How to Get Rid of Spider Mites & Aphids

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Aphids and spider mites pierce plant leaves to feed on the juices. A severe infestation will quickly make a plant unhealthy and can ultimately kill a plant. Treat the plants as soon as you find these pests. The sooner you catch and treat the infestation, the easier it is to eradicate.

Aphid Identification

Aphids are small, pear-shaped, soft-bodied insects that can be nearly any color. The adults of some species have wings but most do not. In addition to sucking plant juices, they excrete a clear, sticky substance, called honeydew, which attracts ants. The ants will protect aphids from natural predators to gain access to the honeydew. Leaves of infested plants develop light yellow dots, curl and pucker. Black sooty mold grows on the honeydew.

Tip

  • Grow flowering annuals or perennials that will bloom from spring to fall to encourage the presence of praying mantises and ladybugs. They eat aphids and spider mites.

Spider Mite Identification

Spider mites are so tiny they are barely visible to the naked eye. They can be nearly any color and look like spiders. Use a magnifying glass to identify them or hold a white piece of paper under the plant and tap the branch so they fall onto the paper. They will look like tiny moving dots on the paper. As spider mite infestations progress, some species will spin a fine webbing between the plant leaves and branches. The leaves of infested plants look silvery or bronzed.

Prune Them Out

Prune off leaves or branches that are heavily infested with aphids or spider mites. Use pruners that have been sprayed with household disinfectant to avoid exposing the stressed plant to bacterial or fungal diseases. Rinse the disinfectant off the pruners and dry them before using them. Plants can be damaged by the disinfectant. Put the infested leaves or branches in a plastic bag immediately, seal it and put it in the trash.

Water Well

Water plants and grass during dry periods. Herbaceous perennials, annuals and lawns usually need 1 to 2 inches of water each week. Shrubs and trees often need more water, especially if they are large and the weather is hot. This will help the plants stay healthy and recover more quickly from aphid and spider mite attacks. Also, spider mites thrive in dry conditions while their natural enemies do not. Increasing the moisture will discourage spider mites and encourage spider mite and aphid predators.

Tip

  • Sprinkle talcum powder around the foundation of the house and along window ledges in fall and spring to keep red clover mites from entering the house.

Wash Them Off

Blast the aphids or spider mites off the plants with a strong spray of water from the garden hose. The force of the water will kill most of them and those that survive will have difficulty getting back on the plants. Spray in the morning so the plants will dry before the end of the day. This helps prevent fungal diseases. Spray the undersides of the leaves, where aphids and spider mites often hide, as well as the tops of the leaves and the stems. Spray the plants every few days, if the aphids or spider mites return, until they stay gone.

Reduce Nitrogen Applications

Limit the supply of nitrogen. Nitrogen encourages lush, green growth which aphids flourish on. Use slow-release fertilizer instead of fast-release nitrogen. A common application rate for 18-6-12 slow-release fertilizer is 2 pounds per 100 square feet.

Warning

    • Insecticidal soap and horticultural oil can damage some plants. Spray a few leaves, wait two days then check for damage before treating the entire plant.
    • Although insecticidal soap and horticultural oils are less toxic than other pesticides, wear long sleeves, long pants, gloves and eye protection when working with them.

Use Pesticides as a Last Resort

Insecticidal soap or horticultural oil can be used to get rid of stubborn aphid and spider mite infestations on perennials, annuals, shrubs and trees. These sprays only work when they cover the pests -- there is no residual effect. They are sold in ready-to-use and concentrated forms. Dilute insecticidal soap and horticultural oil concentrates at a rate of 5 tablespoons in 1 gallon of water, or according to the the label instructions. Pour the mixture into a garden sprayer. Spray the plants thoroughly, especially the undersides of the leaves, until they are wet but not dripping. Treat plants in the morning or evening when temperatures are below 90 degrees Fahrenheit. Rinse insecticidal soap off the plants with water from the garden hose after an hour or two to help prevent damage to the leaves. Spray the plants again after a week or two if the aphids or spider mites return.

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