Capturing the economic value of biological control in western tree fruit

Abstract

The economic value of biological control in apple in central Washington and pear in northern Oregon was estimated by comparing pest management programs following practices thought to reduce negative impacts on natural enemies to programs following traditional practices. Pest management costs in three apple orchards that had transitioned to the use of codling moth mating disruption (CMMD) plus reduced-risk or organophosphate-alternative pesticides were compared with four orchards that had not adopted these practices. Pest management costs in five pear orchards using CMMD were compared to four orchards not using CMMD. In both cropping systems the impact of pest management programs on biological control was determined by the need to use pesticides to control secondary pests, aphids and spider mites in apple and spider mites and pear psylla in pear. The disruptive nature of pesticides was categorized into four levels from none (0) to high (4) based on data presented by Mills et al. (2016) and Beers et al. (2016), as well as other published information. Some reduced-risk and OP-alternative pesticides proved detrimental to natural enemies and disruptive of biological control in apple and pear. In apple, the use of pesticides with low risk to natural enemies reduced the need to apply controls for secondary pests. In pear, the use of CMMD reduced the need to control secondary pests, spider mites and pear psylla, in summer. The use of pesticides with a high risk to natural enemies increased the cost of secondary pest control by about 50% in apple and pear. A stepwise increase in natural enemy risk values increased total pest management costs by $46/ha in natural enemy unfavorable apple orchards and by $44/ha in pear orchards not using codling moth mating disruption.