Agrilus cuprescens
Pest description and crop damage: Rose stem girdler (RSG) is a small copper-green-colored Buprestidae family beetle pest of caneberry crops and ornamental brambles (Rubus and Rosa species). This Eurasian pest is relatively new to the PNW and is closely related to the invasive emerald ash borer. Damage is increasingly being reported throughout the south Puget Sound basin to the southern Willamette Valley region of Oregon, and in some parts of the inland PNW. It has also been confirmed in Snohomish, Skagit and Whatcom counties (WA) in 2022.
Infestations can reduce berry yield or kill canes that are compromised or completely girdled by RSG larvae. The images in Figure 1 illustrate RSG symptoms and damage. Infested canes may wilt (Figure 1A) and easily snap points where spherical or spiral swelling occurs from larval RSG damage. Spherical galls may be more apparent in the first year and/or softer canes (Figure 1B and C), whereas spiral-shaped swelling may be more prominent on older and/or firmer canes (Figure 1D). Damage from larvae can eventually have a partial or complete girdling effect on the cane (Figure 1C). Cane breakage more readily occurs when weighed down by ripening berries, during gusty weather, or during cane-tying/trellising operations. Berries on damaged canes may also desiccate prematurely. Economic loss is most reported in young plantings that are not yet well-established, on primocane varieties grown for fall harvest, or the primocanes of floricane-fruiting cultivars. Yield loss in new infestations of floricane-fruiting plantings can otherwise be relatively inconspicuous if substantial girdling does not occur before harvest. Damage may also superficially resemble typical cane dieback after harvest, wilting from root pathogens, water stress, and/or nutrient stress. Damage patterns are often highly variable and may be unpredictably concentrated into certain "hotspots" and certain seasons where infestation is more pronounced and damage is severe (~60-90% loss of yield potential).
Biology and life history There is only one RSG generation each year. The life stages of RSG are illustrated in the images in Figure 2. Peak adult beetle emergence is most likely to occur when approximately 900 hours ≥55°F have accumulated since Jan 1 in a given year. This threshold most commonly occurs between mid-May and mid-June in the western PNW. Adults chew their way out of canes leaving behind a ~2 mm-wide D-shaped emergence hole (Figure 2A). Peak adult emergence & activity may occur over a 2 to 3-week period but residual activity has been observed to last for up to 8 weeks in the PNW. Individual adults live for ~1 to 3 weeks once emerged and may move ~400 to 1200 ft from their emergence location within a season. Prior to mating (Figure 2B) and egg-laying, adults feed on leaves, leaving behind large, irregular holes in foliage. Females typically lay single eggs (Figure 2C) on the basal 1/3 of primocanes, or on multiple points higher up on older canes. Larvae hatch within two weeks and flat-headed larvae bore directly beneath their eggshells into the canes. Larvae are cream-colored (Figure 2D) and throughout summer feed in a spiraling and upward pattern through the cane's vascular tissue (Figure 1E) causing damage that becomes apparent in the latter half of summer into fall. By early fall, most larvae will have moved into the cane pith where they remain through the pupation (Figure 2E) into adult beetle stage (Figure 2F) in late spring.
Larvae are very winter hardy and require ~4.5 months of temperatures ≤ 45°F to complete their life cycle. Nonetheless, larvae do not always remain viable in the cane. This may be partially due to a naturally occurring parasitoid wasp, Baryscapus rugglesi. This parasitoid can follow an initial infestation and reduce RSG activity in the following year. When the wasp is present, there may be variable, but noteworthy reductions in infestation, and/or damage to canes.
Management-cultural and chemical controls-HOME and COMMERCIAL USE
Spread of RSG occurs when infested plant material is moved between locations, and from adult beetles moving incrementally through any landscape habitats with Rubus and/or Rosa species. Abundant wild Rosa and Rubus species in the PNW leads to persistent RSG corridors along roadsides, railroad tracks, and waterways and RSG harbors on field peripheries, making eradication impractical. Nonetheless, spread can be mitigated when movement of infested plant material is prevented, and when wild host stands near Rubus or Rosa plantings are removed whenever possible. Diligent, thorough pruning and destroying of RSG-damaged canes provide significant, foundational control of RSG, especially when wild hosts near Rubus and Rosa plantings are also removed. All infested, pruned-out canes need to be thoroughly destroyed in early spring, because larvae can remain viable in canes pruned out from late summer onward. Burning canes is the most effective destruction method. Canes may also be finely chopped/chipped or buried below 2 inches of soil if it is thorough and consistent.
Insecticides can also be used to intercept RSG infestations, especially when influxes from infested wild hosts near Rubus and Rosa plantings cannot be controlled. Try to first confirm presence/risk of RSG infestation to know whether insecticide applications may be warranted or not. Scout for characteristic cane swelling and spiral tunneling under the bark of canes in the field or in wild hosts nearby (Figure 1B-D). Scouting for RSG adult beetles is also highly informative if scouting is early enough to catch adult emergence. Adult RSG beetles are often not abundant enough to be easily spotted, although they are often easiest to spot in mid-morning on host plant leaves as the weather is warming. If risk of RSG infestation is found, growers may also choose to prioritize insecticide management to vulnerable new/young caneberry plantings and/or fall-harvest primocane varieties if needed.
There are currently no insecticides specifically labeled for RSG control, but a list of insecticides effective on RSG has been published in Utah State University Extension guide ENT-178-15. Sprays must be targeted at the adult beetles to prevent egg-laying, so sprays must only occur after adult emergence. Insecticide applications made before adults emerge are not effective, and systemic insecticides targeting pre-emergence RSG have not been proven to be practical or effective in most contexts. The Rose Stem Girdler Emergence Model and its pest alerts on WSU's AgWeatherNet use real-time and forecasted data from nearby weather stations to help determine adult emergence timing, or more ideally, to indicate when to begin scouting for adult emergence (~500 hours). Apply insecticides as full cover sprays, including the basal area of the canes, beginning immediately after first adult emergence and continued according to the reapplication interval listed on the product's label to maintain effective coverage while adults are present. This is usually a minimum of 2-3 weeks but may be up to 6-8 weeks. Attend to maximum seasonal spray limits, especially if sprays for other pests are needed later in the season. Also, because adults can often emerge around bloom, it is imperative to follow all pollinator protection guidelines that may appear on the pesticide labels. Currently the only pesticides on Utah State University Extension's that are relatively reduced risk to pollinators are
Management-chemical control: COMMERCIAL USE
- azadirachtin/neem-oil products
- Beauveria bassiana var. GHA,
- Bt subspecies galleriae strain SDS-502
Pollinator-safe crop protectants, barrier sprays and repellents (Not tested for efficacy)
- cinnamaldehyde
- chlorantraniliprole
- cryolite
- kaolin clay