Eighty-one Trifolium ambiguum accessions, representing the germ plasm collection for that br omide t soil wa and wit species, and selected accessions of T. alpestre, T. hybridum, T. medium, T. pratense, and T. repens methyl bromide at 76.4 kg/ha and kept were evaluated in the field from 1981 through 1983 for overall vigor, persistence, yield, and covered with plastic for 48 hr. Threedays susceptibility to virus infections. Infections by bean yellow mosaic virus, clover yellow vein virus, before planting, disulfoton, fensulfothion, white clover mosaic virus, and red clover vein mosaic virus were common in many accessions. and benomyl were incorporated into the Accessions of T. ambiguum and T. medium were the least affected by virus infections and persisted soil at 1.1, 8.4, and 48.9 kg/ha, better than other species. Symptoms of virus infection appeared early and spread rapidly in respectively. Foliar sprays of triadimefon, accessions of T. hybridum, T. pratense, and T. repens and were associated with loss of vigor and applied monthly, and methoxychlor, death of most of the plants by 1983. T. alpestre accessions were only moderately affected by viruses malathion, and benomyl applied biweekly, but showed neither the rapid growth of T. hybridum, T. pratense, or T repens nor the persistence of were used throughout each growing T. ambiguum or T. medium. Several accessions of T. ambiguum compared favorably with season at 0.14, 3.4, and 0.51 kg/ha, developed cultivars of T. pratense after 2 yr of field exposure.respectively. Disulfoton was broadcast

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To our knowledge, reports of Betula spp. resistance against damage caused by the birch leafminer, Fenusa pusilla (Lepeletier), have not been published. Becker (1938), Friend (1933), and Johnson and Lyon (1976) We examined leaves under a microscope at 15 X to ensure that no leafminer eggs were present. All leaves, except 2 or 3 young leaves (5 to 15 mm maximum width) per branch tip were removed and the branch tips were placed in 125 ml Erlenmeyer flasks containing water. Cotton was placed in the neck of each flask to hold branch tips upright and prevent adult leafminers from contacting the surface of the water. Leafminer adults up to 18 h old, reared from late instar larvae were confined to leaves using 10.2 cm diameter x 20.3 cm long sections of cellulose dialysis tubing as cages. The tubing was sealed to the neck of the flasks with tape and, after adults were introduced, sealed at the top by twisting. Tests were conducted throughout the summer as young leaves and leafminer adults became available. Each test consisted of 3 replications for a tree species with 6 to 9 young leaves (3 branch tips) per replicate. Test conditions were 16 h of light at 15" to 20°C, B. populifolia leaves were used as a susceptible standard in all tests. Normally two females were used per leaf with an equal number of males. In several tests, five or 20 females were used on B. davurica. B. populifolia and B. davurica were tested 5 times throughout the summer; B. pendula forma Dalecarlica, B. nigra, and B. alba were tested once. After adults had died (3 or 4 days after introduction) leaves were examined at 15 X with transmitted light.At Geneva, 0,0.35, 0.75, 0.25, and 0.50% of the leaves of B. davurica were darnaged by birch leafminer compared with 3 1,48,20,30, and 27% of the leaves of B. pendula during the respective five seasons. At Dansville, averages of 64% of the leaves of B. populifolia, 52% of B. pendula forma Dalecarlica, and 60% of B. nigra were damaged. Damage to B. davurica was consistently less than damage to B. pendula. Results from Dansville indicate equal susceptibility among the three species observed. In our laboratory tests, regardless of numbers of adult females used, no eggs were deposited in B. davurica and no evidence of attempted oviposition was observed. The average number of eggs deposited by two females per leaf for all other species of Betula tested ranged from