Spider Mites

God's Warrior · Spider Mites

Spider Mites
• Spider mites are common plant pests. Symptoms of injury include flecking, discoloration (bronzing) and scorching of leaves. Injury can lead to leaf loss and even plant death.
• Natural enemies include small lady beetles, predatory mites, minute pirate bugs, big-eyed bugs and predatory thrips.
• One reason that spider mites become a problem is insecticides that kill their natural predators.
• Irrigation and moisture management can be important cultural controls for spider mites.

Spider mites are common pest problems on many plants around yards and gardens in Colorado. Injury is caused as they feed, bruising the cells with their small, whiplike mouthparts and ingesting the sap. Damaged areas typically appear marked with many small, light flecks, giving the plant a somewhat speckled appearance.

Following severe infestations, leaves become discolored, producing an unthrifty gray or bronze look to the plant. Leaves and needles may ultimately become scorched and drop prematurely. Spider mites frequently kill plants or cause serious stress to them.

Spider mites (Family: Tetranychidae) are classed as a type of arachnid, relatives of insects that also includes spiders, ticks, daddy-longlegs and scorpions. Spider mites are small and often difficult to see with the unaided eye. Their colors range from red and brown to yellow and green, depending on the species of spider mite and seasonal changes in their appearance.

Many spider mites produce webbing, particularly when they occur in high populations. This webbing gives the mites and their eggs some protection from natural enemies and environmental fluctuations. Webbing produced by spiders, as well as fluff produced by cottonwoods, often is confused with the webbing of spider mites.

The most important spider mite is the twospotted spider mite (Tetranychus urticae). This mite attacks a wide range of garden plants, including many vegetables (e.g., beans, eggplant), fruits (e.g., raspberries, currants, pear) and flowers. The twospotted spider mite is also the most important species on house plants. It is a prolific producer of webbing.

Evergreens tend to host other mites, notably the spruce spider mite (Oligonychus ununguis) on spruce and juniper, Oligonychus subnudus on pines, and Platytetranychus libocedri on arborvitae and juniper. Honeylocust, particularly those in drier sites, are almost invariably infested with the honeylocust spider mite (Platytetranychus multidigituli). Other mites may affect shade trees such as elm, mountain ash and oak.

Another complex of mites is associated with turfgrass, including the clover mite and Banks grass mite. These are discussed separately in fact sheet 5.505, Clover and Other Mites of Turfgrass. Clover mites also are the common mite that enters homes in fall and spring, sometimes creating significant nuisance problems in the process.

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Life History and Habits

Spider mites develop from eggs, which usually are laid near the veins of leaves during the growing season. Most spider mite eggs are round and extremely large in proportion to the size of the mother. After egg hatch, the old egg shells remain and can be useful in diagnosing spider mite problems.

There is some variation in the habits of the different mites that attack garden plants, trees and shrubs. Outdoors, the twospotted spider mite and honeylocust spider mite survive winter as adults hidden in protected areas such as bark cracks, bud scales or under debris around the garden. Other mites survive the cool season in the egg stage. As winter approaches, most mites change color, often turning more red or orange. This habit may be why they are sometimes called "red spiders."

Most spider mite activity peaks during the warmer months. They can develop rapidly during this time, becoming full-grown in as little as a week after eggs hatch. After mating, mature females may produce a dozen eggs daily for a couple of weeks. The fast development rate and high egg production can lead to extremely rapid increases in mite populations.

Other species of spider mites are most active during the cooler periods of the growing season, in spring and fall. This includes the spruce spider mite and most of the mites that can damage turfgrass. These cool-season spider mites may cease development and produce dormant eggs to survive hot summer weather.

Dry conditions greatly favor all spider mites, an important reason why they are so important in the more arid areas of the country. They feed more under dry conditions, as the lower humidity allows them to evaporate excess water they excrete. At the same time, most of their natural enemies require more humid conditions and are stressed by arid conditions. Furthermore, plants stressed by drought can produce changes in their chemistry that make them more nutritious to spider mites.

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Biological Controls

Various insects and predatory mites feed on spider mites and provide a high level of natural control. One group of small, dark-colored lady beetles known as the "spider mite destroyers" (Stethorus species) are specialized predators of spider mites. Minute pirate bugs, big-eyed bugs (Geocoris species) and predatory thrips can be important natural enemies.

