How to Manage Pests

UC Pest Management Guidelines

Populations 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.

DAMAGE
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 populations feed on nearly mature fruit, the silvering may persist. High populations 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.

MANAGEMENT
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 populations than previously thought and treatment is not normally required in healthy orchards under a biologically based IPM program. Populations tend to be heavier in spring and fall, especially in orchards where natural enemies are destroyed by the use of broad-spectrum insecticides such as formetanate hydrochloride (Carzol), methidathion (Supracide), and dimethoate. Monitor orchards and use narrow range selective miticides whenever possible.

Biological Control
Predaceous mites, predaceous insects, and a virus are important in regulating citrus red mite populations. The most important natural enemies are the predaceous mites, Euseius tularensis and E. stipulatus. These beneficial mites can establish their populations before citrus red mites are numerous because they have alternate food sources (pollen, citrus thrips larvae, 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. Eggs hatch and develop into adults in about 8 days.

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 populations are high and can rapidly reduce the mite population. 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 populations.

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

Organically Acceptable Methods
Cultural and biological controls and petroleum oil sprays are acceptable on organically managed citrus.

Selectivity
Miticides available for controlling citrus red mite include dicofol (Kelthane), propargite (Omite), fenbutatin oxide (Vendex), pyridaben (Nexter) and oil; of these miticides, some are more selective than others. Dicofol and pyridaben are of intermediate selectivity because they act primarily against mites with minimal impact on beneficial insects such as lacewings, lady beetles, and Aphytis melinus, which help control worms, scale, thrips, and other pests. However, these two materials are toxic to predaceous mites such as Euseius tularensis. Propargite is more selective than dicofol because, when used at low rates, it is relatively nontoxic to beneficial mites. Petroleum oil sprays can suppress beneficial mite populations for several months. Oil is frequently used as a miticide because it is cheaply and easily combined with treatments for other pests. Fenbutatin oxide has the least effect of all on natural enemies. Euseius tularensis populations vary in their tolerance to various miticides and insecticides with some populations being fairly resistant to many materials because of past exposure.

Monitoring and Treatment Decisions
In February, 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 March, or when mites are present, begin monitoring about every 2 weeks by sampling five leaves/tree from all sides of four trees. Determine the average number of adult female mites/leaf and count the beneficial mites on the underside of leaves as well as the percentage of virus-infected mites. Use a ratio of one to two female red mites to one predaceous mites to help assess the need for treatment.

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

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

In southern California and coastal areas, spring and summer populations of citrus red mite do not require treatment, but fall populations can be very damaging in conjunction with the Santa Ana winds if naturally occurring control is upset by nonselective pesticides or dust. Begin monitoring orchards in late summer, and consider applying a treatment before Santa Ana conditions if there are more than eight to ten citrus red mites per leaf.

Use of Oils
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 treatments 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 and 440 oils were specifically developed for use in California to limit these concerns. Precautions for using petroleum spray oils are listed at the beginning of this guideline. Because mites are on the outside of the tree and sprayed with outside coverage, risks of phytotoxicity due to oil are less than with a scale application. For additional information, see Managing Insects and Mites with Spray Oils, UC ANR Publication 3347.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O’Connell, UC Cooperative Extension, Tulare Co.
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura Co.
C. E. Kallsen, UC Cooperative Extension, Kern Co.
D. R. Haviland, UC Cooperative Extension, Kern Co.
Acknowledgments for contributions to the insect, mite, and snail section:
J. Barcinas, E. S. I., Corona, CA
R. Dunn, Badger Farming Co., Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
H. Griffiths, E. S. I., Corona, CA
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
T. Roberts, E. S. I., Corona, CA
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

Top of page