Mealy Plum Aphids

Credit: James K. Lindsey/ Wikipedia

Q: I have what looks like either aphids or tiny white flies on my prune plum there are hornets all over eating them is this ok will the hornets eradicate them?

These sound like mealy plum aphids, which are small and whitish green, and could easily look like whiteflies. The hornets are likely attracted by the sweet honeydew produced by the aphids, which drips onto the leaves beneath the aphid colonies. Feeding by the aphids cause the leaves to curl up, cupping the aphid colonies inside. Sometimes, especially in drought stressed trees, the leaves at the tip of nearly every shoot may show aphid attack. In mid-summer, the plum aphids all fly away from the trees to infest reed grasses or cattails. Adult aphids return to plum trees in the fall to lay their eggs. There are many natural enemies of aphids (lady beetles, hover flies, aphid midges, parasitic wasps, lacewings), however, their numbers may not be high enough in early summer to control the aphid infestation. If there are a lot of curled leaves and if the aphids are still present on the tree right now, you can try blasting the leaves with water spray to knock aphids off. Check before you do this as by now the aphids may have largely departed the trees, leaving only damaged and sticky leaves behind. This particular aphid overwinters as tiny eggs laid around the base of leaf buds therefore applying a dormant oil spray next winter can be quite effective at controlling the population for next year.