Keep conifers vigorous and healthy to prevent pest problems.

How to Kill Spider Mites on Conifers

by Marylee Gowans

Spider mites are annoying sap-sucking insects that cause conifer needles to brown, dry and drop from the plant. Thankfully, spider mites are not a serious problem. Unfortunately, many chemical pesticides used to treat spider mites can actually cause more harm than good by eliminating predatory insects. Less toxic insecticides are available and -- when used in conjunction with cultural care and organic methods -- can effectively control spider mites on conifers without harming beneficial insects.

Hose conifers off to dislodge spider mites from the plant. Do this weekly to control small infestations of spider mites.

Wait for a calm, dry day when temperatures are not below 40 degrees Fahrenheit and will not exceed 90 degrees Fahrenheit. Put on rubber gloves and safety goggles.

Mix 1.3 fluid ounces of horticultural oil per gallon of water if treating the conifer during the summer months. Alternatively, mix 2.6 fluid ounces per gallon of water if applying during the dormant period.

Pour the horticultural oil into a pump sprayer. Coat the entire conifer -- including the needle sheaths -- with the diluted insecticidal soap. Repeat the treatment every two weeks, but don’t apply more than four times during the growing period.

Items you will need

  • Water hose
  • Rubber gloves
  • Safety goggles
  • Horticultural oil
  • Pump sprayer


  • Never apply pesticides to water-stressed plants.
  • Follow the manufacturer’s directions and warnings on the insecticide label for best results.


  • Horticultural oil may discolor the needles of blue-colored conifers.

About the Author

Marylee Gowans has written about gardening for both online and print publications. She attended the University of Akron, graduating with a Master of Fine Arts in creative writing. In 2009, she received master gardener certification from the Master Gardeners of Summit County, Ohio.

Photo Credits

  • Comstock/Comstock/Getty Images