Christmas tree pests and weeds facts for kids

Pine and fir trees, which are grown especially to become Christmas trees, can face many problems. These include tiny pests, weeds, and diseases. Many of these cone-bearing trees, called conifers, can get sick or even die from pests like the balsam woolly adelgid and other similar insects. Aphids are another common insect pest.

Christmas trees can also be harmed by tiny fungal germs that cause illnesses like root rot. In California, a disease called sudden oak death can also affect them. Douglas fir trees are especially at risk from plant germs like R. pseudotsugae.

Larger animals can also cause trouble for Christmas tree farms. Mammals such as deer, gophers, and ground squirrels can damage tree roots and buds. Some birds, like the pine grosbeak, eat conifer buds and are also considered pests.

Wild plants, both small herbaceous plants and larger woody plants, are also a problem. They compete with Christmas trees for water and food. Farmers must control these weeds using methods like mowing, special chemicals called herbicides, or tilling the soil.

Tiny Tree Invaders: Insects

An adult balsam woolly adelgid, a major pest for Christmas trees.

The different types of conifers grown for Christmas trees can be attacked by many insects. Most of these insects cause damage that makes the trees look bad, which is a big problem for Christmas tree sellers.

The balsam woolly adelgid (Adelges picae) is a tiny, soft-bodied insect. It attacks Fraser fir trees. These insects look like white, woolly spots on the tree. If not treated, they can kill the fir tree. This adelgid came from central Europe and arrived in the United States before 1900. Here, it has no natural enemies.

Balsam twig aphids (Mindarus abietnus) are another type of pest. They affect fir and spruce trees in the spring. A lot of these aphids can stop trees from growing properly. Heavily damaged trees might not be able to be sold. Other types of adelgids also bother fir trees. These include the pine bark adelgid, the Cooley spruce gall adelgid (Adelges cooleyi), and the eastern spruce gall adelgid (Adelges abietis).

Bagworms are another serious pest. If there are too many, they can eat all the leaves off a tree. The damage from their silk webs can also last for years.

Invasive insects, like the pine shoot beetle and the gypsy moth, also threaten Christmas tree crops. When gypsy moths were a problem in Canada, Christmas tree growers in affected areas had to follow strict rules. These rules included checking their farms often, actively getting rid of moths, keeping good records, and joining government programs to remove moths. If growers didn't follow the rules, they could lose their "approved grower" status.

Different Christmas trees are affected by different insects:

• Douglas firs are most often bothered by the Cooley spruce gall adelgid.
• True firs are very sensitive to insects like the balsam gall midge (Paradiplosis tumifex) and the balsam twig aphid.
• Spruce trees can be attacked by insects such as the white pine weevil (Pissodes strobi), Cooley spruce gall adelgid, and the pine needle scale (Chionaspis pinifoliae).
• Pine trees often get infestations from the pine root collar weevil (Hylobius radicis), Zimmerman pine moth (Dioryctria zimmermani), pine needle scale, and white pine weevil.

Sick Trees: Fungal Pests and Diseases

A hillside affected by sudden oak death. This disease has been found on Christmas tree farms in California.

Christmas trees can also get large infections from various fungal germs, called pathogens. In 2002, people in the U.S. Pacific Northwest worried about a new fungal disease called annosus root rot (Heterobasidion annosum or Fomes annosus). This disease spreads through tiny fungal spores carried by the wind. It was first found on Northwest Christmas tree farms in 1983.

Phytophthora ramorum is a fungus-like germ that causes "sudden oak death" (SOD). It was identified in the early 1990s. By 2002, SOD was found along the California coast and the Oregon Coast. Two types of conifers, Douglas fir and coast redwood, were found to carry the germ.

Between 2003 and 2005, P. ramorum was found on Christmas trees in Santa Clara County. It affected Douglas fir, grand fir, white fir, and California red fir. In 2003 and early 2004, Camellia plants brought from California to British Columbia caused a big SOD scare. This led to plant recalls in Canada and steps to stop the disease from spreading. The SOD scare in 2003–2004 also reached nurseries and farms in Washington and Oregon.

