Evaluation location: Arizona, United States
An experimental elm plantation was established near the Navajo County Fairground in the City of Holbrook, east central Arizona. The city landscape is dominated by Siberian elm trees, which sustain heavy defoliation by elm leaf beetles annually. Elm seedlings 2-4 yr old and between 30 and 45 cm in height were obtained from a variety of commercial and university sources for planting. Newly acquired trees were initially kept under shade near the Northern Arizona University Greenhouse Complex, and they were irrigated as needed until they were planted in the field. The plantation was established from 1995-1998, using a completely randomized design with 10 single-tree replicates per elm accession. Trees were planted on a 21-row by 14-column grid at 3.6- by 3.6-m spacing. In spring 1995, each accession, replicated 10 times, were randomly planted. The soil around each plant was mulched using a 1-sq m piece of black shade cloth covered with pine wood chips. Plants were watered regularly with a drip irrigation system that supplied water to the base of individual plants. Defoliation was estimated every third week of July, from 1996 to 2001. A 15-cm-long shoot was randomly selected from the north, south, east, and west quadrants of each plant and evaluated for percentage of defoliation. Defoliation was independently visually estimated to the nearest 5% by two trained technicians and their estimates were averaged.