CTN - 020
Jill R. Sidebottom,
Extension Forestry,1993
Updated November 1, 1995
Introduction
The balsam woolly adelgid (Adelges piceae) (BWA), previously called the balsam woolly aphid, is a tiny, soft bodied insect which appears as white, woolly spots on Fraser fir. It is different from an aphid which continually moves around the plant, probing with its feeding tube. The BWA has only one stage in its life cycle -- the crawler, which can move from place to place. Once the crawler finds a suitable feeding site, it sinks its feeding tube into the tree bark and never moves again. The crawler must find a suitable site within two days or die.
The BWA is native to silver fir of central Europe, and was introduced to this continent before 1900. European firs are not seriously affected by BWA, but BWA can kill American firs, especially Fraser fir.
These adelgids are very small and difficult to see. It takes several months before trees develop symptoms of insect damage. Because of this, BWA can increase unnoticed and cause serious losses to unsuspecting growers. Luckily, the BWA takes a year or more to spread to many trees, so through careful scouting and conscientious control, serious losses can be avoided.
How BWA Moves into Trees
The BWA can only live when it is on a living fir. These insects can not fly, and can only be carried by the wind, or moved when firs (such as seedlings) are moved. The BWA can be found in all of the natural stands of Fraser fir and can be moved with seedlings pulled from natural stands. In addition, the BWA can blow from natural stands, other Fraser fir plantations especially if they are not well managed, and Fraser fir yard trees. Isolated plantations of Fraser fir may never be bothered with the BWA.
Only the crawler can move to a new tree. Since crawlers are only present from April through October, the rest of the year the BWA can not infest new trees.
How BWA Damages Trees
The tree reacts to the adelgid feeding and tries to protect itself by producing reaction wood. Fraser fir will produce this type of wood in response to any injury. This wood is very hard and limits the proper movement of water, nutrients, and hormones through the tree. The internal water stress can kill a tree, and will slow and distort plant growth. Even a tree with so few BWA that the tree still looks healthy will be more likely to shed needles once it is cut. Heavily infested trees should not be marketed.
Excluding BWA from Trees
The first line of defense against the BWA is to exclude the insect, as much as possible, from your trees. If you pull seedlings from natural stands, treat them with an insecticide as soon as they are planted on your farm. Remove any large Fraser fir that can not be treated for BWA. If you have neighbors that have fir in their yards or have abandoned Christmas trees, do everything you can to either have those trees removed or treated with an insecticide, even if you have to do it yourself.
Finding BWA in Trees
The only way to know if you have BWA in your trees is to observe the tree symptoms of BWA damage. The primary symptom is a flat top or weak leader. Other symptoms include dead shoots or branches, swelling around the shoot nodes (gouting), reduced shoot growth, a stiff trunk, and growth rings with red, hard wood instead of the healthy, creamy white wood (observed when trees are cut). A tree showing symptoms has had the BWA on it since before bud break of that growing season. It usually takes several months for symptoms to develop.
These same symptoms can be caused by other problems. A weak top, for instance, is often caused by multiple tops in the tree. Therefore, to confirm that the cause of the symptoms is BWA, look for the white wool of the adult female on the trunk of the tree. These insects seem to prefer to hide under the branch/trunk union, though they are found anywhere on the trunk, branches, buds and shoots.
To make sure a white spot is BWA, cut it off and examine it with a handlens. The BWA can be mistaken for dried resin or lichens. Only the adult BWA will have a mound of white wool covering her. (See CTN-018: Common Fraser Fir Insect Pests). The adult female may have cinnamon colored, oblong eggs behind her.
In the winter, only the immature nymphs are present. Since they do not have thick woolly covering of the adult, it is sometimes hard to confirm that BWA is present. They are smaller than the adult, are black, and have rows of white waxy rods along their backs. These nymphs are more easily found on the buds of the tree. From April through October, however, the adults are active. As the season progresses, more and more white wool should become apparent as the adelgids continue to multiply.
