Homeowners who want green foliage year-round often place evergreen bushes in their yard or garden. While evergreens are generally healthy, they are often attacked by defoliating pests. One of the most common defoliating pests of evergreens is the caterpillar. A wide range of caterpillars feed on evergreens, causing them to appear ragged and unkempt. Caterpillars can be detrimental to the health of the host plant when actively feeding in large numbers.
Sawfly larvae are damaging pests of evergreens. This caterpillar is the larval form of the adult sawfly, which is similar to a non-stinging wasp. Sawfly larvae typically feed during the summer months, with many evergreens not showing damage until the larvae have fled from the host plant. Light infestations of sawfly larvae are not detrimental to evergreen bushes, but very severe infestations can cause significant damage to the plant. Bagworms also frequently defoliate evergreens. This caterpillar places brown bags on the host tree, where it lives until it leaves the bag to feed. Female bagworms never leave their bags and place up to 1,000 eggs inside. Once these eggs hatch, new larvae emerge to feed on the host plant. Large bagworm populations are often deadly for evergreens. The larval stage of the Gypsy moth is a common evergreen pest. This caterpillar feeds on over 300 different plant species and in large numbers cause serious damage to evergreens. Blue spruce and white pine are especially susceptible to defoliation by the Gypsy moth caterpillar.
Pine sawfly larvae begin feeding in the early part of May and continue for up to three weeks. This caterpillar feeds on the young, tender needles of evergreens with the most damage occurring when populations are high. Bagworms also feed on the needles of evergreens. Trees that fail to grow new foliage can die from heavy infestations. Gypsy moth caterpillars damage evergreens in the same way as bagworms and sawfly larvae, but often they leave green excrement known as frass everywhere. Some people have serious allergic reactions when they come into contact with the hairs on the Gypsy moth.
Caterpillars are often easily controlled by hand-picking them from the evergreen bush. Bagworms should be removed by plucking the brown, silky bags from the tree. Place caterpillars in a bucket of soapy water after removing them. Hand removal works best when small numbers of caterpillars are present. Removing caterpillars by hand should be done during the fall or winter, before the eggs hatch and new larvae emerge. Placing a burlap cloth around the bottom of the infested evergreen may help capture caterpillars. Caterpillars hide under the cloth, making them easier to dispose of.
Heavy infestations of caterpillars often require chemical control products. Foliar sprays with active ingredients such as acephate or malathion are often effective in caterpillar control. Gypsy moth caterpillars are most vulnerable to the effects of Bacillus thuringiensis or BT. BT products are a good choice for those who have children or pets, because they are non-toxic.