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Integrated Pest Management Manual

Mites

mites

This module is intended to serve as a source of basic information needed to implement an integrated pest management program for mites. Any pest management plan or activity must be formulated within the framework of the management zones where it will be implemented. Full consideration must be given to threatened and endangered species, natural and cultural resources, human health and safety, and the legal mandates of the individual parks. Recommendations in this module must be evaluated and applied in relation to these broader considerations.



Mites are members of the order Acarina, which also includes ticks. Hundreds of species of mites occur in the United States. This module describes life histories and integrated pest management strategies for seven species that have been found to be of greatest concern in the National Park System. Six of the mite species in this package are in the family Tetranychidae (which includes the mites commonly known as spider mites), while the seventh, the eriophyid mites, are in the family Eriophyidae. All are extremely small, requiring a hand lens to determine their presence and numbers. Mites do not have a true head, wings, or abdomen. There are four pairs of legs and a pair of leg-like palps associated with the mouthparts. Mouthparts consist of a pair of needle-like stylets (chelicerae) used to pierce cell walls, allowing the mouth to suck up cell contents. This is important because the type of mouthpart creates the stippled appearance associated with Tetranychid mite injury. The injury caused by Eriophyid mites is much more variable, and includes yellowed foliage, distorted foliage, or a variety of leaf and petiole galls. Mite-feeding injury is often confused with injury caused by insects or air pollution. Refer to Table 1 for more information on differentiating mite and insect injury.


Table 1. Plant pests and diseases which produce injury similar to mites

Pest Symptoms Detection Control/Prevention
Tetranychid mites Leaves or needles get pale yellow to bronze stippled areas at any time from early spring on. Usually on one-year-old growth of broad-leaved and deciduous plants. Tap branches onto white paper and examine with a 10x hand lens for small green or red spiders or shiny round eggs. White cast skins may be seen on leaf undersides. Look for eggs at any time, mites when temperatures are above 50 degrees. Dormant oil in late winter; insecticidal soap, summer oil or miticide at other times as needed.
Ref: Grossman; Johnson and Lyon
Eriophyid mites Yellow to bronze areas at tips of needles or twisted, distorted foliage or witches'-broom. On hemlock, entire plant becomes chlorotic. Many types of leaf or petiole galls on deciduous plants. Look for clear, cigar-shaped mites with a 10x hand lens or microscope. On conifers, they are at the base of the needle under the needle sheath, except on hemlock, where they are found on all parts of needle underside. They are difficult to detect. Insecticide or miticide when present.
Ref: Johnson and Lyon; Keifer et al; Smith (pg 70)
Lace bugs Leaves have yellow to bronze speckled appearance with tar spots on leaf undersides Look for symptoms throughout season. Don't plant host plants in full sun; apply insecticidal soap or registered insecticide when nymphs or adults are active.
Ref: Johnson and Lyon
Leafhoppers/ Planthoppers Stippled, bleached, or distorted foliage. Observation of the pest or its cast skins in mid- and late summer Registered insecticide when insects are active.
Ref: Johnson and Lyon
Thrips Stippled or bleached upper foliage or flowers, often with black frass on injured areas. Stippling often seen in rows Stippling appears from spring on, depending on region and thirps species. Examination of stippled areas with a 10x hand lens shows that leaf tissue has been scraped away. Registered insecticide when insects are active.
Ref: Johnson and Lyon
Ozone injury Large bronze to brown stippled areas seen only on upper surface of leaf. Visual observation of injury is related to a period of poor air quality or a temperature inversion Replace with a resistant variety or species if one is available.
Ref: Sinclair et al.



