I have a 10-year-old, 16-foot white pine in my backyard. It has been doing fine for most of its life, but in the last two years has taken large amounts of damage from a heavy infestation of white pine aphids and accompanying sooty mold. By the end of the summer, every branch is coated with the bugs; some branches have died altogether, needles are dropping early, and many of the needles the tree still has are yellowing and stunted. No natural predators appear to be present. What control measures would you recommend for this? The tree is a tough one, and has a good chance of recovery if the aphids can be eliminated.
There are a number of steps that you can take to combat the aphid infestation. First, improve the health of your tree by making sure that it is well watered. I also suggest removing the dead branches. A dormant oil spray can be applied to to the bark and limbs of the tree in May to kill the overwintering nymphs before they begin to produce eggs. Dormant oil can also be applied in the summer . It may take a number of sprays at weekly intervals to kill the newly hatched aphids. Insecticidal soap is an effective treatment for aphids. It must be applied regularly to ensure that the next generations of aphids are killed as they appear. You can also spray the tree with water to knock the aphids off. Finally you can ensure you can plant a diversity of plants in your garden to attract aphid predators such as lady buds and parasitic wasps. Note that lady bugs are biological controls which are also available at garden centres, but you will have more success attracting them to you garden than seeding them in your garden, as they may very well fly off it not induced to stay!
It you are successful in eliminating the aphid infestation, the soot mold should disappear.