Blackberry and Raspberry-Rose stem girdler

Agrilus cuprescens

Pest description and crop damage Rose stem girdler is a damaging, small coppery metallic beetle (family Buprestidae) pest of cane fruit, increasingly being reported by growers throughout the Willamette Valley region of western Oregon and in southwest Washington. It has also been confirmed in eastern OR, two eastern WA counties, 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. Canes with feeding damage are more susceptible to winter injury. Economic loss, particularly in blackberry cultivars with softer stems, has been reported. In addition to raspberry and blackberry, its host range includes wild Rosa and Rubus species and cultivated/ornamental roses. Once RSG is present in an area, persistent hosts on field peripheries 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, and vice versa. 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 be as late as early June), adults will emerge from the stem, leaving behind an elliptical emergence hole.

Adult emergence & activity may occur for 2 to 3 weeks, with individual adults living ~1 week. Prior to egg-laying, adults must feed on leaves, resulting in a tattered appearance. Once reproductively mature, females lay their eggs generally on the basal 1/3 of primocanes; in floricane-fruiting varieties, eggs may be commonly laid higher up on the cane as well. Eggs hatch within two weeks and flat-headed larvae bore directly beneath their eggshells into the canes. Larvae are cream-colored and feed just below the bark of the primocanes. During early summer, first and second instar larvae feed within the vascular tissue resulting in a characteristic spiral and/or gall-like swelling. Spiral damage patterns may be more prominent on infested second year floricanes, whereas prominent galling may be particularly apparent on first year soft and tender canes. Other symptoms include presence of elliptical emergence holes, wilted top growth appearing in mid-summer, and weakened canes which easily snap, particularly canes weighted by ripening berries. By mid-summer, third instar larvae move 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 is negligible.

Management-chemical control:

Diligent, thorough pruning and destroying of RSG-killed canes can help reduce field populations considerably (up to 80%). If pruned canes are left in the field, they should be tilled in below 2 inches to prevent emergence since RSG larvae remain viable in dead canes after the 4th instar. Integrating effective insecticide controls with pruning practices may provide near-full control of in-field populations. There are no insecticides labeled specifically for RSG control but applications of insecticides that are registered for use on caneberries (that are relatively safe for pollinators) may provide some measure of control. Chemical management is targeted at the adult beetles to prevent egg-laying. 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.