Growth and reproduction of Sclerotinia trifoliorum as influenced by herbicides

Abstract

This study was conducted to determine the effect of herbicides registered for use on seedling alfalfa (Medicago sativa) on mycelial growth, Sclerotium production and subsequent carpogenic germination, and ascospore germination of Sclerotinia trifoliorum. One or more growth or developmental stages of S. trifoliorum were affected by each herbicide tested. Mycelial growth and Sclerotium production were completely inhibited by pronamide at 10 (μg active ingredient (a.i.) mL^-1. Pronamide had no effect on ascospore germination at concentrations up to 100 μg a.i. mL^-1 but reduced ascospore germ tube length at 1 μg a.i. mL^-1. Mycelial growth was reduced by 2,4-DB at 1 μg a.i. mL^-1. Mycelial growth, Sclerotium production, and ascospore germination were completely inhibited by 2,4-DB at 100 μg a.i. mL^-1. Bromoxynil reduced mycelial growth at 10 μg a.i. mL^-1, and reduced Sclerotium weight, ascospore germination, and germ tube length at 100 μg a.i. mL^-1. Mycelial growth and Sclerotium production were completely inhibited by bromoxynil at 1000 μg a.i. mL^-1. Sethoxydim reduced mycelial growth at 10 (xg a.i. mL^-1, and Sclerotium weight at 1000 μg a.i. mL^-1. Imazethapyr reduced mycelial growth at 1000 μg a.i. mL^-1, had no effect on Sclerotium weight and ascospore germination, but enhanced carpogenic germination at 100 μg a.i. mL^-1. The fungicide vinclozolin was more toxic to S. trifoliorum than any of the herbicides tested, in that it completely inhibited mycelial growth and ascospore germination at 1 ug a.i. mL^-1.

Key Words:

• apothecia
• bromoxynil
• 2,4-DB
• carpogenic
• germination
• imazethapyr
• mycelia
• pronamide
• sclerotia
• sethoxydim