   Arizona Cypress - September 19, 2018 Jeff Schalau, Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Fall is the best time to plant coniferous evergreen trees and shrubs. These include pines, junipers, arborvitaes, cypress, cedars, yews and others. I purposely did not list spruce or fir because they often perform poorly below 6,000 ft elevations. Similarly, I do not recommend planting Leyland Cypress due to their susceptibility to Seiridium canker. Arizona cypress is now named Hesperocyparis arizonica but was Cupressus arizonica prior to 2013. It is a native species and widely planted in the Verde Valley. 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. 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. 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 many areas of the Verde Valley, 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. Ask a local nursery professional which cultivars they stock and their characteristics. Unfortunately, many native-grown and planted Arizona Cypress trees have died in recent years. A combination of factors led to these premature deaths. The droughts of 1996 and 2002-03 induced water stress on many native plants including Arizona Cypress. Following extended periods of drought, cypress bark beetles colonized and killed susceptible trees. Cypress bark beetles are native insects that occur throughout Arizona. 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 (like 2017-18) 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 fillit periodically with water. During critical periods, irrigate deeply (two feet) twice a month. 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 attacking 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 require increased irrigation to support the additional growth. Below I have included photos and additional resources. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8992 or e-mail us at verdevalleymg@gmail.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Photos 
Native Arizona cypress (Hesperocyparis arizonica) growing in Sedona, Arizona (photo by Jeff Schalau).
Three smooth-barked Arizona cypress (Hesperocyparis arizonica var. Glabra) cultivars in center of photo showing differences in foliage color and growth form in a demonstration planting (John Ruter, University of Georgia, Bugwood.org).Resources Description and photos of Arizona Cypress Yavapai County Native and Naturalized Plants cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Cupressus&species=arizonica Cypress Bark Beetles University of Arizona Cooperative Extension extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1316.pdf Using Insecticides to Prevent Bark Beetle Attacks on Conifers University of Arizona Cooperative Extension extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1380.pdf Scientists Dig Up the Past in Packrat Middens High Country News www.hcn.org/issues/48.3/scientists-dig-up-the-past-in-packrat-middens  |