Citrus bud mite (Acari: Eriophyidae): An economic pest of California lemons?

Abstract

The citrus bud mite, Aceria sheldoni (Ewing), has a reputation as being a serious pest of lemons in California, although recent studies failed to reveal a consistent economic impact. To resolve some previous inconsistencies, we evaluated the economic value of treatments to suppress citrus bud mite populations on a commercial scale over 3 yr. Experiments were conducted in 6 groves and included 2 treatments of 100 trees each. In 1 treatment (treated), trees were managed according to conventional commercial practices and included 1-2 annual applications of narrow-range oil to suppress citrus bud mite populations. In the other treatment (untreated), experimental trees were managed identically as treated trees, except that oil spray applications for citrus but mite were withheld. Bud mite density and incidence on experimental trees were monitored monthly, as were the number of fruit and the proportion of distorted fruit. Fruit from all 100 trees in each treatment per grove were commercially harvested, graded and packed. Crop volume, grade, size distribution, and value were compared across treatments. Although oil sprays effectively suppressed citrus bud mite populations, this yielded no consistent benefit to crop volume, grade, or value. For all groves, the value of fruit from treated trees was not significantly greater than that from untreated trees, even before the cost of oil sprays was subtracted. In 4 of 6 cases, crop value was numerically lower in the treated treatment. Results suggest that the oil sprays themselves may have had deleterious effects on fruit initiation and abortion. The potential phytotoxicity of oil sprays, although long known, may not be fully considered in contemporary treatment decisions for the citrus bud mite.