Potential Biological Control Strategies for Management of Aphids in Organic Pecan Orchards

The blackmargined aphid (Monellia caryella (Fitch)), yellow pecan aphid (Monelliopsis pecanis (Bissell)), and black pecan aphid (Melanocallis caryaefoliae (Davis)) are considered crucial pests of pecan. Pecan aphids have a short life cycle and high reproductive potential, thus aphid populations are able to increase rapidly in favorable conditions in pecan. Biological control of the aphid complex in organic pecan orchard relies on the ladybeetle, Harmonia axyridis. Planting intercrops in between the pecan tree rows enhances ladybeetle populations by providing ladybeetles with habitats and alternate prey aphids. Different intercrops–cool-season and warm-season intercrops were evaluated for the pecan aphid management. The abundance of the ladybeetles in the intercrops was recorded, and also the abundance of the pecan aphids were monitored in the trees in intercropped plots to determine the effects of the understory intercrops on pecan aphid biological control. The results showed that the cool-season intercrops of clover, vetch, joint vetch and clover/vetch, all had lower pecan aphid abundance than the mowed sod (control treatment). Among the warm-season intercrops, hairy indigo and hairy indigo/alyce clover/buckwheat, the combination of hairy indigo, alyce clover and buckwheat had lower abundance of pecan aphids than mowed sod.