Bagworm. Scouting: January - Look for overwintering bags.
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.
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.
Balsam Twig Aphid. Scouting: Start in early April to determine the amount of damage present. Walk through the field in a Z or W pattern. Scouting for Balsam Twig Aphid can be done at the same time as the Spruce Spider Mite scouting.
Threshold for Christmas Tree Growers: Treat only if the trees are within 2 years of harvest. If more than 10% of the trees have at least one damaged twig then consider treating. The amount of damage an individual grower/buyer will tolerate is variable as some buyers consider a small amount of twig damage good because the upturned needles give the tree a silvery appearance. This may take a number of seasons of working with buyers to perfect how much damage you can leave and still not reduce your price.
Mechanical Control: None known.
Cultural Control: Maintain the trees in good growing condition and trees should continue to vigorously grow even with populations of Balsam Twig Aphid present.
Chemical Control: Treat between mid-April and bud break. If you wait until after bud break it is too late for control this season and you should postpone treatment until next year. See Fact Sheet 444-22 for more detail.
Balsam Woolly Adelgid (BWA). Scouting: The best time to scout is in July as the adelgids are covered with a white cottony wax and are easily observed. In the winter they are much smaller and lack the woolly covering making them much harder to see. Look also for the trees that are flattening out on the top or have a crooked leader, this is early damage from the BWA. Walk through the field in a Z or W pattern.
Threshold for Christmas Tree Growers: Treat the entire block if an infestation is found.
Mechanical Control: If only one or two infested trees are found, wrap the infested trees in a tarp and cut down and remove. You will still need to spot spray the surrounding trees.
Cultural Control: Avoid excess use of nitrogen fertilizer.
Chemical Control: See the latest edition of the Pest Management Guide for Horticultural and Forest Crops, Virginia Cooperative Extension Publication 456-017. See Fact Sheet 444-233 for more detail.
White Grubs. General Comment: White grubs are seldom a problem on plantations where a grass strip is maintained between the trees. Scouting should be performed in areas where new trees are to be planted or where yellowing or slow growth occurs on established trees.
Scouting: Check especially in areas where trees are yellowing or not growing. Look also in areas with poor grass growth or where polecats or foxes are digging up grubs. In June lift up 1 foot square sections of sod, five sites per 2 acres.
Threshold for Christmas Tree Growers: Treat if you find on average more than 1 grub per hole and you have damage.
Mechanical Control: None known.
Cultural Control: Maintain as much grass growing between the trees as possible as the white grubs prefer to feed on grass roots and only move to tree roots when nothing else is available.
Chemical Control: Treat with Diazinon or Oftanol in the same manner you would treat a lawn.