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Tending and protecting your pines

Deer browse
During the winter, white-tailed deer like to feed on white pine seedlings and saplings. Deer can chew off any twig tips within their reach. Serious damage is caused when the terminal (or topmost) bud is destroyed because the seedling is stunted and may be kept stunted by browsing year after year.

Bud capping for deer protection. White pines can be protected from deer browse by a number of methods including repellants, fencing, wire cages and bud capping. Bud capping is one of the cheapest and easiest methods, but must be done every year until the terminal bud is out of the reach of deer. A bud cap is a piece of paper that is folded and stapled around the terminal (top) bud of the seedling to keep deer from chewing the buds off. This protects the terminal bud of the tree in the fall when the deer are likely to feed on it, yet allows the bud to expand and grow up through the paper sleeve during the next growing season. Deer will feed on the side branches but the bud cap usually protects the more important terminal bud. It's not necessary to remove the bud caps in the spring.

  1. Bud caps should be applied in the fall before snow covers the ground, usually by November 1st .
  2. Use light -weight paper such as typing or computer paper. The bud cap needs to last only a few months and should fall apart by the next growing season.
  3. Cut the paper into 4" X 6" sizes. Smaller caps of 3" X 4" may be used for small trees.
  4. Bud caps should be held on the tree by catching needles in at least three staples.
  5. The terminal bud of the tree should be placed at least ½ inch below the top of the paper but not lower than the midpoint of the paper.
  6. Bud caps should be applied every year until the tree is at least five feet tall or out of reach of the deer.

Plant competition
Weeds, grasses and shrubs compete for light, water, nutrients and space with the white pine seedlings. Seedlings can grow slowly, be stunted or die from competition

Maintaining good height growth and survival of the white pine will likely require control of competing grasses, weeds, shrubs and overstory trees. Try to maintain 1 to 1 ½ feet of height growth per year after the trees have been in the ground for six to eight years. 1. Grasses and weeds can be controlled by mowing, mulching, use of individual "weed control" mats or herbicides. 2. Competing brush and shrubs greatly reduce the survival and growth of white pine and must be controlled. This can be done by hand cutting or herbicides. Consult with a professional forester on types, timing and application methods for herbicides. 3. The shade from overstory trees should be maintained at 40 to 60 percent. Partial overstory release may be necessary to accomplish this. Overstory trees can be felled or girdled. 4. When growing pines under an overstory, maintain the overstory trees until the pines are at least twenty years old.

White pine blister rust
White pine blister rust is a fungal disease of white pine. It causes branch death, stem cankers, topkill and can be fatal. Live needles are the first to be infected then the fungus grows into the twig and towards the stem of the tree. A blister rust canker is the result of an infection that has been growing under the bark of a branch or stem for several years and is cutting off the supply of food and water to parts beyond the infection. This disease becomes more common and more serious as you go north and east in Minnesota, but blister rust can occur anywhere in the state where late summer weather is cool and moist.

Tree size can affect the severity of blister rust. Old, large trees can live a long time with blister rust. Often, these trees are topkilled because infections in the upper crown girdled and killed the main stem, yet, the lower crown can survive for decades. Infected side branches die before the fungus can grow down them, so the fungus can't reach or girdle the main stem. In contrast, young, small trees die when they are infected with blister rust because all infections reach and girdle the main stem.

How to prune for blister rust
Careful pruning of white pine branches helps reduce the risk of damage from blister rust and white pine weevil. It also helps trees to grow straighter and produce higher quality wood products. Pruning is one of the most effective ways to reduce blister rust infections and tree mortality. Pruning is beneficial on any size tree. However, pruning is most beneficial when started on young trees and continued until all the branches, on at least the lower nine feet of the stem, have been removed. The "natural target" method of pruning allows the tree to quickly close the pruning wound with minimum risk of future decay.

How 1. If the branch is large or heavy, first cut it off more than six inches away from the final cut to prevent tearing of the bark when the branch falls. 2. For the final cut, locate the branch collar and the branch bark ridge. 3. Make the final cut at the line AB. Always avoid cutting into the branch collar.

When 1. Branches can be pruned almost anytime of year. The best time to prune live branches is during the fall and winter when the tree is dormant. Spring is the only time trees should NOT be pruned because the bark is easily damaged. 2. Begin pruning the lowest branches when the trees are two or three feet tall.