IDENTIFICATION AND BIOLOGY OF TETRANYCHID MITES


The life cycle of tetranychid mites includes the following stages: egg, larvae, nymph (up to several nymphal instars), and adults. In some species, males are unknown and reproduction is believed to be parthenogenic (Johnson and Lyon 1988; Weidhaas 1979). This means that females give rise to offspring without mating, enabling rapid reproduction and population increases. Because of the large number of generations in a single season, high infestations of mites can develop rapidly (Huffaker et al. 1969; Johnson and Lyon 1988; Helle and Sabelis 1985; Westcott 1973; Yepsen 1984). In general, mites deposit two to twenty eggs in a single day, the exact number determined by environmental factors and the species or strain involved. Silk production by mites varies from species to species, with some producing copious amounts of silk, others little or none.

Habitats for the mite species in this module consist mainly of the foliage of suitable host plants. Larvae and nymphs tend to feed on the underside of leaves, while adults and older nymphs feed on both undersides and tops of leaves as well as occasionally on buds and shoots.

Mites feed by rupturing leaf cells with a pair of needle-like stylets (chelicerae) and inserting the mouth parts to draw up the cell contents while the chelicerae are pushed deeper. Feeding causes small chlorotic spots to appear, which eventually coalesce. Stippling occurs and large portions of the leaf or the entire leaf becomes yellowed, bronzed, or whitened in appearance. Leaf injury on evergreens may last for several seasons; injury on other plants may cause premature leaf drop or may result in the death of the host plant.

Boxwood mite (Eurytetranychus buxi [Garman]). Adults are 1/32" long, yellow green to reddish brown. Eggs are yellow, rounded, with flattened ends. This species produces silk and is found throughout the United States on boxwood, specifically varieties of American and European boxwood (Buxus sempervirens). Japanese boxwood (B. microphylla) is rarely infested. The boxwood mite eggs overwinter on the undersides of leaves and hatch in mid-April. Early nymphs feed on undersides of leaves, second instar mites feed on both sides of the leaf, and third instars move from leaf to leaf to feed. Adults feed on shoots and upper surfaces of leaves. Populations are highest from early spring to early summer, with a second peak in the fall.

Clover mite (Bryobia praetiosa [Koch]). Adults are brownish red to red, 1/16" in length. Eggs are brick red, the nymphs red. These mites are easily recognized under low magnification by their long front legs, which are over twice as long as the other legs, and by the featherlike plates on the body. This species does not produce silk, so the presence of webbing cannot be used as a sign of this pest. Distributed throughout the United States on suitable host plants, clover mites are also common indoors, frequently entering buildings in large numbers in the fall.

Clover mite eggs overwinter in cracks in concrete foundations, between the exterior and interior walls of buildings, and on the underside of the basal bark of trees. These mites also overwinter as adult females or in other life stages. Clover mites can become active at temperatures slightly above freezing. Eggs hatch in late winter or early spring; one generation is usually complete before mid-summer. Males of this species are unknown; reproduction is parthenogenetic (Boudreaux 1963). Most eggs deposited by this generation aestivate until September, but some hatch in early summer and produce several small successive summer generations.

These mites feed on a wide variety of plants including clover, grasses, dandelion, iris, ivy, mallow, strawberry, peas, tomato, violet, and zinnia. A related species, the brown mite, feeds on tree foliage.

European red mite (Panonychus ulmi [Koch]). Adult mites are 1/32" long and velvety red, with four rows of curved hairs on back arising from tan or white humps (tubercles). Eggs and first instar nymphs are bright red; each egg has a single central stalk or hair. Second and third instar nymphs are dull green or brown. This species produces silk and thus webbing is seen at high population levels. European red mites occur throughout the United States on suitable host plants. They feed on apples and other fruits, nuts, and their ornamental varieties. They may occasionally be found on elm, rose, mountain ash, and a variety of other ornamental plants. European red mite overwinter as eggs and hatch in early spring as new growth begins. Feeding activity and plant injury occur throughout spring into early summer.

