This will cause the tip to wilt. Damage becomes more profound as the larvae tunnel to the base of the plant, causing the entire cane to die off before the fruit can ripen.
Rednecked cane borers may infest as much as 50 percent of the canes in one or two year old plantings. . Infested canes die or become so weakened they cannot support a crop the following season.
By early June they reach adulthood and remain within the cane for 10 days or more while gnawing a "D"-shaped exit wound in the cane.
Once they emerge in early summer they begin feeding on young primo cane foliage for up to a week before laying eggs. Eggs are attached to the cane with a cement similar to that produced by mud daubers or gypsy moths. The egg hatch depends on the temperature , in warm climates they hatch in as little as 4 -5 days, in cooler regions in can take up to 3 weeks.
The larvae chew into the cane and create spiral tunnels, much like a leaf miner.
Organically acceptable insecticides, such as rotenone, pyrethrin, Neem oil, or insecticidal soap. Insecticidal control application is recommended to coincide with the adults emergence in early summer. Do not spray until adult emergence has been observed.
Neem prevents the larvae from developing normally and is also a good alternative for later larval stages. Neem degenerates rapidly in nature and needs to be reapplied frequently.
Bacillius thuringiensis [Bt] is somewhat effective against the larvae stage only and should be applied as soon as the larvae are first noticed or suspected.
Inter-plant Garlic among susceptible plants. Garlic is a known deterrent, it also discourages aphids, Flea beetle, Japanese beetle, spider mites as well as vampires and members of the opposite sex. See - Raspberry Companion Planting
Winter pruning is a good time to ascertain the extent of rednecked cane borer penetration.
If the number of galled primo canes is greater than the number of canes you expected to prune out, you have a problem and control is advisable to salvage the subsequent seasons anticipated crop. You should prune out all the galled canes and destroy them . Nearby refuges of cane borers should also be removed and destroyed during the dormant period.
Dormant oil sprays can be applied to cull populations that overwinter, but will not eradicate them as they are somewhat shielded within the canes.
Handpicking is not always feasible in larger gardens. In small gardens, handpicking is somewhat helpful. Destroy adults and larvae, New adults may eventually migrate to your garden, so be sure to check your plants on a regular basis. You may notice random localized swellings along the canes of your raspberry plants long before you ever see a cane borer. This is a telltale sign of their presence.