Oh Christmas Tree, Oh Christmas Tree! How important is IPM for your branches!

You don’t have to travel very far—indeed you just need to go as far as your neighborhood “big box” or grocery story—to find a healthy offering of Christmas trees. In the Southern US, Fraser firs are among the favorite. In fact, Frasers are one of the favorites of White House residents, as it has graced the Blue Room more than any other tree since the 1960s. The Internet is lush with information about how to size a tree for the space it will occupy and how to care for the tree once you’ve gotten it home. I’m going to focus on a topic that few people want to think out—pests and diseases that can affect Christmas trees.

In the November/December issue of Sierra magazine, writer Nate Seltenrich raises the topic of Christmas tree pests with a short article about Phytophthora cinnamomi, a root mold that affects not only Fraser fir, but other trees as well, including chestnut, avocado and other firs.

That article brought to mind several other diseases and pests that Christmas tree farmers fight every year. You most likely won’t see symptoms of these pests and diseases when looking for a tree, but some symptoms don’t show up until well after Christmas is over. Therefore, although these problems should not influence your Christmas tree purchasing, you may reconsider the fate of the tree after Christmas.

Diseases

Phythophthora cinnamomi

Sand pine with p.cinnamomi. Photo by Edward L. Barnard

Phytophthora cinnamomi: Since I’ve already brought it up, I figured I’d start with this one. P. cinnamomi is a root-rot pathogen that causes certain death once it has infected a plant. The pathogen originated in Papua New Guinea and spreads through the soil, so infected trees that are planted can spread the infection to other susceptible plants. According to Seltenrich, the disease originally plagued the Southeast but is beginning to move north.

Rhizosphaera pini: Although not found in the southern US, R. pini is a common plant pathogen in the Lake States, Northeastern States and Canada. R. pini is often considered to be a weak pathogen, occurring on stressed foliage or foliage killed by other causes. However, it has been observed causing significant damage on balsam fir and Fraser fir. It appears to be particularly damaging in shaded, damp areas and when the trees are under other stress. (Source: Forest Service Pest Alert)

Insect pests

Symptoms of balsam woolly adelgid

Bent tops caused by balsam woolly adelgid

Balsam woolly adelgids (Adelges piceae): BWA is native to central Europe and was discovered in the southern Appalachians in the 1950s, where it had already destroyed acres of Fraser fir in the Mount Mitchell area. Research is currently being done to produce BWA-resistant Fraser firs both for Christmas tree and to supplement regrowth in the North Carolina mountains. See the Alliance for Threatened Forests website for more information.

BWA infested trees do not develop symptoms for several months; however, the insects themselves are visible as adults during the summer. They appear as small cotton-like pinpoints on the trunk of Fraser fir. One of the first symptoms of BWA attack is a crooked top (see photo). Other symptoms include dead branches, swelling around the shoot nodes, a stiff trunk and growth rings with red, hard wood instead of the usual white wood. BWA is typically treated in the Christmas tree farm with insecticides, but it is very expensive to control. If you live in an area where BWA is present (see map), consider discarding your Fraser fir after the holidays are over rather than replanting. Christmas tree farmers must use more pesticides to treat their trees if they are near untreated residential trees.

Balsam twig aphid

Symptoms of balsam twig aphid

Balsam twig aphids (Mindarus abietinus): These aphids are small, pale green insects that feed on fir and spruce in the spring. Symptoms of past infestation are curled needles and stunted growth, although heavy damaged trees are usually not sold.

Spruce spider mites (Oligonychus ununguis): These tiny mites suck sap from the needles. Infested needles look speckled when viewed up-close, and as the number of mites increases, needles can turn bronze or brown in color. Most growers practice strategies that reduce the incidence of infestation from these mites.

Spruce spider mites

Symptoms of spruce spider mites

Rust mites (Nalepella spp.): These tiny mites are not visible to the naked eye; you need a hand lens or microscope to see them. Damage usually occurs in the summer, where infested needles turn brown and die, and often are confined to one area of the tree.

Rosette Bud Mites (Tricetacus spp.): These mites cause deformed buds on Fraser fir, rounded instead of pointed. The buds do not break in the spring, and if they do, they form weakened shoots. A tree with several of these buds will develop holes in the canopy and typically is not sold.

Nothing can be warmer and homier than the smell and sight of a real Christmas tree. Below are more links to webpages with tips on how to choose and care for your real Christmas tree. After the holidays, though, you may want to inspect your tree for signs of any of the above pests and diseases, and if you’re unsure, it’s best to leave that tree by the curb for pickup than to plant it in your backyard and risk affecting neighboring trees, especially if you live near a Christmas tree farm.

The information about insect pests comes from NC State University’s webpage on North Carolina Christmas Trees.

For general information about choosing a Christmas tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/xmas_treetypes.html

For tips on where to buy your real tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/xmastreefinder.html

For information about how to judge the freshness of a market Christmas tree, see http://www.ces.ncsu.edu/fletcher/programs/xmas/treefreshness.html

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