Symptoms: Damage by spider mites usually results in a discoloration of the leaves or needles into what is called a "stipled" effect. The may have yellow, white or bronze colors mixed randomly in with the green chlorophyll. In extreme cases, there may silken webbing on the leaves, needles or stems. New growth on the plant may be stunted or distorted.
 

Diagnosis: If you see the symptoms mentioned above, you should check for spider mites. Since they are so small, they are difficult to see with the unaided eye. One approach is to take a tablet or clipboard with white paper on it and hold it beneath the suspect foliage. Tap the foliage with your fingers and small green, red or yellow specks will fall onto the paper. If the specks move around, they are spider mites. If not, it is just dust.

As their name implies, spider mites are not insects but are actually relatives of spiders. They have 8 legs instead of the 6 found on insects. They have sucking mouth parts and, during feeding, they pull chlorophyll molecules out of the leaf or needle. This is what causes the stipling color effect.

Different types of mites thrive in different environmental conditions. Some are favored by temperatures above 70 F while others do best in cool, moist weather of the spring or fall. The damage of either type shows up most when the weather is hot and dry and the injured tissues dies.
 

Treatment: Always check to be sure that the spider mites are still present before using any treatment. Often, populations will expand rapidly, cause the damage and then more or less disappear. So, be sure they remain on the plant before reaching for the spray can.

Since they are not insects, not all insecticides will control spider mites. Always check the label of the product to be sure that mites are included. Pesticides called miticides are aimed specifically at this pest but these are often not available in quantities suitable for the home gardener.

Insecticidal soaps may be effective against spider mites. Be sure to apply to the bottom of the leaves since soap products must land on the target critter to work. Sometimes aiming a strong spray of water at the infested area may be enough to know the spider mites off the plant. Driving rain is one reason that they may have already left the plant.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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