Getting ready for those early insects

It’s never too early to begin scouting your trees and fields for early season pests, such as Zimmerman pine moth and white pine weevil.

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

Zimmerman pine moth in Scotch and Austrian pines

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! (View maps of average dates 50 GDD50 and 100 GDD50 occurs in Michigan for reference.)

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.

Warm days bring out 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 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.

Remember, 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 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. In a few weeks, some of our early season pests will begin their activity. Now is the time you should be planning your scouting and management activities for some of our early season pests.

Tip: Bookmark this web page for maps for average calendar dates in Michigan when particular accumulations of growing degree days base 50 are reached.