Buckeye Yard and Garden onLine

Despite its common name, the weevil will infest a wide range of conifers including: Scotch, jack, red, and pitch pines; Norway, white, and Colorado blue spruces; and Douglas-fir. In early spring, overwintered females feed briefly on the terminals of conifer hosts, and then they lay eggs into this feeding material. The resulting white, legless, slightly curved, grub-like larvae tunnel downward just beneath the bark until pupation. Larval development is typically completed by mid- to late summer. The weevil has one generation per year.

The tops of infested trees become wilted, turn brown, and die. Main leaders are often curved into a shepherd's crook. The removal and destruction of infested terminals remains a highly effective method to reduce localized populations of this insect, as long as care is taken to cut below the downward progress of the larvae. A good sanitation program in combination with properly timed insecticide applications provides good control of this weevil.

Dave Shetlar noted that although the window for control is rapidly closing, Christmas tree growers may still achieve some suppression of this weevil by using dimethoate. Two applications are generally recommend with the first made 7-10 days after forsythia reaches full bloom and the second application made 3 weeks later. There may still be time to follow this recommendation in northern Ohio; however, it may be too late for the first application in the central and southern parts of the state. While a single application made now will help to reduce the total level of infestation, some damage may still be experienced.

Dimethoate is not labeled for landscape applications, and it is too late for topical applications of labeled pyrethroids to be effective. Infested terminals should be removed as the season progresses and plans made to make a fall soil drench/injection application of imidacloprid (e.g. Merit) at the highest labeled rate.

For more information, see:

• White Pine Weevil Factsheet
• White Pine Weevil