Christmas Tree Notes

CTN - 023

MINOR PESTS OF FRASER FIR CHRISTMAS TREES

Extension Forestry, September,1995

Updated November 1, 1995

Introduction

Most growers of Fraser fir Christmas trees in western North Carolina are familiar with its major pests: spruce spider mites, balsam twig aphids and balsam woolly adelgids. But there are several minor insects and diseases that growers may occasionally encounter.

Pesticides are not usually applied for minor pests because these pests do not cause sufficient damage to warrant treatment. In rare instances, pesticide applications may be needed to control a minor pest that is causing economic damage to trees. Therefore, it is important that growers recognize these pests and their potential for causing damage.

Insects

CINARA APHIDS Cinara are a group of several species of large brown or black aphids that feed on many conifer species including Fraser fir. They are much larger than balsam twig aphids, and are usually found in the early spring in dense clusters or colonies of up to several hundred aphids on the terminal, trunk, and upper whorl of branches. They feed (suck the sap) from the bark between needles. Several dozen to several hundred trees in an acre may be infested while the rest remain aphid-free.

In most instances, Cinara aphids have no apparent effect on Fraser firs. They are easy prey to predators such as ladybugs, and usually disappear after several weeks. However, Cinara aphids can promote the growth of sooty mold (see SOOTY MOLD below) on the foliage of infested trees. In rare instances during years of drought, extremely high numbers of Cinara aphids feeding on trees before bud break can reduce terminal growth and produce smaller, yellow-green needles on the upper whorl of branches.

Though Cinara aphids seldom damage Fraser fir, they can be a nuisance to consumers after they have set up the Christmas tree in their home. In warm indoor temperatures, aphid eggs can hatch and the aphids become active, crawling from the tree to other decorations, gifts or furnishings. Aphids leave a purple stain on fabrics when mashed.

Because Cinara aphids can damage trees or become a nuisance to the consumer, it may be necessary to control them in go-to-market trees. Usually control is only necessary if there are high numbers on many trees in a field block. Contact your local Cooperative Extension Agent to determine if treatment is warranted. Any insecticide labeled for aphid control in Fraser fir will control Cinara aphids. Consumers can treat Christmas trees by washing the tree outside with a garden hose to remove the aphids, treating trees with household insecticides, or vacuuming aphids.

ROOT APHIDS.

Root aphids (Prociphilus americanus) are large, white aphids that feed on the roots of Fraser fir. The root aphid alternates between ash trees (the primary hosts), and true firs (the secondary hosts).

Root aphids are often seen on the roots of Fraser fir transplants when they are lifted for planting in the spring. When transplants are examined later in the year, the aphids have usually disappeared.

Occasionally, root aphids are also found on poorly growing trees in the field. These trees have usually been in the field less than two years, and may exhibit poor shoot growth, yellowing needles, and poor root growth. In all cases, root aphids are also found on healthy trees in the same field. Some other cause such as transplant shock, improper planting, or inadequate nutrition is usually identified as being associated with this poor tree performance.

To date, there has never been a proven instance where root aphids have damaged Fraser fir. Therefore, chemical control of root aphids is not currently recommended.

RUST MITES. Rust mites are eriophyid mites (Nalepella ). They are very small and require a handlens or microscope to see. With a microscope, rust mites appear tan and wedge-shaped with four legs at the front end. They live on the surface of the needle, usually of hemlocks. Occasionally, they can be found on Fraser fir. Rust mites are active when the weather begins to warm in the spring, sometimes as early as February. Mites usually become dormant during hot weather though they may remain active on trees at high elevations and during humid seasons.

The rusting or bronzing of the upper side of the needle which these mites cause may be mistaken for nutrient deficiencies. To distinguish the difference requires a handlens. Needles damaged by rust mites have tiny marks or scratches parallel to the mid-rib. When damage is extensive, needles will begin to drop off. Often this damage will be on one side or section of the tree.

Usually, rust mites are only present in low numbers on Fraser fir. Occasionally, there will be enough mites to require chemical control. Contact your local Cooperative Extension Agent to determine if treatment is necessary.

