SPIDER

Integrated Management in the Home Garden

Mites (Fig. 1) are common pests in resemble adults, except the newly landscapes and gardens and can be hatched larvae have only six legs (Fig. found feeding on many fruit trees, 2). Eggs are spherical and translucent, vines, berries, vegetables, and orna- like tiny droplets, becoming cream col- mental . Although related to in- ored before hatching. sects, mites are not insects but members of the class along LIFE CYCLE with spiders and . The spider In some parts of California, spider mites, also called webspinning mites, mites may feed and reproduce all year (actual are the most common pests and on plants that retain their green size) among the most ubiquitous of all pests through the winter. In colder areas and in the garden and farm. on deciduous trees that drop their leaves, webspinning mites overwinter The webspinning spider mites include as red or orange mated females under Pacific spider mite, twospotted spider rough bark scales and in ground litter mite, spider mite, and sev- and trash. They begin feeding and lay- eral other . Most common ones ing eggs when warm weather returns are closely related species in the in spring. Figure 1. Spider mite. and cannot be reli- ably distinguished in the field. How- Spider mites reproduce rapidly in hot ever, there is little need to do so since weather and commonly become nu- leaves—can be damaging to plants, their damage, biology, and manage- merous in June through September. If especially herbaceous ones. At first, the ment are virtually the same. temperature and food supplies are fa- damage shows up as a stippling of vorable, a generation can be completed light dots on the leaves; sometimes the IDENTIFICATION in less than a week. Spider mites are leaves take on a bronze color. As feed- To the naked eye, spider mites look generally favored by hot, dusty condi- ing continues, the leaves turn yellow like tiny moving dots; however, you tions and are usually found first on and drop off. Often leaves, twigs, and can see them easily with a 10X hand trees or plants adjacent to dusty road- fruit are covered with large amounts of lens. Adult females, the largest forms, ways or at margins of gardens. Plants webbing. Damage is usually worse are less than 1/20 inch long. Spider mites under water stress are also highly sus- when compounded by water stress. live in colonies, mostly on the under- ceptible. As foliage quality declines on surfaces of leaves; a single colony may heavily infested plants, female mites Loss of leaves will not cause yield contain hundreds of individuals. The catch wind currents and disperse to losses in fruit trees during the year of names “spider mite” and “webspin- other plants. High mite populations infestation unless it occurs in spring or ning mite” come from the silk webbing may undergo a rapid decline in late very early summer, but it may impact most species produce on infested summer when predators overtake next year’s crop. On annual vegetable leaves. The presence of webbing is an them, host conditions become crops, such as squash, melons, and wa- easy way to distinguish them from all unfavorable, the weather turns cooler, termelons, loss of leaves can have a other types of mites. or following rain. significant impact on yield and lead to sunburning. On crops such as sugar Adults have eight legs and an oval DAMAGE peas and beans, where pods are at- body, with two red eyespots near the Mites cause damage by sucking tacked, spider mites can cause direct head end of the body. Females usually contents from leaves. A small number damage. On ornamentals, mites are have a large, dark blotch on each side of mites is not usually reason for con- primarily an aesthetic concern, but can of the body and numerous bristles cov- cern, but very high populations—levels kill plants if populations become very ering the legs and body. Immatures high enough to show visible damage to high on annual plants. Spider mites are

PEST NOTES Publication 7405 University of California Division of Agriculture and Natural Resources Revised December 2000 December 2000 Spider Mites

also important pests of field-grown the predatory mites, including the good guideline is that one predator is roses. western predatory mite, Galendromus needed for every ten spider mites to (=Metaseiulus) occidentalis, and Phy- provide control. More than one appli- MANAGEMENT toseiulus species. Predatory mites are cation of predatory mites may be re- Spider mites have many natural en- about the same size as plant-feeding quired if you want to reduce pest emies that often limit populations. Ad- mites but have longer legs and are populations rapidly. Concentrate re- equate irrigation is important because more active. Various insects are also leases in hot spots where spider mite water-stressed plants are most likely to important predators—the sixspotted numbers are highest. Once established be damaged. Broad-spectrum insecti- thrips (Scolothrips sexmaculatus), the on perennials, predatory mites may cide treatments for other pests fre- larvae and adults of the spider mite reproduce and provide biological con- quently cause mite outbreaks, so avoid destroyer lady beetle (Stethorus picipes), trol indefinitely without further aug- these when possible. Sprays of water, the larvae of certain flies including the mentation unless nonselective insecticidal oils, or soaps can be used cecidomyid Feltiella acarivora, and vari- are applied that kill the for management. Always monitor be- ous general predators such as minute predators. For information on where to fore treatment. pirate bugs, bigeyed bugs, and lace- buy these predators, write or call Cali- wing larvae. The purchase and release fornia Department of Pesticide Regula- Monitoring of predatory mites can be useful in es- tion, P.O. Box 942871, Sacramento, CA Mites are tiny and difficult to detect. tablishing populations in large plant- 94271-0001, (916) 324-4100, and ask for Usually plant damage—stippling or ings or orchards, but the best results a free copy of their leaflet “Suppliers of yellowing of leaves—will be noticed are obtained by creating favorable con- Beneficial Organisms in North before you spot the mites themselves. ditions for naturally occurring preda- America,” or view it on the World Check the undersides of leaves for tors—for instance, by avoiding dusty Wide Web at http://www.cdpr. ca.gov/ mites, their eggs, and webbing; you conditions and pesticide sprays. docs/ipminov/bensuppl.htm. will need a hand lens to identify them. To observe them more closely, shake a The major predator mites commercially Cultural Control few off the surface onto a white available for release are the western Cultural practices can have a signifi- sheet of paper. Once disturbed, they predatory mite and . The cant impact on spider mites. Dusty will move around rapidly. Be sure western predatory mite is more effec- conditions often lead to mite out- mites are present before you treat. tive under hot, dry conditions. These breaks. Apply water to pathways and Sometimes the mites will be gone by predators do not feed on foliage or be- other dusty areas at regular intervals. the time you notice the damage; plants come pests; thus if pest mites are not Water-stressed trees and plants are less will often recover after mites have left. available when predatory mites are tolerant of spider mite damage. Be sure released, the predators starve or mi- to provide adequate irrigation. Mid- Biological Control grate elsewhere. If you wish to estab- season washing of trees and vines with Spider mites have many natural en- lish predators in a heavily infested water to remove dust may help pre- emies, which limit their numbers in orchard or garden that has few preda- vent serious late-season mite many landscapes and gardens, espe- tors, use a soap spray or selective miti- infestations. cially when undisturbed by pesticide cide to bring pest mites to a lower level sprays. Some of the most important are and then release predatory mites. A In gardens and on small fruit trees, regular, forceful spraying of plants with water will often reduce spider mite numbers adequately. Be sure to get good coverage, especially on the undersides of leaves. If more control is required, use an insecticidal soap or oil in your spray (as described below), but test the product on one or two plants to be sure it is not damaging to plants.

