Spider Mites Information
Species & Identification
Spider mites are problematic pests of many ornamental plants. They fall into the categories of warm- and cool-season mites depending on when they are active.
Warm-season mites are problematic in the summer months. The twospotted spider mite is the most common spider mite species on ornamental plants. This species affects a wide array of plants. Although they vary greatly in body color, individuals generally have a dark spot on each side of the body. The Lewis mite is most common on poinsettias and strawberries and looks like the twospotted spider mite, but the Lewis mite has more spots on its body.
Cool-season mites are more problematic in the fall and spring. The spruce spider mite commonly infests conifers and is black or tan in color. The southern red mite mainly affects woody plants, has a red-purple colored body, and lays red eggs.
Damage & Symptoms
Spider mites puncture leaf cell walls and suck out the cell contents. The empty plant cells appear silvery, which creates stippling on infested leaves. Severely stippled leaves appear bronzed or bleached. Spider mites are capable of producing silken web. Plants may become covered in webs when infestations are extremely severe. Spider mites damaging growing terminals can also cause distortion in growth.
Life Cycle
Eggs are laid on the underside of leaves. Eggs are spherical and clear at first, but the color changes to match that of the spider mite developing inside the egg. Hatchlings have three pairs of legs. They gain a fourth pair of legs as hatchlings develop through the next two instars and become adults. All spider mite life stages can be found on the underside of leaves, but as the infestation becomes more severe, individuals can also be found on the upper side of leaves. All spider mite species can complete development from egg to adult within one week. Each female can produce up to 100 eggs in her lifetime.
Scouting
A 10 to 15 times magnification hand lens is necessary for mite detection and identification. The most obvious symptom for detection is the stippling on the leaves. If stippled leaves are found, flip over the leaves and look on the underside with the hand lens to check for mites and determine their abundance. One could also hold a piece of white paper underneath leaves or branches and sharply strike the plant to dislodge any possible mites. Creatures and debris collected on the white paper should be examined with a hand lens to detect the presence of spider mites.
Cultural Control
Plants covered in webs from a severe infestation of spider mites should be discarded immediately, and neighboring plants should be treated immediately as well. Maintaining healthy plants can help them withstand a low level of mite infestation. Forcefully spraying plants with water may dislodge spider mites but is not a sole management tool for managing infestations. Wetting pathways to reduce dusty conditions may help reduce spider mite population growth (spider mites prefer a dry environment), but additional research is needed to fully evaluate this practice.
Biological Control
Native predators and some mass-reared and commercially available predatory mites may help control spider mite populations on ornamental plants grown in the outdoor environment. It is often not practical to purchase biological control agents and release them in outdoor landscapes. The most practical approach to enhancing biological control in outdoor landscapes is to reduce the use of broad-spectrum insecticides and miticides, which can reduce the existing population of natural enemies and cause a spider mite outbreak. Release of commercial biological control agents can be successful in managing spider mite infestation in greenhouses and nurseries. Biological control agents available for purchase include several predatory mite species (Amblyseius andersoni, Galendromus occidentalis, Mesoseiulus longipes, Neoseiulus californicus, Neoseiulus fallacis, and Phytosieulus persimilis), predatory midge (Feltiella acarisuga), and predatory beetle (Stethorus punctillum). The predators are most effective when they are released against a small spider mite population. The predators should be provided with their favorable environmental conditions and be protected from the application of broad-spectrum pesticides to ensure their success.
Chemical Control
Pre-plant dip of liners and seedlings with horticultural oil (0.1%) or a mix of insecticidal soap (0.5%) and Beauveria bassiana are effective in reducing spider mites and keeping a relatively low density of spider mites on the crops for up to 8 weeks after the dip. Miticides should be applied foliarly as soon as mites or their damage are detected to avoid permanent damage. Always check labels for application instructions and susceptible mite species and life stages. Mites have a high possibility of developing resistance to miticides. Therefore, one should use a miticide of different IRAC numbers at each application. When biological control is practiced, miticides that are compatible with the biological control agents should be used to avoid a negative impact on the survival and effectiveness of the biological control agent. Consult with your biological control agent suppliers for compatibility information.
Selected Insecticides for Spider Mite Control
Here are some selected insecticides for controlling spider mites:
- Horticultural Oil (0.1%): Effective as a pre-plant dip for liners and seedlings.
- Insecticidal Soap (0.5%) and Beauveria bassiana: A mixture effective in reducing spider mites for up to 8 weeks after application.
- Miticides: Apply foliarly as soon as mites or damage are detected. Rotate miticides with different IRAC numbers to prevent resistance.
- Compatibility with Biological Control Agents: Use miticides that are compatible with biological control agents to ensure their effectiveness.
