Spider Mites

Spider mites are common pests in the urban landscape and can inflict serious damage to trees, shrubs and flowers. Both evergreen and deciduous plants may be attacked. Spider mites are not insects but are more closely related to ticks and spiders. Their common name is derived from their ability to produce silk, which most species spin on host plants. Mites are tiny—about the size of the period at the end of this sentence. They can also be very prolific, which is why infestations often go unnoticed until plants exhibit significant damage.

Spider mites have needle-like mouthparts and feed by piercing the leaves of host plants and sucking out the fluids from individual plant cells. This causes the leaves to have a stippled or flecked appearance, with pale dots where the cellular contents have been removed. Prolonged, heavy infestations cause yellowing or bronzing of the foliage and premature leaf drop similar to drought stress. Severely-infested plants may be stunted or even killed. Most of the mites feed from the undersides of leaves, although the damage is most evident from the upper surface.

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

Elimination of moderate to heavy infestations of spider mites usually requires the use of specific pesticides known as miticides. Some, but not all, insecticides will also control mites. Some kill only active mites while others also kill eggs. Always read and follow the directions accompanying the product you are using. Some miticides may harm or discolor certain types of landscape plants.