egg larva Chemicals protonymph Spider mites frequently become a prob- lem after the application of insecti- cides. Such outbreaks are commonly a deutonymph result of the killing off the natural enemies of the mites, but also adult occur when certain insecticides stimu- late mite reproduction. For example, Figure 2. Spider mite life cycle: development of a typical plant-feeding spider mite. spider mites exposed to carbaryl

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(Sevin) in the laboratory have been use soaps or oils on water-stressed Sulfur dusts are skin irritants and eye shown to reproduce faster than un- plants or when temperatures exceed and respiratory hazards. Always wear treated populations. Carbaryl, some 90°F. These materials may be phyto- appropriate protective clothing. organophosphates, and some pyre- toxic to some plants, so check labels throids apparently also favor spider and/or test them out on a portion of COMPILED FROM: mites by increasing the level of nitro- the foliage several days before apply- Flint, M. L. 1998. Pests of the Garden and gen in leaves. Insecticides applied dur- ing a full treatment. Oils and soaps Small Farm: A Grower’s Guide to Using ing hot weather usually appear to have must contact mites to kill them so ex- Less Pesticides, 2nd ed. Oakland: Univ. the greatest effect on mites, causing cellent coverage, especially on the un- Calif. Agric. Nat. Res. Publ. 3332. dramatic outbreaks within a few days. dersides of leaves, is essential and repeat applications may be required. OTHER REFERENCES If a treatment for mites is necessary, Sulfur dust or spray can be used on Dreistadt, S. H., J. K. Clark, and M. L. use selective materials, preferably in- some vegetables, but will burn cucur- Flint. 1994. Pests of Landscape Trees and secticidal soap or insecticidal oil. bits. Do not use sulfur dust if tempera- Shrubs: An Integrated Pest Management Petroleum-based horticultural oils or tures exceed 90°F and do not apply Guide. Oakland: Univ. Calif. Agric. neem oils are both acceptable. Do not sulfur within 30 days of an oil spray. Nat. Res. Publ. 3359.

For more information contact the University of California Cooperative Extension or agri- cultural commissioner’s office in your coun- ty. See your phone book for addresses and phone numbers.

EDITOR: B. Ohlendorf TECHNICAL EDITOR: M. L. Flint DESIGN AND PRODUCTION: M. Brush ILLUSTRATIONS: D. Kidd

PRODUCED BY IPM Education and Publi- WARNING ON THE USE OF CHEMICALS Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations cations, UC Statewide IPM Project, Univer- given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, sity of California, Davis, CA 95616-8620 away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially This Pest Note is available on the World gardens containing fruits or vegetables ready to be picked. Wide Web (http://www.ipm.ucdavis.edu) Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Either use the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that they may contaminate water supplies or natural waterways. The University of California prohibits discrimination against or harassment of any person employed by or To simplify information, trade names of products seeking employment with the University on the basis of race, color, national origin, religion, sex, physical have been used. No endorsement of named products or mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status, is intended, nor is criticism implied of similar products age, sexual orientation, citizenship, or status as a covered veteran (special disabled veteran, Vietnam-era that are not mentioned. veteran, or any other veteran who served on active duty during a war or in a campaign or expedition for which This material is partially based upon work supported a campaign badge has been authorized). University Policy is intended to be consistent with the provisions by the Extension Service, U.S. Department of of applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be Agriculture, under special project Section 3(d), directed to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture and Integrated Pest Management. Natural Resources, 1111 Franklin, 6th Floor, Oakland, CA 94607-5200; (510) 987-0096.

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