Monitoring the health of spruce trees


Colorado Blue Spruce have few pests, but I do suggest that you visit your trees each year. At the end of spring the new growth will be lush and the insect activity will be at its peak. Occasionally a pest population can grow out of control and put stress on the trees. Following is a description of some problems that have been observed in the Airdrie area.

If the new needle growth is ragged or the branches are bare, spruce sawfly larvae may be feeding on the tender needles. The larvae are active in June and early July. They can be hand picked or washed off with a spray of water. If the sawfly population increases from year to year you should consult an arborist to discuss chemical controls.

If the older needles near the trunk at the base of the tree are speckled with brown spots and the tree has a dull gray appearance, spruce spider mite may be feeding on the old needles. Their webbing collects dust and makes the tree look dull. The mites are very small but can be seen if you place a white sheet of paper under a tree branch and shake the branch. Mites are about the size of the period at the end of this sentence. If the dots are moving, you have spider mites. Spraying the trees with a forceful jet of water in June can dislodge or even kill spider mite. If the population is increasing from year to year and you have excessive needle drop, you should call an arborist to discuss chemical control.

Browning of the spruce needles in the spring is often a sign of winter injury. Injury can result from moisture loss due to the chinook winds. The browning starts at the tip of the needle and works its way down. In severe cases the tree may lose needles on one side or over the entire tree. In many cases the buds are still viable and will produce new growth. Watering in September and October will prepare the trees for a mild winter and help prevent winter injury.