Arizona Cypress: A Plant Dinosaur - July 8, 1998
Jeff Schalau, County Director, Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Arizona Cypress is a graceful evergreen that and well suited to many sites in the Verde Valley. These trees are part of the Sedona's native plant community and can be found thriving next to intermittent streams and in the cooler canyons. A short geology lesson gives insight into the current distribution of native Arizona Cypress. During the Pleistocene Epoch, the desert southwest was much wetter and cooler than it is today. Arizona Cypress was widespread over in the prehistoric southwest landscape. Botanists think that when the Pleistocene ice retreated northward about 10,000 years ago, the distribution of Arizona Cypress began to diminish and fragment. Today, this plant dinosaur only clings to scattered sites in the southwest where the microclimate permits its survival and reproduction.
Arizona Cypress trees are planted in many landscapes in the Verde Valley. It is distinguished by its conical crown, smooth reddish bark, blue-green foliage, and small round cones. Arizona Cypress (Cupressus arizonica) is a fast grower reaching up to 50 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. Unfortunately, today many Verde Valley Arizona Cypress trees are dead or in the process of dying.
A combination of factors led to these premature deaths. The drought of 1996 induced stress on all plants including Arizona Cypress. Native plant populations suffered along with landscape plants from the dry spring and late, almost nonexistent monsoon season. Once drought weakened the trees, Cypress bark beetles seized the opportunity to dine on defenseless trees.
Cypress bark beetles are native insects that occur throughout Arizona. They are not usually aggressive and also 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 twigs and kills branch tips. These dead branches remain hanging on the tree (called flagging). In weakened, drought-stressed trees, the beetles will infest the trunk. Here, beetles chew vertical tunnels between the bark and wood laying eggs along the way. The larvae hatch and tunnel outward destroying the tissue that transports nutrients from the top downward. In severe cases, this kills the tree by starving the live tissue below that point.
No insecticide has proven effective in controlling Cypress bark beetle infestations of the trunk. So, what can we do? We keep in mind that Arizona Cypress trees have thrived in the southwest for more than 10,000 years, but only under conditions where soil moisture is available. This means providing supplemental moisture through irrigation. This is especially critical during May, June, July, or until the monsoon season is well under way. The simplest way to irrigate is with soaker hoses (porous black hose). During critical periods, irrigate deeply (two feet) twice a month in an area at least one and one-half the diameter of the drip line of the tree. The beetles still may "flag" the tree, but should not be successful at attacking the trunk. Your water invigorated Arizona Cypress trees will have a greater chance of survival.
Planting a diverse mix of tree species can also decrease catastrophic pest problems. When only one tree species is planted, this creates a monoculture. Monocultures are open invitations to pest attack. Don't wait for the R.S.V.P., add resiliency to your landscape by plant three or more tree species. To learn more about other species of trees suitable for this area, ask for the University of Arizona Cooperative Extension Publication: Drought Tolerant Trees for the Verde Valley.
For more information about tree selection, planting, care, and other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113. Or E-mail us: firstname.lastname@example.org. Be sure to include your address and phone number.
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