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Spider Mites

Spider Mites

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Estimated read time: 4-5 minutes

This archived news story is available only for your personal, non-commercial use. Information in the story may be outdated or superseded by additional information. Reading or replaying the story in its archived form does not constitute a republication of the story.

Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

If your plants are looking stressed right now, the culprit may be almost unseen. Our recent hot weather caused an explosion in the spider mite populations. These creatures have run amuck and are damaging many different plants in your gardens. They are attacking plants that normally show no infestations. If you want to place blame, blame the hot, dry, dusty conditions.

The reason these culprits are almost unseen is because of their tiny size. Spider mite adults are less than 1/50 inch long, which makes them roughly the size of the period at the end of the sentence. They feed on the backside of the leaves and are mostly hidden from view to the casual observer.

Early detection of spider mites, before damage is noticed, is important. The easiest way to detect the mites is to take a piece of white paper and vigorously shake the leaves over it. Look for the dust and if it starts to walk around, you have mites.

Spider mites are not insects, but are closely related to spiders. This genetic difference is very important in controlling the pests. These arachnids have four pairs of legs, no antennae and a single, oval body region.

Spider mites are sucking creatures so their feeding causes tiny yellow or white speckles on the leaves. When feeding damage is severe, the foliage takes on a yellow or bronzed cast. Once the leaves turn bronze, they often drop prematurely. Heavily infested plants may be discolored, stunted or even killed.

Most spider mites can produce fine silk webbing. Web producing spider mites coat the foliage with the fine silk that collects dust and looks dirty.

Many species of spider mites are found in Utah landscapes, gardens and orchards. These include the two spotted spider mite, European red mite and honey locust spider mite. The two spotted spider mite is an example of a 'warm season' mite. This pest has been reported on more than 180 host plants including field crops, ornamental plants, house plants and weeds.

One reason mites are such pests is their tremendous reproduction rate. The females become active in April and May and lay their eggs on the undersides of leaves on suitable hosts. Each female lays more than 100 eggs and produces a new generation in as few as five days to as much as 20 days, depending on the temperature. In a short time, millions of these might be on a single plant.

Mite control measures are often difficult. Times have changed and spraying with ever increasing doses of pesticides is not the best way to manage mite populations.

The following are some control options for spider mites. Start with the first and only move to the next one if you are not successful with the less aggressive methods.

Option 1: Cultural Control - Maintain healthy vigorous plants as an important preventive measure for keeping mite populations low.

Option 2: Syringing or using a strong stream of water can keep spider mites under control on most ornamental plants in the landscape. Wash the underside of the leaves! This technique helps conserve natural predators.

Option 3: Cultural Control: Quarantine and Inspection - Spider mites are often introduced on infested bedding and house plants. When purchasing new plants, inspect the lower leaf surface for any signs of mites. Quarantine new plants until you are sure that no mites are present.

Option 4: Biological Control Option 1 Predators - Numerous insects (lacewings and lady beetles) prey on spider mites. The most commonly sold predators are predatory mites. Some 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 5: Chemical Control "Soft Pesticides" - Most mites are controlled by insecticidal oils and soaps. Horticultural oils can be used on perennial and woody ornamentals during the summer. Higher rates of horticultural oil (3-4 percent) are used for controlling eggs and dormant adults in the fall and spring. Insecticidal soaps are used in the warm season. Soaps and oils are contact insecticides so thorough coverage of the plant is necessary for good control.

Option 6: Chemical Control Miticides Spider mites are not usually controlled by insecticides, so check the pesticide label to see if a "miticide" is present. Insecticides claiming Amite suppression" are usually weak miticides and do not work well. Acephate (Orthene), dimethoate (Cygon), diazinon, disulfoton (Di syston), and malathion have mites on the labels but are considered weak miticides. Dicofol (Kelthane) is registered for homeowner use.

Mites are often serious pests in our gardens. hot dry conditions make them worse. Avoid unnecessary spraying because many insecticides kill the predatory mites. Spraying often makes the problem much worse. Carefully plan your mite control programs to make them effective and to avoid creating more problems. The plants you save may be your own.

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