Raspberry Cane Damage Abundant in 2011
During the summer of 2011, wilting tips of raspberry canes caused by the raspberry horntail were a common sight. In autumn, cane death from two other insect culprits, the rose stem girdler and raspberry crown borer, becomes apparent. As fall-bearing raspberries reach peak production, it is frustrating to lose fruiting canes to these insect pests. This article will describe the two insects and best management practices.
ROSE STEM GIRDLER
The rose stem girdler, introduced from Europe, is a small (ca. 1/5 in), bronze- and greencolored flat-headed beetle (Family Buprestidae). It infests wild and cultivated roses, red raspberry, black and red currants, and gooseberry. The Utah Plant Pest Diagnostic Laboratory database has records from Sanpete County, Utah, and north, with the majority of records from the Wasatch Front, Cache, and Rich Counties.
The rose stem girdler has a single generation per year and spends the winter as a mature larva within a cane. Adults emerge during May and June. Females “cement” eggs singly onto canes, and the white, flattened larva bores into the cane through the bottom of the egg. Larvae grow up to ½ in long and have a pair of brown projections on the tail end. Larvae feed in the cambium just under the bark in a spiraling pattern causing the cane to swell. Researchers in Utah (Davis and Raghuvir 1964) found that most larvae tunnel upward in canes and that primocanes (1st year) are more susceptible than loricanes to attack. Feeding injury often girdles the cane causing it to break off later in the summer. The larva can survive the winter in the broken cane, so removal and destructionof infested canes is critical to reduction of the overwintering population. In addition to pruning, insecticides applied as a full cane drench in May through early June when adults are active can reduce infestations. Several applications are usually needed to cover the entire activity period. Insecticide groups with efficacy against rose stem girdler and registered on raspberry include botanical (pyrethrin(*H), carbamate (carbaryl(*H), insect growth regulator (azadirachtin(*H), neonicotinoid (acetamiprid(*H), imidacloprid, and thiamethoxam), organophosphate (diazinon, malathion(*H), and synthetic pyrethroid (bifenthrin(*H), esfenvalerate, fenpropathrin, permethrin(*H), and zeta-cypermethrin). Removal of rose and other hosts near raspberry fields and gardens may also help reduce populations of rose stem girdler in the local area. (*H - available for homeowner use)
RASPBERRY CROWN BORER
Raspberry crown borer primarily feeds in the crown and roots and causes the entire cane to dieback, tip over, and be easily pulled from the plant crown. Cane death is evident in late summer to early fall. Earlier in the summer, infested cane tips may wilt and curl into a shepherd’s crook. The raspberry crown borer is a clearwing moth in the Family Sesiidae. The adult is a thick-bodied, day-flying moth (1 to 1 ¼ in wing span) that mimics a wasp (yellow stripes on a black body). The larvae are white with a brown head and grow up to 1 ¼ in long. In northern Utah, the insect spends 2 years feeding and developing within the plant to complete its life cycle, and injury is most evident in the second year. Adults are active in August through September. Females emit a pheromone to attract males. Researchers in British Columbia (BC), Canada have identified the pheromone, but it was unstable and volatilized quickly in BC and Utah field tests resulting in poor trap capture. Efforts are continuing to produce a stable pheromone lure. Female moths lay eggs on the lower leaves of canes and young larvae crawl down the canes and tunnel into the crown. The optimal timing for insecticide control is in the early fall (late September to early October) before young larvae tunnel into the crowns to spend the winter (McKern et al. 2007). A crown and root drench with a product containing bifenthrin(*H), diazinon, or imidacloprid will kill the young larvae (*H - homeowner products available). Treatments should be applied for at least two consecutive years to successfully reduce the infestation.
Davis, D. W., and N. N. Raghuvir. 1964. The biology of the rose stem girdler, Agrilus rubicola communis, on raspberries in Utah (Coleoptera: Buprestidae). Annals of the Entomological Society of America 57: 154-159.
-Diane Alston, Entomologist