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 necessary 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.
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. The shoot or terminal wilts and dies at the point of entry. 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 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 and damage has never recurred the following year. 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 including Japanese beetles (Popillia japonica), grasshoppers, weevils, caterpillars, and even mice. These pests usually eat the bark and/or needles, leaving lesions on the terminal. Damage is usually limited to 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.
One of the weevils that has attacked Fraser fir terminals is pales weevil (Hylobius pales). When white pines are harvested next to a Christmas tree farm, the weevils will sometimes move into the Frasers after feeding on the downed pines, resulting in damage to the terminals. Another pest attracted by harvested pines is the sawyer beetle (Monochamus spps.)
Several species of loopers have been identified feeding on Fraser fir. These have included species of Campaea and Elaphria. Caterpillars have the potential to be of the more widespread, affecting many trees. Unfortunately, however, once the damage is noticed, the pest is usually no longer present. Many of these caterpillars are nocturnal feeders, making it hard to find in the day.
BAGWORMS. Bagworms (Thyridopteryx ephemeraeformis), have a very wide host range among conifers but are usually associated with arborvitae or juniper. They are not common on Fraser fir. However, there have been a few Fraser fir Christmas tree fields where bagworm numbers have increased to the point that treatment was warranted. Bagworms are caterpillars of a moth that live in spindle-shaped bags made of silk and bits of foliage of the host plant. Made to protect the caterpillar from birds and other predators, they blend in with the tree making them hard to see until considerable damage is done. Bagworms eat the foliage, defoliating the tree.
Winter is spent as eggs (500 to 1000) in the mother's bag. They hatch in May and June to small larvae that spin silken threads so the wind can blow them to a new feeding site. Upon reaching a suitable host, the worm begins to spin its bag, enlarging the bag as it grows. In August the worms mature and molt into the pupal stage. The bag is firmly attached by a sturdy silk band. During August and September, male moths emerge from their bags to mate. After mating, females lay their eggs inside the pupal cast skins and die.
Apparently when the newly hatched larvae reach a plant which is different from its parents' host plant, these insects often have difficulty in adapting to it and may die or may produce only a few offspring. After several years of struggling to keep from dying out, the population may hit on the right combination of genes for the "new" plant and "suddenly" the new plant is covered with bagworms. This has apparently happened in Fraser fir at a few sites, making it important to keep an eye on bagworm problems.
When practical, bagworms can be removed with scissors or a sharp knife. Bagworms are attacked by several kinds of parasitic wasps. Insecticides are effective particularly when applied in June or early July when the bagworms are small and easily killed. Using materials specific to lepidopterous species (butterflies and moths) will reduce impacts on natural predators. Scout for bagworms in June in areas with infestations the previous year to determine the need for pesticide treatment.
GYPSY MOTH. Gypsy moth (Lymantria dispar) only occasionally defoliates Christmas trees, being primarily a pest of deciduous trees. The real problem with Christmas tree production is if the presence of gypsy moth in the county results in a quarantine requiring the treatment of the Christmas tree before sale to uninfested areas of the country. To date, no county in North Carolina producing Fraser fir has been under such a quarantine, but the possibility exists. North Carolina has adopted the "Slow The Spread" program which has so far been successful in keeping gypsy moth numbers to a minimum in western North Carolina.
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, some of which have a hard shell for protection. Many species of scales have been observed on needles, stems, terminals, and trunk of Fraser fir Christmas trees. The elongate hemlock scale (Fiorinia externa) and Cryptomeria scale (Aspidiotus cryptomeriae) are both serious pests of Fraser fir that require immediate attention (see CTN-037, Elongate Hemlock Scale, for more information). However, other scales can be found on Christmas trees that either do not cause damage, or are not widespread enough to become a problem. These include pine needle scale (Chinaspis pinifoliae), pine tortoise scale (Toumeyella parvicornis), spruce bud scale (Physokermes hemicryphus), hemlock scale (Abgrallaspis ithacae) which is a native pest, and Oystershell scales (Lepidoaphes spp.). These seldom require pesticide treatment though they may cause damage on a handful of trees.
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 sometimes warrant treatment as once the disease if noticed, controls are ineffective.
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 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.
FERN/FIR RUST. There are several species of rusts that alternate between firs and ferns, many of which are a problem in other states. The fir/fern rust in western North Carolina is Uredinopsis americana (formerly called Uredinopsis mirabilis) which alternates between Fraser fir and primarily sensitive fern is seldom a problem. On Frasers, infected needles appear yellow to brown and will drop from the tree prematurely. White spores of the fungus are found on the underside of current-years needles breaking through the epidermis of the needle. Spores produced on the ferns infect new fir needles in spring and aecia are formed on needles in late spring to early summer. Controls can include removing the alternative host (ferns) from the surrounding woods or treating Christmas trees with a registered fungicide such as Bayleton in the spring. Very few Fraser fir fields in western North Carolina have had recurring problems with this disease, suggesting that weather plays an important role in disease severity.
