WOOSTER, Ohio - From soil-applied systemic insecticides to tree guards, Ohio State University entomologists are looking for ways to control one of the most economically damaging insect pests in Ohio's nursery industry.
The white pine weevil, a North American native that attacks pine and spruce trees, has become more problematic over the past several years, threatening tree nurseries in Ohio and timber industries in states such as Pennsylvania and Michigan.
"The white pine weevil has become the No. 1 pest encountered by Ohio Department of Agriculture nursery inspectors," said Dan Herms, an Ohio State entomologist with the Ohio Agricultural Research and Development Center. "Historically it's been an important pest for the timber and Christmas tree industries in eastern Ohio, but the last couple of years it's really taken off throughout the state, hop-scotching across ornamental landscapes and nurseries."
Herms said the insect emerges in the spring, bores into the terminal, or lead, shoot of the tree and lays eggs under the bark. The larvae hatch and feed on the inside of the tree, causing dieback.
"The insect doesn't kill the tree, but destroys the symmetrical growth pattern that conifers exhibit. The tree forms multiple shoots, looking bushy and asymmetrical," said Herms. "It costs the nursery industry a tremendous amount of money because companies can't sell the tree until it re-establishes itself. A single insect attack can eliminate two to four years of growth. Insect feeding also reduces the quality of trees as saw logs."
Herms said the white pine weevil is a threat to nursery and timber industries because the insect is not so easy to control.
"Methods for control, mainly insecticides, are no longer available, either because the labels have been cancelled by the EPA (Environmental Protection Agency) or it's not economically feasible for companies to carry such products," said Herms. "Plus there is a desire to limit pesticide applications to reduce the risk of human exposure."
With problems of the insect increasing and available effective control methods decreasing, Herms and OARDC entomologist Dave Nielsen have begun a two-year project to find effective, environmentally friendly insecticides, as well as pesticide alternatives, to help keep the white pine weevil in check.
Researchers are currently studying systemic insecticides - chemicals applied to the soil at the base of the tree that are effectively taken up by the plant and protect it from larval feeding.
"Other insecticides used are extremely toxic, but the presence on the market of non-toxic systemic insecticides is a new development," said Herms. "The systemic insecticides offer the advantage of being easier to time their application accurately. Sprays must be timed to coincide with adult emergence during the spring, which is difficult to detect.
"We are studying whether the systemic product, which requires four to six weeks for uptake by the tree, may be effectively applied anytime during the previous fall. Studies with other pests suggests that the fall applications may be effective throughout the next growing season."
Researchers are also studying physical barriers for controlling white pine weevil populations, including the effects of wrapping a plastic tree guard around the terminal shoot to prevent females from laying eggs in the terminal shoot.
"The insects will still be present, but we may be able to prevent them from reproducing," said Herms.