Question: Last week the temperature at our house near Oakville dropped into the low teens. Imagine our surprise to find a branch covered with live caterpillars on our fir tree as the snow began to melt. What are these? Should we spray them with something?
Answer: Based on your description, more than likely the caterpillars on your fir tree are the larvae of the silver spotted tiger moth. I usually refer to these small, furry, rusty brown or black-ish caterpillars as the "polar bears" of the insect world since cold temperatures do not affect them. Although they usually hibernate during the winter months in the dense webs they spin, it is not unusual to find them feeding on warmer January days. Feeding is restricted to the needles at the ends of the lateral branches. Whole branches are often stripped of their leaves, making individual trees appear quite unsightly at times. Cases of total defoliation are rare. Damage is most often limited to one or a few limbs of a tree. Since the buds are not harmed, the new growth will cover the damaged area by early summer.
In general, this caterpillar is not considered to be a serious pest. They are generally reduced by the same parasitic Trachnid flies that attack tent caterpillars and these parasites keep populations under control. Another option, is to simply prune out the infested branch and dispose of the caterpillars.
Question: Every year our blue spruce tree looks just awful in the spring. A lot of the needles turn yellow, while others turn completely brown and eventually fall off. I am to the point of thinking we should have the tree removed. Do you have any suggestions?
Answer: Based on the symptoms you are describing, there is no question that the damage to the needles is due to feeding by the spruce aphid.
What these little monsters lack in size, they make up for in large numbers. What makes them unusual is that they are feeding now, during the coldest time of the year. The spruce aphid is often referred to as the "winter aphid" because its number peak during the winter months and it literally vanishes during the summer months. Populations start to build as early as October and then peak in February and early March. There are several generations annually.
An interesting fact about the spruce aphid is that all of them here are females. They reproduce by a phenomenon called parthenogenesis, which basically results in a clone of the female.
Right now, while you are within the warm, cozy environment of your home, the spruce aphids may well be sucking the life right out of your spruce tree. Soon after feeding the needles become a discolored yellow or brown. Since they are light intolerant, these aphids are found on the lower end branches in towards the trunk and are usually concentrated low on the tree. High infestations however, can occur everywhere in the tree. Affected needles die back and eventually drop off the twig.
Unfortunately, the damage really doesn't become noticeable until about June and by then the aphids are long gone. The best method for attacking this pest is to begin examining your spruce tree now to see if aphids are present. Get a sheet of clean, white paper and a hand lens. Brush two branches together over the paper and look carefully using the hand lens. If aphids are present, they will have shaken onto the paper.
For the home gardener, with just a tree or two, the simplest control option, is to simply hose the aphids off the branches with a high-pressured stream of water. This will knock them off the branch onto the ground where they will not re-infest the tree. You should continue to check the tree weekly to see if aphids are present.
Question: Will the cold temperatures earlier this month mean fewer insects this summer?
Answer: Probably not. WSU entomologists have found that during periods of unusually cold temperatures, it's usually the "good bugs" that fall victim to the frigid temperatures. Unfortunately, in most cases, they are far less hardy than those insects that feed on our favorite garden plants. In all likelihood, with decreased "biological controls" in place, we may well have more of an insect problem this year than would normally occur.
EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: email@example.com.