Impacts of applied Sclerotinia sclerotiorum on the dynamics of a Cirsium arvense population

Abstract

SummaryA field experiment was conducted from October 1992 to March 1997 in a sheep‐grazed pasture in Canterbury, New Zealand, to determine the effects of the fungus Sclerotinia sclerotiorum on the long‐term dynamics of a population of Cirsium arvense. The pathogen was applied in mid‐spring either once or in three consecutive years when the C. arvense shoots were vegetative rosettes, using a granular, mycelium‐on‐wheat preparation that lodged on the C. arvense leaves, stems and in the leaf axils. The single application caused disease in the C. arvense that was confined to the application year. The disease resulted in a temporary (17 months) reduction in population size through initial mortalities among treated shoots and resultant reductions in root growth, adventitious root bud, subterranean shoot and, subsequently, aerial shoot population sizes. The soil seedbank was 80% lower in the treated plots than in the control plots in the first year. Seedlings were never found. The annually repeated application of S. sclerotiorum did not result in the expected continuing decline in the C. arvense population relative to the control population.