Bark Beetles in Arizona Cypress and Junipers - May 19, 2021
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

Arizona Cypress is an evergreen tree well suited to elevations from 3,000 to 6,000 feet in Arizona (USDA Plant Hardiness Zones 7-9). These trees are part of the Sedona's native plant community and can be found next to intermittent streams and in cool canyons in many areas of Yavapai County. It is also susceptible to a native bark beetle.

During the Pleistocene Epoch, the desert southwest was much wetter and cooler than it is today. Arizona Cypress was widespread in the prehistoric southwest including the Salt and Gila River valleys. The distribution of Arizona Cypress began to diminish and fragment when the Pleistocene ice retreated northward about 10,000 years ago. We know this from pollen preserved in prehistoric packrat middens.

Today, naturally occurring Arizona cypress populations cling to scattered sites in the southwest where the microclimate permits its survival and reproduction. Locally, these areas also include Pine, Payson, and the southern Bradshaw mountains. It can also be found in isolated canyons in southern Arizona’s Sky Islands and south into Mexico’s Sierra Madre Occidental.

Arizona Cypress trees have been widely planted in Arizona landscapes and beyond. It is distinguished by its conical crown, smooth reddish bark, blue-green foliage, and small round cones. Arizona Cypress is a relatively fast grower often reaching 40 feet in height and spreading to 30 feet in as little as 20 years. It is widely planted as a windbreak or to form a screen for privacy along fence lines. Several Arizona cypress cultivars have been developed and propagated to be more compact and pyramidal in shape. I do not recommend planting Leyland Cypress due to their susceptibility to Seiridium canker.

Unfortunately, many native-grown and planted Arizona Cypress trees have died in recent months. A combination of factors led to these premature deaths. The drought of 2020-21 has induced water stress on many native plants including Arizona Cypress. Following extended periods of drought, cypress bark beetles colonize and kill susceptible trees.

Cypress bark beetles are native insects that occur throughout Arizona. Current research by the USFS Rocky Mountain Research Station is looking at the two known species and their similarities/differences. In addition to Arizona cypress, they use native juniper trees and Leyland Cypress as host species. They normally breed in limbs and trunks of weakened, broken, dying, or felled trees. When soil moisture is abundant, the 1/8" long beetle bores into a twig and kills the branch tip above the point of entry – usually a portion between 8 to 10 inches long. These dead branch tips often remain hanging on the tree (called “flagging”) or fall to the ground below the tree. In severely drought-stressed trees, the beetles migrate from branch tips to colonize the trunk. Here, beetles chew vertical tunnels (galleries) between the bark and wood laying eggs along the way. The larvae hatch and tunnel outward destroying the phloem tissue that transports nutrients from the top downward usually killing the affected tree.

Once bark beetles colonize the trunk of an Arizona cypress, little can be done to save the tree. So, homeowners need to provide supplemental irrigation to these trees. Irrigation is especially critical during droughty winters and in May, June, July, or until the monsoon rains have wetted the soil profile. A simple way to irrigate any tree is to construct a berm at the tree’s dripline and fill it periodically with water. During critical periods, irrigate deeply (18”) twice a month during dry summer periods. Drip irrigation may be adequate during tree establishment, but as the tree grows, it can become inadequate to support irrigation requirements of a larger tree. Cypress bark beetles may continue to "flag" the branch tips of irrigated trees, but should not be successful at colonizing the trunk.

Individual, high-value Arizona cypress trees can also be protected with appropriate insecticides prior to beetle colonization. This practice is also used to protect pine trees prior to bark beetle colonization. However, in my experience, periodic irrigation is the best method to maintain Arizona cypress tree vigor. Regular fertilizer applications are not recommended because this results in increased growth rates which requires increased irrigation to support the additional growth.

Look at additional resources included below to learn more about Arizona cypress, cypress bark beetles, and individual tree protection with insecticides.

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Arizona cypress tree (Cupressus arizonica) growing in Sedona, Arizona (photo by Jeff Schalau, University of Arizona).

Cypress bark beetle, Phloeosinus spp. (photo by Jeff Schalau, University of Arizona).

Cypress bark beetle galleries taken after a tree has died and shed it's bark (photo by Jeff Schalau, University of Arizona).

Cypress bark beetle damage that indicates they are active and present in the branch tips of the tree. These mined tunnels will often contain a single cypress bark beetle in the portion remaining on the tree. The dead branch tips are sometimes called "flags" (photo by Jeff Schalau, University of Arizona).

Additional Resources

Photos and Description of Arizona Cypress, University of Arizona Cooperative Extension

Cypress Bark Beetles, University of Arizona Cooperative Extension

Watering Trees and Shrubs, University of Arizona Cooperative Extension

Using Insecticides to Prevent Bark Beetle Attacks on Conifers, AZ1380, University of Arizona Cooperative Extension

Addendum to AZ1380 by Jeff Schalau
This addendum adds to information provided in "Using Insecticides to Prevent Bark Beetle Attacks on Conifers, AZ1380" and was reviewed by members of the AZ/NM Bark Beetle Task Force. The information was developed to offer additional single tree protection strategies for ponderosa pines having Ips bark beetles. I believe injections of ememectin benzoate as describe in the Addendum also would offer protection to individual, high value cypress and juniper trees colonized by cypress bark beetles.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: May 13, 2021
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