Plant Health Problems
Diseases caused by Fungi:
Cytospora canker, Leucostoma kunzeii.
This disease is characterized by progressive dieback of twigs and branches. It is usually first evident on lower limbs and gradually proceeds up the tree. Sunken areas of bark appear on branches or the main trunk. A white resin is usually associated with the cankers and can be so excessive that it drips onto foliage and lower branches. Needles may drop from infected, girdled branches. Colorado blue and Norway spruce are particularly susceptible.
Helpful practices to manage this diseases include pruning and removing symptomatic twigs and branches as soon as they are evident and when the bark is dry. Cuts should be made at least 8-10 inches below visible symptoms. It is also important to maintain tree vigor by watering and fertilizing since drought-stressed or winter-injured trees are more vulnerable. Care should be taken in selecting the planting site so as to ensure adequate soil moisture for the tree at maturity.
Rhizosphaera needlecast, Rhizosphaera kalkhoffii.
Needles on lower branches are usually attacked first and the symptoms gradually progress up the tree. Diagnostic symptoms may develop in September but typically don't appear until spring when infected needles turn a distinctive lavender or purplish-brown. Upon close inspection with a hand lens, rows of fuzzy black spots appear in place of the rows of white stomates on the needles. Significant needle drop usually occurs and defoliated twigs and branches eventually die.
It is helpful to prune and remove infected twigs and branches during the winter when the bark is dry to eliminate the source of the fungus. Maintaining vigor by fertilizing and watering is also important since drought-stressed trees are highly susceptible. Control can also be achieved with the use of fungicide sprays beginning in early June. Several applications may be necessary, especially when wet weather persists. Among the compounds registered for use in Connecticut are chlorothalonil and copper. Consult the label for dosage rates and safety precautions.
Spruce needle rusts, Chrysomyxa spp.
Various needle rusts may attack spruce but usually are not serious. Symptoms first appear as whitish blisters on the surface of the current season's needles in either late winter and early spring or midsummer, depending upon the particular type of rust fungus. These blisters burst open and reveal distinctive yellow-orange, "rusty" spores. Premature defoliation may occur on heavily infected trees. Some of the rusts require alternate hosts such as leatherleaf, Rubus spp., and Labrador tea, whereas another type of rust has no alternate host.
Control measures are usually unnecessary since conditions conducive to heavy infection seldom occur. However, if the rust requires an alternate host, it is helpful to remove that host from the vicinity of the spruce trees. Other methods that maximize tree vigor help counteract premature needle drop due to disease. For more information, see the fact sheets on Disease Problems in Connecticut Christmas Tree Plantations and Spruce Needle Rusts in Connecticut.
Gray blight, Botrytis cinerea.
New growth is suddenly killed and a gray fuzzy mass of the fungus covers the dead needles during prolonged cool wet weather. This disease is usually not a serious problem since it only affects the new, emerging shoots. After the tips die, new shoots are usually initiated from dormant or adventitious buds and these mask the damage.
Since this disease is not very serious, controls are usually not necessary. However, it is helpful to maintain the vigor of the tree by following sound cultural practices. Steps to improve air circulation and overcrowding are also effective.
One species has been collected on spruce in Connecticut, but evidently aphids are not a serious pest here. Should they occur in great numbers, spraying with insecticidal soap or horticultural oil, which are among the compounds registered for use against this pest in Connecticut, will control them. Application of imidacloprid as a systemic to be taken up by the roots will also give control. Consult the labels for dosage rates and safety precautions.
Balsam fir sawfly, Neodiprion abietis.
The larvae of this sawfly are dark green with darker longitudinal stripes and head, and when mature are about 1/2" long. They feed on the leaves of spruce, balsam fir, and, to some extent, pitch pine. The adult is a small black sawfly. A spray of malathion or spinosad, which are among the compounds registered for control of this pest in Connecticut, as needed in August or September will protect the needles from injury. Consult the label for dosage rates and safety precautions.
Eastern spruce beetle, Dendroctonus piceaperda.
This small bark beetle emerges in June and July in large numbers from small round holes, resembling shot holes. Weak trees of the native red, white, and black spruce in particular are infested, and the insect seems to prefer trees a foot or more in diameter. Infested trees show exuding gum more or less mixed with sawdust on the trunk. The females lay eggs in June and July and the grubs tunnel under the bark while feeding, overwintering in the burrows as adults or in a partially grown condition and completing their development the following spring. There is one generation each year. Infested trees should be cut, and the bark removed before the middle of May to prevent beetle emergence. This helps to protect adjacent uninfested trees from attack. Maintain adequate irrigation to trees to prevent infestation. There are several other small bark beetles that commonly breed in the living bark of stumps, injured, or dying spruce trees. Some of the more important species are the red turpentine beetle and the pine engraver. Keeping living trees in good condition, especially by irrigating deeply during periods of drought.
Small spruce bud scale, Physokermes hemicryphus.
This insect occurs primarily on spruce, but it also attacks fir. The adult scale is 1/8" in diameter, globular in outline, and resembles the new buds. There is one generation a year. Winter is passed in an immature condition at the base of the terminal buds. Eggs hatch during early June and the young attack the new growth. A dormant horticultural oil spray will control the overwintering scales, but the overall color of white or blue spruces are affected by oil. Malathion, which is among the compounds registered for control of this pest in Connecticut, sprayed when the young scales are active in mid-June will give satisfactory results. Consult the labels for dosage rates and safety precautions.
