Side effects of mancozeb on Typhlodromus pyri (Acari: Phytoseiidae) in vineyards: results of multi-year field trials and a laboratory study.

The side effects of mancozeb on the predatory mite Typhlodromus pyri were studied in 4-year field trials on grapevine and in the laboratory. In the field, the effect of mancozeb varied according to previous mancozeb use. In vineyards where mancozeb had commonly been used over years, this fungicide is generally slightly toxic, in some cases moderately toxic and rarely toxic. In plots were mancozeb has never been used, its effect on T. pyri was more pronounced and varied from moderately toxic to toxic. Despite the toxicity of mancozeb, T. pyri populations have never been eradicated. Laboratory results obtained with the French CEB guideline no. 167 confirmed those of the 4-year field study: mancozeb was significantly more toxic to T. pyri populations collected in plots where it had rarely been used before the field experiment. In plots where mancozeb had been used for a long time, the susceptibility of T. pyri populations to this fungicide was reduced and female survival, fecundity but also viability of female progeny were less affected by mancozeb. Even though toxicity of mancozeb increased in controlled conditions, a significant correlation was established between field and laboratory results.