Twospotted spider mites in home gardens
How to identify twospotted spider mites
The two-spotted spider mite, Tetranychus urticae, is a type of arachnid, related to insects. Other arachnids include spiders and ticks. All arachnids, including mites, have two main body parts and eight legs.
- They are very tiny, about 1/50th of an inch long.
- Yellow-orange in color, with two dark spots, one on each side of the body.
- When a heavy infestation occurs webbing will also be present.
Biology of twospotted spider mites
Twospotted spider mite attacks 100’s of plants in gardens and landscapes including:
- Fruits, such as blackberry, blueberry, and strawberry
- Vegetables, such as cucumbers, snap beans, peas, tomatoes, and lettuce
- Annuals and perennials, such as lantana, marigolds, New Guinea impatiens, salvia, and viola
- Trees and shrub, such as arborvitae, azalea, spruce, and rose
Twospotted spider mite infestations are particularly common during hot, dry summer weather.
- They live through the winter as eggs on vegetation.
- Larvae hatch and complete development in 1-2 weeks depending on the temperature.
- Under high temperatures (>90°F) colonies can reach high numbers in less than two weeks.
- After hatching, the mites build colonies on the undersides of leaves and produce webbing over infested leave surfaces. This webbing gives them the name “spider” mites.
Damage caused by twospotted spider mites
How to protect your plants from twospotted spider mites
Check plants regularly for spider mites
- Examine plants for stippling and/or webbing.
- Look closely with a hand lens on the underside of discolored leaves for the presence of spider mites.
- You can also hold a white piece of paper or cardboard underneath potentially infested leaves; shake the leaves and look for spider mites that have fallen.
- Check garden plants every 3-5 days, especially under drought conditions.
Keep plants healthy
Spider mites thrive on plants under stress. Keep plants well-watered to reduce the chances of a spider mite attack.
- Most plants should receive about one inch of water a week to avoid stress conditions.
- Conserve moisture through proper mulching.
- Select drought-tolerant plants for locations that are particularly hot and dry.
- Do not fertilize plants during drought, as this can add further stress to plants.
- Do not overwater as this can lead to root rot.
Physically remove them
Use a high-pressure water spray to dislodge twospotted spider mites. This can also wash away their protective webbing.
Natural enemies can reduce twospotted spider mites
Certain species of lady beetles (e.g. Stethorus sp.) and predatory mites (e.g., Phytoseiulus persimilis) naturally control twospotted spider mite populations.
If the twospotted spider mite population is high, natural enemies are less effective at controlling them.
Using long-lasting pesticides like bifenthrin and permethrin kill natural enemies and should be avoided to encourage natural enemies.
There are few pesticides available for use in home gardens and landscapes that are effective against twospotted spider mites.
Insecticidal soap and horticultural oil
Insecticidal soaps are made from potassium salts of fatty acids (don’t make a homemade soap solution as this can burn and damage plants). Horticultural oils are made from either petroleum oils, vegetable oils (like cottonseed oil), or neem seed oil.
Soaps and horticultural oils are reasonably effective against mites and have little impact on people, animals and nontarget insects.
These products will only kill mites that the pesticide directly contacts. They do not have any residual activity.
Target the underside of leaves as well as the top.
Repeat applications may be needed.
Long-lasting insecticides, such as bifenthrin and permethrin can be used on twospotted spider infestations. However, these insecticides also kill natural enemies and could possibly make infestations worse in the long run.
Twospotted spider mite infestations occur when it is hot and dry.
Water plants thoroughly before spraying pesticides for spider mites.
Spray in the early morning or early evening.
These steps will reduce the risk of further stressing plants and causing injury.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
If twospotted spider mites continue to be a problem after control efforts have been attempted, and the plants are valued, consider hiring a landscape professional to treat them. Landscape professionals have the training, experience, and wider array of pesticide products to effectively deal with spider mite infestations.
Jeffrey Hahn, Extension entomologist and Suzanne Wold-Burkness, College of Food, Agricultural & Natural Resource Sciences
How to identify twospotted spider mites Identify and control spider mites found in gardens