The balsam twig aphid is an insect that feeds on the emerging shoots and new buds of evergreen trees such as firs and spruces. Armed with mouth parts that have been adapted for piercing, they suck the sap from the tree's needles, resulting in curled and twisted needle development and stunted tree growth. Control of balsam tree aphids is not difficult, but the window of opportunity for successful treatment is fairly narrow. Treatments must be applied before the spring buds break open; if the aphids manage to make their way into newly emerged buds, they can easily avoid contact with insecticides.
Prepare a simple soap solution to treat trees by mixing 2 tbsp. soap flakes and one cup vegetable oil with a quart of water. Stir until the ingredients are well blended, and then transfer the mixture into a bottle with a sprayer attachment. Soaps contain fatty acids that disrupt the internal cell structures of certain insects when they come into direct contact with it.
Make a second solution by combining 15 cloves of minced garlic with 2 tsp. vegetable oil and 1 tsp. liquid detergent. Blend thoroughly and then add the resultant mixture to three cups of water. The odor and flavor of garlic in this solution will help make the tree less appealing to aphids and other insect pests.
Watch your tree closely. Beginning in the late spring, visually inspect the needles of the tree, searching for signs of aphid infestation. First generation twig aphids will be wingless green bugs that will be busy building white, waxy-looking egg deposits on and under the tree's needles. The ideal time to treat the tree is just after the eggs have hatched but before the buds have opened.
Spray the tree with water from your garden hose when the time is right. Use a high pressure nozzle and thoroughly soak the foliage, working from the top of the tree to the bottom. Be sure to spray the undersides of the branches as well was the tops. This will effectively remove most of the aphids from the tree. Once on the ground, they rarely make their way back to the branches. If you're not sure of the timing, start early and treat the tree once a week until you're certain you've conquered the aphids.
Apply the insecticidal soap to the tree and allow the solution to dry. They apply the garlic solution. Re-apply these insecticides once a week throughout the spring and into the early summer for the greatest effect.