Balsam twig aphids hatch in the spring
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.
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 spray is at 100 to 140 GDD50 after the stem mothers have hatched but before the sexuparae (second generation) aphids are present. 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. It is very important to control the stem mothers before they produce the sexuparae. The sexuparae typically feed inside the expanding bud and are well protected from insecticides.
Growers (particularly in the southern half of the Lower Peninsula) that had Fraser or balsam fir trees that were heavily damaged by this aphid last year, should be scouting now. Scout the trees damaged last year, as that’s where you will be most likely to find aphids this year. If you had heavy damage last summer and you are planning to harvest trees this year, you can apply an insecticide this spring. To prevent damage to your trees, you will need to kill the stem mother – this first generation.
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.
Dr. McCullough’s work is funded in part by MSU‘s AgBioResearch.