WHITE PINE CONE BEETLES. The white pine cone beetle (Conophthorus coniperda) is a small, black beetle that burrows into the cones and shoots of white pines to feed and lay eggs. In some years, the white pine cone beetle attacks Fraser fir, burrowing into the terminal or one of the branches in the first whorl. A tiny hole can be seen where it enters the shoot. Sometimes a beetle can be found inside the shoot, or a second hole where the beetle exited can be found. Fraser fir is not a good host for this insect and it does not appear to reproduce on Frasers. The shoot or terminal wilts and dies at the point of entry.

The white pine cone beetle usually affects only a few trees in a field. Damage appears in June. Treatment is not warranted for this pest because once damage is observed, the beetle is already inside the shoot or has already left. No more trees will be damaged. Damaged shoots or leaders can be pruned off the tree.

OTHER TERMINAL ATTACKERS. There are many other pests that will attack the terminals of Fraser fir. Japanese beetles, grasshoppers, weevils, caterpillars, and even mice have all been observed feeding on Fraser fir terminals. These pests usually eat the bark and/or needles, leaving lesions on the terminal. Damage is usually limited to only a few trees. Treatment of these pests is often unnecessary because in most instances they have left the tree by the time damage is observed.

SEED AND CONE INSECTS. There are two major pests of Fraser fir cones and seeds, leaf-footed pine seed bugs (Leptoglossus corculus) and the balsam fir chalcid (Megastigmus). Both are native pests.

Leaf-footed pine seed bugs, so called because of their leaf-shaped hind legs, are sucking insects and both the adults and nymphs pierce through cones to feed on seeds. The adult pine seed bugs start to feed on pines and fir at flowering time. They fly from tree to tree and feed on the developing male flowers. Following the flowering season, adults also feed on succulent shoots. Eggs are laid about a month after flowering. The nymphs and adults feed on the cones until they ripen in the fall. The seed bugs cause a reduction in pollen production, abortion of conelets, and damage to seeds, causing low yields of seed, high number of empty seeds, poor seed viability, and mold in germination tests. Seed damage is seen in radiographs (X-ray photographs of seed) as empty seeds, shriveled seeds, and small feeding holes in the seeds.

The balsam fir chalcid wasp overwinters in fir seed on the ground, with adults emerging in spring. Females lay eggs in the seed embryo of newly developing cones in June, and the larvae feed in the seed where the egg was deposited. As many as seven larvae can be found in a single seed. On the outside, the seed appears normal -- until the following spring when the wasps start to emerge. Only by using radiographs can the percentage of infested seeds be determined. The larvae of the chalcid can be seen in a radiograph as 'C-shapes' inside the seed.

Control of cone pests may be necessary in Fraser fir seed orchards if damage is seen in radiographs of seed from the previous year. Control of the chalcid is much easier because only the developing cones must be protected. The seedbug feeds throughout the year, and multiple pesticide applications may be needed. Getting adequate coverage of tall seed orchard trees is also a problem. Treatment of these pests in Christmas tree plantations is not warranted.

SCALES. Scales are small soft-bodied insects that form a hard shell over themselves. Many species of scales have been observed on needles, stems, terminals, and trunk of Fraser fir Christmas trees. To date, treatment for these scales has not been necessary.

Diseases

BOTRYTIS SHOOT BLIGHT. Botrytis shoot blight (Botrytis cinerea), sometimes called gray mold, is a fungus that infects the base of shoots of Fraser fir. A sunken lesion forms on the underside of the shoot where it joins the branch. The affected shoot may droop at that point, or it may wilt and die. Occasionally, the gray spores of the fungus can be seen on the dead or dying shoot. Dead shoots often drop off the tree. Only the current year's growth is affected.

Shoots are probably infected during bud break in the spring. Infection occurs inside the sheath of bud scales at the base of the shoot. Botrytis shoot blight is worse during wet springs and in fields which stay humid because of little air movement. Currently, there is no control for Botrytis shoot blight, even though damage may warrant treatment.

SOOTY MOLD. Sooty molds are black-colored fungi that grow on honey dew excreted by aphids onto the surface of needles and shoots. Sooty molds do not actually damage the tree, but they are unsightly and can reduce the grade of marketable trees. The only way to control sooty mold is to control the aphids before sooty mold starts to grow.

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.