Spider Mites and Conifer Trees

July 18, 2017 Blog Comments Off on Spider Mites and Conifer Trees

Spider Mites and Conifer Trees

Conifer trees are an important part of our landscape. They offer shade, natural beauty, shelter for birds and small animals such as squirrels, and food for the same. Those that grow in our yards or in public places deserve to be cared for to the best of our ability. Keeping them free of disease and destructive pests is as vital to the health of the tree as is watering, pruning, and fertilizing. Educating yourself on the types of destructive pests that can attack and affect your conifer is the first step in giving it proper care.

Spruce Spider Mites are one of the most destructive pests known to attack conifers. They especially like sugar and other pines, western red cedar, spruce, juniper, and arborvitae. The spider mite feeds by piercing the conifer needles with a mouth part and sucking out the liquid contained in the cells of the needles. The result is speckled, discolored needles, stunted tree growth, needle drop, and may even result in the death of the tree. The speckles are tiny, yellowish-green spots at first, then progress to “bronzing,” or browning of the needles. This stage is followed by the needles falling from the tree. Any needles that have turned brown cannot be restored. If a good portion of the tree has turned brown, it will likely need to be taken out and a new tree planted.

Spider Mite Season

Spider mites are active in the spring and fall of the year when temperatures are cooler. After feeding all spring, come the heat of summer they go dormant as “resting” eggs. They revive themselves in the fall when it cools off again to continue their destructive feeding. The damage they do in the spring will likely not show up until fall or even later. By that time it’s too late to do much other than regular watering and mulching to keep your tree as healthy as possible, and of course, try to rid the tree of the spider mites.

Verify Spider Mites Are Present

Spider mites are so tiny it is very difficult, if not impossible, to see them on the tree. To be sure that your tree’s problem is spider mites, check the branches for fine webbing. If you see this webbing, take a sheet of white paper, hold it underneath a branch, then shake the branch over the paper. Wait for 10 seconds or so, then carefully allow any excess debris to slide off the paper. If you have spider mites, you should see tiny black dots moving slowly across the paper.

Smear your finger lightly across the paper. If the streaks left are greenish in color, you have spider mites. If the streaks are red, orange, or yellow, they are predator mites. You may have both. If so, the predator mites will do their job, saving you from having to do it, providing they outnumber the spider mites. If the spider mites are in the majority, you’ll need to step in and help out the predator mites.

Ways to Rid Your Tree of Spider Mites

One cheap and easy way to rid your conifer of spider mites is to just get the hose and spray the tree good and hard with water. This will wash away the adult mites but not the eggs. Spray your tree in this manner for at least four days in a row to get all the mites as they hatch out. To prevent reinfestations, wash your conifer down thoroughly three or four times a year.

Horticultural Oils

Another method of destroying spider mites is to spray the tree with a horticultural oil, such as cottonseed or neem oil. These oils have no residual effects, so spray the tree thoroughly to cover all the mites. The horticultural oil must come into direct contact with the mites in order to kill them. Repeat as often as necessary

Predator Insects

Releasing predator insects such as ladybugs, western predatory mites, lacewings, or western flower thrips onto your infested tree is another way to combat the spider mite problem. These beneficial insects feed on spider mites, thereby ridding your tree of them. Release these insects directly onto the branches that show signs of mite feeding.

Using a Miticide

If your spider mite population is especially stubborn, you may have to resort to using a commercial miticide. If you choose a product that contains kelthane, it will kill the adult spider mites without harming the beneficial insects. Because the miticides available in stores won’t kill mite eggs or the young, spray your tree again within five to 10 days to kill the mites that hatched or matured after the first application.

Other Tree Sprays

Some other sprays available besides the horticultural oils and miticides include insecticidal soap, permethrin, and malathion. The oils and soaps are harmless to the tree and other vegetation in the area, but they will only kill the spider mites that are sprayed directly. Therefore, you must spray the affected conifer thoroughly and more than once. Some of the miticidal sprays may also kill the predatory mites along with the spider mites. The destructive spider mites are likely to regain their ground in your conifer sooner than the predatory mites come back. So it will behoove you to use a method less harsh so you destroy only the spider mites. The less harmful sprays will be a better choice, one that your conifer and its beneficial insects can live with.

By tending to your conifer regularly and examining it periodically for these destructive pests, you will be able to spot and identify a spider mite infestation in its early stages before too much harm has been done. Then you can take immediate steps to eliminate the problem before it progresses. Caring for your tree with regular watering, mulching, fertilizing, and pruning as needed, watching for spider mites and other pests, and signs of disease will ensure that you will have a beautiful, healthy tree to enhance your landscaping for many years to come. Contact Austin Tree Surgeons for additional information.


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