Thumbnail Image

Evaluation of Organic Insecticides To Control Harlequin Bug, Murgantia Histrionica (Hahn), and Yellowmargined Leaf Beetle, Microtheca Ochroloma Stl, On Leafy Greens

Overall, Lisa Marie
This study was undertaken to evaluate laboratory and field efficacy of organic registered insecticides to control the harlequin bug, Murgantia histrionica (Hahn) (Heteroptera: Pentatomidae) and yellowmargined leaf beetle, Microtheca ochroloma St�l (Coleoptera: Chrysomelidae) on leafy greens in southern Oklahoma. Both insects are common pests of Brassica crops (collards, turnips, mustards, Broccoli) in the eastern United States and both are effectively controlled using conventional synthetic insecticides such as pyrethroids and carbamates. However, in the absence of conventional insecticides, both the harlequin bug (HB) and the yellowmargined leaf beetle (YMLB) have potential of occurring in large numbers and reducing the marketable portions of the crops. Currently, organic producers of leafy greens lack reliable means to control sporadic outbreaks of these pests. Laboratory toxicity studies using leaf dip bioassays were implemented to estimate a concentration-response relationship. To compare the results with field application rates, a field trial followed. Insecticides evaluated were spinosad, azadirachtin, and pyrethrum. The LC50,90 values estimated for the HB treated with spinosad were 398 ppm active ingredient (AI) (95% CI: 223-791) and 4,763 ppm AI (95% CI: 1,948-25,204), respectively. For Pyrethrum, the LC50,90 values were 2,964 ppm AI (95% CI: 2,484-3,517) and 8,615 ppm AI (95% CI: 6,609-13,179), respectively. Likewise, spinosad and pyrethrum were effective in inducing mortality of the YMLB. The estimated LC50,90 for spinosad inducing mortality were 1.80 ppm AI (95% CI: 0.22-3.30) and 11 ppm AI (95% CI: 7 - 64), respectively. For pyrethrum, the LC50,90 values were 224 ppm AI (95% CI: 162 - 290) and 801 ppm AI (95% CI: 610 - 1,145), respectively. In 2007, results indicated that spinosad and pyrethrum significantly reduced YMLB adult numbers 96% and 63%, respectively, compared to the untreated plots one day post treatment. In 2006 and 2007, spinosad and pyrethrum significantly reduced HB adults 61% and 73%, respectively, compared to the untreated plot one day post treatment. These results are being used to develop IPM strategies for producing organically grown leafy greens.