Aphids in Abundance

Several aphid species appear to be in greater-than-average abundance so far this summer. This includes the leafcurl ash aphid, a minor annoyance that cause the leaves on the ends of green ash twigs to tightly coil into a gnarled mess, the pine bark aphid discussed 3 weeks ago, and two or more species of aphids on maple foliage.

Leafcurl ash aphid is annoying and aesthetically displeasing but does not have a significant impact on otherwise healthy trees. I suggest pruning out the deformed terminals that can be reached and ignoring the rest. Only systemic insecticide sprays would reach the aphids that are on the inside of the leaf coil, and damaged leaves do not recover even if sprayed. Biological controls, especially syrphid fly larvae and lady beetle larvae are often abundant amongst the aphids.

Honeysuckle aphid is just now starting to make the characteristic witches-brooms on the ends of honeysuckle twigs. The small tassel or cluster of twigs at the ends of the branches forms as a result of toxins injected as the aphids feed at the tips of the new growth. As we have said since this east European immigrant aphid was first found in Iowa in 1981, treatment is not warranted in the landscape.

Maple aphids are always present but populations usually remain below a noticeable level. Some reports this spring indicate population densities the are causing leaf curling, discoloration and drop. It is difficult to justify insecticide treatment of large, well-established maple trees. Sprays as discussed for cottony maple scale in last weeks newsletter are available for small or heavily stressed trees.

This article originally appeared in the June 24, 1994 issue, p. 98.


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