Insect pest and natural enemy populations in paired organic and conventional apple orchards in the Yakima Valley, Washington

Abstract

Insect pest and natural enemy populations were evaluated during the 1990 growing season in five paired certified organic and conventional apple orchards in the Yakima Valley, Washington. Each orchard pair was managed by one grower and had similar conditions of location, extent, cultivars, and tree density. Organic orchards had not been treated with synthetic insecticides for 1-2 years before this study. Fruit injury from codling moth and population densities of phytophagous mites, sucking bugs, rosy apple and green aphids, leafminers, leafhoppers, and selected natural enemies were monitored throughout the season. Damage from codling moth was over 3% in three of the five organic orchards. Densities of phytophagous mites were high in one conventional orchard at the end of the season. Organic orchards had significantly higher populations of sucking bugs at bloom than did conventional orchards. There was no significant difference between orchard types in the densities of rosy apple aphid colonies per tree, but colonies in conventional orchards had significantly more aphids and significantly less parasitism than in organic orchards. The population density of green aphids was higher in conventional than organic orchards during the second half of the season. There was little difference in numbers of adult leafhoppers caught on sticky traps between orchard types, but captures of a leafhopper egg parasite were significantly higher in organic than in conventional orchards throughout the season. Immature leafminer populations were significantly higher and parasitism of leaf miner was significantly lower in conventional than organic orchards after July. Parasitism of codling moth was not found in any orchard.

Key words: Codling moth; organic; apple; pest management; aphid; mite; leafhopper; leafminer; egg parasite