As the weather begins to warm, growers should be on the lookout for several early insect pests such as white pine weevil and Zimmerman pine moth.
Posted on April 17, 2014 by Jill O'Donnell, and Erin Lizotte, Michigan State University Extension
White pine weevil adults mating. Notice very small punctures on the leader and sap droplets associated with spring feeding and egg deposition. Photo credit: Daniel Herms, OSU, www.cnchemicals.com
White pine weevil
White pine weevil is an insect that becomes active early in the growing season on warm, spring days. Over-wintering adults move from their overwintering sites in the litter and climb up the tree trunk to the leader where they mate and lay eggs. The adult female weevil carves out a small, round hole in which she lays one or two eggs. You may see a little resin oozing out of these feeding and egglaying holes, but otherwise may not notice the feeding. Over a few weeks, a single weevil may lay up to 200 eggs on the terminal. The eggs hatch within a couple of weeks and larvae will bore into the terminal to just under the bark to feed in the cambium area.
There are a couple of methods Michigan State University Extension recommends to detect when adults begin to emerge in the spring. Research in Pennsylvania has shown that emergence begins once soil temperatures in the top 2 inches were above 50 degrees Fahrenheit. Check out the data from your nearest MSU Enviro-weather station to see what the soil temperatures in your area have been or purchase a soil temperature probe for use on your farm.
Growers may also try using tedder traps to detect white pine weevil adult activity. Historically, we have trapped the first weevils in Michigan around 35 growing degree days (GDD) base 50. Place tedder traps next to trees that were damaged the previous year. Weevils over-wintering at the bases of the trees are attracted by the scents of alcohol and turpentine that mimic the odor of pine trees. Tedder traps can also be purchased through Great Lakes IPM in Vestaburg, Mich.
Controlling white pine weevil involves applying a registered pesticide to control the egglaying females in the spring. Growers should make sure to thoroughly cover the leader and the upper part of the tree. Growers can also reduce future populations by removing dead and dying leaders that contain the developing larvae, effectively interrupting their lifecycle. Dead leaders should be removed from the field and burned or buried to prevent infestation.
Zimmerman pine moth
Zimmerman pine moth is another insect that can be a real problem if you have Scots and Austrian pine. This insect overwinters as a tiny caterpillar and bores under the bark early in the spring. The larvae will tunnel under the bark for several weeks during the summer causing large, soft masses of pitch to flow from the tree.
Pitch mass from Zimmerman pine shoot moth on the trunk of an Austrian pine. Photo credit: Rayanne Lehman, Pennsylvania Dept. of Agriculture, www.cnchemicals.com
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. 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.
If you plan to use an insecticide to control this pest, the insecticide must be present 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 lifecycle and not susceptible to pesticide application. If you are unable to get good coverage, then spraying will not be effective.
This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).