Advantages and disadvantages of using pyrethroids in Nova Scotia apple orchards.

A commercial pest management company recorded data on use of insecticides and miticides, insect and mite densities, and insect and mite injury to fruit and foliage in 132-175 orchard blocks from 1980 to 1983. The pyrethroids permethrin and fen valerate were used mostly before bloom for control of the winter moth (WM), Operophtera brumata (L.). Fenvalerate was used, mostly after bloom, to control the spotted tentiform leafminer (TLM), Phyllonorycter blancardella (F.). In 1980, blocks in which a pyrethroid was used had lower levels of WM injury to fruit and fewer fruit stings caused by mirids (mostly Atractotomus mali (Meyer) and Camylomma verbasci (Meyer)), than did the blocks with no pyrethroid treatment (nonpyrethroid blocks). Prebloom applications of pyrethroids led to lower numbers of first- and second-generation TLM mines per leaf, whereas applications after bloom led to reduced counts of second-generation mines. In 1980 and 1983, the percentage of fruit injured by insects was lower in pyrethroid-treated blocks than in non pyrethroid blocks. In 1981, densities of insects were less frequently above their economic thresholds and fewer insecticide applications were needed in orchard blocks that had a single prebloom fen valerate treatment or prebloom plus postbloom pyrethroid treatments than in blocks with no pyrethroids the previous year. However, disadvantages were associated with pyrethroid use. Higher counts of first- or second-generation TLM mines sometimes were associated with fenvalerate or multiple pyrethroid use the previous year. Single applications of fenvalerate, multiple pyrethroid applications in one year, or applications in two successive years were associated with higher counts of the European red mite, Panonychus ulmi (Koch), and the apple rust mite, Aculus schlechtendali (Nalepa), higher levels of leaf bronzing by mites, and more frequent use of miticides. Fenvalerate was implicated more frequently than permethrin. The greater influence of fenvalerate was attributed to its greater toxicity to the predatory mite, Typhlodromus pyri Scheuten, and to its longer residual activity.