GROWTH AND REPRODUCTION OF SCLEROTINIA-TRIFOLIORUM AS INFLUENCED BY HERBICIDES

This study was conducted to determine the effect of herbicides registe red for use on seedling alfalfa (Medicago sativa) on mycelial growth, sclerotium production and subsequent carpogenic germination, and ascos pore germination of Sclerotinia trifoliorum. One or more growth or dev elopmental stages of S. trifoliorum were affected by each herbicide te sted. Mycelial growth and sclerotium production were completely inhibi ted by pronamide at 10 mu g active ingredient (a.i.) mL(-1). Pronamide had no effect on ascospore germination at concentrations up to 100 mu g a.i. mL(-1) but reduced ascospore germ tube length at 1 mu g a.i. m L(-1). Mycelial growth was reduced by 2,4-DB at 1 mu g a.i. mL(-1). My celial growth, sclerotium production, and ascospore germination were c ompletely inhibited by 2,4-DB at 100 mu g a.i. mL(-1). Bromoxynil redu ced mycelial growth at 10 mu g a.i. mL(-1), and reduced sclerotium wei ght, ascospore germination, and germ tube length at 100 mu g a.i. mL(- 1). Mycelial growth and sclerotium production were completely inhibite d by bromoxynil at 1000 mu g a.i. mL(-1). Sethoxydim reduced mycelial growth at 10 mu g a.i. mL(-1), and sclerotium weight at 1000 mu g a.i. mL(-1) Imazethapyr reduced mycelial growth at 1000 mu g a.i. mL(-1), had no effect on sclerotium weight and ascospore germination, but enha nced carpogenic germination at 100 mu g a.i. mL(-1). The fungicide vin clozolin was more toxic to S. trifoliorum than any of the herbicides t ested, in that it completely inhibited mycelial growth and ascospore g ermination at 1 mu g a.i. mL(-1).