The suitability of abamectin 3.4 EC for mite management programs in European apple orchards

Phytophagous mites are the major foliar feeding pests in apple orchards in Europe. The most serious is the European Red Spider Mite Panonychus ulmi Koch. The Apple Rust Mite Aculus schlectendali Nalepa is also economically important in parts of Europe, causing fruit russeting on various apple varieties. Feeding by mites removes chlorophyll from leaf mesophyll cells resulting in decreased photosynthetic activity, observable as leaf bronzing at high infestations, which may lead to leaf fall and reduction in crop yields the following year. High pest mite infestations often result from the application of a wide range of non-specific fungicides and insecticides which cause mortality to resident populations of pest mite predators, specifically phytoseiid mites. Phytoseiids may provide stable control of low populations of pests mites when the pest-predator ratio is maintained below certain thresholds. Populations of P. ulmi are known to be resistant at least to organophosphates and carbamates, which has limited options for chemical control. An ideal acaricide for pest mite management is therefore one which has a unique chemistry, preventing cross-resistance, and for which a single early-season application provides almost complete long-term residual control without irradicating resident predatory mite populations. A low phytophagous mite infestation over the season would result in leaf damage below economically significant levels while avoiding multiple applications would reduce the possibility of resistance developing. Where phytoseiids are present, the maintenance of a balanced pest-predator ratio should enable them to maintain population equilibrium during the entire season. Field trials were implemented over Europe from 1993-95 to assess the efficacy of the 3.4 EC formulation of abamectin (EPIMEK 33.75 g a.i. per litre) against mites in apple orchards when applied with paraffinic oil early post-bloom at a rate of 13.5 g-27 g ai per ha. In areas where phytoseiids are historically absent or not observed abamectin provided control of P. ulmi for 6 to 10 weeks. Where phytoseiids were present, acceptable long-term control of P. ulmi and A. schlectendali was maintained while having minimal adverse impact on phytoseiid mite populations, enhancing pest-predator ratios in the predator's favour. Abamectin is a suitable acaricide for integrated mite management programs