Even though it's late in the season, we're still getting a lot of questions about wasps swarming trees—especially poplars, aspen trees, and some evergreens.
Most visitors asks which insecticides are best for getting rid of wasps, and, yes, our line of Knock Down insecticides will do the trick. But the wasps are not actually the problem: aphids are.
Aphids are insects which suck on the leaves of trees to get to the protein inside. They're especially fond of trees weakened by underwatering. Weak trees are easy targets and underwatering makes the protein in the leaves less diluted and even more concentrated. Yum!
Aphids are messy pests and they leave a sticky, sugary mess of "honeydew" on the outside of the leaves they siphon. The wasps, in turn, are attracted to this sodapop-sweet honeydew, and start swarming the trees.
To complicate matters even further, ants will sometimes join the mess and begin to "farm" the aphids and move them around from branch-to-branch or from tree-to-tree.
Many other stores will be happy to recommend wasp insecticide right off the bat, and it will fix the problem temporarily... until new wasps move in. But to really fix the problem, you need to treat the aphids.
So whenever somebody comes into our greenhouse complaining of wasps, we always ask them a few more questions to find out if the issue is really wasps or if they're just a side-effect of a larger aphid issue.