Four groups of mites are important in the greenhouse (Table 1): 1) spider mites (two-spotted spider mites); 2) false spider mites or flat mites; 3) broad and cyclamen mites; and 4) bud, gall, rust or eriophyid mites. Mites are small and are thus difficult to identify. However, knowledge of the species and its biology is the first step in designing a strategy to best manage them:

Identification

1) Two-spotted spider mites (Fig. 1) have round, pale yellow to reddish eggs deposited on the undersurfaces of leaves; nymphs and adults have two prominent greenish to brownish dots on their bodies; these mites spin webs for protection and dispersal; damage includes stippling or bronzing of leaves.

2) False spider mites or flat mites have a longer life cycle than two-spotted spider mites; eggs are bright red and oval-shaped and are laid in clusters on both surfaces of leaves; adults are reddish with black patterns on their backs and produce no webbing; damage includes silvering of leaves, but stems are also attacked.

3) Broad mites (Fig. 2) produce eggs with many tubercles or facets which appear like "jewels" under the microscope; nymphs remain in cracks and crevices of leaves and plants; after some development, nymphs enter a quiescent of sessile stage; females are clear after emergence but soon turn straw- colored and develop a prominent white stripe down their backs; damage appears on the younger foliage and on the undersides of leaves, giving leaves scalloped edges resembling physiological damage.

Cyclamen mites (Fig. 2) produce clear, pearlescent oblong eggs; nymphal stage bodies are constricted behind the third pair of legs; females are clear after emergence but turn amber with age; damage includes deformed buds, and these mites are not found on open leaf surfaces; they do not attack chrysanthemums.

4) Bud and rust or eriophyid mite bodies are elongate and cone-shaped, tapering toward their back-ends and the legs are very short (Fig. 3); damage includes galls, deformed or discolored plant tissue.

Monitoring methods. Mites are small and difficult to see with the naked eye. Using a 10x hand lens will enhance your ability to see mites and their eggs. Some mites (eriophyid mites, broad and cyclamen mites) are so tiny that a dissecting scope may be necessary.

Spider mites can be detected by looking for the typical mite-caused damage, mites or symptoms of mite infestations such as cast skins and webbing. Spider mite damage is easy to see. Their mouthparts are small toothpick-like structures (chelicerae) that they use to poke holes in cells before they suck out the cell contents using their other mouthparts (palpi). The result is small clusters of empty cells that appear from a distance like stipples. These stipples turn brown or bronze after a while. Injured leaves take on a bronze appearance, with most of the damage occurring around major leaf veins.

The mites, eggs and cast skins can best be seen by examining the under surfaces of randomly-selected leaves. Mites can also be sampled using the "beat method" whereby plant parts are beaten onto an off-white piece of paper or card. The dislodged mites can then readily be seen crawling on the paper. This method works particularly well for evergreens and small-leaved plants.

Cultural control. A number of greenhouse production practices can affect mite outbreaks. Use of clean, pest free plants and cuttings is essential. Knowledge of mite prone species/varieties can enable the grower to avoid these plants or to monitor these most closely as "indicator" plants. Watering practices affect spider mite populations. Drought-stressed plants are most prone to mite outbreaks while overhead sprinkler systems are less favorable for mite outbreaks.

Biological control. A number of predatory mite species are available for spider miter control in the greenhouse: Phytoseiulus persimilis, Mesoseiulus longipes (=Phytoseiulus longipes), Metaseiulus occidentalis (=Galendromus occidentalis), and Neoseilus californicus (=Amblyseius californicus) have been marketed for released into greenhouses, occasionally under products names such as Spidex® Shaker Bottle, Spidex-Plus® Paper Sachets. These mite predators have unique properties. For instance, M. occidentalis tolerates a wide range of humidities and some strains are tolerant of azinphosmethyl (Guthion®) and carbaryl (Sevin®). M. longipes better tolerates high temperatures and drier conditions. N. californicus is better able to survive at lower spider mite densities and take longer to suppress populations. Frequently, combinations of two or more species are released. They are best used as preventive releases made periodically at or before the first detection of spider mites or their damage. Occasionally they are applied as "biotic insecticides" using an "inundative release" to try to bring down an existing population. The price, availability of obtaining and releasing these predaceous mites should be considered and may be prohibitive. Furthermore, pesticide use before and after making releases may impact the success of augmentive releases.