Douglas-firs can get two plant diseases that cause Rhabdocline needlecast: Rhabdocline pseudotsugae and Rhabdocline weirii. R. weirii only affects Douglas-fir trees. This disease often makes Douglas fir trees unsellable as Christmas trees, which impacts the Christmas tree farming business. Douglas firs can also be affected by Phaeocryptopus gaumanni, which causes Swiss needlecast.

Red band needle blight is a fungal disease that affects cone-bearing trees, especially pines, all over the world. It is caused by the fungi Dothistroma septosporum. Since the late 1990s, it has become more common in the United Kingdom. Corsican pine is one of the most affected trees, and the disease has been a big problem in Thetford Forest. Even though the disease spread quickly in September 2007, Christmas tree growers were still confident that their crops would not be affected.

Animal Pests: Mammals

Small mammals can cause big problems for new tree plantings and Christmas tree farms. Voles, also known as meadow mice, can damage young conifer trees. Voles are most likely to be a problem when the land has a lot of grass and plants, which is common on farms that used to be old pastures with many voles.

In the U.S. Pacific Northwest, gophers (pocket gophers) damage conifer seedlings across thousands of acres. This causes a lot of money to be lost in the region. Gophers tend to harm root systems and chew bark off the bottom of young trees. Other mammal pests on Christmas tree farms include porcupines, rabbits, deer, and thirteen-lined ground squirrels.

Other Pests: Spiders and Birds

A young pine grosbeak. This bird is seen as a pest by Christmas tree growers.

Other types of pests that affect Christmas tree production include tiny spider-like creatures called arachnids. These include spruce spider mites (Oligonychus ununguis) and rust mites (Nalepella).

Some birds are also considered pests by Christmas tree farmers. Examples include the pine grosbeak (Pinicola enucleator) and the yellow-bellied sapsucker (Sphrapicus varius). The pine grosbeak eats buds on conifers, including Christmas trees. This stops the tree's growth, makes it grow strangely, and makes its leaves thinner. As a pest, the pine grosbeak usually affects Scots pine, but it also bothers eastern white and red pine, as well as spruce trees.

The yellow-bellied sapsucker is a Christmas tree pest that likes Scots and Austrian pine trees. Sapsuckers peck holes in the bark of young trees, causing sap to leak out. This can kill the trees and allow insects and diseases to get inside.

Unwanted Plants: Weeds

The types of plants considered weeds on Christmas tree farms change from one area to another. No matter what kind of plant it is, from small weeds to larger woody plants, weeds are a problem for Christmas tree farms for several reasons.

Young trees are very sensitive to weeds because weeds compete for water and nutrients. But even older, established trees can be outcompeted by too much weed growth. Some specific weeds cause more serious problems. For example, the bracken fern can increase diseases in fir trees. Also, workers might feel less motivated and efficient when weeds like poison oak, Canada thistle, and wild blackberries grow on the farms.

On top of that, too much weed growth can provide hiding places for wild animals. These include deer, gophers, and field mice, which can also damage Christmas tree crops.

Controlling Pests and Weeds

Controlling Weeds

One main way to control weeds on Christmas tree farms is by using chemical herbicides. The use of herbicides and other pesticides is one reason why Christmas tree farms have faced criticism from environmental groups. When applying herbicides, growers must figure out the right amount to spray and the best time to do it.

There are different types of herbicides for different weeds, and they fall into two main groups:

• Soil-applied herbicides fight against new seedlings that are just starting to grow. Some also help control newly established plants. These herbicides need to be spread evenly over the soil and then get some moisture to work well.
• Foliar-active herbicides control weeds that are already grown and actively growing. When applying these, farmers must be careful not to get them on the Christmas trees themselves.

Non-chemical ways to control weeds include using rotary mowers and flail mowers. Rotary mowing cuts unwanted plants about 5–7 cm (2–3 inches) above the ground. Flailing cuts the plants closer to the soil surface. These methods help reduce the loss of soil moisture and nutrients by making the weeds smaller and slowing their growth.

The act of cultivation (tilling the soil) also disturbs weed growth, especially when they are young seedlings, by breaking up the soil around their roots. Another way to fight problem weeds, in areas that haven't responded to other methods, is to use a hoe or till the soil in small spots.

See also

• Christmas tree cultivation
• List of Douglas-fir diseases