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Effect of citrus bud mite (Acari: Eriophyidae) on lemon yields

Walker, G.P., Voulgaropoulos, A.L., Phillips, P.A.
Journal of economic entomology 1992 v.85 no.4 pp. 1318-1329
Citrus limon, Eriophyes sheldoni, crop quality, crop yield, integrated pest management, economic threshold, California
The effect of high population densities of citrus bud mite, Aceria sheldoni (Ewing), on the quantity and quality of lemon yields was studied for 4 yr in four commercial groves in coastal southern California. There were two treatments in each grove: treated plots where bud mite was suppressed with acaricide treatments whenever infestation levels increased markedly, and untreated plots where bud mite was not controlled. Average percentage of axillary buds infested with citrus bud mite was 7-15% in treated plots and 45-70% in untreated plots over the 4-yr period. Citrus bud mite feeding results in distortion of fruit shape which can result in commercial downgrading. Citrus bud mite control significantly reduced fruit distortion in all four groves and significantly improved commercial packout in three of the four groves. However, significantly less distortion in fruit was not detected in treated trees until harvests greater than or equal to 10-13 mo after the initial acaricide treatment (lemons in coastal California are harvested three or four times per year). This supports the hypothesis that distortion in fruit is caused by citrus bud mite feeding on embryonic fruit tissue in the buds; once fruit set, they are unaffected by further citrus bud mite feeding. Up to 21 mo after the first acaricide treatments, the cumulative yield did not differ significantly between treated and untreated plots. In two of the four groves, in the eight harvests between 24 and 48 mo after the first acaricide treatments, the cumulative yield was often significantly greater (9-13% greater) from treated than from untreated trees. The other two groves showed no significant differences in cumulative yield between treated and untreated trees up to the time of the last harvest (28 and 49 mo after the first acaricide treatment). In two groves, economic loss justified the cost of bud mite suppression, and in two groves, the cost of suppression exceeded the economic benefit of suppression.