Enhancement of Efficacy of Ascochyta caulina to Control Chenopodium album by Use of Phytotoxins and Reduced Rates of Herbicides

The use of toxins produced by Ascochyta caulina to enhance the efficacy of this mycoherbicide agent for the biological control of the noxious weed Chenopodium album was investigated. A method of purification of the fungal culture filtrate was developed to produce large amounts of a mixture containing three main toxins: ascaulitoxin, its aglycone, and trans-4-aminoproline. Greenhouse experiments showed that the use of toxin solutions (at 1 mg/ml) in conjunction with spores of A. caulina (at 106/ml) strongly improved the biocontrol efficacy of this fungus by more than 30%. Furthermore, the simultaneous application of toxins or fungal spores, together with low doses of herbicides (metribuzin and rimsulfuron at 1/5 of the labeled rate), gave better results than single-agent treatments.