Effect of Abamectin on Fungal Growth and its Efficacy as a Miticide in the Laboratory.

Abamectin was tested for use with solid agar media in the laboratory to eliminate or kill the common mold mite Tyrophagus spp. in fungal cultures of Phaeomoniella chlamydospora (Pch) and Phaeoacremonium minimum (Pmin), two important grape pathogens involved in grapevine trunk disease. Abamectin concentrations tested were at or below the recommended dose for abamectin in greenhouse spray applications (≦625ug/mL) to control mites and determine if: a) fungal growth would be inhibited, and b) mites would be killed or their activity suppressed. Abamectin was added either to the media before autoclaving, or filter-sterilized and added after autoclaving, to test the effects of autoclaving on abamectin efficacy. Streptomycin (100µg/mL) was also added to a set of treatments to determine if this commonly-used antibiotic would impact abamectin efficacy against mites, or have an effect on fungal growth when in combination with abamectin. Filter-sterilized abamectin in the range of 62.5 - 312ug/mL, delivered to the media after it had been autoclaved, provided the most effective control of mites while also showing limited inhibition of fungal growth on solid agar media in the absence of streptomycin. The addition of filter-sterilized streptomycin had no significant effect on fungal growth for Pch, while for Pmin a small but significant reduction in growth with streptomycin occurred at abamectin concentrations above 62.5 ug/ml.