Bagworm. Scouting: Look for overwintering bags in January.
Cultural Control: Pick off and destroy bags in the fall and winter. Bags can be destroyed by dropping them in a can of kerosene or burying them at least 6" deep.
Chemical Control: It is important to treat in mid-June when the larvae are small and susceptible to insecticides. Larger larvae with bags are not easily controlled. See the most recent Virginia Pest Management Guide for insecticides labeled for control of bagworms.
Biological Control: Spraying with Bacillus thuringiensis (B.t., Dipel, Thuricide, etc.) in early to mid June should give satisfactory control.
White Pine Weevil (WPW). Scouting: Look for resinous bleeding in late March or early April to find when adult females are feeding and laying eggs. Check trees also in June to determine which tops are actively infested with WPW. Check for a final time in fall to determine the percent of trees that are infested.
Threshold for Christmas Tree Farms and Forestry Plantations: If fall surveys indicate that more than 5% of the trees were infested with WPW the previous season plan on treating the whole plantation or block.
Mechanical Control: Prune out and destroy infested tops in late June. Make sure stems are cut below where weevils are feeding. Tops must be cut before the weevils make exit holes and leave.
Cultural Control: Remove all old unattended stands of white pine and Norway spruce that may by harboring populations of WPW.
Chemical Control: Treat the terminal leader with a registered insecticide before the buds open. Do not treat the lateral shoots as they are not the infestation point. Apply the insecticide no later then late March or early April. For valuable specimen trees it may be necessary to treat each year. Consult the latest Virginia Pest Management Guide for current labeled insecticides.
Remarks: Repeated terminal dieback caused by WPW can give trees an asymmetrical crooked appearance that is aesthetically pleasing to many people. Often the nice old gnarly pine tree has been given its appearance by repeated attacks by WPW.
Spruce Spider Mite. Scouting: Start scouting in mid April and continue scouting once a month until the first heavy frost. Walk through the plantation in a Z or W pattern. Pick a tree at random once every 50 feet. Check the shoot for mites or mite damage, you may need a 10X hand lens to see the mites. You should be examining at least 15 shoots per acre. Carry a sheet of paper with two columns marked to record the total number of shoots sampled and the total number of shoots with mites. The presence of damage alone is not enough record it as positive if you find the mites or mite eggs. Based on research in North Carolina, that is applicable to Virginia, the economic threshold is based on the size of the tree. On trees less than waist high, treat if the percentage of shoots with mites exceeds 40%. On trees waist high to year before sale treat if the percentage of shoots with mites exceeds 20%. On trees at the year of sale, treat if the percentage of shoots with mites exceeds 10%. Use these guidelines for determining when to come back and sample again. If no mites or eggs are observed then return in 6-8 weeks. If less than 10% of the shoots have mites or eggs return in 4-5 weeks. If more than 10% of the shoots have mites or eggs return in 2 weeks. If there are more than 10 days of hot, dry weather check the trees sooner.
Cultural Control: Avoid having bare earth under trees as this will reduce the number of predators on the tree and increase the number of Spruce Spider Mites.
Mechanical Control: None Known.
Chemical Control: See Fact Sheet 444-235 for more detail.
Coolly Spruce Gall Adelgid. Before you start, only Norway Spruce plantation with Douglas-fir planted nearby suffer from this problem. If no Douglas fir are nearby it is not advisable to scout for this insect. Scouting: Start scouting in April and look for small tufts of cotton like material at the base of buds. Look again in August and September to determine when the galls have opened up.
Threshold for Christmas Tree Farms: Treat when 5% of the trees have ten or more galls, spot spraying may work with smaller infestations.
Cultural Control: Avoid planting Douglas fir within 500 yards of Norway Spruce.
Mechanical Control: None known.
Chemical Control: Treat with dormant oil in February or March. In severe cases treat with an insecticide in August or September just as the galls turn from brown to green and small openings are created for the adelgids to exit. Treatments can also be applied in April but this is trickier as it needs to be done when the small adelgid is feeding at the base of the needle just before the gall is formed. The adelgids will be covered with a small tuft of wax.