Executive Summary Purpose

The purpose of this study was to examine the trends and regional patterns of organophosphate (OP) use in California almond orchards from 1992 to 2000, and to identify factors that may have influenced those trends, including weather, pest pressure, and use of alternative practices to control pests. Background Growers use OP pesticides to control arthropod pests in almonds. An OP may be applied to dormant orchards during the winter (called a dormant OP spray). These dormant OPs are usually applied with a narrow-range oil, which is added to improve the effectiveness of the OP and because the oil itself kills some arthropods by suffocating them. Dormant OPs with oils are used primarily to control peach twig borer (PTB), San Jose scale (SJS), European red mite, and brown mite. Dormant sprays have traditionally been considered the most effective way to control all these pests. Applications during the winter are considered less disruptive to non-target organisms, such as natural enemies, than applications during the spring and summer since most organisms are less active during the winter. Thus, in the past a dormant OP spray was routinely applied. However, recen