Evaluation location: Maryland, United States
Trees were planted into a field plot at Glenn Dale, MD, in April 1993, in a randomized block design with 7 blocks and, when available, 4 trees per block per clone in each block. Inoculations were made on May 21, 2002, into a 2.4 mm (0.1 in) hole in the bottom one third of the main trunk of each tree with an aqueous spore suspension containing 3.72 × 10^6 spores/ml of a mixture of two strains of Ophiostoma novo-ulmi and two strains of Ophiostoma ulmi in a 2:1 ratio of O. novo-ulmi to O. ulmi spores. The percentage of the crown showing wilting or death of foliage was estimated on all trees 4 weeks after inoculation. The percentage of the crown showing dieback (lack of foliage) was estimated one and two years after inoculation. For all data collected on foliar symptoms and crown dieback, estimates were made by two observers examining a given tree at the same time, after which a consensus score was recorded.