Implementation of a Citywide Monitoring Program to Base Treatment Decisions on Elm Leaf Beetle Abundance

Between 1995 and 1999, a monitoring program was implemented in the City of Sacramento, California, U.S., where treatment decisions for elm leaf beetle (Xantho-galeruca luteola) were made based on presence or absence of egg clusters at each generation egg peak. The damage prediction model proposed by Dahlsten et al. (1994) was effective at predicting damage in Sacramento in both the first and second generations. Addition of the Sacramento data collected between 1995 and 1999 to the model does not change the treatment threshold for the first generation but does raise the treatment threshold in the second generation to approximately equal that for the first. A similar model for the third generation suggests a much higher treatment threshold; however, more data are needed for this generation. Subsampling 20% of the susceptible trees and resampling additional trees in areas where egg clusters were found is effective in locating areas of beetle activity. Between 1995 and 1999, an average of 11.3% of trees managed using the monitoring system required treatment. This finding represents a dramatic reduction in pesticide use and cost when compared to the previous strategy of treating all susceptible elms on a calendar basis.