Scouting for BWA to prevent damage. To prevent BWA from causing damage to your trees, scout trees once a year from the time they are waist high until harvest. Scout trees sooner in a rotation if they are near large, untreated Fraser firs.
Trees can be scouted any time except from bud break until the new growth has fully elongated. The best time to scout is in July, because this gives you the first opportunity to see if any trees have developed new symptoms.
Enter the field at one corner, stepping two to four rows into the field. Walk the full length of the row, scanning from side to side up to five rows in each direction depending on the size of the trees. You need to see the leader of every tree in the field. In a field to 6-8 foot trees, you may only see three rows well. When you reach the end of the row, step over six to ten rows depending on tree size. Continue this pattern until you've covered the entire field.
Any tree with dead branches or a crooked leader should be examined for the BWA. Feel free to leave the row you are walking to examine a tree, but be sure to return to that row to continue walking.
Controlling BWA
If any BWA are found, it will be necessary to treat the field for the BWA before bud break of the following year, unless all of the trees are to be harvested that fall. The BWA have few predators in western North Carolina and will continue to increase in your trees unless treated chemically. Spot treatment of the field is only possible if the trees are a year or less from harvest, and only one portion of the field has BWA.
Do not treat for the BWA unless it is found in your trees. Through scouting, you will know when BWA first comes into your trees. Preventative treatments do not work because coverage is not adequate. Treating unnecessarily wastes time and money, and may create problems with other insect pests.
Good control requires complete coverage of the tree. Thorough coverage is more important than what insecticide is used. Good coverage is easiest with a high-pressure and apply at least 200 gallons per acre. Depending on the size of the trees and their density, as much as 400 gallons per acre may be necessary.
Spray trees from at least two directions. The base of the tree trunk and under the branch/trunk union are two difficult places to reach. Practice spraying trees with water, checking immediately to see if the entire tree is wet.
When treating a field of trees, also treat stumps of trees cut within the last 6 months, and stumps with live branches still on them. Adelgids will survive on cut stumps for several months. Trees can be treated any time of year except from bud break until the end of June. Some materials should only be used in the fall or winter because of problems with burn or with control at other times of the year (see below).
Materials labelled as of July, 1993 include: Asana XL (10 oz./100 gal.), horticultural oil (1 gal./100 gal.), insecticidal soap (2 1/2 gal./100 gal.), lindane (2 qt./100 gal.), Lorsban 4E (2 qt./acre). Asana and lindane can be used any time of year that trees can be treated. Lorsban and insecticidal soap should only be used from November through March. Any other time of year, a second application will be necessary after four weeks. Horticultural oil should only be used from December through February because it may burn trees if they are not dormant.
Using either lindane of Asana may cause an increase of the spruce spider mite because they kill mite predators. When using these materials in the spring, summer, or fall, consider adding a miticide to the spray mix.
Several of these materials may burn trees if sprayed during hot weather. On hot, sunny, humid days, do not treat during the hottest part of the day.
Several months after treatment, check to see if trees have developed any more white, woolly spots. Examine new and old spots under a microscope to see if the adelgids are dead. Large growers may want to purchase an inexpensive microscope that has 20X or 30X power. You may also take them to local Cooperative Extension Office for the County Extension Agent to examine.
Heavily infested, badly damaged trees often will not recover even after the adelgids are killed. Trees that will never make a saleable Christmas tree should be cut down and burned. Only do this in the winter months when crawlers are not present. Otherwise you may spread crawlers to healthy trees when the infested ones are carried out of the field.
Will one treatment last me three years? Many growers feel that treatment for the BWA should last them three years. This is not always true. How soon a field needs re-treatment depends on several factors. If the field is heavily infested, it may require re-treatment the following year. Large trees (over 8 feet) often require more frequent treatment. Fields near natural stands, abandoned Christmas tree plantations and yard trees may need more frequent treatment. Only through scouting, will you know if re-treatment is necessary and when.
Recommendations for use of agricultural chemical brand names and any mention of commercial products or services does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned in this publication.