Pine Tree Disease: Spruce Spider Mites

Pine trees dying off from the bottom up? Silky webbing on branches and needles? Could be spruce spider mites. Find out more.

This pine tree plant disease is caused by the pest oligonychus ununguis, dark green, black or red mites which are easily seen against a white background. They are one of the most dangerous pests to evergreen trees.

Spruce spider mites cause damage to pine trees which will often have webbing or a silky looking substance on the branches or twigs. Eventually needles become stippled yellow and dirty looking. Mites are either red, black or dark green and their presence can easily be identified by placing a sheet of white paper underneath the needles. By tapping the foliage lightly you will dislodge the spruce mites and they will be readily visible on the sheet of paper. They will appear like pepper grounds, but will quickly begin moving around.

Often damage to pine trees is first thought to be due to pollution damage because major infestations of mites quickly multiply during the growing season. Spider mites first appear between early April but can manifest anytime until late June. They hatch from eggs laid the previous fall and begin rapidly sucking sap from beneath the needles. Damage to young pine trees can be so severe that they die in their first season. Older trees typically do not die unless the spruce spider mites go uncontrolled for several seasons. The first signs of damage to elder trees may be lower branches dying off and damage going upward to the top of the tree.

In order to control spruce spider mites, you will need to spray the infested pine trees with hexakis containing insecticide. You should repeat the application a total of three times, spraying thoroughly. Repeat applications of the hexakis containing insecticide no sooner than every seven days and no later than every ten days. In cases where surrounding trees are infested, but no noticeably so, you may need to respray again later in the season, as pine trees easily become reinfested.

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