March/April 2000

Gardeners Information Service

Two more of my most promising new shrubs have been chewed off just below the soil line by voles. I can see the tell-tale marks from their nasty little teeth! I have tried traps, Ramik pellets, and castor oil-based repellent drenches-with only mild success. I have some hardware cloth to make protective "root cages" for replacement plantings, but I need suggestions on the best way to make them. -C. W., Richmond, Virginia

Young trees and shrubs can be protected from voles by installing cylindrical tree guards made of quarter-inch wire mesh. The guards should be taller than the average snow depth and extend three inches into the soil. The diameter of the wire mesh cylinder should be large enough to allow for five years of growth. Herb Reed, an extension educator in Calvert County, Maryland, also suggests keeping mulch shallow-no deeper than one inch-because thick layers of organic mulch provide an ideal habitat for voles. Mulching with pebbles or crushed stone will create a less inviting habitat to voles; they will either avoid the area or be more easily spotted by predators. Encouraging predators is an effective way of keeping rodent populations under control. Hawks, owls, crows, black snakes, and king snakes feed on voles. Try placing ordinary mouse traps, baited with peanut butter or a small piece of apple peel, in or near the open end of the tunnel. A cardboard box placed over the trap and the end of the tunnel will reduce the likelihood of other animals being trapped. The use of poison baits is not recommended because of the risks to children and non-target animals. Long-term management of vole populations should be based on habitat reduction and predator encouragement rather than reliance on chemical controls.

Fire Blight Controls 

During the last growing season I think I identified fire blight on my cotoneasters and spireas. Branches are turning brown and drying up at random spots. All the books I've consulted recommend streptomycin. What is this and will it do the job? -P. D.,Dover, New Hampshire

Fire blight is a serious disease caused by the bacterium Erwinia amylovora, which afflicts members of the rose family (Rosaceae), including pears, apples, and ornamentals such as cotoneasters and spireas. Scott Aker, integrated pest management specialist at the U. S. National Arboretum in Washington, D.C., recommends the following measures to protect your plants from the disease's spread. Carefully inspect all branches for holdover cankers-darkened irregular collars or ridges on the bark-that serve as a reservoir for resting fire blight bacteria. Cut back affected branches well below the canker, at least six to 12 inches into healthy tissue; dispose of pruning debris with household garbage. Make sure to dip pruners into a mild bleach solution (one part bleach to 10 parts water) between plants and after completing the job to prevent cross-contamination. Streptomycin, an antibiotic, is no longer recommended as a control because the fire blight bacterium has developed a resistance to it. Spray instead with Bordeaux mix-a blend of copper sulfate and hydrated lime-when plants are dormant, just before they leaf out in the spring. Follow manufacturers directions for spraying precautions.