecticides on alfalfa weevil, predators and yield in 1998 and 1999. More specific objective was to search for options to reduce insecticide usage while implementing an effective pest control, thereby developing more economically and environmentally sound alfalfa production systems. The treatments used included: i) recommended rate insecticide (malathion) at population level of 5 weevils/sweep, ii) recommended rate at population level of 10 weevils/sweep, iii) 50% of recommended rate at population level of 10 weevils/sweep, iv) stripe spray of 50% rate at population level of 10 weevils/sweep, where insecticides were applied only on 0.5 m stripes in plots while the next 0.5 m stripes were not treated and v) control. The results indicated that the recommended rate insecticide application at 5 weevils/sweep level provided the highest reduction in the weevil densities in both years. No significant differences occurred among the weevil densities in the plots received the recommended rate, the 50% rate and the stripe spray insecticide treatments at 10 weevils/sweep level. Predators were in general more abundant in the insecticide treated plots compared to the control. The insecticide applications, except the stripe spray in 1999, led to increases in yields.