LATE FALL HARVEST, WINTER GRAZING, AND WEED-CONTROL FOR REDUCTION OF ALFALFA WEEVIL (COLEOPTERA, CURCULIONIDAE) POPULATIONS

This study was conducted during 1983-1987 to determine influence of late fall cutting and winter grazing in combination with control of cool-season weeds on egg deposition and seasonal occurrence of peak larval populations of the alfalfa weevil, Hypera postica (Gyllenhal), in Oklahoma. Alfalfa weevil egg numbers were reduced by an average of 55% by late fall cutting and 67% by grazing in winter by cattle compared with the ungrazed treatment. However, peak larval numbers were not lower due to fall cutting and were reduced by an average of just 25% with grazing. Numbers decreased least in years when the majority of eggs were laid in late winter rather than fall or early winter. There seems to be potential to delay occurrence of peak larval numbers up to 10 d by grazing if most eggs are laid in fall or early winter. Larval numbers per stem changed little with changing stem densities and the extent of weed infestation. As a consequence, larval numbers per 0.1 m2 tended to be higher with greater stem densities in treatment combinations that promoted stand longevity.