By Linda Williams, Forest Health Specialist, Woodruff;
Linda.Williams@wisconsin.gov, 920-360-0665
Have you ever wondered just how much sap can be sucked out of a tree by aphids?
Aphids insert their piercing, sucking mouthparts into needles, twigs or bark, depending on the species of aphid.
Once their mouthparts are inserted, they begin to suck sap and will excrete excess moisture as small droplets of water called honeydew.
A photo of balsam twig aphids with white, woolly filaments excreting drops of honeydew as they suck the sap of a balsam fir. / Photo Credit: Linda Williams, Wisconsin DNR
In spring 2023, a high population of woolly aphids were observed on the twigs of a young spruce tree. These aphids were probably balsam twig aphid, which some sources say can also feed on spruce. The warm, sunny days of spring and early summer, combined with the aphids removing a significant amount of sap from the tree, caused the foliage to wilt severely. Although balsam twig aphids will cause twisting and distorted needles in fir trees, literature says that spruce shows fewer impacts.
If you saw the tree on one of the days when it was badly wilting, you would have thought it was dying. But the aphid population didn’t remain on the tree for long, so it was able to recover with no further impacts observed.
On some plants, you may want to control aphids, so they don’t do significant damage to your plant. Aphids are soft-bodied insects and can easily be killed with traditional insecticides, insecticidal soaps or even a strong spray of water.
Because natural enemies of aphids are plentiful, you may not need to implement control. Insects such as ladybugs, lacewings and wasps enjoy feeding on the soft small morsels of food, and several species of tiny, parasitic wasps attack aphids. On the other hand, ants can “farm” the aphids and protect them from predators and parasitoids, so it’s important to evaluate your situation before deciding on what control methods, if any, you should practice.
A spruce tree’s branches wilt severely after balsam twig aphids fed on the tree. The spruce was able to rebound with no lingering effects. / Photo Credit: Wisconsin DNR