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Spider mites are not insects but are more closely related to spiders. Learn about the different insects and pests that affect gardens, lawns and food crops, and how to deal with them. |
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Spider Mites and Their Control
Spider mites are not insects but are more closely related to spiders. These arachnids have four pairs of legs, no antennae and a single, oval body region. Most spider mites have the ability to produce a fine silk webbing. Spider mites are very tiny, being less than 1/50 inch (0.4mm) long when adults.Submit your comments, tips, or suggestions you'd like to share with other users regarding this article. Reference: Ohio State University Extension
Many species of spider mites can be found in Ohio landscapes. The twospotted spider mite, Tetranychus urticae (Koch), and spruce spider mite, Oligonychus ununguis (Jacobi), are the most common pests. Other species with fewer host plants include: European red mite, Panonychus ulmi (Koch), found on apple trees; honeylocust spider mite, Platytetranychus multidigitali (Ewing); southern red mite, Oligonychus ilicis (McGregor), on a variety of plants; boxwood spider mite, Eurytetranychus buxi (Garman); and the oak mite, Oligonychus bicolor (Banks). Types of Damage Heavily infested plants may be discolored, stunted or even killed. Web producing spider mites may coat the foliage with the fine silk which collects dust and looks dirty. Life Cycles and Habits All spider mites go through the same stages of development. Adult females usually lay eggs on their host plants. The eggs hatch in days to weeks into the first stage, called a larva. Larvae are round bodied and have only three pairs of legs. The larvae feed for a few days, seek a sheltered spot to rest and then molt into the first nymphal stage. The first nymph now has four pairs of legs. The first nymphs feed a few days, rest and molt into the second nymph. The second nymphs feed, rest and molt into the adult stage. The males are usually the size of the second nymph and have pointed abdomens. The females have rounded abdomens and are the largest mites present. Most spider mites spend the winter in the egg stage but the twospotted spider mite overwinters as adult females resting in protected places. Twospotted Spider Mite The twospotted spider mite is an example of a 'warm season' mite. This pest has been reported from over 180 host plants including field crops, ornamental plants, house plants and weeds. The females overwinter in the soil or on host plants. The females become active in April and May when they seek out the undersides of leaves on suitable hosts. Each female may lay over 100 eggs. A single generation may require as much as 20 to as few as five days, depending on the temperature. These mites prefer hot, dry weather and often do not reach damaging populations in cool, rainy periods. In the summer, the adults and nymphs are white with two greenish spots. However, overwintering females usually turn reddish-orange and can be mistaken for other mite species. Spruce Spider Mite This mite spends the winter in the egg stage attached to host plants. The eggs hatch in March to April and the mites can complete development in 3 to 4 weeks. If summer temperatures are constantly over 90 F, this mite becomes dormant and lays resting eggs. These eggs and adults resume activity in the fall when cooler temperatures return. Conifers often react slowly to the feeding of this mite. Yellowing and bronzing of the needles may not become apparent until the heat of the summer, even though the damage may have occurred the previous fall and spring. Control Strategies Option 1: Cultural Control - Syringing Since rainy weather seems to knock off spider mites, using a forceful jet of water from a hose (syringing) can perform the same task. A regular syringing can keep spider mites under control on most ornamental plants in the landscape. This technique also helps conserve natural predators. Option 2: Cultural Control - Quarantine and Inspection The twospotted spider mite is often introduced on infested bedding and house plants. When purchasing new plants, carefully inspect the lower leaf surface for any signs of mite activity. New house plants should be quarantined from other plants until you are sure that no mites are present. Option 3: Biological Control - Predators There are numerous insects (lacewings and lady beetles) that prey on spider mites. However, the most commonly sold predators are other types of mites. Predatory mites (usually Phytoseiulus spp., Amblyseius spp. or Metaseiulus spp.) can be purchased and released onto infested plants. Be sure to check listings to determine which species is appropriate. Some species are host specific and each predator works better under different weather conditions. If predators are used, do not apply pesticides that will kill them. Option 4: Chemical Control - "Soft Pesticides" Most spider mites can be controlled with insecticidal oils and soaps. The oils, both horticultural oil and dormant oil, can be used. Horticultural oils can be used on perennial and woody ornamentals during the summer at the 1 to 2 percent rate. Higher rates of horticultural oil (3 to 4 percent) or dormant oil are useful for killing mite eggs and dormant adults in the fall and spring. The insecticidal soaps are useful in the warm season. Remember that mites are very tiny and soaps and oils work by contact only. Therefore, thorough coverage of the plant is necessary for good control. Option 5: Chemical Control - Miticides Spider mites are usually not killed by regular insecticides, so be sure to check the pesticide label to see if "miticide" is present. Pesticides claiming "for mite suppression" are usually weak miticides and will not perform well. There are few products available to the homeowner. Dicofol (=Kelthane) is registered for over-the-counter use but is difficult to find. Acephate (=Orthene), dimethoate (=Cygon), chlorpyrifos (=Dursban), diazinon, disulfoton (=Di-syston), and malathion have over-the-counter product labels but are considered weak miticides. Avermectin (=Avid), bifenthrin (=Talstar), dienochlor (=Pentac), fenbutatin-oxide (=Vendex), fluvalinate (=Mavrik), oxamyl (=Vydate), oxydemeton-methyl (Metasystox-R), oxythioquinox (Morestan), and propargite (=Omite) are restricted use pesticides available only to licensed applicators.
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| Data Source: Ohio State University Extension. Articles and resource may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide and it is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. |
