By Oscar Liburd and Zulaikha Mazlan
Several mite species have been reported to be important pests of blueberry in Florida. These include the blueberry bud mite Acalitus vaccinii Keifer, southern red mite Oligonychus ilicis (McGregor) and twospotted spider mite Tetranychus urticae Koch. In addition to these species, false spider mites or flat mites Brevipalpus yothersi Baker, was recently described infesting southern highbush blueberry in this state.
The blueberry bud mite belongs to the family Eriophyidae. It is a microscopic mite (1/125 of an inch) that lives in large clusters within the blueberry bud scales. Bud mites feed on the epidermal regions of closely packed developing buds. During high infestation, the buds fail to develop. There are several symptoms on the blueberry plant that can characterize the presence of bud mites. These include reddening of the infected buds and flowers, pimpled ripe fruit, and reduced fruit set. The cryptic nature of bud mites feeding leads to more challenging management of this pest. One of the recommended cultural management practices for bud mites is the removal of infected branches through pruning, and the removal pruning of old canes.
The southern red mite and the twospotted spider mite belong to the family Tetranychidae. These mites look very similar and it can be relatively difficult to distinguish between these two species for untrained growers. In north-central Florida both mites are commonly found during the cooler months of the year – November to March. Tetranychids use their stylets to penetrate developing buds and suck juices from the leaves resulting in chlorotic spots on the leaves. The buds fail to develop, becoming deformed and leaving pimples on the developing fruit (Fig. 1.). Therefore, cultural practices including removing weeds from nearby host plants to reduce the number of overwintering mites, and water management to reduce plant stress is highly recommended. Other biological management tactics include periodically releasing predatory mites.
The False spider mite or flat mite is known to be an economically important plant feeding mite in citrus. However, recently this mite was found to feed on southern highbush blueberry by Dr. Liburd’s lab from the University of Florida. This was the first report of the infestation of this pest
Chemical control. Twospotted spider mites have been reported to develop resistance against many acaricides in several crops. At present, there are no true miticides that are registered for mite control in blueberry. Horticultural oil and dormant oil can be used in the fall and spring if the temperature is below 80 0F. If blueberry plants have already started to set flowers, the use of oils should be restricted, as flowers are easily damaged from oil sprays. The application of sulfur and the use of conventional synthetic pyrethroids including Danitol® (Fenpropathrin), Mustang® (Zeta-cypermethrin) and bifenthrin® offer some protection against mites especially those belonging to the family Tetranychidae (southern red mite and twospotted spider mite).
Miticidal soaps including M-Pede work well during the warm season. Fenproximate (Portal®) is a miticide that is currently being reviewed by IR4 and EPA for use in highbush blueberries. This can be a lengthy process and no one knows exactly how long it will take before it is legal to use Portal® in highbush blueberries