Virginia pines grown as Texas-grown Christmas trees can
be killed by infestations of the deodar weevil (Pissodes
nemorensis Germar),also known as the northern pine weevil. Trees
are usually observed to begin dying in December, but mortality
can continue to occur through mid-March.
The deodar weevil is primarily a secondary invader, meaning that infestations occur only in trees that are dead or dying due to other causes (mechanical damage, water stress, etc.). However, they are certainly successful at "finishing off" a stressed tree. Furthermore, if populations build up, they may attack other nearby seedlings and stressed trees. The deodar weevil has also been reported to attack spruces and junipers.
Knowledge of this species' biology is the first step in selecting a proper management strategy. In the south, the deodar weevil is reproductively active in late summer and fall (August-October). At that time, mating and egg-laying occurs. Eggs are deposited in fresh stumps and trunks of stressed trees and hatch into small grub-like white-colored legless larvae with brown head capsules. Many larvae have been found in individual trees. Full grown larvae are about 1/3 inch long and can be found beneath the bark of dead or dying trees or dead stumps. There is often no external evidence that the weevil larvae are inside and infested trunk. Larvae mature and pupate under the bark in 1/2 inch-long elliptical chambers lined with wood shavings or "chip cocoons" in the spring (February-April).
Adult deodar weevils are 3/8 to 1/4 inches long, reddish brown,
mottled with black marks. They have two distinctive whitish spots
on the wing covers near the end of the body.
Adults emerge from the trees through exit holes they make in the trunk and feed on the inner bark of twigs and small branches throughout the summer. There, they make small circular feeding wounds ("drill holes") at the base of injured shoots. Piech may ooze from the wounds and damaged shoots may fall down ("flag") becoming discolored or deformed. Adults remain reproductively inactive until they fall. Heavy feeding by adults may kill some shoots, leaving dead spots in the crown and slightly degrading Christmas trees. Heavy infestations may kill seedlings. Adult weevils are only active after dark.
Monitor for adult damage by inspecting trees for pitchy "drill holes" or flagged tips on seedlings and older trees. Treat the entire nursery or plantation if seedlings show any injury or if older trees have five or more flagged tips per tree. Infestations lighter than this do not need control, because most flags will fall off before harvest. Insecticides used to control the Nantucket pine tip moth may or may not reduce weevil numbers. Dycarb or Turcams (bendiocarb) used at the labeled rate (20-40 oz and 2 lb 10 oz. of product, respectively, mixed in 100 gal water) can be used to control adults. Treatments applied when adults appear in the fall may reduce reproductively active and egg-laying females, but earlier treatments should be applied primarily to prevent twig and seedling damage.
Larval control i9 difficult using insecticides alone. The cultural practice of sanitation is the best method for eliminating developing populations. Remove and destroy all infested and non-infested dead or dying pines and fresh stumps before spring. This will reduce the number of adults emerging and destroy breeding sites for the next generation of immatures.
If fresh stumps are not removed, they should be sprayed with an approved insecticide like lindane or chlorpyrifos (Dursban@). In northern Christmas tree producing regions, stumps are sometimes drenched with diesel or motor oil, or with insecticides mixed with kerosene or fuel oil. However, in east Texas plantings proned to flooding, this practice would be questionable. Stump treatments are applied in the fall to kill egg-laying adults or in the spring to kill emerging adults.
When harvesting, leaving one whorl of live, pest-free branches on each stump will keep the tree alive and therefore unattractive to egg-laying weevils. Destroy these stumps within three years. However, do not leave live branches that have needlecast diseases.
Of course, the best management strategy is proper site selection. Avoid planting Virginia pine trees on poor and poorly drained soil. Maintenance of good growing conditions throughout the production period on good soil will make trees less proned to attack by the deodar weevil.
Reference: Benyus, J. M. 1983 tree manual. USDA, Forest Service, North Carolina Forest Experiment Station, St. Paul, MN 108 pp.
The USER is always responsible for the effects of pesticide residues on his livestock and crops, as well as problems that could arise from drift or movement of the pesticide from his property to that of others. Always read and follow carefully the instructions on the container label.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.
Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.
1989
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Last modified: March 18, 1997 by Edgar Cross