Cypress Bark Beetles - June 16, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

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 natural forests and woodlands, bark beetles act as natural thinning agents that remove dying, overcrowded, and unhealthy trees. Under drought conditions, populations of cypress bark beetles can increase allowing them to colonize and overcome seemingly healthy trees. Careful observation can also alert you to their presence on your property.

In Arizona, the preferred host trees are Arizona cypress (Cupressus arizonica), Leyland cypress (Cupressocyparis leylandii), and native Junipers (Juniperus spp.). They often breed in the limbs and trunks of weakened, broken, dying, or felled trees and are common in juniper firewood. Occasionally, I have removed a juniper on my property and stacked it for firewood. When Ive done this in late spring, summer, or early fall, cypress bark beetles colonize the stacked wood within a week.

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.

Newly emerged adults also bore into small twigs a few inches from the branch tips. This 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. Maintaining tree health and vigor will also reduce the risk of beetle colonization. This is easily accomplished in residential landscapes by slow, deep, infrequent irrigation (twice per month) of susceptible trees species during drought periods (April-June and longer if needed). Irrigation can be applied using a soaker hose placed at the drip line of the tree.

Pesticides can be used to prevent colonization of healthy trees. Pesticide treatments must target the adults by spraying the bark so that beetles are killed when they land on trees and attempt to bore into the bark to lay eggs. Highly valued, uninfested host trees may be protected by spraying their bark with a persistent, registered insecticide. Common active ingredients in these insecticides are carbaryl and permethrin, but read the label to ensure it is labeled as a preventive spray for bark beetles. Seriously infested trees, or trees that are dead or dying due to previous beetle attacks, cannot be saved with insecticide treatments and should be removed.

Systemic insecticides, meaning those that are implanted or injected through the bark or applied to soil beneath trees, have not been shown to prevent attack or control populations of bark beetles. Although new systemic products are being investigated, they are not currently recommended for bark beetle management.

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Additional Information

Cypress Bark Beetles - University of Arizona

Using Insecticides to Prevent Bark Beetle Attacks on Conifers - University of Arizona

Bark Beetle Management Guideleines - University of California

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: June 21, 2010
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