   Cypress Bark Beetles - November 6, 2002 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Have your Arizona cypress or Leyland cypress trees been losing branch tips lately? Have you lost a cypress tree this year? If so, then chances are cypress bark beetles have visited you. The Cottonwood Master Gardener desk at the Cooperative Extension office has received an unprecedented number of calls about this insect over the past few weeks. I have prepared a publication (which includes photos) about cypress bark beetles. It is available on the Yavapai County Cooperative Extension web site (ag.arizona.edu/yavapai/) or by request from the Cottonwood Master Gardener desk at 928-646-9113 ext. 14. Below are some highlights from this publication. Cypress bark beetles (Phloeosinus spp.) are native insects that occur throughout Arizona. They are common in the Verde Valley, Prescott, Payson, and Kingman areas. In healthy trees, these insects seldom cause mortality. Under natural conditions, most bark beetles act as natural thinning agents that remove dying, overcrowded, and unhealthy trees. However, under drought conditions, populations of these insects can increase allowing them to colonize seemingly healthy trees. In Arizona, the preferred host trees are Arizona cypress (Cupressus arizonica), Leyland cypress (Cupressocyparis leylandii), and native Junipers (Juniperus spp.). Cypress bark beetles can be found in native cypress and juniper stands as well as ornamental plantings. They often breed in the limbs and trunks of weakened, broken, dying, or felled trees and are common in juniper firewood. Natural stands of Arizona cypress are often found in riparian areas or where precipitation is higher than surrounding areas. Property owners often assume that because these trees are native they can survive without supplemental irrigation. This misconception causes many trees to die unnecessarily during Arizona's periodic droughts. Adult Cypress bark beetles are small, reddish brown to black, often shiny, and about 2-3 mm long. The beetles colonize trees using two distinct methods. In weakened or stressed trees, adult beetles attack the bole (trunk) and larger branches of the tree where they mate and lay eggs. After the eggs hatch, the larvae (grubs) create new galleries which radiate outward from the central gallery. As they consume the inner bark, cambium, and outer sapwood, the tree is effectively girdled. Occasionally, beetle colonization causes top-kill or branch mortality, but often it leads to tree mortality. Trees are often colonized in the spring and summer and one generation per year is common. This year, I will go out on a limb (so to speak) and say that we had at least two, and maybe three generations. Newly emerged adults also bore into small twigs a few inches from the branch tips. This almost always kills the branch tip causing it to fade in color. The dead branch tip often remains hanging on the tree (called "flagging") for a short period before breaking off. Upon close inspection of the branch tips, a hollow area can be seen where the beetle mined the twig. When beetle populations are high, hundreds of branch tips may accumulate on the ground. Cultural practices can decrease the probability of beetle colonization. Dead and dying material should be pruned out of individual trees during winter. Cut, dead, or down material should be promptly removed from the site. Maintaining tree health and vigor will reduce the risk of beetle colonization. This is easily accomplished in residential landscapes by slow, deep, infrequent irrigation of susceptible trees species during drought periods (April-June and longer if needed). Irrigation can be applied using a drip irrigation system or a soaker hose placed at the drip line of the tree. Pesticides are not effective at control and, while pretreatment insecticides are available, they are not practical or known to be effective. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |