Spider Mite Problems

The two-spotted spider mite is the most common and destructive mite on deciduous ornamentals. It feeds on many varieties of trees, shrubs, flowers, weeds, fruits, and garden crops. Immature stages and adults are yellow to green with two dark spots on either side of the body. The spherical eggs are translucent. Strands of webbing spun by the mites can cover infested leaves and stems.

Figure 1. Two-spotted spider mites and eggs (Photo: Lee Townsend, UK)

Figure 1. Two-spotted spider mites and eggs (Photo: Lee Townsend, UK)

Two-spotted spider mites overwinter as adult females in the soil or under the bark of host plants. They become active during the spring and may feed and reproduce throughout the summer and into fall provided conditions remain favorable for plant growth. It is considered a warm season mite that thrives under hot, dry summer conditions. Damaging populations seldom develop during wet, cool weather.

Scouting for Spider Mites

Timely inspection of susceptible landscape plants, especially during periods favoring mite outbreaks is key to preventing serious damage. Pay particular attention to plants having a history of mite problems. Spider mites often re‑infest plants year after year.

Inspect stippled and distorted leaves to determine if mites are present. Thrips, leafhoppers, and lace bugs can cause similar symptoms. Spider mites prefer to feed on the lower leaf surface, so examine there first. A 10X to 20X hand lens is essential for clearly seeing the mites. Also visible on the leaf surface may be pale‑colored cast “skins” shed by developing mites, as well as the eggs.

An efficient way to sample vegetation for mites is to hold a sheet of white paper or foam board under a branch and tap or shake the foliage sharply. If mites are present, some will be dislodged and appear as slow‑moving, dark specks on the paper.

Management

Spider mite infestations are easiest to control when detected early, before the mite populations have reached very high levels.

  • Spraying plants with a strong stream of water from a garden hose can dislodge many. The approach is generally more effective on smaller plants with open foliage and low mite populations. Water sprays should be directed upward against the lower leaf surface. Repeat as needed.
  • Low populations of spider mites may be held in check by naturally occurring predatory mites that feed on both eggs and active stages.
  • Homeowner options include horticultural oils, and insecticidal/miticidal soaps. Products such as Bon-Neem Insecticidal Soap, Green Light OMRI Listed Insect/Disease Control, Bayer Natria Insect, Disease, and Mite Control (with sulfur) and Ortho Elementals Garden Insect Killer with pyrethrins and canola oil can be used for mite control on ornamentals and vegetables. Bayer 3-in-1 Insect, Disease, and Mite Control is an option for trees, shrubs, and flowers. Spectracide Triazicide Insect Killer Once & Done is labeled for spider mite control on a range of ornamental trees, shrubs, and flowers.
  • Good spray coverage is essential when treating for mites. Thoroughly wet the foliage and try to contact as many mites as possible. Pay particular attention to leaf undersides where most mites are living. In most cases, two or more applications at 5 to10 day intervals will be needed for satisfactory control.
  • Multiple applications of carbaryl or many of the pyrethroid insecticides can trigger mite outbreaks, as can systemic use of imidacloprid drenches.

 

By Lee Townsend, Extension Entomologist

 

Posted in Landscape Trees & Shrubs, Ornamentals