Physical control: High-volume, high pressure water sprays, as achieved through some application devices such as the Water Wand and Jet-All Water Wand, can dislodge many mites from foliage and temporarily suppress mite populations. Rose growers in east Texas are reportedly using these devices successfully for spider mite suppression.

Chemical control. Table 2 presents a partial listing of currently registered products available for control of ornamental plant insect/mite pests. The objective in developing this list was to list specific examples of products containing various active ingredients. There are many other products marketed that contain the same active ingredients that may or may not be similarly formulated.

Many insecticides also have miticidal activity, while some insecticides affect only some types of mite species (Table 1) or have no effect on mites at all. In fact, over-use of some insecticides (ie. carbaryl) can actually lead to spider mite outbreaks later on. Insecticide/miticide products are best used when a complex of mite and insect pests are present. Before releasing predatory mites, insecticidal soap can be applied to reduce the number of spider mites without leaving a harmful residue after it dries that will affect these natural enemies. Whenever possible, use the most target-specific, least toxic available, and use in strict accordance to directions provided on the product label.

Different miticides have different performance characteristics. For example, Avid® is somewhat systemic in that it penetrates into treated foliar plant cells where it remains active while the material that remains on the leaf surface rapidly breaks down; has a unique mode of action on the nervous system; and has few phytotoxicity problems. Pentac® is relatively slow acting; is U.V. light sensitive; has few phytotoxicity problems; has no reported resistance; has some ovicidal activity; and usually requires two applications. Thiodan® is phytotoxic to some varieties of chrysanthemums and geraniums. Insecticidal soap is a contact miticide/insecticide and has no residual activity. Sulfur, registered as a miticide on some vegetable crops, is highly phytotoxic; forms residues on treated plants; has some fungicidal activity; and is inexpensive. Some products have a greater negative impact on natural enemies than others and some strains of predaceous mites have been selected to be able to tolerate some pesticides.

Adjuvants. Tank additives (spreaders, stickers, buffers, etc.) can affect the performance of miticides applied. A good rule of thumb to follow is: use an adjuvant only when increased performance has been demonstrated. Use of a spreading or wetting agent will improve the efficacy of most miticides, particularly on waxy-leaved plants. Insecticidal soap has been used to increase penetration of miticides into the mites. Conversely, use of some types of adjuvants may actually decrease effectiveness of some miticides (ie. Nu-Film-P plus Avid®) or lead to phytotoxic responses treated plants (ie. spreader-sticker materials or agricultural oils plus Joust®). Check with product labels or manufacturers for specific information regarding tank mixtures and use of adjuvants. Results of evaluations to determine if the addition of the mite pheromone product, Stirrup-M®, increases performance of miticides have been inconclusive.

Resistance management. There is height-ened concern about the proper use of available products to extend their effectiveness because of 1) the continuing loss of insecticide/miticide products available to the commercial nurseryman (ie. Kelthane®, Plictran®, Temik® 10G, Vendex®, Vydate®), and 2) the ability of certain mite species to become resistant to pesticides (ie. spider mite resistance to Kelthane®, pyrethroids).

Spider mites breed rapidly and can therefore resistant/tolerant strains can develop quickly. Use of products with any single mode of action (particularly on the nervous system) can provide such selection pressure. Theoretical methods used to avoid intensive selection pressure include: 1) Use insecticide/miticides only when mites or plant injury they cause is first detected; 2) Use the lowest effective miticide rates initially, reserving use of increased rates as pest densities increases; 3) Use "long" rotation of miticides with different modes of activity. Use of tank mixtures containing two or more products with different modes of action on the mite's nervous system or use of "short" rotation (use of a product with different mode of activity for every treatment) is believed to select for "multiple resistance".

