Tips on Controlling Southern Red Mite and False Spider Mite in Blueberries

Mite damage can be significant on blueberries, and high infestations can result in defoliation. The southern red mite (Oligonychus ilicis) is the primary pest in both open-field and protected (e.g., greenhouse or high tunnel) production on southern highbush blueberry (SHB) in Florida. The false spider mite, or flat mite (Brevipalpus yothersi Baker), was first reported on SHB in 2016, and is more typically seen during the summer. 

Description and Life Cycle

Southern red mite (SRM) populations develop and expand during cooler drier months, typically October to March when temperatures are between 60 – 86 °F. In north-central Florida populations peak during the fall, whereas in the southern parts of the state peaks are observed in January and February. Under ideal conditions, (80 oF, 65% relative humidity) life cycles can be completed within two weeks, and with overlapping generations, populations can double within five days. This increases the possibility of significant yield impacts. Adults can appear similar to the red form of twospotted spider mites (Tetranychusurticae Koch) and other red tetranychids. Southern red mites are red or brown to deep purple in color with lighter colored legs and are about 0.4 mm (0.016 in) in length. Females have a more rounded body shape than males and are slightly larger. Eggs are red to brown and spherical and hatch into pale six-legged larvae. Mites develop eight legs and darker coloration in the nymph stages (Fig. 1).  

Figure 1. Southern red mite adult female and male mating, and one egg (right).

Credits: L. Buss

Flat mites typically complete their life cycle in about 19 – 20 days when temperatures are around 77 °F with 60% relative humidity. Adult females are approximately 0.3 mm (0.012 in) in length, flat and oval, with red-orange coloring (Fig. 2). Males and immature stages are smaller but similar in appearance and color to females. Eggs are bright red to orange with an elongated shape.

Figure 2. Female adult flat mite

Credits: R. Akyazi

Injury

Southern red mites spend most of their lives feeding and reproducing on the underside of SHB leaves. The mite inserts its mouthpart into the leaf and feeds on cell contents, resulting in a bronzing of the leaves, which intensifies as the level of injury increases (Fig. 3). This can cause a decrease in the rate of photosynthesis. A buildup of shed white skins is usually observed when there are high mite populations (Fig. 4). Alternatively, plants heavily infested with flat mites typically develop necrotic brown spots on the leaves (Fig. 5).

Figure 3. Bronze-colored blueberry leaves associated with southern red mite feeding injury.

Credits: D. Phillips

Figure 4. Southern red mite shed skins.

Credits: D. Phillips

Figure 5. Necrotic brown spots on leaves due to feeding injury by false spider mites or flat mites.

Credits: R. Akyazi

Monitoring and Management

There are differences between southern red mites and flat mites other than color and shape that must be considered when monitoring for the presence of mites. Southern red mites typically feed over the entire underside of leaves and construct webbing to cover the infested surface as a protection against predators. Flat mites usually feed only near the secondary veins and midrib on the leaf underside and do not create webbing. Also, southern red mites can be observed with the naked eye or a 10x hand lens and tend to move more quickly, while flat mites must be observed with at least a 20x hand lens or microscope, and tend to move more slowly. 

Frequent scouting for mites is essential for the early identification of any infestations, before significant feeding injury occurs, especially during hot dry conditions when mite populations typically increase. Scouts can check for bronzed leaves for southern red mites and necrotic spots for flat mites. It is important to record both eggs and motile (all stages except egg) numbers. The egg stage gives information about future population. To scout for the presence of mites, examine the underside of leaves to look for adults, shed skins, and webbing. Alternatively, the person scouting can sharply tap the foliage onto a sheet of white paper to dislodge and observe any adults.

Mites prefer dry dusty conditions, and plants that are drought-stressed can be more susceptible to mite injury. Water should be regularly applied to roadways or other dusty areas when conditions are hot and dry, and plants should be supplied with sufficient irrigation to avoid becoming drought-stressed.

Three miticides have recently been registered for use in highbush blueberries:

• Magister® with the active ingredient fenazaquin

• Portal® with the active ingredient fenpyroximate

• Kanemite® with the active ingredient acequinocyl 

These miticides target tetranychids. Magister® has recently added the southern red mite to its label. Kanemite® also has the southern red mite on its label. These miticides control all developmental stages of southern red mites (larvae, nymphs, and adults). Magister® also provides contact control of eggs, in addition to controlling other stages by both contact and ingestion. Our most recent field trials were conducted in the fall of 2020, testing eight miticides. The data from this trial indicates that Magister® and Portal® were the most effective products of those included in the trial at suppressing southern red mite populations and allowing plants to recover from mite feeding injury. This is consistent with the results in our 2019 trials. Kanemite® also showed effectiveness at reducing southern red mites in the 2020 trial. Only one application per year can be made with Magister® and two applications per year with Portal® and Kanemite®. 

In addition to these miticides, two sulfur-based products were tested in our 2020 field trials. Sulfur – CARB™ is a suspended sulfur soil amendment (with elemental sulfur and molasses), which is sometimes used by growers in foliar applications to repel mites and insects. Sulfur – CARB™ provided good control of mites only after a 2nd application (14 days apart), and by the end of the trial there were lower levels of leaf bronzing. However, this product is not specifically labeled for southern red mites in SHB. The other sulfur-based product, Cosavet DF® with the active ingredient sulfur, was not effective at reducing southern red mite populations. Since flat mites have only recently been reported as a pest on blueberries, there are no established management and control guidelines or information on miticide effectiveness for this pest. Flat mites are a pest of citrus, and any management techniques at this point are from studies in that crop.

Predatory mites have been an important tool that is used for controlling mites in some crops, however, at this point, they have not been successfully evaluated in blueberry systems.

Scouting for the early identification of mites and implementing management techniques before populations become high are recommended to avoid significant feeding injury and associated yield impacts. 

For more information see UF/IFAS EDIS Publication ENY-1006, Mite Pests of Southern Highbush Blueberry in Florida (edis.ifas.ufl.edu/in1284). 

CREDITS
by OSCAR LIBURD,, Professor, Entomology and Nematology Department, UF/IFAS; LORENA LOPEZ, Post-doctoral Research Associate, Entomology and Nematology, UF/IFAS; and DOUG PHILLIPS,  Blueberry Extension Coordinator, UF/IFAS