How can I remove spider mites from my hemlock bush without toxic sprays?

April 20, 2023 Ask the Expert, Managing Insect, Diseases, and Animal Pests

Question:

How can I remove spider mites from my hemlock bush without toxic sprays?

Hemlock bush
Used with permission by the client.

Answer:

Kate Garland, Horticulturist

Thank you for sending the photos so I can be sure of the plant you’re dealing with. Pesticide products used on the wrong plant can potentially cause serious damage.

Here are two main options to consider from this OSU fact sheet:

  1. “Since rainy weather seems to knock off spider mites, using a forceful jet of water from a hose (syringing) can perform the same task. Regular syringing can keep spider mites under control on most ornamental plants in the landscape. This technique also helps conserve natural predators.”
  2. “Most spider mites can be controlled with insecticidal/miticidal oils and soaps. The oils—both horticultural oil and dormant oil—can be used. Horticultural oils can be used on perennial and woody ornamentals during the summer but avoid spraying flowers, which can be damaged. Dormant oils are actually the same as horticultural oils, but they are used to kill mite eggs and dormant adults in the fall and spring. The insecticidal/miticidal soaps are useful in the warm season. Remember that mites are very tiny and soaps and oils work by contact only. Therefore, thorough coverage of the plant upper and lower leaf surface is necessary for good control.”

Here’s another helpful resource for additional information: https://extension.psu.edu/spruce-spider-mite. Timing is important, so please be sure to read the product label of whatever you end up applying carefully.