Borers and miners are the larvae of various insects, particularly beetles, flies and moths. Many of the miners that cause damage to annuals, perennials and vegetables as well as woody plants are the larvae of sawflies. For solutions to problems caused by the larvae of beetles and moths, see Beetles - Borers and Miners and Caterpillars - Borers and Miners. As with all non-chemical solutions to pest problems, it is important to determine the specific pest before ascertaining the appropriate control method.
Many woody plants are vulnerable to sawflies, of which there are two main types: gall sawflies and stem sawflies. Gall sawflies are mostly leaf feeders, although some burrow internally in buds, petioles, twigs, or stems, usually producing galls. Susceptible trees include maples and willows. If the leaves of your maple trees begin to wilt, yellow or turn brown and drop beginning in mid-May, the petioles may be infested with sawflies; rake and burn or otherwise destroy the infested fallen petioles promptly and daily. Damage to willows is likely to occur west of the Rockies, and is generally limited to the formation of unsightly galls which may also weaken stems. There are a number of natural predators that help to keep these pests in check, including several species of birds as well as ants and grasshoppers. Some commercially available parasites have also proven to be effective controls.
Stem sawflies bore into tender shoots of trees and shrubs, occasionally inflicting serious damage in localized infestations; however, injury is seldom widespread. Vulnerable woody plants include blackberry, currant, raspberry, and roses, as well as some oak species, poplar, viburnum, and willows. If the canes of your roses or berry plants wilt and die back, you may have a sawfly problem; prune suspect canes below infested section and destroy them. Keep the larvae from entering pruned canes by inserting a flat-headed tack in the end or plug with grafting wax, putty or paraffin. The above-mentioned trees are most likely to manifest damage through wilting and drooping terminals and branch ends. In these instances, the most effective control entails pruning and destroying infested growth. Birds may feed upon the larvae, some of which will also be killed by cold winter weather. In the particular case of currants, some commercially available parasites have also proven to be effective controls for sawfly infestations.