Hydrangeas are a beautiful flowering plant whose many varieties are enjoyed as an indoor house plant, a colorful addition to a flower garden or as a landscape shrub. Indoor hydrangea plants are not generally subject to infestation, but outside plants are susceptible to caterpillars, aphids and more specifically spider mites. Spider mites can cause distorted growth in new shoots, and infestation is greater during hot, dry and dusty conditions. Females outnumber males three to one and can lay 200 eggs at a time that hatch seven days later.
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Use a magnifying glass to spot spider mites on a houseplant, since they are visible as only small dots with the naked eye. Mites live on the underside of the leaves and their eggs can be seen with the naked eye.
Remove spider mites and their eggs from indoor plants by washing the leaves with an insecticidal soap or horticultural oil, according to package directions. A variety of these products are available at garden centers.
Treat spider mites in an outside garden once weekly by forcefully spraying the underside of hydrangea leaves with a garden hose. Spider mites lay eggs that hatch every seven days and spraying with water drowns them.
Spray the underside of leaves of outdoor hydrangea plants with an insecticidal soap or horticultural oil to remove mites and to inhibit propagation.
Use pesticides only when absolutely necessary to treat spider mites in outside gardens. Spider mites have many natural predators that generally keep the population under control. Use of pesticides that reduce the number of these predators, especially predator spider mites, will result in an increase of pest spider mites.
Purchase predator spider mites and release into the garden to control pest spider mites. Predator mites do not eat foliage and will starve or migrate elsewhere if pest mites are not available as food. Predator mites are available at garden centers and the rule of thumb is one predator for every 10 pest mites.
Wash leaves with clear water after using an insecticidal soap. Use natural methods to control spider mites such as washing and predator spider mites.
Water hydrangea plants regularly to inhibit spider mites since the mites prefer a dry, dusty environment.