The effects of mancozeb and metiram upon the predatory mite Typhlodromus pyri Scheuten (Acarina:phytoseiidae) : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Horticultural Science with Honours in the University of Canterbury

Abstract

The toxicity of two orchard fungicides, mancozeb and metiram, to various life stages of the phytoseiid mite predator, Typhlodromus pyri Scheuten, was assessed in a laboratory study. Slide dip tests showed neither fungicide caused significant adult or nymphal mortality. Exposure to mancozeb residues did not cause adult mortality, reduce fecundity, egg hatch or subsequent nymphal development. Application of the fungicides to eggs caused significant reductions in hatching with metiram being more suppressive than mancozeb. Field rate applications (0.125g Product/100ml) of mancozeb and metiram to young (0-24 hour old) eggs reduced hatching by 19% and 36% respectively over controls (92%). At half field rates the suppressive effects were reduced with hatching percentages for mancozeb and metiram being 14% and 12% lower than controls. A negative linear relationship was found between percentage egg hatch and increasing mancozeb application rates. Treatment of older (24-48 hour) eggs also caused significant reductions in hatching. The degree of suppression caused by both fungicides was less than that found for younger eggs. At field rates mancozeb and metiram reduced the hatching of older eggs by 6% and 18% respectively over controls. A known degradation product of mancozeb, thiourea, was shown to have significant ovicidal activity upon the predator eggs.