Look out for these Christmas tree pests during mid-May

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included. 

Mites

We are starting to find spruce spider and eriophyid mites on spruce, Fraser and concolor fir. Although the insects may be actively feeding by now, we often don’t see damage until later in the June or July.

Spruce spider mites

Spider mites have tiny mouthparts modified for piercing individual plant cells and removing the contents. This results in tiny yellow or bronze speckling on the needles. When many of these feeding spots occur near each other, the foliage takes on a yellow or bronzed cast. Once the foliage of a plant becomes bronzed, it often drops prematurely. Growers should keep an eye out for the dark mites or their webbing, especially if you had damage from mites last year. Scout the oldest foliage, near the stem of the tree – that’s where the mite populations build up first. Rap foliage over white paper or cardboard on a clipboard. If mites are there, you should see them moving on the paper.

Eriophyid mites

Eriophyid mites are very tiny, carrot-shaped and cream-colored. In order to see them, you need at least a 10x handlens. Even then, the insects are barely noticeable. Eriophyid mites discolor and distort foliage by feeding on the buds and needles. Look for pale yellow to bronze needles. This damage can be confused with other symptoms from drought, winter or herbicide injury, etc. If you see this type of damage, you may want to send a sample into MSU Diagnostic Services to confirm whether or not you have Eriophyid mites.

Pine needle scale

Applying insecticides at the proper time is a key element in controlling pine needle scale. Pine needle scale is most vulnerable to insecticides during the crawler stage. Although crawlers are tiny, they are readily visible on the needles, especially if you use a hand lens or magnifying glass. The ideal time to apply an insecticide spray is after nearly all the pine needle scale eggs have hatched and most crawlers have reached the hyaline stage. At this point, the young crawlers are exposed on the needles and have not yet started to produce the hard, white armor. Spring generation eggs hatch in May or early June at roughly 300 GDD50. Usually eggs hatch within about a week and most crawlers should be in the hyaline stage by 400 to 500 GDD50.

Eastern spruce gall adelgid

In the southern Lower Peninsula, the pineapple-shaped, green-to-purple galls caused by Eastern spruce gall adelgid should be visible at the bases of new shoots of white, Black Hills or Norway spruce. With small populations, you can clip off and destroy the green galls now before they turn brown and open in late July. If you have an unacceptable amount of damage, your next control window is this fall.

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