Southern red mite (Oligonychus illcis [McGregor]). Adult females are 1/32" in length, blackish red, with backward curving spines. Adult males, nymphs, and eggs are light red. This species produces silk. They are common in the southeastern United States, New England, Ohio, and the Great Lakes states but are particularly damaging in the deep south. Southern red mite feed on broad-leaved evergreens, especially Japanese holly, Pyracantha, azalea, and Camellia, as well as other hollies, laurel, and Rhododendron. They overwinter as eggs on the foliage and twigs of their hosts. A cool weather pest, Southern red mite develop damaging populations in early spring and late fall. These mites thought to aestivate in the egg stage during summer, with small populations becoming active during cool periods.

Spruce mite (Oligonychus ununguis [Jacobi]). Adults are 1/32" in length with spines on the back, dark green or reddish green to nearly black with tan legs. Eggs are reddish tan and nymphs greenish with tan legs. Spruce mites produce copious webbing between needles of host plants. They are widely distributed and may be found wherever suitable hosts occur. They attack only conifers; primarily hemlock, spruce, arborvitae, Chamaecyparis, and juniper. Fir and pine are attacked to a lesser extent. This mite overwinters as eggs on the foliage and twigs of host plants. They are most active in cool weather, so tend to increase in numbers and injury levels in early spring to early summer, and again in the fall, while they may go into aestivation to avoid hot, dry weather. Adults may be active in summer during cooler periods.

Twospotted mite (Tetranychus urticae ([Koch]). The common "spider mite." Adults are large (1/8"), and yellowish with two or more predominant dark spots on the back, which is sparsely covered with spines. These spots, which become more apparent as each instar matures, are caused by accumulated food material in the digestive tract. The eggs and nymphs are lemon yellow. They are found throughout the United States, especially indoors and in greenhouses. There are over 250 known host plants including flowers, foliage plants, corn and other field crops, vegetables, brambles, and other herbaceous plants. They can be a serious pest of roses, flowering fruits, and shrubs, and are frequently brought outdoors on plants which were propagated or overwintered in the greenhouse. They overwinter as eggs on host plants and cause damage to host plants throughout the growing season. The warmer the temperature, the greater the rate of feeding and reproduction. The twospotted mite becomes especially destructive during periods of hot, dry weather, but also feeds and reproduces during cooler periods.

The twospotted mite can acquire several plant-infecting viruses during feeding on infected hosts, but has not been shown to transmit them to new host plants (Orlab 1968). Mites that enter houses can create a nuisance to homeowners and can cause stains if they are crushed.


MONITORING AND THRESHOLDS FOR TETRANYCHID MITES

Mite population cycles can be unpredictable, so timing of management practices must be based on observations of the pest. Timing of monitoring for mites is directly related to mite biology. For example, spruce mites may be active anytime temperatures are over 50

F, but once prolonged, hot, dry weather occurs in summer they enter a type of dormancy known as aestivation and generally do not become active again until fall. Aestivation occurs at about the end of June in the mid-Atlantic region, when daytime temperatures are consistently above 80 F. Spruce mite aestivation corresponds to the time when the activity level and generation times of other mite species, such as the twospotted mite, the European red mite, and the southern red mite, are increasing. Consult the information presented for each species as well as the references for more detail on the population cycles of each mite species.

Mites are very small, so they must be knocked off the plants they are feeding on to be counted. This is done by holding a piece of white paper or a clipboard painted white under the plant and striking the branches with a rubber hose or ruler. Generally the plant is struck three to five times before the mites are counted. The number of times that this is done is not as important as doing it the same number every time. Ten to fifteen seconds must pass before examining the clipboard for mites, since it takes this long for them to begin moving after being knocked off their host. Moving dots about the size of a period on this page should be examined with a hand lens to determine that they are indeed mites and to identify the species if possible. Population levels can be measured in a variety of ways, including a simple presence/absence, ranges (e.g., 1-10, 11-20, etc.), or actual population counts. In most cases, estimation of a population range will suffice. Eggs tend to remain attached to the plant, so individual branches must be examined to look for these. Again, estimating relative numbers is more important than an absolute count. The number of eggs relative to the number of adults will indicate if the population is increasing or decreasing.

