As their name indicates, these mites attack preferably leaf and flower buds. The death of the growing points on twigs and inflorescences causes distortion of leaves, blossoms and young shoots. Rosette-like leaf formation appear on branches. The growth of trees is stunted, leading among others to a reduced fruit set. Infested fruits are severely deformed and show light yellow to silver discolorations and wound spots that may provide entry for fungal infection. They may fall off at early stages of development. Fruits that reach maturity may have a lower market value because they produce less juice and of inferior quality. These mites attack all citrus species, but damage is usually worst in lemons.
The symptoms are caused by the citrus bud mites Aceria sheldoni. They are not visible to the naked eye but they can cause significant damage to citrus orchards and reduce yield all the same. With a magnifying glass, tiny, worm-shaped, typically creamy white or translucent mites can be seen on buds. During the winter months, they seek protection under the bracts of buds. In spring, when conditions are favorable, females emerge and lay their eggs in the bud scales of new growth. The nymphs attack the growing points of the twigs and the inflorescences, causing malformation of young leaves, flower buds and shoots. As a consequence, the growth of the trees is retarded. Fruit set may be retarded too, and fruits may be severely malformed. Population can increase rapidly under warm, dry weather and in those conditions even light infestations may cause serious damage.
But mites are generally not well controlled by natural enemies. Predatory mites could be used to keep the bud mites under fairly good control. Biopesticides may be the best way to manage an infestation. Solutions containing sulfur at a concentration of 2% applied at low infestation levels can help to control bud mites. This treatment should not be applied at a temperature above 30° C and a 4 week interval between treatments should be respected.
Always consider an integrated approach with preventive measures together with biological treatments if available. The damage of the mites on buds can be offset by spraying phytotoxic narrow range oils on foliage. Products based on abmectin, fenbutatin oxide, chlorpyrifos, spirotetramat, fenpyroximate or combinations thereof can be used together with oils for an enhanced effect.