Silver flecks on the leaves of your roses and other shrubs, aside from marring the beauty of your landscape, indicate a possible pest problem with spider mites. Nearly microscopic, tiny spider mites suck the sap from the leaves of roses and many other ornamental shrub species, including azalea, arborvitae, juniper and boxwood. They leave tiny, white or silvery flecks that, as damage progresses, gives leaves a bronzed or silvery appearance. You may also observe webbing on infected leaves and branches. Infected leaves may eventually yellow and die, and severe infestations can cause dieback of branches and, eventually, death of the shrub. Controlling spider mites involves progressing through control measures with an emphasis on using chemicals as a last resort.
Confirm the presence of spider mites by holding a white piece of paper under an infected leaf and tapping the leaf to dislodge the mites onto the paper. You may be able to see the tiny mites on the paper, or rubbing your hand across the paper will produce a red streak.
Spray plants with a strong jet of water from a hose upon first detecting spots on the foliage. Aim for the undersides of the leaves where spider mites tend to gather. This dislodges adult mites, their webs and eggs. Continue spraying every few days until mite populations are under control.
Water plants thoroughly prior to applying horticultural oils or insecticidal soaps, low-risk pesticides derived from natural ingredients that can control spider mites.
Spray the foliage of infected shrubs with insecticidal soap. Insecticidal soaps can harm certain plant species, so check the label carefully for restrictions before spraying. If in doubt, test the product on a single leaf two days before treating the entire plant. Insecticidal soaps require contact with the mites in order to work, so thoroughly cover infested areas, such as the undersides of leaves.
Spray the foliage of the shrubs with a summer application of horticultural oil, bringing the oil into contact with mites on the plant. Like insecticidal soaps, horticultural oils can damage some shrubs, especially junipers and cedars, so check the label carefully before application. Apply on a cool day with low humidity to reduce the risk of plant injury.
Apply a miticide labeled for control of spider mites on the plant you're treating.
Things You Will Need
- White sheet of paper
- Insecticidal soap or horticultural oil
- Dormant oil (optional)
- Some spider mite species overwinter on shrubs, especially evergreens. Applications of dormant season horticultural oils before growth resumes in the spring can bring mite populations under control before they have a chance to damage your plants in the spring and summer.
- Mites are not insects and, therefore, most insecticides will not control them. In fact, spraying insecticides in an attempt to control spider mites can worsen the problem by killing insect species that feed on mites, while leaving mite populations unharmed. Only use miticides approved for spider mites and the plant you're treating.
- Avoid pesticides labeled for suppression of spider mites, as these products tend not to be effective.
- Clemson Cooperative Extension; Rose Insects & Related Pests; Janet McLeod Scott; November 2009
- Virginia Cooperative Extension; Spider Mites; Eric Day; May 1, 2009
- Colorado State University Extension; Insect Control -- Soaps and Detergents; W.S. Cranshaw; May 12, 2010
- Colorado State University Extension; Insect Control -- Horticultural Oils; W.S. Cranshaw, et al.; May 12, 2010