Mite populations on plants that have cupped leaves, such as Japanese holly, also need to be determined by examination of the individual plant, since mites tend to remain in the cupped leaves when the plant is tapped.

Monitoring for mites is a time-consuming process. If you are willing to tolerate some mite injury, the time required for monitoring can be reduced by focusing monitoring efforts on plants in hot, dry areas, plants which have been under heavy nitrogen fertilization, or plants which have had the most serious problems in the past. If low mite populations are seen on these plants, then monitoring of less susceptible plants can be skipped at that time. This is not recommended if the aesthetic threshold of the plants being monitored is very low (i.e. no injury can be tolerated).

Leaf discoloration and stippling caused by mite feeding can easily be confused with several other insect and disease injury symptoms (refer to Table 1). It is important not to assume that just because stippling is seen, mites are the cause. Mites, eggs, or shed skins on leaf undersides will facilitate a diagnosis. Stippling with tar-like frass on leaf undersides indicates lace bug; lack of frass or mite signs is a clue that the injury is from air pollution.

Once mite activity is detected, a decision must be made as to whether implementation of additional mite management tactics are warranted, and if so, which is most appropriate. While a few action levels for mites have been published (Hamlen et al. 1982; Nielsen 1989), it is unclear how these apply in a generalized way. There is considerable evidence to show that host plant nutrient status and drought stress (Jepsen et al. 1975; Mattson 1980) contribute to host plant suitability as a food source for mites. This means that action thresholds determined under one set of conditions may not be applicable in another system. Published thresholds should be used as a guide, but to modified as the need arises. The resource manager must keep accurate records of mite population levels, plant injury symptoms, soil fertility, and rainfall at the individual park. Relate these to timing and type of management strategies used in the past to determine what works best at a particular site or on a certain plant species.


NON-CHEMICAL CONTROL OF TETRANYCHID MITES

Good mite management combines regular monitoring to detect pest occurrence and timely implementation of the most appropriate management tactics. Monitoring is an essential part of a mite integrated pest management program because injury cannot be seen until after feeding takes place and because mites may be active any time microhabitat temperatures rise above 50 F. This means that even though the ambient air temperatures are below 50 F, mites could be active on certain plants, such as those in sunny locations next to a building.

Cultural Control

As was mentioned earlier, there is a considerable amount of evidence to indicate that mite populations are higher on plants that have been under high nitrogen fertilization regimes (Mattson 1980). Thus, plants that have mites should not be heavily fertilized.

Physical Control

A strong, steady stream of water from a hose will wash mites from the surface of some plant leaves. Prolonged (several hours) periods of heavy rain have the same effect. This is only a temporary measure, most suited to an area where no pesticides can be applied. Adult mites will generally return to the plant within 24 hours.

Biological Control

A vast number of predators and pathogens have been examined for their potential to serve as biological control agents for mites (Helle and Sabelis 1985). Some are currently being successfully used, others show potential, while the feasibility of others seems unlikely.

Mites in the family Phytoseiidae are important predators of plant-feeding mites and have been used in biological programs for several pest species, particularly in greenhouses. Spiders, beetles, flies, thrips, true bugs, and lacewings have all been observed feeding on mites. Species in the lady beetle genus Stethorus are voracious predators of mites and often eliminate infestations of European red mite and spruce mite. However, the control often occurs after the mite populations have peaked (Johnson and Lyon 1988). Tetranychid mites are also susceptible to fungal and virus infections, but no pathogenic bacteria have been reported as occurring in mites. There are no known insect parasitoids of mites (Helle and Sabelis 1985).

Predaceous mites have been used in greenhouses to control twospotted and other mite pests with good results. Predatory mites are available from commercial suppliers. See Anonymous 1991 for a list of sources. Some commonly used predatory mites include the following.

