Factors Affecting Populations of the Citrus Bud Mite in Southern California Lemon Orchards and Acaricide Treatments for Control of This Eriophyid1

Studies of populations of the citrus bud mite, Aceria sheldoni (Ewing). over a period of 2 to 5 years in treated and untreated plots in four southern California lemon orchards are reported. In untreated plots a rapid increase in infestations in lemon buds started in Mayor June and peaked in August or September. In some years high populations were maintained throughout the fall and winter; in other years populations gradually decreased during the winter. In either case, populations fell to an annual low during April and May. These general population trends were correlated with seasonal climatic changes and plant growth cycles. Warm summer weather favorable for plant growth and also for mite dispersal resulted in rapid increase in infestation, whereas winter conditions appeared to reduce movement from one bud to another. Periods of low humidity during the winter or spring appeared to be major factors in the decline of infestation within the buds during this period. An unusually hot period in September 1955 resulted in a sharp decrease of infestation, especially in the orchard farthest from the coast. The summer population increase was about 1 month later under fruit buttons than in the buds. Populations under fruit buttons were higher than bud populations during most of the year. Applications of petroleum oil and of Aramite in both fall and spring were necessary for adequate control. Chlorobenzilate was most effective when applied between the first of June and the last of September, and a single application during this period kept mite populations low for a year.