Biological control of clover rot on red clover by Coniothyrium minitans under natural and controlled climatic conditions

The ability of Coniothyrium minitans, contained in the commercial product Contans(R)WG, to control the development of clover rot in red clover, Trifolium pratense, was for the first time investigated in the field. Studies were performed on an established ley with a grass-clover mixture and on a newly sown pure red clover ley, both at a field site naturally infested with Sclerotinia trifoliorum. In the latter experiment the biocontrol agent was applied either prior to sowing or to growing seedlings. In addition, the ability of sclerotia of two S. trifoliorum isolates to cause disease in detached leaves was studied in a controlled environment. The effect of Contans(R)WG treatments at temperatures between +5 and +15 degrees C and incubation periods of up to 7 weeks were included. Application of the biocontrol agent to the established ley during early summer, significantly reduced the number of groups of apothecia that developed during autumn in the following year in treated plots, compared to untreated plots. Twice as many red clover plants of the cultivar SW Torun survived in the pure red clover stand experiment the year after Contans(R)WG application as in the untreated plots, irrespective of how the agent was applied. In the laboratory studies, administering biocontrol treatments to sclerotia significantly reduced disease scores in the detached leaves at all temperatures at an exposure time of 7 weeks. Shorter incubation periods did not always negatively affect sclerotial viability.