BLUEBERRY BUD MITE
The blueberry bud mite [Acalitus vaccinii (Keifer)] is a tiny arthropod that lives and feeds inside the fruit buds of blueberries and huckleberries throughout most of eastern North America. The mite's range extends from the maritime provinces of Canada to southern Florida and Texas (Jeppson et al. 1975, Keifer et al. 1982), but severe infestations are most common in the southern part of its range where mild winters probably contribute to rapid population growth (Marucci 1966).
The bud mite is a translucent white arthropod with a soft, spindleshaped body and two pairs of short legs near the anterior end (most other mites have four pairs of legs). At maturity, the adults are only about 0.2 mm in length (1/125 inch), and are not visible without a microscope. The short legs and sac-like body allow these mites only feeble powers of locomotion (Keifer 1941).
- Line drawing of a blueberry bud mite.
- Distinctive red blisters caused by bud mites.
- Fruit injury resulting from bud mite infestation.
Symptoms and Damage
The blueberry bud mite feeds on the bud scales and on the leaf and floral parts within the blueberry bud. Distinctive red blisters develop on injured tissues within two weeks after infestation, and continued feeding may eventually kill the entire bud. Developing fruit is also subject to feeding injury; the affected berries appear roughened or misshapen and also display the characteristic red blisters. Persistent feeding by large mite populations may result in extensive loss of fruiting potential. Irreversible damage can occur by mid August (Keifer 1941, Baker and Neunzig 1970).
Life Cycle and Seasonal Distribution
Mites spend nearly all of their life cycle inside fruit buds. Eggs are laid on the inner surfaces of bud scales where the young nymphs hatch and begin feeding. Under optimal conditions, mites can reach sexual maturity within 15 days (Baker and Neunzig 1970). As the buds open in the spring, mites are exposed to desiccation and gradually leave their overwintering sites. They migrate along the stem to the base of young shoots where they feed until new buds begin to form. Eventually the mites move into these buds and resume reproduction. As the colony increases in size, the mites move farther into the center of the bud. By the beginning of September some mites can usually be found deep within infested buds (Jeppson et al. 1975). Feeding, egg laying, and population growth continue throughout the fall and winter, with peak density in December or January. Population growth seems to be greatest during cool weather, and consequently, bud injury tends to be most severe following a mild winter (Baker and Neunzig 1970).
A fungal parasite, Hirsutella thompsonii, and several species of predatory mites have been found in association with the blueberry bud mite (Baker and Neunzig 1968, 1970). Although some of these organisms may be abundant at times, there is little evidence that they have much effect on bud mite populations.
Scouting, Management, and Control
From February through April the presence of bud mites is relatively easy to detect by looking for the distinctive red blisters on bud scales, flowers, or fruit. From August through March, the infestations can be found by examining the scales of dissected buds under at least 4OX magnification (Keifer 1941).
No blueberry cultivars are completely immune to the bud mite, but infestations are usually more common in varieties that ripen early in the season and begin to set new fruit buds by the end of June. Mite populations suffer extensive mortality in late spring when they are forced to migrate to new fruit buds; survival is correlated with climatic conditions as well as the duration between one year's bud break and the next year's bud set. Probably for this reason cultivars of the rabbiteye blueberry (V. ashei), a late ripening species, are usually less heavily infested than those of the early-season highbush blueberry (V. corymbosum).
Selectively pruning out old canes will help to reduce bud mite populations in established plantings. Non-susceptible varieties often need no additional mite control, but when infestations are severe (or invade susceptible cultivars) two applications of an approved miticide (one month apart immediately following harvest) should give adequate control. It is important that these sprays be applied before mites penetrate too deeply into the buds and destroy the tissues that produce next year's fruit.
- Baker, J. R., and H. H. Neunzig. 1968. Hirsutella thompsonii as a fungus parasite of the blueberry bud mite. J. Econ. Entomol. 61 : 1117-1118.
- Baker, J. R., and H. H. Neunzig. 1970. Biology of the blueberry bud mite. J. Econ. Entomol. 63: 74-79.
- Jeppson, L. T., H. H. Keifer, and E. W. Baker. 1975. Mites injurious to economic plants. Univ. Calif. Press. 614 pp.
- Keifer, H. H. 1941. Eriophyid Studies XI. Bull. Calif. Dept. Agr. 30: 196-216.
- Keifer, H. H., E. W. Baker, T. Kono, M. Delfinado, and W. E. Styer. 1982. An illustrated guide to plant abnormalities caused by Eriophyid mites in North America. USDA Agr. Handbook 573. pp. 134-135.
- Marucci, P. E. 1966. Insects and their control. In: Eck, P., and N. Childers. (eds.) Blueberry Culture. Rutgers Univ. Press, NJ. pp. 159-235.
Last updated: 5 June 1997
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