The twospotted spider mite develops in roughly two weeks (5 to 20 days, depending on temperature and conditions). As an example of a "long" rotation program, could include: 1) a series of applications using one miticide such as Avid® (with or without insecticidal soap) for a two week period (approximate length of one gener-ation) followed by 2) if mites are still present, apply a series of treatments using a miticide with a different mode of action such as Pentac® (with or without insecticidal soap) for another two weeks. Thereafter, a series of treatments using a miticide with yet a third mode of action or reverting back to using Avid could be initiated if needed. Frequency of applications and rates should be based on the presence and density of spider mites, avoiding treatments when mites are undetectable.

Table 1. Mite classification and registered uses for miticides, 1994.

MITES (unspecified), Acari: diazinon, dienochlor, dimethoate, disulfoton (Di-Syston 15G), fenthion, fluvalinate, insecticidal soap, methiocarb, naled, oxamyl, oxydemeton-methyl (Inject-A-Cide, Metasystox-R 2), oxythioquinox (nymphs, adults and eggs), pyrethrins + rotenone, resmethrin, sumethrin

I. spider mites (unspecified), Tetranychidae: avermectin, bifenthrin, dicrotophos (Inject-A- Cide B), horticultural oil, malathion, pyrethrins, resmethrin
...	A. clover mites, Bryobia praetiosa Koch: chlorpyrifos, cyfluthrin, diazinon B. European red mites, Panonychus ulmi (Koch): bifenthrin, diazinon, fenpropathrin C. honey locust (spider) mite, Platytetranychus multidigitali (Ewing): acephate (Acecap 97) D. Pacific strawberry mite(?) (Pacific spider mite, Tetranychus pacificus McGregor; strawberry spider mite, Tetranychus turkestani Ugarov & Nikolski): propargite E. southern red mite, Oligonychus ilicus (McGregor): chlorpyrifos, fenpropathrin, sumithion F. twospotted spider mite, Tetranychus urticae Koch: bifenthrin, diazinon, fenpropathrin, propargite G. "red" spider mites - chlorpyrifos, dichlorvos, petroleum oil, sulfotep
II. false spider mites, Tenuipalpidae
	A. privet mites, Brevipalpus obovatus Donnadieu: diazinon
III. Tarsonemidae
	A. broad mite, Polyphagotarsonemus latus (Banks): bifenthrin B. cyclamen mite, Phytonemus pallidus (Banks): diazinon, endosulfan, propargite
IV. Eriophyidae (bud mites, gall mites, rust mites)(unspecified): carbaryl, sumithion
...	A. carnation bud mite/carnation shoot mite: diazinon B. Fuchia gall mites: carbaryl C. gall mites - horticultural oil D. Taxus bud mites: endosulfan

Table 2. Miticides registered for use on Texas greenhouse* grown ornamental plants, 1994.

