Citrus Red Mite

Adult female citrus red mites are oval and globular; the male is smaller and has a tapered abdomen. Each female lays 20 to 50 eggs at a rate of 2 to 3 a day, depositing them on both sides of leaves. The life cycle from egg to egg may be as short as 12 days during warm weather.

Mite numbers increase in spring, late summer, and early fall in response to new growth; citrus red mites prefer to feed on fully expanded young leaves but will also infest fruit.

On leaves, citrus red mite feeding results in a pale stippling visible primarily on the upper surface of the leaf. In severe infestations, the stippling enlarges to dry necrotic areas (commonly called mesophyll collapse). Eventually, leaves may drop and twigs dieback. Stippling or silvering also occurs on green fruit but usually disappears when fruit change color. If large numbers feed on nearly mature fruit, the silvering may persist. High numbers can also cause fruit sunburn if hot weather is occurring. During fall Santa Ana winds, low levels of citrus red mite can cause a blasting or burning of foliage and leaf drop in coastal and Southern California growing areas.

Citrus red mite is more of a problem when trees are water stressed and conditions are hot and dry. Research on San Joaquin Valley navels and coastal lemons showed citrus can tolerate much higher numbers than previously thought and pesticides are not normally required in healthy orchards under a biologically based IPM program. Mite numbers tend to be higher in spring and fall, especially in orchards where natural enemies are destroyed by the use of broad-spectrum insecticides such as pyrethroids, organophosphates, carbamates and neonicotinoids. Monitor orchards and use narrow range oils and selective miticides whenever possible.

Predaceous mites, predaceous insects, and a virus are important in regulating citrus red mite numbers. The most important natural enemy is the predaceous mite (Euseius tularensis). These beneficial mites can establish their populations before citrus red mites are numerous because they have alternate food sources (pollen, citrus thrips larvae, leaf sap, nectar, and honeydew). They mainly attack immature stages of the citrus red mite. The female of both species is about the same size as the female citrus red mite but is pear-shaped, shiny, and translucent. Predator eggs are clear, oval, and about twice the size of citrus red mite eggs.

Other predators of the citrus red mite include a small black lady beetle (Stethorus picipes), a predaceous dustywing (Conwentzia barretti), and the sixspotted thrips (Scolothrips sexmaculatus). In addition, a disease caused by a virus specific to citrus red mite is widespread in citrus-growing areas. The disease becomes epidemic under warm, moderately dry conditions when mite numbers are high and can rapidly reduce them. Symptoms of virus-infected mites include stiff movements, legs curled under the body, and subsequent disintegration of the body. If diseased mites are mounted on a slide and examined under a polarizing microscope, internal crystals that shine in the polarized light are evident.

Besides predators and the virus, hot temperatures (above 90°F) and low humidity also reduce citrus red mite numbers.

Mites increase their reproduction on water-stressed trees. Good irrigation reduces red mite outbreaks. Water roads to limit dust buildup, which also promotes mites.

Use cultural and biological controls and petroleum oil sprays on organically managed citrus.

Miticides available for controlling citrus red mite (bearing orchards only) include acequinocyl (Kanemite), fenbutatin oxide (Vendex), hexythiazox (Onager), oil, pyridaben (Nexter), spirodiclofen (Envidor), and fenpyroximate (Fujimite). For nonbearing orchards only, bifenazate (Acramite) can be used.

Of these miticides, some are more selective than others. Acequinocyl, bifenazate, fenbutatin oxide, and oil have the least effect of all on natural enemies, including predatory mites, but they also provide a shorter period of control of pest mites. Etoxazole, hexythiazox, pyridaben, fenpyroximate, and spirodiclofen are of intermediate selectivity because they harm both pest mites and predatory mites for up to 6 weeks but cause minimal harm to beneficial insects such as lacewings, lady beetles, and Aphytis melinus, which help control caterpillars, scale, thrips, and other pests.

In February in the San Joaquin Valley, survey each orchard to determine if mites are present. Scan several leaves per tree at various sites, and use a hand lens to check a few leaves for eggs and immatures. In Southern California and coastal areas, depending on the local situation, consider monitoring beginning in late summer.

Monitoring in the San Joaquin Valley

In March, or as soon as mites are detectible, begin monitoring by collecting a total of 100 fully expanded leaves from throughout the orchard. Select leaves from just inside the shady region of the tree. Using this sample:

• Determine the average number of pest mites per leaf by dividing the total number of mites found by 100.
• Count the number of active stages of predatory mites and calculate the average number of predatory mites by dividing the total number of predatory mites by 100.
• Note the presence of virus-infected citrus red mites.
• Repeat this sampling about every 2 weeks until red mite numbers decline below 1 per leaf and petal fall has occurred. Keep records of your monitoring results (example form—PDF).

In San Joaquin Valley navel oranges, economic loss will not occur if citrus red mite densities do not exceed eight mature females per leaf by 2 to 4 weeks after petal fall. Vigorous, well-irrigated trees can tolerate more. Low-to-moderate numbers are considered to be beneficial as they provide food for natural enemies. High temperatures and virus reduce mite numbers in June and July and no pesticides are generally required during summer.

In orchards where nonselective pesticides have destroyed natural enemies, pesticides may be required in spring to prevent excessive mite numbers at petal fall. Use the application times listed in the following table when applying oil sprays.

Monitoring in Southern California and Coastal Areas

Spring and summer populations of citrus red mite generally do not require regular monitoring or pesticide application. However, fall populations, in conjunction with the Santa Ana winds, can be very damaging if nonselective pesticides or dust upset naturally occurring control. In late summer, monitor orchards about every 2 weeks as described above for the San Joaquin Valley. Consider applying a pesticide before Santa Ana conditions if there are more than eight to ten citrus red mites per leaf.

Extensive research on the use of oil sprays against various mite and scale insects has resulted in the development of recommendations that use specific rates and timing of pesticide applications on different varieties of citrus in different regions of California in order to achieve expected pest control and limit the potential for leaf or fruit drop or fruit damage as a result of phytotoxicity. The narrow range 415, 440, and 455 oils were specifically developed for use in California to limit these concerns. Precautions for using petroleum oil sprays are listed at the beginning of this guideline. Because mites are on the outside of the tree and sprayed with outside coverage, phytotoxicity risks from oil during mite sprays are less than with a scale application. For additional information, see Managing Insects and Mites with Spray Oils, UC ANR Publication 3347.

• Citrus red mite monitoring form (PDF)
• Photos of natural enemies of mites