Utah Pests News Spring 2007

The Japanese beetle, Popillia japonica, was first detected in Utah this summer, and is just the latest example of another invasive introduction to Utah. In July 2006, an Orem resident and USU Master Gardener noticed leaf damage on her wisteria plant in her backyard. She investigated for potential insects and quickly found a shiny, metallic beetle. After initially bringing the insect to the Utah Department of Agriculture and Food (UDAF) for identification, the specimen was confirmed in the Utah Plant Pest Diagnostic Laboratory by Alan Roe. Since July, more than 600 adult Japanese beetles have been collected in a two square-mile area in Orem. Adults were trapped with a special "double lure" system developed by Trece Incorporated (www.trece.com) that includes a floral lure and a pheromone sex attractant.

Adult Japanese beetles are oval, and metallic green with bronze-colored wing covers. Males are usually slightly smaller than females, but in general, adults are about ½-inch long. An obvious distinguishing character of the adults includes six white tufts of hair along each side of the abdomen. Immature Japanese beetle larvae are called grubs, and are about 1-inch long when fully developed. Grubs are C-shaped and are creamy white in color. Japanese beetles are closely related to other scarab beetles, such as May/June beetles and masked chafer beetles; therefore, the grubs are difficult to identify to species without a high-quality microscope.

	Beetles mating and feeding on corn

The Japanese beetle is a concern because of the potential damage the adults and immature grubs can cause to ornamental plants. Japanese beetle grubs, like most white grubs, feed on turfgrass roots. High numbers of grubs can severely weaken a turfgrass root system. Adult Japanese beetles can feed on more than 300 host plants and often congregate in large numbers to feed and mate. Adults are active during the warmest part of the day and will likely be feeding on suitable host plants during that time. Ripening fruits are especially attractive, but adults also prefer rose, apple, stone fruits (e.g., peach, plum, cherry), basswood/linden, willow, elm, grape, birch, Japanese and Norway maple, pin oak, horse chestnut, and sycamore. All of these plants can be found throughout Utah and are the most likely to have adult feeding damage.

Unfortunately, Japanese beetles are not a new pest to the United States. Japanese beetles were first discovered in the eastern United States in 1916 and are considered a highly destructive pest along the east coast. Since the 1920’s, the beetles have threatened horticulture and agriculture and have slowly moved south and west. Many states, including Utah, have deemed the Japanese beetle a quarantine pest, which restricts movement of plant material. Because of the thriving horticulture and fruit industries in Utah, UDAF has carefully monitored for adults along the Wasatch Front for several years. Japanese beetle populations throughout the midwest have not caused the economic damage as seen on the east coast; however, an eradication program in Colorado is in progress. Although no one can say how the beetles arrived in Utah, it was likely an accidental introduction with transporting plant material.

	Japanese beetle grub

Once Japanese beetle becomes established, complete eradication is unlikely based on its other U.S. populations. There are effective biological control agents, such as parasitic flies and wasps, which can help suppress beetles to tolerable levels. In most cases, chemical control for adults and grubs is not necessary. Homeowners can be proactive by discouraging Japanese beetles from causing significant plant damage with the following tips:

• Keep susceptible plants healthy by following a recommended irrigation and fertilization schedule.
• Encourage the diversity and density of biological control agents by incorporating flowering plants that produce nectar and pollen.
• Include a mix of non-attractive plants, such as lilac, dogwood, magnolia, and American holly, to discourage large numbers of adults.
• If you notice adults feeding on ornamental plants, simply remove them by hand or shake the plant above a jar of soapy water to kill them.

The actual extent of plant damage Japanese beetle will cause in Utah is largely unknown because of the many unique climate conditions. The Japanese beetle may never become a persistent problem, but UDAF and USU will be carefully monitoring this new pest. For more detailed information about Japanese beetle, including its life cycle, susceptible plants and control options, see the fact sheet on the Utah Plant Pest Diagnostic Lab web site.
 

-Erin Hodgson, Extension Entomologist (No longer at USU)
 

 Picture of the Quarter

Black tar spot on maple is easy to diagnose, and is rarely damaging. Notice that the pathogen is causing the leaf tissue around it to retain chlorophyll longer than healthy tissue. -Photo by Kent Evans