When you see discolored, bare, or dying branches on your Colorado blue spruce tree (Picea pungens) the problem is likely the result of either insect infestation or disease. This stately tree, known for its vibrant blue-green needles is particularly vulnerable to two specific insect pests and two types of disease. All of these problems can be exacerbated by stress which can be caused by drought, poor soil conditions, mechanical damage, and climatic conditions such as warm humidity. First, learn how to identify these pests or diseases and the harm that they cause, then learn how to treat a blue spruce affected by them.
Dying branches (branch dieback) or branches that are shedding needles are common symptoms that Colorado blue spruce trees exhibit when they have been attacked by insect pests. One such pest is the aphid, a sap-sucking insect. There are various kinds of aphids; for example, the melon aphid is Aphis gossypii. The aphids that commonly attack Colorado blue spruce are called spruce aphids (Elatobium abietinum). They are about 1/16 inch long and can be found in great numbers on the needles of the tree during an infestation. Mature spruce aphids have olive-green bodies (young aphids have a lighter green color) and two sets of wings.
Earlier symptoms of an infestation include yellowing of the needles. This discoloration may be accompanied by honeydew (a sticky material excreted by pests such as scale and aphid). You may see an unusual number of ants on the tree as they are attracted to the honeydew. The needles may later turn brown and drop off.
A healthy tree will probably survive an aphid attack without treatment, but aphids can kill a tree that has been stressed. If you detect aphids on your Colorado blue spruce tree, try spraying first with the horticultural oil, Neem. It is organic, and it will not hurt your tree, so there is no harm in trying Neem oil to solve your problem. If your aphid problem continues, you can take the preventive measure of spraying with a dormant oil next year.
The key to the effectiveness of such spraying is timing. Aphid eggs overwinter, and they hatch in spring. Spray with the dormant oil in January to prevent hatching.
Cooley Spruce Gall Adelgids
The adelgid is another sucking insect that can cause needle drop and branch dieback on blue spruce. As with aphids, there’s more than one kind. The type that attacks blue spruce trees is the Cooley spruce gall adelgid (Adelges cooleyi); an example of another kind is the Hemlock woolly adelgid (Adelges tsugae), which attacks Canadian hemlock trees (Tsuga canadensis). In the process of sucking juices out of their host plant, spruce adelgids cause an irritation in the plant tissue that leads to the formation of cone-like galls.
It is during the nymph stage that they do their damage. Spruce adelgid nymphs look a bit like aphids, so the best way to tell if you have an infestation of spruce adelgid is to look for the galls at the tips of tree branches. Generally, these infestations will not damage the health of the tree: The damage they cause is more of an aesthetic concern unless infestations are constant and/or the tree is stressed.
Complicating identification of the galls is the fact that they have a spiky appearance, rather like that of the tips of a spruce branch, itself. In fact, although they can be other colors, sometimes they are green, allowing them to blend in. So you really have to study your tree and develop an awareness for any spiky object you find on it that doesn’t belong.
When you find such an object, pick it off with your hand and destroy it, because it may well be a gall. Removing the gall will halt the adelgid life cycle in its tracks. This preventive measure is the best way to control spruce adelgids.
This is a fungal disease that affects older spruce trees, most commonly those more than 15 years old. Symptoms include branches with brown needles (that may eventually fall off) as well as the appearance of a white residue that looks like bird droppings. The residue is caused by resin oozing from infected parts of the tree. Eventually, dead or leafless branches may develop on the tree. The lowest—and oldest—branches usually die first, followed by higher branches as the problem worsens. Cytospora canker rarely kills a tree, but the resultant loss of branches may mar a specimen’s appearance.
For control, affected branches should be pruned off in winter when the tree is dormant (sanitize the pruning tool between cuts). The only other treatment is to care properly for the tree (to improve its vigor and to minimize drought stress) through diligent watering. There is no chemical treatment for the disease so prevention, by maintaining the tree in good health, is the best approach.
This is the common name for various fungal diseases, including Rhizosphaera, Stigmina, and others. Needle cast diseases cause blue spruce trees to shed (or “cast”) their needles. The disease usually infects new shoots at the ends of the branch, but the infected needles don’t die until the next year, creating an odd pattern where trees have an outer layer of live needles surrounding dead inner needles. As with cytospora canker, it is rare for an affected tree to be killed, but, if the onslaught is continual and enough branches are lost, the tree will eventually lose its vitality.
Needle casts can be controlled somewhat with fungicide treatment, but this protects only new growth; it does not revive dying branches. Fungicide treatments may need to be repeated for two or three years for maximum effectiveness.
Average Lifespan of a Blue Spruce
With appropriate care and attention, this popular tree will survive in your home landscape for 40 to 60 years. In the high elevations of its native range in Colorado, this tree can survive in the wild for up to 200 years. Blue Spruce can be grown in USDA growing zones 2 through 8 and thrives in cooler, humid climates. To keep your tree going as long as possible choose a location with plenty of sunshine, keep it evenly moist and, in zones with warmer temperatures, mulch to keep soil cool and moist.
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