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 pest is relatively new to the PNW. Damage is increasingly being reported throughout the south Puget Sound basin to the Willamette Valley region of Oregon, and in Spokane County WA. It has also been confirmed in other inland PNW counties, and was confirmed in Snohomish, Skagit and Whatcom counties (WA) in 2022. Infestations can reduce berry yield or kill canes. Damage patterns in infested regions or within fields may be highly variable and confined to certain "hotspots" where infestation is particularly heavy, and damage may be severe. Economic loss is most commonly reported in young plantings that are not yet well-established, on primocane varieties grown for fall harvest, or on the upcoming year's floricanes in floricane plantings. Weakened canes may easily snap, particularly if weighted by ripening berries or during cane-tying/trellising operations. Berries on damaged canes may show signs of water stress, and desiccate prematurely. Yield loss in floricane plantings can otherwise be relatively inconspicuous if substantial girdling does not occur before harvest. In those cases, RSG damage may superficially resemble typical cane senescence after harvest. It may also resemble wilting from Phytophthora root rot or water stress. Canes with damage can also be more susceptible to winter injury. RSG may commonly begin to infest an area through infested plant stock/transplants, or move incrementally through corridors where wild hosts are abundant. Abundant wild Rosa and Rubus species in the western PNW can lead to persistent RSG corridors along roadsides, railroad tracks, and waterways and RSG harbors on field peripheries, making eradication impractical.
There is only one RSG generation each year. Recent research has shown that adult beetle emergence timing is primarily associated with seasonal temperatures; cool spring conditions will delay RSG emergence, and vice versa. 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 late May and late June in the western PNW. Adults chew their way out of canes leaving behind a ~2 mm-wide D-shaped emergence hole. 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 week once emerged, and have been observed to move at least 400 ft from their emergence location within a season. Prior to egg-laying, adults feed on leaves, which can result in a tattered appearance. Females typically lay eggs on the basal 1/3 of primocanes or on multiple points higher up on older canes. Eggs hatch within two weeks and flat-headed larvae bore directly beneath their eggshells into the canes. Larvae are cream-colored and during early summer feed within the cane's vascular tissue resulting in a characteristic spiral and/or gall-like swelling on canes. Spiral-shaped swelling damage patterns may be more prominent on firm second-year canes, whereas spherical galling may be particularly apparent on first year and/or soft and tender canes. Damage from larvae can eventually have a girdling effect on the cane leading to wilted top-growth beginning in mid-summer through fall. By early fall, most larvae will have moved into the cane pith where they remain until the following year. Larvae do not always remain viable in the cane, which may be partially due to buildups of the naturally-occurring parasitoid wasp Baryscapus rugglesi, which can follow an initial infestation and reduce RSG activity in the following year, establishing a cyclical pattern of damage severity. When this happens, some years may have significant reductions in infestation, and/or damage may be apparent but the canes will not be girdled.
Management-cultural and chemical controls-HOME and COMMERCIAL USE
Diligent, thorough pruning and destroying of RSG-damaged canes can help reduce in-field populations considerably, especially if wild hosts near field edges can be also removed. Insufficient field cleanup has been observed to lead to buildups of in-field pest populations even when insecticides are used. Larvae are more unlikely to survive in canes if pruned out before late summer, but can remain viable in canes pruned after they reach their overwintering stage inside the cane pith. If these later-pruned canes are left in the field, they should thoroughly destroyed and/or tilled in below 2 inches to prevent emergence the following year. Integrating effective insecticides with pruning practices may provide near-full control by reducing in-field populations and controlling influxes from infested wild hosts on field edges. Growers should try to confirm presence/risk of RSG infestation before resorting to chemical management. Scouting for RSG can be difficult because beetles are often not abundant enough to be easily spotted, but are most likely to be seen on bramble leaves between late May into early July in the western PNW. Otherwise look for characteristic cane swelling and spiral tunneling under the bark of canes in the field or in wild hosts nearby; spotting cane damage may be easier in the fall and winter after leaves have dropped. There are no insecticides specifically labeled for RSG control but a list of caneberry insecticides that are 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, meaning that sprays must occur after adult emergence. Insecticide applications made before adults emerge are not effective. Growers are highly encouraged to use the Rose Stem Girdler Emergence Model and its pest alerts on WSU's AgWeatherNet (https://weather.wsu.edu/) which uses real-time and forecasted data from nearby weather stations (including Agrimet stations for Oregon locations) to determine adult emergence timing. Insecticide applications should be applied as full cover sprays, including the basal area of the canes, beginning immediately at adult emergence and continued while adults are present (3 to 6 weeks), not allowing ≥7 days to lapse without effective coverage. Attention should be given to not exceed maximum seasonal spray limits stated on a given product's label, especially if spotted wing drosophila control sprays are needed later in the season. Because adults can emerge around bloom, also follow all pollinator guidelines that may appear on the pesticide labels. Growers may choose to prioritize new/young caneberry plantings and/or fall-harvest primocane varieties for management if necessary.