Submitted to: Journal of Insect Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/4/2007
Publication Date: 5/1/2008
Citation: Metzger, C., Boydston, R.A., Ferguson, H., Williams, M., Zack, R., Walsh, D. 2008. Interactions between population density of the Colorado potato beetle, Leptinotarsa decemlineata, and herbicide rate for suppression of solanaceous weeds. Journal of Insect Science 8:38. Available: http://www.insectscience.org/papers/2008/. Interpretive Summary: Solanaceous weeds, including volunteer potato, hairy nightshade, and cutleaf nightshade are present throughout potato crop rotations in the Pacific Northwest and can reduce the effectiveness of crop rotations designed to reduce disease and pest problems associated with potatoes. Volunteer potato is difficult to control due to its ability to sprout numerous times from the mother tuber. Colorado potato beetle is a common pest of potato and related crops and can quickly defoliate many solanaceous plants. This research evaluated control of volunteer potato and two weedy nightshade species with combinations of Colorado potato beetle and three herbicides. Colorado potato beetle reduced the amount of fluroxypyr and prometryn herbicides required to achieve 90% reduction in volunteer potato or weed biomass. These data suggest that integrated weed management systems targeting volunteer potato, cutleaf nightshade, and hairy nightshade can be more effective when herbicide applications are combined with feeding by Colorado potato beetle. Allowing or promoting natural populations of Colorado potato beetle by altering insecticide programs in rotation crops could improve control of these nightshade species and volunteer potato while reducing effective herbicide dose.
Technical Abstract: The presence of volunteer potatoes Solanum tuberosum L., cutleaf nightshade, S. triflorum N., and hairy nightshade, S. physalifolium Rusby (Solanales: Solanceae), throughout potato crop rotations can diminish the effectiveness of crop rotations designed to control disease and pest problems associated with growing potatoes. In greenhouse bioassays, larvae of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chyrsomelidae) were placed in population densities of 0, 5, 10, and 40 per potato (cv. Russet Burbank) plant and 0, 5, 10, and 15 per cutleaf nightshade and hairy nightshade plant. Plants were treated with a range of herbicides including fluroxypyr, prometryn, and mesotrione rates, and the physiological response on the potato plants was assessed by weighing shoot biomass 14 days after treatment. Consistently, across all bioassays, rate response functions were shifted as L. decemlineata density increased, such that less herbicide was required to achieve control. For instance, the herbicide rate needed to achieve 90% reduction in potato biomass was reduced from 62 to 0 g fluroxypyr per hectare and 711 to 0 g prometryn per hectare as L. decemlineata density was increased to 40 larvae per plant. Herbivory at higher L. decemlineata population densities and herbicides above certain rates resulted in large reductions in cutleaf and hairy nightshade biomass. Differences in rate response functions among L. decemlineata population densities indicated that L. decemlineata contributed to weed suppression in combination with herbicides. These data suggest that integrated weed management systems targeting volunteer potato, cutleaf nightshade, and hairy nightshade can be more effective when herbicide applications are combined with herbivory by naturally occurring Colorado potato beetles.