Pine root collar weevil

A serious pest of Scots, red, jack and, occasionally, white pines is the pine root collar weevil, Hylobius radicis. The grub-like larvae girdle the root collar (where stem and roots meet), as well as roots of young pines larger than 1/2 inch in diameter. Complete girdling kills trees and those trees weakened by these weevils may fall over and die within one to four years after being attacked. Larger trees may also be attacked. Look for yellow to red needles on infested pines, including some pines that may be leaning or that have failed at the root collar. Black, pitch-coated bark at the root collar and blackened pitch-soaked soil close to the root collar can also be found on infested pines. Galleries in this pitchy soil can contain yellow-white, legless, C-shaped larvae which are up to 1/3 inch long and have amber brown heads. Adults may also be found in this pitchy soil.

Each weevil is nearly 1/2 inch long and is dark reddish brown to nearly black in color with irregular patches of white to yellow hair-like scales.

Each female lays l0 to 70 eggs from early May to early September on root collars or in the nearby soil. Eggs hatch in 7 to l7 days, depending on temperature, and these larvae burrow through the bark and feed on the live inner bark and cambium tissue, thereby restricting transport of nutrients and causing flow of pitch into the nearby soil. Adults feed on live pine shoot bark until autumn and overwinter in the litter or bark crevices at the bases of trees. They can live and reproduce for 2 or more years.

To control this insect on living trees, prune off basal whorls of branches up to 4 feet above the ground, depending on size of tree, and rake away litter and two inches of soil from around the root collar, as adults are sensitive to heat and light. A persistent insecticide such as acephate or diazinon can be applied as a drench at the root collar to kill larvae and adults and prevent reattack or new attacks on healthy pines. Foliar sprays of these insecticides in mid-May, and again in August, can control adult weevils feeding on shoots. Removal and disposal of dead and dying pines, followed by insecticide drench of stumps and pitchy soil, is also recommended.