RHIZOSPHAERA NEEDLECAST. Rhizosphaera pini, similar to Rhizosphaera kalkoffi which causes a needle blight on Colorado blue spruce and other conifers, is not believed to be an aggressive pathogen of Fraser fir. The fungus is seen as black spores erupting from the stomates on the underside of usually dead and brown needles. The fungus is found on trees which drop their needles in the fall, and is associated with poor fertility and high humidity sites. Spores on the dead needles fallen to the ground are still viable and cause infections the following year. Usually only a few trees in a block are affected. No treatment for this disease has been necessary to date. Further investigations of the site and especially fertility problems, are more helpful to control.
ANNOSUM ROOT AND BUTT ROT. Caused by the fungal pathogen Heterobasidion annosum (formerly Fomes annosum), this root and butt rot is found infrequently in Fraser fir Christmas trees in western North Carolina. This disease has become important in noble fir in the Pacific northwest in recent years and has also been a problem in Wisconsin.
Symptoms in Fraser fir are similar to Phytophthora root rot, however, the disease is very different. The air-borne fungal spores infect fresh cut stumps of conifer trees, particularly pines. Spores are present throughout the year, but particularly in the fall. Spread occurs to living trees which may include Fraser fir Christmas trees through root to root contacts. Therefore in western North Carolina, disease has only occurred near areas where pine woods have been cleared. Infected trees occur in pockets called infection centers. It may take 1 to 3 years or longer for symptoms to become apparent. In the Pacific northwest, diseased trees are usually only apparent at the end of the rotation. Problems in pine timber stands are often linked to soil type, but in the mountains, eastern white pine is very susceptible to infection by Annosum root rot regardless of soil type.
Above-ground symptoms of Phytophthora root rot and Annosum root rot are similar. Tree growth is reduced and foliage is yellowish. With Phytophthora root rot, roots appear blackened. The outer portion of the root slips off of the inner core. With Annosum root rot, the wood in the trunk and roots appear stringy and will be white to yellowish in color. There may be rot pockets that are narrow, elongated and whitish just under the bark. The trunk or roots may be resin soaked or there may be dried resin at the base of trees on the roots. The trees are easily dislodged from the ground. Fruiting bodies called conks may be observed at or below the soil line on infected trees. In noble fir in the Pacific northwest, trees infected with the pathogen have irregularly shaped dark stained older wood in the tree trunk that is evident when the tree is cut.
To prevent this disease, treat freshly cut stumps with granular Borax when Christmas trees will be planted adjacent to and where coniferous forest trees have been cut. Freshly cut stumps are susceptible for about one month. Once the disease is found in a plantation, removing stumps and roots and reducing root contact to still healthy trees may reduce spread. Research has indicated that treating cut stumps with biocontrol agents such as the antagonistic fungus, Phlebiopsis gigantea will reduce disease development, but it is not commercially available in the US.
ROSELLINIA BLIGHT. First reported in 1914 in native stands of Carolina hemlock in western North Carolina, Rosellinia blight is an infrequent pest of Fraser fir and hemlocks. From a distance, infected trees have a scalded appearance as if the branches have died from shading due to close spacing of plants. Upon closer observation, needles and twigs with exhibit a grayish-brown, tawny mat of fungus attached to the underside of needles and twigs. It is similar to the snow molds found on Christmas trees in the northern states. As needles become infected, they turn brown and hang on the plant intertwined within the fungus mat. There will be numerous fruiting bodies that appear as tiny balls attached to the fungal mat.
The fungus, Rosellinia herpotrichioides, is favored during periods of cool, wet weather and high relative humidity. The fungus only attacks trees in areas with little air movement, and usually on heavy density trees growing close together, during periods of excessive rainfall. Rosellinia typically appears in mid-summer or early fall.
Once observed, this pest has already done its damage. Blighted foliage will not grow back. Increasing air movement by thinning trees will reduce the possibility of spread. In general, treatments with fungicides in Christmas trees is not warranted.
NECTRIA CANKER. Nectria canker caused by Nectria balsamea has been found on cankers and dead branches and trunks of Fraser fir. Often, the entire top half of the tree is killed.Small red bumps containing fungal spores can be seen on the dead tissue. Caused by a very weak pathogen that mostly attacks tissue that is already dead, Nectria canker may be aggravated by wounding and other stresses trees including poor fertility and herbicide injury. To date, no fungicide treatments have been necessary. Care should be taken while shearing trees not to spread the fungus to healthy trees with a shearing tools. Do not shear infested trees. Culling is the best means of control.
Publication date: April 23, 2014
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