Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2006
Publication Date: 6/20/2006
Citation: Possey, F.R., White, W.H., Gravois, K., Salassi, M.E., Reay-Jones, F.P., Leonard, B.R., Reagan, T.E. 2006. Sugarcane Borer (Lepidoptera: Crambidae) Management Threshold Assessment on Four Sugarcane Cultivars. Journal of Economic Entomology. 99(3):966-971. Interpretive Summary: The sugarcane borer is the most important pest of sugarcane in Louisiana. It is responsible for significant crop losses due to direct damage and also a cost to the grower in chemicals to control damaging infestations. Current recommendations for controlling the sugarcane borer in Louisiana require that pesticides be applied when 5% of the sugarcane stalks are infested with borer larvae. This generalized action threshold is a ‘one size fits all’ recommendation and does not take into account the natural resistance to the borer that some sugarcane varieties posses. In a two-year field study we investigated the feasibility of adjusting the recommended action threshold upwards or downwards depending upon if the sugarcane variety was resistant or susceptible. In this study we applied a pesticide on sugarcane plots based on differing action thresholds and then monitored insect damage and yield losses in these plots. We found that susceptible varieties should be treated as close to the 5% action threshold as possible, but resistance varieties could be safely treated at higher infestation intensities. Extremely resistant varieties could probably be treated at even higher action thresholds. These results are of direct importance to farmers and their agricultural consultants, as they will allow fewer pesticide applications on appropriate varieties thus reducing farmer inputs. Higher thresholds will also be a benefit to the non-farming community as less pesticide will be place into the environment.
Technical Abstract: Judicious application of insecticides is an important component of integrated pest management of the sugarcane borer, Diatraea saccharalis (F.) in Louisiana. Timing of these applications if critical for effective control and applications of insecticides has been traditionally set at a 5% infested stalks threshold. This threshold is an average threshold and does not discriminate between with resistance to this stem borer. In a two-year study involving four commercially produced sugarcane (Saccharum spp. hybrids) cultivars and four insecticide treatment thresholds, cultivars LCP 85-384 and HoCP 91-555 were the most susceptible based on percentage of bored internodes. In 2001, the 10% infested stalks threshold was not as effective as the 5% early season - 10% late season and 5% full season for cultivar HoCP 91-555. Based on D. saccharalis injury under natural infestation conditions, susceptible cultivars often appear to require a lower threshold than the more resistant cultivars to achieve adequate injury reduction. Among yield components, only the theoretical recoverable sugar per stalk was significantly increased by applying insecticides. With the resistant cultivar HoCP 85-845, differences were not detected among treated vs. untreated management regimes. The resistant cultivar HoCP 85-845 had higher levels of fiber in our study, however no clear pattern on resistance mechanisms was established, as the resistant cultivar CP 70-321 had comparatively low levels of fiber. The development of cultivar specific thresholds is expected to lower the amount of insecticide used for D. saccharalis management in the sugarcane industry, reduce selection pressure, and delay the development of insecticide resistance.