SOAPS AND OILS - These materials trap and suffocate small soft-bodied insects and impair the waxy layer on their exoskeleton, resulting in suffocation.
....	horticultural oil (unsulfonated residue of refined petroleum distillate) FOLIAR SPRAY insecticide/miticide - SunSpray Ultra-Fine Spray Oil (Safer Incorporated) CAUTION. insecticidal soap (potassium salts of fatty acids) FOLIAR SPRAY insecticide/miticide. - M-Pede (Mycogen) CAUTION. petroleum oil (dormant/summer oil) insecticide/miticide/ovicide - Volck Oil Spray (Chevron Chemical Company, Ortho Consumer Products Div.) CAUTION.
BOTANICALS - These plant-derived products have various modes of action.
	pyrethrins insecticide/miticide - Xclude Encapsulated Natural Pyrethrum PT 1600A (Whitmire Research Laboratories, Inc.) CAUTION.
DERIVATIVES OF PYRETHRINS - These products destabilize nerve cell membranes and quickly kill arthropods contacted, but are quickly deactivated and have little residual activity
	resmethrin FOLIAR SPRAY insecticide/miticide - PT 1200 Resmethrin (Whitmire Research Laboratories, Inc.) WARNING. sumethrin AEROSOL - PT 1400 Sumethrin (Whitmire Research Laboratories, Inc.) WARNING.
PYRETHROIDS - These materials destabilize nerve cell membranes but are much more stable and can persist in the environment longer than pyrethrins and their derivatives.
	bifenthrin FOLIAR SPRAY insecticide/miticide - Talstar 10 WP (FMC Corporation). WARNING. cyfluthrin FOLIAR SPRAY insecticide/miticide - Decathlon Ornamental Insecticide (Olympic Chemical Company, Inc.). CAUTION. fenpropathrin FOLIAR SPRAY insecticide/miticide - Tame 2.4 EC Spray (Valent) WARNING. fluvalinate FOLIAR SPRAY insecticide/miticide - Mavrik Aquaflow (Sandoz Crop Protection) CAUTION.
CHLORINATED HYDROCARBONS - These materials destabilize nerve cell membranes, preventing them from transmitting nervous impulses.
	dicofol - Kelthane dienochlor FOLIAR SPRAY target-specific miticide. - Pentac Aquaflow (Sandoz Crop Protection). WARNING. endosulfan (organophosphate) FOLIAR SPRAY insecticide/miticide - Thiodan 3 EC (FMC Corporation). DANGER. - Thiodan 50 WP (FMC Corporation). DANGER.
AVERMECTINS - These materials affect the GABA-dependent chloride ion channel and inhibit this nerve transmitter.
	avermectin B1 FOLIARLY-APPLIED LOCAL SYSTEMIC insecticide/miticide - Avid 0.15 EC Miticide/Insecticide (MSD AgVet). WARNING.
CARBAMATE - These materials inhibit cholinesterase and prevent the termination of nerve impulse transmission.
	methiocarb FOLIAR SPRAY, BAIT insecticide/miticide/slugicide (molluscicide) - Mesurol 75% Wettable Powder Insecticide-Molluscicide (Mobay Corp.) WARNING. - PT 1700 Methiocarb (Whitmire Research Laboratories, Inc. DANGER. oxamyl SYSTEMIC FOLIAR SPRAY, SOIL TREATMENT insecticide/miticide/nematicide - Oxamyl 10% Granular (B G Pratt, Miller Chemical & Fertilizer Corp.) WARNING.
ORGANOPHOSPHATES - These products inhibit cholinesterase and prevent the termination of nerve impulse transmission.
	chlorpyrifos FOLIAR SPRAY, DORMANT SPRAY, SOIL TREATMENT insecticide/miticide - Dursban 50 W Insecticides (DowElanco). WARNING. diazinon FOLIAR SPRAY, AEROSOL, SOIL TREATMENT insecticide/miticide - PT 1500R Knox.Out Microencapsulated Diazinon (Whitmire Research Laboratories, Inc.) CAUTION. - PT 265 Knox Out 2 FM (Whitmire Research Laboratories, Inc.). CAUTION. dichlorvos, DDVP FUMIGANT insecticide/miticide - Prentox Greenhouse Spray (Prentiss Drug and Chemical Co., Inc.). DANGER. naled FUMIGANT insecticide/miticide - Dibrom 8 Emulsive (Valent U.S.A.). DANGER.
MISCELLANEOUS COMPOUNDS
	propargite (miticide) FOLIAR SPRAY miticide - Ornamite (Uniroyal Chemical) DANGER. sulfotep (tetraethyl thiodiphosphate) FUMIGANT insecticide/miticide - Plantfume 103 Smoke Generator (Plant Products Corp.) DANGER.

* Miticides and insecticide/miticides registered for ornamental plants but not in greenhouses include carbaryl (Sevin SL, 80S, 50W), dimethoate (Dimethoate 2.67EC), disulfoton (Di-Syston 15G), fenthion (Baytex 4E), malathion (Malathion 5EC), oxythioqu inoxy (Joust Ornamental Miticide, Morstan 25% WP) and sumithion (Pestroy 4EC). Carzol SP Miticide/Insecticide (formetanate, hydrachloride, a carbamate from Nor-Am Chemical Co.) is registered for using in Texas (EPA SLN No. TX-920019) for control of western flower thrips in the greenhouse.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

1994

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Last modified: March 18, 1997 by Edgar Cross