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Concolor Fir Needle Deformities
Concolor fir is a conifer species that is relatively free from major issues in Iowa. But in the past week several samples have raised concerns. These samples in general had scattered dead branch tips, newly emerging needles that were twisted and distorted, and hints of sticky, shiny glaze on the new growth.
There are a couple of things happening that explain the damage. The first is a common problem with landscape plants—environmental damage. The occasional dying branches are an understandable concern, but the key has been to look a bit lower on the branches where secondary buds are breaking with tufts of needles emerging. Just parts of the branch extremity were killed, but the branch is trying to reestablish itself with new growth. This was caused by accumulated stresses to the plant that culminated in drying out during the winter, killing a few of the branch ends. All in all, as long as the tree is responding well, it should recover. In nature some of that happens anyway in a process called natural pruning. If you have a concolor fir with these symptoms, keep an eye on it, and make sure the new needles are coming along well.
The twisted new needles and accompanying sticky glaze to new growth is indicative of another problem, this one caused by a grayish sucking pest called the balsam twig aphid. Like most aphid species, these guys are specialists, feeding on concolor, Fraser and balsam firs. Balsam twig aphids feed on the new growth, causing distortion of new needles. The sticky, shiny needles at twig tips are the result of honeydew the aphids exude as they feed. Damage is most critical in Christmas tree plantations, and less important on windbreak and specimen landscape trees that generally recover fairly well. Balsam twig aphids have one generation per year that coincides with bud break and growth of new needles. Adult female aphids will be laying eggs in bark crevices in late May and most of the feeding damage this year is over—that means here is no point of treating now this year. If you notice concolor firs with the characteristic twisted, sticky new needles, note that to watch next year when buds begin to break. Small trees can be sprayed with insecticidal soap, or there are some available insecticide products. But in most cases, the aphids will not kill the tree, but just cause early season cosmetic damage.