Oh, those 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.
With the warmer March temperatures, many of the early insects are starting to wake up and begin rocking and rolling. Looking at growing degree information on Enviro-weather it appears that in some areas we are about normal and other about a week or two ahead of schedule.
Zimmerman pine moth is an insect that can be a real problem if you have Scotch and Austrian pines. 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. If you don’t see any boring dust, larvae have probably not become active and you still have time to treat. If you do see the boring dust, it may be too late for sprays to do much good. With this pest it is better to be early than too late.
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 is another insect that becomes active early in the growing season on warm spring days. Over-wintering 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. The adult weevil makes a small round feeding puncture on the terminal lead. You may see a little resin oozing out of the holes, but otherwise you won’t notice the feeding. However, every time a female weevil feeds, she lays an egg or two in the feeding hole. Over a few weeks, a single weevil may lay up to 200 eggs on the terminal. The eggs will hatch in a couple of weeks and larvae will bore into the terminal. They feed in the cambium area, just under the bark. 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.
Scouting is important. Take time now to walk through your fields and examine your trees carefully. What sorts of insect damage are left from last year? Bronzing foliage from spider mites? 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, tells you if the problem is located in one spot or generally across the field, and whether the damage is enough to require treatment.