Phytoseiulus persimilis is a predatory mite used primarily in Europe to control mite pests of greenhouse-grown tomatoes, cucumbers, and sweet peppers. It must be released periodically at carefully timed intervals for optimal control. It is used infrequently on greenhouse-grown ornamentals due to lower damage tolerance levels and lack of resistance to pesticides (Field and Hoy 1984).

Insecticidal soap is toxic to the adult predatory mite at rates needed to obtain satisfactory phytophagous mite control. Insecticidal soap can be applied three days after predator release without significantly reducing control, apparently because it does not cause significant egg mortality (Osborne and Petitt 1985). A recent study of the effect of abamectin (a pesticide derived from a bacterial toxin) on this mite and the pest mite, Tetranychus urticae, demonstrated that abamectin will reduce the population of both, with a greater reduction in the population of the pest mite species than in the predatory mite. Thus it could be used in an integrated pest management program to reduce the predator/prey ratio and increase the effectiveness of Phytoseiulus persimilis as a predator (Zhang and Sanderson 1990).

Phytoseiulus macropilis, a related predatory mite, was found by Hamlen and Poole (1982) to give acceptable control on twospotted mite on greenhouse-grown Diffenbachia when applied at a ratio of 1:10 or lower and reintroduced every eight weeks. As with P. persimilis, predators must be introduced into low-density spider mite populations (Samlen and Lindquist 1981).

Mataseiulus (Typholdromus) occidentalis is a predatory mite that has been developed into several strains, one of which is resistant to most organophosphate insecticides and to carbaryl. Another strain does not go into dormancy under low light or short photoperiod conditions. These strains are preferred in that they can prey upon twospotted-mites throughout the year in greenhouses. M. occidentalis is preferred for mite control for ornamentals and long-term crops (such as roses grown for cut flowers) because it gives long-term control from a single release. This predator is unlikely to bring about full control without leaf damage caused by the pest mite; therefore, application of selective acaricides are useful in an integrated program (Field and Hoy 1984). Field and Hoy (1986) suggest that although this species does not give as good control of twospotted mite as does P. persimilis, it would be a better choice as a biological control agent in long-term crops on which pesticides will be used. They suggest that P. persimilis would be a better predator for twospotted mite on short-term crops that are grown with minimal pesticide inputs. For current information on pesticide resistance in M. occidentalis, see Hoy and Conley (1987).


CHEMICAL CONTROL OF TETRANYCHID MITES

Recent advances in the development of horticultural oils have made this the first pesticide to consider in the management of mites (Baxendale and Johnson 1988; Baxendale and Johnson 1989; Davidson 1990; Davidson et al. 1990; Grossman 1990). New oil formulations do not have the problems of phytotoxicity that were so common among older formulations. Their effective control of mite populations with minimal impact on beneficials make them well-suited to an integrated pest management program. A drawback to the use of oils is the necessity of contacting the pest to be killed. Thus oils tend to give unsatisfactory control in dense plantings, on leaves that are cupped (e.g., Ilex crenata `Convexa'), or on plants that are in hard-to-reach areas. In these instances, pesticides with some residual activity could be used. Consult your regional Integrated Pest Management coordinator concerning the best choice of pesticide for your situation.


IDENTIFICATION AND BIOLOGY OF ERIOPHYID MITES

Eriophyid mites are a diverse family of arthropods, containing many species with a wide range of plant hosts and biologies. They can be divided into three categories based on the type of plant injury they cause: galls, twisted, distorted foliage and chlorotic, stunted growth. The gall makers are rarely detrimental to plant health, but are a concern among the public because they are so obvious. In general, the mites that cause these galls overwinter as adults and begin feeding on expanding leaves in the spring. This induces formation of a gall which surrounds the mite as it feeds. Eggs are laid within the gall; nymphs mature within the gall and the emerging adults infest new foliage.

