HORTICULTURAL ENTOMOLOGY Citrus Bud Mite (Acari: Eriophyidae): an Economic Pest of California Lemons? J. DANIEL HARE, M. RAKHA, 1 AND P. A. PHILLIPS 1 Department of Entomology University of California, Riverside, CA 92521 J. Econ. Entomol. 92(3): 663Ð675 (1999) 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 1Ð2 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 beneÞt to crop volume, grade, or value. For all groves, the value of fruit from treated trees was not signiÞcantly 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. KEY WORDS Arachnida, Aceria sheldoni, economic thresholds, oil spray, phytotoxicity, integrated pest management CITRUS BUD MITE, Aceria sheldoni (Ewing) can be an economically important pest of citrus in different parts of the world (Talhouk 1975). In California, the citrus bud mite is largely conÞned to the coastal growing districts of southern California, where cultivars of lemon, Citrus limon (L.) Burmann, predominate; lem- ons are not grown commercially to any great extent elsewhere in California, and citrus bud mite generally is not a problem on other citrus cultivars. The mite and the damage that it inßicts upon lemons have been described extensively (Boyce and Kors- meier 1942, Sternlicht 1969, Walker et al. 1992a, Phil- lips and Walker 1997). Brießy, the mite inhabits shel- tered locations within lemon trees. Examples of such locations are beneath bud scales, under the calyces of fruit, or in developing buds and blossoms. By feeding upon embryonic tissue, these tissues are damaged, and the twigs, leaves, and fruit that develop from these tissues are distorted. Injury to the embryonic tissues occurs some 10 Ð13 mo before fruit maturing from those tissues are harvested (Walker et al. 1992a). Many distorted fruit preferentially abort and abscise before commercial harvest; those that do not are culled in the packinghouse. Thus, it has long been assumed that the citrus bud mite imposes economic losses by increasing fruit abortion and reducing the value of fruit that survive (reviewed by Walker et al. 1992a). Historically, petroleum-based oil sprays were widely, and frequently, used for control of citrus bud mite, and other pests of citrus. This material kills by suffocation and is therefore effective against a wide range of plant pests (Davidson et al. 1991). Two oil sprays per year, one in the spring and another in the fall, usually were recommended for the management of citrus bud mite; citrus red mite, Panonychus citri McGregor (Acari: Tetranychidae); and various scale insects on southern California coastal citrus until the 1950s (e.g., Boyce and Korsmeier 1942, Riehl and Jeppson 1953, Jeppson et al. 1958). Later, oil sprays were replaced by a number of synthetic insecticides after World War II. For the citrus bud mite, 1 summer application of the chlori- nated hydrocarbon, chlorobenzilate provided season- long suppression of citrus bud mite populations (Jepp- son et al. 1955). Thus, because 1 application of chlorobenzilate provided similar levels of suppression as 2 applications of oil without the risk of phytotox- icity, chlorobenzilate became the preferred material for citrus bud mite control until it was voluntarily withdrawn by the manufacturer in 1989. Unfortu- 1 Current address: University of California Cooperative Extension, 669 County Square Drive, Suite 100, Ventura, CA 93003Ð5401. 0022-0493/99/0663Ð0675$02.00/0  1999 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/92/3/663/2217045 by guest on 14 December 2022