Christmas trees and forestry: Spring’s here, getting ready for early insects

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.  

It has been a long cold, snowy winter, but it will soon be time to think about aphids, adelgids, borers, weevils and other pests. Take time now to walk through your fields and examine your trees carefully. What sorts of insect damage are left from last year? Do you see galls on your spruce trees? Did white pine weevil kill the terminal leaders of some of your pine or spruce trees? How do the needles of your Douglas fir trees look, are they curled or bent from Cooley adelgid? Maybe you see little white pine needle scales or maybe black sooty mold on your Scotch pine needles? Don’t forget to look at the stems of your trees. Big pitch globs on the stem usually mean that Zimmerman pine moth is present.

Good scouting is one of the most important parts of integrated pest management (IPM). It helps you get a jump on insect pests that may cause you problems this year, tell you if the problem is located in one spot or generally across the field, and whether the damage is enough to require treatment. In a few weeks, some of our early season pests will begin their activity. So now is the time to plan your scouting and management activities for some of our early season pests.

Zimmerman pine moth

Zimmerman pine moth is an insect that can be a real problem if you have Scotch and Austrian pine. This insect overwinters as a tiny caterpillar and bores under the bark early in the spring. It will tunnel under the bark for several weeks during the summer causing large soft masses of pitch to flow from the tree. Zimmerman pine moth larvae usually bore into large branches or more commonly, into the stem of the tree, often right at the branch whorls. The tunneling can kill branches, and tree stems may break off above the wound.

If you plan to use an insecticide to control this pest, the insecticide must be on the bark as the caterpillar bores in (25-100 GDD50) otherwise, it will be well protected under the bark for the rest of its life cycle. In addition to applying the insecticide early, it is also important to adequately cover the bark of the stem and large branches. If you are unable to get good coverage, then spraying will not be effective.

Also, we have found that trees attacked the previous year were more likely to be attacked again. This means you need to look for heavily infested, individual trees. Cut and destroy those trees by chipping or burning them as early in the season as possible. That should help remove the most attractive trees from the field and will kill the developing larvae.

White pine weevil

White pine weevil is another insect that becomes active early in the growing season on warm spring days. Overwintering adults move from the litter to the treetops to mate and lay eggs. When we have used the weevil traps, we usually catch our first weevils around 35 GDD50. Controlling this pest involves applying a registered pesticide to control the egg-laying adults. Make sure to thoroughly cover the leader and the upper part of the tree. Then in the growing season when you see leaders beginning to die, clip them out and remove them from the field.

Pales weevil

Be thinking about Pales weevil if you have trees that have sustained damage in the last one to three years. These weevils overwinter as adults in the litter and duff. In the spring, female weevils are drawn to fresh pine stumps to lay eggs. The larvae feed around the root collar and in the big roots of the stump. Adult weevils emerge in late summer to early fall and gnaw away on the bark of shoots. This feeding causes the shoot to die and flag. They will feed on several different conifer species including white pine, Scotch pine, Fraser fir and Douglas fir.

In choose and cut farms that have fresh pine stumps near or mixed in with live trees, growers should remove these new stumps by early spring to eliminate the weevils’ breeding material. If you have a problem with Pales weevil, you may also want to spray the bark area of the stumps cut this past season with a registered, persistent insecticide. This will need to be done in spring, usually sometime between early and late April, depending on your location and the weather. If interplanting trees, keep an eye on newly planted trees for feeding damage.

Cooley's adelgids

Cooley's adelgids will also complete their life cycle on Douglas fir. They do not form galls on the tree. Instead, the adelgids appear to be small, white cottony balls, usually on the undersides of the needles. Their feeding can cause small, yellow necrotic spots on the needles. Again, scouting is important. There are several windows in which you can control this pest. Watch for tiny black nymphs early in the spring. These are the overwintering females. The nymphs will cover their bodies with cottony-appearing white threads where they will lay 10 to 30 eggs. These will hatch around the time that buds are breaking and move to the newly formed needles to continue feeding. The best time to apply an insecticide is when the females and nymphs are out from under the cottony mass. Another spray may be needed in mid-summer, when another generation of nymphs begin feeding on Douglas fir.

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