Conifers are cone-bearing plants in the taxonomic clade Gymnospermae. Cedars, firs, hemlocks, junipers, larches, redwoods, spruces, and yews all belong to this ancient and noble group. Though less diverse than their angiosperm counterparts, gymnosperms are just as important ecologically. They provide homes and food for countless organisms, capture vast amounts of carbon from the atmosphere, and happen to make beautiful additions to managed landscapes.

Sequoia sempervirens, the coastal redwood, is an incredibly long-lived conifer (with many specimens exceeding 1,000 years in age) and the tallest species of tree. Photo credit – Nick Goltz, DPM.

Though conifers can serve countless roles in the landscape – from privacy screens, to topiaries, to majestic specimens, they are not without their fair share of pests, diseases and abiotic pitfalls. Here are a few such things to be on the lookout for as you maintain the health of your conifers (or consider planting one).

Like all plants, conifer species have their unique preferences for environmental conditions.  While some cedar and cypress species tolerate wet soils well, many others do not. Some popular ornamentals that hate “wet feet” (soggy soil conditions that lead to root damage) include arborvitae, yews, and many pine species. Winter damage, drought, and genetic issues also frequently impact conifers.

Many “dwarf” varieties originally began as “witches’ brooms” selected and isolated from specimens of their full-sized counterparts with a genetic abnormality. The opposite scenario may also occur, where dwarf varieties spontaneously grow “full-sized” branches. When either occurs unwanted on a managed plant, simply prune away the affected branches and monitor carefully.

Sometimes, dwarf varieties can display genetic “reversions” where non-dwarf branches begin to grow. Photo credit – Nick Goltz, DPM.

Sometimes, witches’ brooms can develop following heavy mite infestations. Besides mites, pines are susceptible to insect damage, including from scales, boring beetles, and bagworms. These pests can cause needle yellowing, defoliation, and sometimes vascular damage, girdling, and death.  Severe insect infestations may lead to increased susceptibility to various diseases and warrant management including insecticide applications.

Adult bagworm females (possibly the evergreen bagworm, Thyridopteryx ephemeraeformis) are a common pest of conifers in New England. Photo credit – Nick Goltz, DPM.

Some of the more widespread and damaging diseases of conifers include root-rot diseases caused by oomycetes and fungi including Pythium, Phytophthora, and Fusarium. Others of significance include needle and tip blight diseases caused by fungi from the genera Pestalotiopsis, Mycosphaerella, Phomopsis, and others.

If you have branches browning mysteriously, consider the environmental conditions your plant is experiencing! If too much and too little water isn’t an issue, and you haven’t noticed any insect or mite pests, have your plant examined by a plant pathologist to see if diseases could be affecting your plant. Contact the UConn Home and Garden Education Center at ladybug@uconn.edu to discuss your plant’s health and inquire about submitting a sample to the UConn Plant Diagnostic Laboratory.