Pruning tips 1. You don't have to prune every tree on your site - prune only the best ones. 2. Don't remove too much crown. Do not remove more than 1/3 of the living branches at one time. Always maintain 2/3 of the tree height in live branches. 3. Do not flush cut the branches. Do not leave long stubs, either. Pruning cuts should be made just outside the branch collar. Use "natural target" pruning methods. 4. Pruning shears work best on branches up to the thickness of your thumb. Larger branches require lopping shears or a sharp pruning saw. Shears should have bi-pass blades (like scissors) rather than the anvil type. The anvil type crushes tissue rather than leaving a clean cut. 5. Do not use chain saws, Sandviks, hatchets, bow saws or clubs; this is delicate surgery. 6. Do not paint or treat the pruning cuts.

Pruning to prevent infections. Pruning removes the lower branches that are most likely to become infected. Most blister rust infections occur within nine feet of the ground because cool, moist conditions favor infection. 1. Be sure to find and prune off the lowest branches. These often lay on the ground and are hidden in the grass. 2. Pruning should continue to a minimum height of nine feet but you may want to continue up to seventeen feet (for lumber production). Caution: try to maintain 2/3 of the tree height in live branches. 3. Frequent pruning is most effective because there's a greater chance of removing infections before they reach the main stem. Also, smaller branches are easier to prune.

Pruning already infected branches or leaders. Pruning removes branches that are already infected and prevents the infection from growing down the branch into the stem. 1. Prune off any infected branches higher up in the tree that you can reach. 2. Trees with blister rust cankers on the main stem or on a branch but within four inches of the main stem cannot be saved. Do not waste your time pruning these trees. 3. Pruned branches can be left on site. They won't spread the infection. 4. Since blister rust is not carried from tree to tree on tools used in pruning, as are some fungal diseases, tools do not have to be sanitized between pruning cuts.

Pruning will NOT save every tree from blister rust. Some pruned trees will still be killed or topkilled by blister rust because: 1. Any live needle can become infected and since the terminal leader has needles on it, the stem can be directly infected through one of these needles. 2. An infection can take years to become recognizable, so the stem could already be infected but not recognized as infected at the time of pruning. 3. If the leading edge of a branch canker is four inches or less from the stem, the stem is already infected even though you cut the branch off. 4. In the northern and eastern parts of the state, the weather is cool and moist enough to allow infections to occur in the tops of even the tallest trees. Even here most of the infections occur within nine feet of the ground. So while pruning is an effective way to reduce blister rust infections on trees it is not a guarantee that infection and mortality will not occur.

White pine weevil
White pine weevils are insects that cause the wilting and death of the tree's terminal in June or July. At least two years' height growth can be lost in a single attack and the damage usually causes forking of the stem. Repeated attacks cause the tree to become bushy and stunted. Weevil damage can best be reduced by growing white pines under an overstory. The cooler temperatures and thinner diameter terminal leaders produced in the shade discourage weevil attacks. Damage from weevils can also be reduced by planting white pines at high densities, up to 1200 trees per acre, especially if the trees are open grown. The high density should be maintained until the trees are about twenty feet tall. These trees tend to produce thinner diameter terminals, which discourage weevil attack. Growing in high densities produces straighter trees. If attack does occur, a lateral branch will straighten up faster and take over for the terminal killed by weevils.

Insecticide applications can also be used to kill weevils as they try to lay eggs in the terminal leader. This method is not commonly used.

Corrective pruning for white pine weevil infestation
If a tree is attacked by weevils, a straight tree can be produced by pruning out the damaged terminal and "training" another lateral branch to take over as the new terminal leader. Also, promptly clipping and destroying the currently wilting terminal will help prevent damage next year by killing the next generation of weevils inside the wilted terminal.

1. Use a pruning shears to cut off the damaged terminal leader. Pruning off dead terminal leaders in July will remove the larvae still present inside them. 2. Be sure to remove enough of the terminal and main stem to remove the larvae. Larvae feed down the stem and will be found under the bark at the bottom edge of the damage, two or three whorls of branches down the stem. 3. Collect (bag) and destroy (burn) the infested terminals and infested stems so the larvae cannot complete their development and emerge as adults. 4. Prune the highest whorl of branches by cutting off all the side branches except one or by cutting back and shortening all side branches except one. (See figure at left.) This lateral will straighten up over a period of a few years and become the new terminal.