The eriophyid mites that injure foliage have varied life cycles. They are a more serious concern than the gall-makers because they can cause distortion and dieback of plant tissue. Consult Johnson and Lyon (1988) and Keifer et al. (1982) for more information on eriophyid mite life cycles.


MONITORING AND THRESHOLDS FOR ERIOPHYID MITES


Eriophyid mites are often overlooked because they are so difficult to see and because the injury they cause (especially necrosis and dieback) can be attributed to many other causes. Thus, the first part of developing a management strategy for eriophyid mites is the education of plant monitors about this mite's biology and preferred hosts and the injury it causes. Monitors should realize that they will most likely not see eriophyid mites without a microscope, and that they may need to submit a sample to the Cooperative Extension Service for identification.

It is difficult to outline a monitoring program for these mites because the life cycles vary so much depending on the species. In general, monitors should be aware of the types of injury caused by eriophyid mites, and that the mites will be difficult to observe. In conifers, this is complicated by the fact that these mites often feed below the needle sheaths.


CONTROL OF ERIOPHYID MITES

In the case of the gall-making eriophyid mites, no intervention is warranted. Three cases where intervention often is appropriate is on hemlock, privet, and white pine, where these mites can cause considerable injury. In these cases, an insecticide such as acephate is usually recommended (Davidson et al. 1990; Keifer et al. 1982; Smith 1990), since they seem to give better control than oil or other miticides.

There have been many observations of predatory mites occurring in conjunction with eriophyids, but their role in population regulation is unknown (Johnson and Lyon 1988).



REFERENCES


1. Anonymous. 1967. Controlling clover mites around the home. U.S. Department of Agriculture - Agricultural Research Service, Washington, D.C. Home and Garden Bull. 134.

2. Anonymous. 1991. Directory of producers of natural enemies of common pests. IPM Practitioner 8(4): 15-19.

3. Baxendale, R.W., and W.T. Johnson. 1988. Evaluation of summer oil spray on amenity plants. Jour. of Arboric. 14(9): 220-225.

4. Baxendale, R.W., and W.T. Johnson. 1989. Update note concerning horticultural oil concentrations for verdant use. Jour. of Arboric. 15(2): 51-52.

5. Boudreaux, H.B. 1963. Biological aspects of some phytophagous mites. Ann. Rev. Entomol. 8:137-154.

6. Davidson, J.A. 1990. Recommendations for Insect Monitoring and Control: Trees and Shrubs. University of Maryland Cooperative Extension Service, Bulletin 258.

7. Davidson, J.A., S.A. Gill, and M.J. Raupp. 1990. Foliar and growth effects of repetitive summer horticultural oil sprays on trees and shrubs under drought stress. Jour. of Arboric. 16(4):77-81.

8. Field, R.P., and M.A. Hoy. 1984. Biological control of spider mites on greenhouse roses. Calif. Agric. March/April pp. 29-32.

9. Field, R.P., and M.A. Hoy. 1986. Evaluation of genetically improved strains of Metaseiulus occidentalis (Nesbitt) (Acarina:Phytoseiidae) for integrated control of spider mites on roses in greenhouses. Hilgardia 54(2):1-31. 1986.

10. Green, S.G. 1982. Mites. pp. 739-775. In Mallis, A. (ed.) Handbook of Pest Control, 6th ed. Franzak and Foster Co., Cleveland, OH.

11. Grossman, J. 1990. Horticultural oils: New summer uses on ornamental plant pests. IPM Practitioner 12(8):1-10.

12. Hackett, K., and A.E. Giraldi. 1982. IPM binder for azalea lace bug. John Muir Inst. Napa, CA.

13. Hamlen, R.A., and R.K. Lindquist. 1981. Comparison of two Phytoseiulus species as predators of twospotted spider mites on greenhouse ornamentals. Environ. Entomol. 10: 524-527.

