Borer Article MAY05: the Hole Story the Flatheaded Cedar Borer Can Eat
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Borer article MAY05: The hole story The flatheaded cedar borer can eat at nursery profits, literally By Robin Rosetta Your gaze roams over the young field of arborvitae, then lingers. There in the corner, disappointing the symmetry of green rows, stand yellow and brown stalks of dying Thuja. Mourning the immediate loss, you wonder what fiend has robbed you of potential profit. You may share the nursery with a squatter. The uninvited resident is the flatheaded cedar borer (FCB), Chrysobothris nixa, a native beetle that won’t hesitate to call your plants home. There is scant literature on flatheaded cedar borer and little documentation of its life cycle, impact and management in nursery systems. These borers tunnel into plants in the Cupressaceae family. According to Richard Westcott, a retired Oregon Department of Agriculture entomologist and an authority on this family of beetles, C. nixa has been reported in California, Montana, Nevada, Oregon, Washington and British Columbia on the following hosts: Calocedrus decurrens (incense cedar), Cupressus macrocarpa (Monterey cypress), Cupressus guadalupensis var. forbesii (Tecate cypress), Cupressus nevadensis (Piute cypress), Juniperus occidentalis (Western juniper) and Thuja plicata (giant arborvitae). In Oregon’s Willamette Valley, the borer is reported on Chamaecyparis. Schuh and Mote, in their 1948 publication Insect Pests of Nursery and Ornamental Trees and Shrubs in Oregon, do mention C. nixa as a species “… very common in nurseries in various varieties of junipers and arborvitae” and note that “… attacks always seem to be in plants that have been injured by hoe, by cultivator, or by breakage of the limbs from the main trunk.” No life-cycle information was mentioned in these references. Westcott thinks these borers might have a two-year life cycle in the Willamette Valley region. The flatheaded cedar borer is a buprestid beetle. The Buprestidae family of beetles is so named due to the flattened pronotum just next to the head of the juvenile or larval stage of the beetle. This character is extremely useful for identification of this family of borers. The larval grub is legless and elongate, pale white with a dark brown head capsule. The adult beetles are 0.35-0.57 inches long, slightly metallic, brown to black flattened bodies. The overall look of the adults is described as bullet-shaped. This shape, looking straight on head to tail, also accounts for the oval-shaped emergence hole associated with their exit from the tree. Their wing covers are sculptured and finely serrated along the outer edge at the rear. In fact, Chrysobothris means “gold trenches,” referring to its shiny sculpturing. A common field pattern seen with the borer’s damage is an edge effect. This is particularly noticeable near the exterior of a nursery next to forest borders. The infestations often appear in the field as hot spots involving several plants adjacent to each other. The plants are generally weak and spindly. The foliage in affected fields of arborvitae can range from light green to yellow, tan, nearly orange and brown — undesirable traits in plants not grown for fall color. Individual plant damage can be one-sided, depending on the site of feeding. Most damage occurs near the base of the plant, commonly at the soil line. Flatheaded borers tunnel extensively in the shallow, cambial tissue. They can inflict much damage to a woody plant. This feeding so near the bark’s surface makes damage more evident, revealed in mushy wood and clumped, sawdust\like brown frass in the galleries. Carefully scraping off the outer layers of the wound with a knife may uncover the grub concealed within. Larger larvae can also be found deeper within the stem as they prepare to overwinter in the fall. In the spring, weeping of sap near damage and emergence holes of the adults can be seen on junipers. The dreams of a flatheaded cedar borer surely include the convenience of a dense patch of host material: arborvitae, juniper or cedar grown in a concentrated resource system — a nursery. Add the right conditions: conifers basking in the hot, dry sun where the sprinklers fail to travel adequately. Their thirst evident, the parched plants attract the attention of a female borer taking flight in late spring through the summer. As she flies she assesses the real estate. Seeking a dwelling for her offspring, she veers toward an off-colored plant. Her inclination is to find a plant host too stressed to successfully ward off her penetrating progeny. This eases the path for establishment and survival of her young. Satisfied with her pick, she may lay an egg in the bark crevices near the base of the plant. Management generally aims at reduction of plant stress, removal of infested materials and protection of high-value susceptible plants. How does one successfully attract a burgeoning flatheaded cedar borer population? Drought stress works well. Therefore, irrigation management to consistently meet water demands is critical. Summer-planted arborvitae appear more susceptible than spring-planted. The spring planting allows more time to establish root systems that can withstand summer heat and moisture extremes. Adjust cultural activities when justified. Ordinarily a grower may base the timing of juniper pruning on nonpeak demand for his available labor. When suffering a borer, it can be useful to think entomologically, avoiding pruning during the flight time of the beetle. Pruning cuts are thought to attract borers by emitting a volatile chemical perfume and visual cues irresistible to these opportunists. The female FCB may fly from mid-May through August (the majority of specimens collected in Oregon have occurred from early June through mid-July). Westcott reports that the earliest specimens he has in collection emerged on May 15 and May 29. If pruning is required during this potentially long flight period, timing should avoid periods of plant stress. Once infested plants are identified, shrubs can be rogued and burned, chipped or removed from the production site. Be sure shrubs burn thoroughly if burn piles are used. Currently infestations tend to be sporadic, limited and unpredictable, and chemical control under those conditions is likely not economical. High-value plants may warrant protective applications during the flight period. A search for products that are labeled specifically for flatheaded cedar borer was unsuccessful. Some products though, such as Dursban and Discus, have flatheaded borers on their labels for nursery sites and may have efficacy against this borer as well. Learn what attracts these beetles to a site, and you might learn what will deter them. When next these borers come to visit, give them a little dose of inhospitality and keep Oregon arborvitae green. Disclaimer: This listing of commercial products may not include all products labeled for this pest, and no discrimination is intended. This list implies no endorsement by the author or Oregon State University Extension Service. Reference: Schuh, J. and D.C. Mote. 1948. Insect Pests of Nursery and Ornamental Trees and Shrubs in Oregon. Agricultural Experiment Station, Oregon State College, Corvallis. State Bulletin 449. 163 pp. Robin Rosetta is an Oregon State University Extension Agent in nursery pest management. More information about snails can be found at the Pacific Northwest Nursery Management Web site at http://oregonstate.edu/Dept/nurspest/Flatheaded_cedar_borer.htm. You can reach Rosetta at [email protected] or at (503) 678-1264 ext. 33. The author is grateful to Richard Westcott for his generosity, knowledge and help with this article..