Spruce budworm, Choristoneura fumiferana.
This insect has caused severe injury to spruce and balsam fir in northern forests several times during the last 60 years. The young caterpillars feed on the needles of the new growth of the terminal shoots and those of the preceding season, usually webbing these needles together and eating them off at the base. The webs holding the severed needles and bud scales give the trees a sickly appearance and in fact weaken the trees to such an extent that they become prone to bark beetles and other secondary pests. At maturity the caterpillars are about 3/4" long, and dark brown, bearing cream-colored tubercles. The adult moths have a wingspread of about 3/4", and are brown, marked with gray and white spots. They are most abundant in June and July and the females lay clusters of pale-green flat eggs on the needles. These eggs hatch in 10 days, and the caterpillars overwinter in a partially grown condition. There is one generation each year. Mixed stands with reduced percentage of balsam fir are recommended for forest planting. Sprays of carbaryl, Bacillus thuringiensis var. kurstaki, or spinosad, which are among the compounds registered for use against this pest in Connecticut, can be used to control this caterpillar. Consult the labels for dosage rates and safety precautions.
Spruce epizeuxis, Epizeuxis aemula.
The larvae of this moth web together and feed on the needles. The larvae are brown, covered with warts or tubercles and resemble the spruce budworm. The moth has a wingspread of less than an inch, and is brownish gray, with both front and rear wings crossed by several narrow wavy bands or lines.
Spruce gall adelgids.
Several species of adelgids, also known also as chermids or woolly aphids, form galls on spruce twigs. By far the commonest is the eastern spruce gall adelgid, Adelges abietus, that makes a pineapple-shaped gall at the base of the new growth on Norway spruce. A rather large terminal gall on Colorado blue spruce is caused by a closely related species, Adelges cooleyi, which may spend a portion of its life cycle on the needles of Douglas fir. Spruce gall adelgids overwinter in the form of immature females on the twigs near the buds. They mature in the spring and lay eggs that hatch soon after the new growth begins in May. The young nymphs attach themselves to the base of the needles and form a gall. About the first week in August, these galls break open and the mature nymphs crawl to the needles. They molt and transform to sexual winged females that lay eggs on the needles for the overwintering generation. Thus, there are two generations each season. The most effective control method consists of spraying early in April to control overwintering adults, using a horticultural oil or insecticidal soap, which are among the compounds registered for use against this pest in Connecticut. Horticultural oil removes the bloom from blue and white spruces. An insecticidal soap spray applied soon after the new growth begins in May will give good control of the young before galls are formed. Imidacloprid may be effective as a soil-applied systemic treatment. Consult the labels for dosage rates and safety precautions.
Spruce needle miner, Endothenia albolineana.
The caterpillars of this moth mine the needles, along with several other species. Needles may fall in great numbers, but the branches are not usually noticeably defoliated. Little is known about the life history. Among the compounds registered for use against this pest in Connecticut are malathion, acephate and imidacloprid. Spraying with malathion in June should control the adults. Miners may be controlled by spraying with acephate early in July, or by applying imidacloprid as a systemic to be taken up by the roots. Consult the labels for dosage rates and safety precautions.
Spruce spider mite, Oligonychus ununguis.
Considerable injury is caused each season to conifers in ornamental plantings by the spruce mite, which feeds on the needles and webs them like twospotted spider mites. The trees take on a faded grayish or rusty brown appearance. Ultrafine horticultural oil, which is among the compounds registered for use against this pest in Connecticut, sprayed during the dormant season will control the overwintering eggs. The same material applied during the growing season at a low rate (1/2 - 1%) effectively suppresses spider mites while not eliminating beneficial predatory mites. Oil, however, will cause the waxy bloom on blue or white spruces to permanently darken. This does not injure the tree, but the tree color is affected. Other miticides are available to commercial applicators that will not affect tree color, such as hexythiazox and abamectin (a restricted use product). Consult the label for dosage rates and safety precautions.
Twig injury by squirrels.
Often in winter, spruce twigs of the preceding season's growth fall in great numbers and look exactly as if they had been clipped off. This is the work of squirrels that feed on the large terminal or lateral buds. Probably the squirrels cannot reach them without cutting and dropping them to the ground. No effective control option is known except to see that the squirrels have a supply of nuts or other food at times when it is difficult for them to find food.
White pine weevil, Pissodes strobi.
This insect frequently infests the leaders of Norway and other kinds of spruce. The adult beetles overwinter under dead bark, stones and wherever they may find protection in woodland areas, and appear on the trees in April. During May, they lay eggs in punctures in the bark of the leaders and the grubs feed under the bark, often girdling them so they wilt and die in July. The grubs when mature make cells in the wood of the leader to pupate. The beetles begin to emerge the latter part of July and continue into September. There is one generation each year. The adult is a reddish-brown weevil with white spots, and about 1/4" long. Seedlings planted in shade are seldom injured, but those in sunny situations are infested.