A great many mites in the family Phytoseiidae are predators of spider mites. In addition to those that occur naturally, some of these are produced in commercial insectaries for release as biological controls. Among those most commonly sold via mail order are Galendromus occidentalis, Phytoseiulus persimilis, Mesoseiulus longipes and Neoseiulus californicus. Although these have been successful in control of spider mites on interior plants, effective use outdoors has not been demonstrated in some areas. Predatory mites often have fairly high requirements for humidity, which can be limiting. Most suppliers provide information regarding use of the predator mites that they carry.

One reason that spider mites become problems in yards and gardens is the use of insecticides that destroy their natural enemies. For example, carbaryl (Sevin) devastates most spider mite natural enemies and can greatly contribute to spider mite outbreaks. Malathion can aggravate some spider mite problems, despite being advertised frequently as effective for mite control. Soil applications of the systemic insecticide imidacloprid (Merit, Marathon) have also contributed to some spider mite outbreaks.

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Water Management
Adequate watering of plants during dry conditions can limit the importance of drought stress on spider mite outbreaks. Periodic hosing of plants with a forceful jet of water can physically remove and kill many mites, as well as remove the dust that collects on foliage and interferes with mite predators. Disruption of the webbing also may delay egg laying until new webbing is produced. Sometimes, small changes where mite-susceptible plants are located or how they are watered can greatly influence their susceptibility to spider mite damage.

Chemical Controls
Chemical control of spider mites generally involves pesticides that are specifically developed for spider mite control (miticides or acaricides). Few insecticides are effective for spider mites and many even aggravate problems. Furthermore, strains of spider mites resistant to pesticides frequently develop, making control difficult. Because most miticides do not affect eggs, a repeat application at an approximately 10- to 14-day interval is usually needed for control. Table 1 includes a summary of pesticides that may be useful for managing spider mites.

Control of Spider Mites on House Plants
Control on house plants can be particularly frustrating. There generally are no biological controls and few effective chemical controls (primarily soaps and horticultural oils). When attempting control, treat all susceptible house plants at the same time. Trim, bag and remove heavily infested leaves and discard severely infested plants. Periodically hose small plants in the sink or shower. Wipe leaves of larger plants with a soft, damp cloth. Reapply these treatments at one- to two-week intervals as long as populations persist.

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Pesticides useful to control spider mites in yards and gardens.
Obtained June 2006 - research should be done to see if anything has been recommended later than this date.

Trade name - Orthene, certain Isotox formulations
Active Ingredient - acephate
Comment - Insecticide with some effectiveness against spider mites. Systemic.

Trade name - Avid
Active Ingredient - abamectin
Comment - For commercial use only on ornamental plants. Primarily effective against twospotted spider mite; less effective against mites on conifers. Limited systemic movement.

Trade name - Talstar, others
Active Ingredient - bifenthrin
Comment - Insecticide with good miticide activity.

Trade name - Cygon
Active Ingredient - dimethoate
Comment - Insecticide with fair miticidal activity. Few food crop registrations. Systemic.

Trade name- Kelthane
Active Ingredient - dicofol
Comment - Selective miticide labeled for some food crops in addition to ornamental plants. Some reduced activity at higher temperatures.

Trade name - Hexygon
Active Ingredient - hexythiazox
Comment - For commercial use only on ornamental plants. Selective miticide that affects developing stages and eggs only. One application per season label restriction.

Trade name - Sunspray, others
Active Ingredient - horticultural oils
Comment - Used at the "summer oil" rate (2 percent), oils are perhaps the most effective miticide available for home use.

Trade name - Several
Active Ingredient - insecticidal soap
Comment - Marginally effective against two-spotted spider mite and where webbing prevents penetration. Broadly labeled.

Trade Name - Various
Active Ingredient -sulfur
Comment - Generally sold in dust formulation for control of various fungal diseases and some mites on some ornamental and vegetable crops.

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The two-spotted spider mite is the most common 'warm season' mite. The females over-winter in the soil or on the plants, either in the yard, garden or in potted plants stored for the winter and become active early spring.

