Historical tests of the toxicity of pesticides to Typhlodromus pyri (Acari: Phytoseiidae) and their relevance to current pest management in New Zealand apple orchards 2. Short-term field tests

Abstract

A two-part review is presented relating historical tests of the toxicity of pesticides to Typhlodromus pyri and their relevance to modern pest management in New Zealand pome-fruit orchards. Over the past 30 years, the initial need for T. pyri to be resistant to broad-spectrum pesticides has substantially declined as a growing array of new selective chemicals have come into use. In Part 2, a short-term field test is described for determining the toxicity of single applications of pesticides at recommended rates to European red mite (ERM), Panonychus ulmi, and its predator, an organophosphate (OP)-resistant strain of T. pyri on apples in New Zealand. For each pesticide, changes in mite density were measured from pre-treatment to 2, 7 and up to 25 days post-treatment compared with a water-sprayed control. Density was recorded and analysed for live adult and immature ERM, and live and dead eggs, larvae, nymphs and adults of T. pyri. Fifteen acaricides, 17 fungicides and 17 insecticides were evaluated. Chemicals more toxic to T. pyri than ERM were aminocarb, amitraz, binapacryl, chlordimeform, etrimphos, fenvalerate + azinphos-methyl, mancozeb + dinocap, methidathion, methiocarb, omethoate, oxamyl, pirimiphos-methyl and pyrazophos. Chemicals equally or less toxic to T. pyri than to ERM were acequinocyl, azocyclotin, benzoximate, bromopropylate, chlorpyrifos, clofentezine, cycloprate, cyhexatin, dinocap, mineral oil, propargite, triazophos and vamidothion. The remaining 23 chemicals (primarily fungicides and OP insecticides) had slight or no toxicity to ERM and T.pyri. The short-term field tests provided a useful guide to the long-term effects on ERM and T. pyri populations of almost all the pesticides. However, the potential disruptive effect of pyrazophos was not found in long-term field trials, and conversely, the apparently harmless dithiocarbamate fungicides were later shown to be highly disruptive when repeatedly sprayed, as in commercial practice. Most of the chemicals tested are no longer used in commercial pome-fruit orchards in New Zealand, all of which now practise integrated fruit production or organic fruit production based on selective pest management methods. The tested pesticides of continuing importance are identified and discussed with special emphasis on the current need to retest for dithiocarbamate resistance in T. pyri, some populations of which have been exposed to these compounds for up to 40 years. This and the changes in pesticide use in New Zealand are paralleled by similar developments in most pome-fruit growing areas of the world.