Douglas G. Pfeiffer, Dept. of Entomology, Virginia Tech, Blacksburg VA, and Jayesh B. Samtani, Hampton Roads Agric. Res. and Ext. Center, Virginia Beach VA
Caneberries are a popular crop for many insect pests. During the growing season, because of the way blackberries and raspberries flower and fruit, chemical control is complicated, given issues with preharvest intervals. At this time of year, in winter, we have the opportunity to use some cultural control measures against some important pests.
Pruning for borers
Though caneberry plants are perennial, individual canes are biennial, living two years. In conventional, floricane-bearing cultivars, in the first year, a cane is known as a primocane, and exhibits vegetative growth. In the second year, known as a floricane, these overwintered canes produce flowers and fruits. In newer, primocane-bearing cultivars, flowers and fruits will appear in the latter part of the first year. Canes may be allowed to bear additional fruits in the second season, or all canes may be removed, allowing the production of new primocanes in the second season and eliminating the process of selecting out old floricanes for removal. We can capitalize on these growth habits to aid in the suppression of borers.
In the paragraphs below, we describe the three commonly observed borers and control measures in caneberry production in the southeastern U.S.
Rednecked cane borer
This is a small buprestid beetle, about a quarter inch long (Fig. 1). The elytra, or front wings, are dark gray, and the pronotum (the section right behind the head) is a coppery color. Eggs are laid on canes, and the larvae create a spiraling tunnel beneath the bark. This causes an elliptical gall, and canes decline. Chemical control may include an insecticide spray just before bloom starts, and about two weeks later. But a cultural control would be to remove galled canes in the dormant period or early spring. It is important to discard the canes off-site. Summer pruning may also provide some control, since when new canes appear, they will have avoided much of the oviposition period.
Raspberry cane borer
This cerambycid or long-horned beetle, is a half-inch long, twice the length of the rednecked cane borer. The elytra is dark gray to black, and the pronotum is orange with two black spots (Fig. 2). In the spring, when egg-laying occurs, two rings of punctures are created, easily visible near the shoot tip. One ring is about 6 mm above, and one 6 mm below the egg puncture. After an egg hatches, the larva tunnels downward in the cane. Winter is spent in the cane, and it’s life cycle continues in the following spring. This tunneling can cause cane death. An insecticide may be applied just before blooms open. But a cultural control is removing wilting canes or those with girdling. If tissue is removed within a few days of the appearance of girdling, not much additional tissue needs to be removed.
Raspberry crown borer
Unlike the previous two species, this is a moth pest. Clearwing moths are usually moth mimics, and this one is true to form, being a good mimic of a yellowjacket (Fig. 3). Eggs are laid on the undersides of leaves in the spring, and upon hatching, neonate larvae spin down to the crown of the plant. After spending the winter there, in the following year, the caterpillar tunnels into the crown. In the first summer, feeding occurs in the crown area, causing galling. In the second summer, the larvae tunnels up into a cane, where its girdling can cause the cane to break. Chemical control would include an insecticidal drench at the base of the plant, either in the fall or prebloom in the spring. Cultural control would include the removal of all wilted canes in June or July – not a winter time operation!
The emphasis here is on cultural control; if an insecticide application is needed, see our Southeast Regional Caneberry Integrated Management Guide, available online. Whether chemical control or cultural control are employed, control will be more effective if nearby wild caneberries are removed, to remove immigration pressure.