Use of Medicago sativa (L.) interplantings/trap crops in the management of the green mirid, Creontiades dilutus (Stal) in commercial cotton in Australia
The green mirid, Creontiades dilutus (Stal) is one of the most serious early-season pests of cotton in Australia. The cotton industry currently relies on broad spectrum insecticides for the control of Helicoverpa spp., butthis disrupts biological controlofother major cotton pests. Field experiments to evaluate the use oflucerne, Medicago sativa L., in the management of green mirids on cotton were conducted under mesh house free/no choice and commercial farm conditions at Norwood near Moree, and at Auscott and the Australian Cotton Research Institute atNarrabri in NewSouth Wales from 1992 - 94. In the mesh cage choice tests and under field conditions, lucerne was preferred over cotton by C. dilutus adults for oviposition. However, with no-choice tests, oviposition on lucerne and cotton and also the survival of mirid nymphs on these plants were not significantly different. This indicates that green mirid adults have a distinct preference for lucerne over cotton but in the absence of lucerne the female will not restrain oviposition, and will deposit the same number of eggs on cotton. In an experiment where lucerne was planted as strips within commercial cotton crops, 15 and 35 times fewer mirid adults and nymphs, respectively, were recorded on cotton compared with cotton without lucerne strips. When lucerne was interplanted with commercial cotton under an IPM regime which had no insecticide sprays against Helicoverpa spp., mirid numbers were reduced to levels similar to those achieved by nine conventional insecticide sprays. We conclude that lucerne could be incorporated into an IPM system to control green mirids on cotton.