Development of integrated pest management programs in urban forests: the elm beetle ( Xanthogaleruca luteola (Müller)) in California, USA

Abstract

The elm leaf beetle (ELB) causes severe damage to California's elms. The goal was to develop a management system based on long-term population monitoring for decision making, and environmentally sound control methods. English and Siberian elms with ELB populations in 25 locations from the northeast to the central coast of California were sampled from 1985 to 1990. Population monitoring has indicated that each ELB generation (two to three per season) varies unpredictably in its potential for causing foliage damage. Each generation needs to be sampled and decisions made for control measures most suitable for that generation. From the data base, we have developed a sampling system in which heat accumulation above 11 °C at ELB sites, measured in degree-days, indicates when to sample and, if necessary, when to treat. Sampling elm branch terminals for the presence of ELB eggs during the limited time when egg laying is near its peak provides a cost-effective means of predicting foliage damage, and thus of deciding whether control actions are necessary. Two control options compatible with ELB natural enemies have been tested: trunk banding with Carbaryl and Bacillus thuringiensis foliar sprays. A number of strains of the egg parasitoid Tetrastichus gallerucae have been released and at least one strain has survived over winter. When the number of these parasitoids has increased sufficiently, either through same season releases or from overwintering survival, they have exerted substantial control.