Perfect Spider Mite Weather
Dry conditions greatly favor spider mites, plus plants stressed by drought can produce changes in their chemistry that make them more nutritious to spider mites. Therefore they can develop rapidly during this time, in as little as a week after hatching the females produces a dozen eggs daily for a couple of weeks. The fast development rate and high egg production can lead to rapid increases in mite populations

Early Detection
Early detection of spider mites, before damage is noticed, is important. The tiny spider mites can be detected by holding either a piece of white paper or cardboard under a leaf, then thump the front side of the leaf. If mites are present, they will be dislodged and can be seen walking slowly on the paper.

Quarantine and Inspection.
Mites as well as other insects, virus and fungus are often introduced into your environment on infested plants or their soil. Carefully inspect, preferably with a magnifying lens, any plant or cutting being introduced into your environment. Do the above white paper test for mites and inspect the total plant for other insects and problems. If mites or insects are detected and the plant was purchased it should be immediately returned to the vendor.

If you are bringing in plants without soil or cuttings, swishing it a 10% Clorox solution to which Ivory dish washing liquid has been added will be of benefit as would a dip in a medicide or insecticide solution with good miticide activity such as (Talstar). However if upon inspection mites, are detected on plants you can’t take back, consider toss them before you get attached. If you won’t toss a full mite treatment should be given. Be sure to quarantine all new plants for a minimum of 4 weeks, to insure they are clean.

Spider Mite Treatment
To eliminate Spider Mites, trim, bag and removed heavily infested leaves, clean up all plant debris … discard severely infested plants. Choose one of the following pesticides/miticides and follow the instructions. Be sure to continue your spraying program until all eggs are hatched and the resulting mites are killed. Some of the miticides listed kill both adults and eggs but are very expensive and may not be available to non-professionals.

NOTE: Spider Mites hatch in 3-20 days after they are laid, depending upon the weather. The hotter and dryer it is the faster they hatch. I believe mites have continued to give me a problem because I didn’t spray long enough to kill the last hatching eggs. Also washing them off with the water hose caused them to drop into the soil in and around the pot, so they missed the pesticide.

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Jan 2004 - This list might not be complete and more research should be done to get updated information.

Pesticides useful to control spider mites in yards and gardens. (Not to be used inside the house.)

Active Ingredient Trade Name(s)
Comments second line

Acephate, Orthene & certain Isotox formulations
Insecticide with some effectiveness against spider mites. Systemic.
Personal experience - damages the leaves of some Brugs & tender plants.

Abamectin, Avid
For commercial use only on ornamental plants. Primarily effective against two-spotted spider mite; less effective against mites on conifers. Limited systemic movement.

Bifenthrin, Talstar & others
Insecticide with good miticide activity.

Dimethoate, Cygon
Insecticide with fair miticidal activity. Few food crop registrations. Systemic.

Dicofol, Kelthane
Selective miticide labeled for some food crops in addition to ornamental plants. Some reduced activity at higher temperatures.

Hexythiazox, Hexygon
For commercial use only on ornamental plants. Selective miticide that affects developing stages and eggs only. One application per season label restriction.

Horticultural oils, Sunspray & others
Used at the "summer oil" rate (2 percent), oils are perhaps the most effective miticide available for home use.

Insecticidal soap, several
Marginally effective against two-spotted spider mite and where webbing prevents penetration. Broadly labeled.

Sulfur, various
Generally sold in dust formulation for control of various fungal diseases and some mites on some ornamental and vegetable crops.

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Wintering-Over Brugmansias

Spider Mites in the house can be particularly frustrating because the only safe chemical controls are soaps and horticultural oils, pesticide treatments should be done outside not in the house.

In the home environment spider mites can stay active all winter since the warm season continues. Those stored for the winter where temperatures are cooler, but above freezing should not reach damaging populations.

If spider mites are identified, it is recommended that all susceptible plants, not just your brugmansia be treated at the same time. Trim, bag and remove heavily infested leaves and discard severely infested plants, hose small plants in the sink or shower. Wipe leaves of larger plants with a soft, damp cloth. When the plants are dry use soaps, horticultural oils not necessary to take them outside but if you opt for pesticide do this outside only. Reapply these treatments every 5 days as long as populations persist.