Evaluation location: Maryland, United States
The experiment was conducted at the U.S. Department of Agriculture, Agricultural Research Service station near Glenn Dale, Md., using a research field plot that is part of the U.S. National Arboretum Tree Breeding Program. The field plot consisted of two blocks of trees arranged within rows by elm selection in a completely randomized block design. Blocks were separated by a 9.2 m wide east-west corridor. Each block contained 11 rows 3.7 m apart with 17 or 18 trees separated by 3.1 m within rows. The plot was surrounded by mixed vegetation including such trees as maples and alders, and mowed every other week or as needed. Trees were irrigated only during very hot and dry periods. No fertilizers or pesticides were applied during the course of the study. Two replicate trees were used for each accession (clones for cultivars and half-sib seedlings for wild collected accessions). Yellow sticky traps (97 sq. cm) were hung on the west side of trees on a branch in the lower periphery of each tree at about 4 m above the ground on 1 May 2001. Traps were changed weekly until 28 Aug. 2001. Final traps were taken down on 4 Sept. 2001. Collected traps were examined in the laboratory with a stereomicroscope. Leafhoppers were carefully removed using a dissecting probe, transferred into transparent cups, and counted.