Spring has sprung: Look out for balsam twig aphids and Cooley and Eastern spruce gall adelgids
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 warm temperature this week, growing degree days are starting to accumulate quickly. If you had problems with balsam twig aphid, Cooley and Eastern spruce gall agdelgids you should start thinking about scouting and if needed applying a pesticide. To check where you are with degree days go to Enviroweather - http://www.enviroweather.msu.edu/homeMap.php
Balsam twig aphid
Balsam twig aphid eggs begin to hatch early in spring, typically around late March to mid-April, depending on temperatures and location within the state. Hatching is completed in one to two weeks. Studies in Michigan showed that egg hatch began at roughly 60 to 70 GDD50 and continue until approximately 100 GDD50. The newly hatched aphids are very small and difficult to see, but by mid- to late April, at approximately 100 to 140 GDD50, they have grown enough to be easily visible against a dark background. These first-generation aphids are called “stem mothers.”
Target the stem mothers
When spraying is necessary, it is critical to apply insecticides at the proper time to prevent damage to current-year foliage. The ideal time to target your pesticide application is between 100 to 140 GDD50. It is very important to control the stem mothers before they produce the sexuparae. Typically at this point, buds are swelling but have not yet broken, and the stem mothers have hatched and are exposed at the ends of the shoots. The sexuparae typically feed inside the expanding bud and are well protected from insecticides.
Growers that had Fraser or balsam fir trees that were heavily damaged by this aphid last year, should be scouting now. A simple sampling device consisting of an embroidery hoop covered with black cloth can be used to effectively scout your trees. Hold the hoop in the middle part of the tree canopy and rap the shoots at least three times with a wooden dowel. You will be able to easily see the white to greenish stem mother if they are present. Scouting will help you determine when most of the stem mothers have hatched. Scout the trees damaged last year, as that's where you will be most likely to find aphids this year.
Keep in mind, however, that if aphid populations are not very high and you did not have heavy damage last year, you probably don't need to spray. There are many different kinds of predators that will be happy to feed on your aphids, all summer long.
Left, Balsam twig aphid. Right, Balsam twig aphid damage.
Balsam twig aphid stem mother.
Cooley and Eastern spruce gall adelgid
Cooley's and Eastern spruce gall adelgids are the sap-feeding insects that cause galls to form on the shoots of Colorado blue spruce (Cooley's adelgid) and white spruce (Eastern adelgid). If you had lots of galls on your spruce trees last year, the best time to apply an insecticide is when the buds are swollen, and the buds have not broken. With both of these adelgids the first adults become active at 25 to 120 GDD50. Scout your spruce fields, examining for adelgid activity at the base of the terminal buds for Cooley and the terminal and lateral buds with Eastern.