14. Hamlen, R.A., and R.T. Poole. 1982. Integrated pest management of spider mites. Southern Florist and Nurseryman. Jan. 8, 1982. pp. 27-29.

15. Herbert, H.J. 1981. Biology, life tables, and intrinsic rate of increase of the European red mite, Panonychus ulmi (Acrina: Tetranychidae). Can. Entomol. 113:65-71.

16. Huffaker, C.B., M. van de Vrie, and J.A. McMurtry. 1969. The ecology of tetranychid mites and their natural control. Ann. Rev. Entomol. 14:125-174.

17. Jepsen, L.E., H.H. Keifer, and E.W. Baker. 1975. Mites Injurious to Economic Plants. University of California Press, Berkeley.

18. Johnson, W.T., and H.H. Lyon. 1988. Insects That Feed on Trees and Shrubs. Comstock Publishing Assoc., Ithaca, N.Y.

19. Keifer, H.H., E.W. Baker, T. Kono, M. Delfindo, and W.E. Styer. 1982. An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America. USDA Handbook 573.

20. Helle, W., and M.W. Sabelis, eds. 1985. Spider mites: Their Biology, Natural Enemies and Control. Vol. 1B. Elsevier Scientific Publishers, New York.

21. Hoy, M.A., and J. Conley. 1987. Toxicity of pesticides to western predatory mite. California Agriculture July/August 1987 pp. 12-14.

22. Mague, D.L., and H.T. Streu. 1980. Life history and seasonal population growth of Oligonychus ililis infesting Japanese holly in New Jersey. Environ. Entomol. 9(4).420-424.

23. Mattson, W.J., Jr. 1980. Herbivory in relation to plant nitrogen content. Ann. Rev. Ecol. and Syst. 11:119-161.

24. Nielsen, D.G. 1989. Integrated pest management in arboriculture: from theory to practice. Jour. of Arboric. 15(2): 25-30.

25. Nielsen, D.G. 1990. Evaluation of biorational pesticides for use in arboriculture. Jrnl. of Arboric. 16: 82-83.

26. Olkowski, W., H. Olkowski, and T. Javits. 1979. The Integral Urban House. Sierra Club Books, San Francisco, CA.

27. Orlob, G.B. 1968. Relationships between Tetranychus urticae Koch and some plant viruses. Virology. 35:121-133.

28. Osborne, L.S. 1984. Soap sprays: an alternative to a conventional Acaricide for controlling the twospotted spider mite (Acari: Tetranychidae) in greenhouses. J. Econ. Entomol. 77(3):734-737.

29. Osborne, L.S., and F.L. Petitt. 1985. Insecticidal soap and the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae), used in management of the twospotted spider mite (Acari: Tetranychidae) on greenhouse grown foliage plants. J. Econ. Entomol. 78: 687-691.

30. Schwartz, P.H. 1982. Guidelines for the control of insect and mite pests on foods, fibers, feeds, ornamental, livestock, and households. U.S. Department of Agriculture - Agricultural Research Service, Washington, D.C. USDA ARS Handbook 584.

31. Sinclair, W.A., H.H. Lyon, and W.T. Johnson. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, NY.

32. Smith, S.L. 1990. Chemical briefing. American Nurseryman 172(4):62-74.

33. Weidhaas, J.A. 1979. Spider mites and other Acarina on trees and shrubs. Jrnl. of Arboric. 5(1):9-15.

34. Westcott, C. 1973. The Gardener's Bug Book, 4th edition. Doubleday and Co., N.Y.

35. Yepsen, R.B. (ed.) 1984. The Encyclopedia of Natural Insect and Disease Control. Rodale Press, Emmaus, PA.

36. Zhang, Z., and J.P. Sanderson. 1990. Relative toxicity of abamectin to the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae) and twospotted spider mite (Acari: Tetranychidae). J. Econ. Entomol. 83(5): 1783-1790.


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