Pest description and crop damage Rose stem girdler (RSG) is a damaging, small copper-green-colored Buprestidae family beetle pest of caneberry crops and ornamental brambles (Rosa and Rubus species). This pest is relatively new to the PNW and damage is increasingly being reported by growers and community gardeners throughout the Willamette Valley region of western Oregon and southwest Washington. It has been confirmed in the inland PNW, and as far north as King County in western WA. Infestations can reduce 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, and/or on primocane varieties. Damage to established floricane plantings can be a relatively inconspicuous yield decline, partially due to the infestation going unnoticed; if substantial girdling does not occur before harvest, RSG damage may superficially resemble typical cane senescence after harvest, or wilting from Phytophthora root rot. Canes with feeding damage are also more susceptible to winter injury. Its wild host range includes wild Rosa and Rubus species, which are abundant in the western PNW. Therefore, once RSG is present in an area, persistent hosts on field peripheries can make eradication impractical. Adult beetle emergence is dependent on average humidity and temperatures thresholds: 1) Pupation requires average daytime temps >50°F and >60% average daily relative humidity 2) development into an adult requires average daytime temps >55°F and >70% average daily relative humidity. Therefore, cool and/or dry spring conditions can delay RSG emergence. Once adults have developed, they may stay in canes for 1 to 3 weeks until average daytime temps are >65°F. After this latent period (which may commonly be early June in the PNW), adults will emerge from the stem, leaving behind an elliptical emergence hole.
Peak adult emergence & activity may occur over a 2- to 3-week period but activity has been observed to last as long as 8 weeks in the PNW. Individual adults live for ~1 week once emerged. Prior to egg-laying, adults feed on leaves, which can result in a tattered appearance. Once reproductively mature, females most commonly lay eggs on the basal 1/3 of primocanes or on multiple points higher up on older second-year 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 vascular tissue resulting in a characteristic spiral and/or gall-like swelling on canes. Spiral damage patterns may be more prominent on infested second year canes, whereas prominent galling may be particularly apparent on first year and/or soft and tender canes. Damage from larvae can eventually a girdling effect on the cane leading to wilted top-growth beginning in mid-summer through fall. Weakened canes may easily snap, particularly if weighted by ripening berries or during cane-tying/trellising operations. 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. When this happens, infestation symptoms may be apparent, but damage to cane vitality may be negligible.
HOME and COMMERCIAL USE
Diligent, thorough pruning and destroying of RSG-damaged canes can help reduce field populations considerably (up to 80%). Larvae are 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. Generally, any caneberry production system where canes are absent when adults are active and/or where canes are mowed after infestation may lessen risk of in-field RSG issues in given year. Growers may also choose to try eliminating wild hosts from field edges. Integrating effective insecticide controls with pruning practices may provide near-full control of in-field populations, though RSG may still enter fields annually from wild hosts on field edges if present. There are no insecticides labeled specifically for RSG control but applications of insecticides that are registered for use on caneberries may provide some measure of control. Chemical management applied before adults emerge are ineffective; sprays therefore need to be targeted at the adult beetles to prevent egg-laying. Because infestations in new/young caneberry plantings are most likely to lead to economic loss, growers may choose to prioritize these for chemical management if necessary. Once adults have emerged, weekly 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. Because adults can emerge around bloom, follow all pollinator guidelines that may appear on the pesticide labels.