WINTER CROWN ROT OR SNOW MOLD OF ALFALFA, CLOVERS, AND GRASSES IN ALBERTA: II. FIELD STUDIES ON HOST AND VARIETAL RESISTANCE AND OTHER FACTORS RELATED TO CONTROL

Abstract

Many overwintering cultivated and native plants proved susceptible to the low-temperature basidiomycete which causes winter crown rot or snow mold of forage legumes and grasses in Alberta. Tests were made by inoculation in the late fall, or by planting in infested land. In the legumes, high resistance was found only in Medicago falcata and a Siberian strain of Trifolium pratense. T. hybridum, Melilotus spp., and the commonly grown varieties of alfalfa were particularly susceptible. Bromus spp. and Agropyron spp. proved highly resistant. Resistance was moderate in Elymus spp., Poa pratensis, and Festuca elatior; and slight in F. rubra and Phleum pratense. Agrostis alba, winter wheat, and winter rye were highly susceptible. In tests on horticultural plants, rhubarb and chives appeared to be immune; raspberry, peony, and columbine were resistant; and strawberry, parsnip, iris, and tulip were highly susceptible. A wide range of native plants and weeds suffered severe damage, and only Thalictrum spp. proved highly resistant. Shrubs and trees were not attacked.Following severe damage, crop rotation proved to be essential for the control of winter crown rot. The pathogen did not persist in the soil to any extent for longer than two to three years in land which was summer-fallowed or planted to annual crops or resistant grasses. Brome and other resistant grasses proved helpful in maintaining forage stands. Fertilizer treatments did not reduce the damage. Uncut tops and debris favored spread of the disease in alfalfa stands.