Colorado Blue Spruce Treatments

The following information details a brief description and treatment of the most common pests and diseases that affect Spruce and Fir trees in southern Manitoba.

• Spruce Spider Mites: These pests are present when there are large areas of dead, rusty coloured needles inside the tree and when very small webs can be seen nearby especially in the late Spring and Summer. Concentrated jet of water from a garden hose or a power washer (lower setting) can knock off many Spider Mites, their webbing and other debris on Spruce trees each month during the Spring and Summer. Taking up the debris under the tree afterwards is a good
idea to reduce any pests that may be harbouring and breeding in the debris. A tarp can be used as well. This approach is recommended to reduce the need for chemical pesticide control. The largest populations of Mites generally occur in the lower half of most Ornamental Spruce trees and would therefore benefit from periodic water spraying several times every year. Regular power washing with water is far more effective in controlling Spruce Spider Mites than chemical
pesticides. Hot, dry weather during Summer encourages their populations to increase. The spraying of pressurized water 3 – 4 times from May to September. One year of spraying is rarely effective in controlling Spruce Spider Mites on heavily infested trees. At least three and often four or more consecutive years are required.

•Spruce Spider Mite populations remain low during periods of high humidity and heavy rainfall. Infestation in Ornamental trees can thus be avoided by abundantly spraying the damaged tree on a monthly basis and repeatedly, in order to destroy the silk threads and dislodge mites. This will also increase the moisture level of the foliage and thereby hinder Spider Mite development.

• The following insects are a problem if infestation levels are heavy: Pine Needle Scale, Spruce Aphid, Balsam Aphid, Spruce Adelgid (White Spruce only), yellow headed Spruce Saw Fly Larva, Spruce Bud Scale, Shoot Borer and Spruce Bud Worm. These pests can be reasonably controlled by an application of BT (such as Dipel)
ideally in late May or early June. BT provides environmentally preferred pest control over pesticides such as Malathion. Alternatively, concentrated jets of water from a garden hose or a power washer several times in early Spring can be used to knock off many of these insect pest especially Needle Miners, Adelgids, Aphids, Bud Worms, and Saw Fly Caterpillars. Late season (Summer) spraying for these insects relies on a pesticide such as Malathion.

• Spruce Needle Miners: When present in Spruce trees produce clusters of needles usually laid parallel to one another along the axis of the twig, orstacked in a small pile near a trunk-branch junction. In the lower parts of trees, concentrated jets of water from a garden hose or a power washer can be used to knock off many needle miners. Their egg laying areasin old needles, webbing and accumulated debris on
the twigs and needles can also be knocked off the tree with water. It is best to rake up the debris under the tree after water spraying or lay a ground sheet under the boughs. Pesticides maybe used for late season control of Spruce Needle Miners; however, pressurized water is by far the best control method.

• Spruce Bud Worm: This common caterpillar pest feeds on the ends of new soft twigs by the buds and new needles in June. One sign that it is present will be the presence of the bud cap over some of the new needles. The newly developing caterpillar feeds under the cap as the bud is expanding. Later as the caterpillar grows larger and changes colour from light green to medium brown with a black head, it will use it’s webbing to bind two small new soft needle twigs together. It
forms a cocoon in the needles. Breaking them apart later in June should reveal the caterpillar and its cocoon. Early Spring treatment involves using BT when the caterpillars are very small. Later season treatment requires a stronger pesticide.

• Spruce Sirococcus tip blight disease causes slightly or prominently curled ends of the twigs usually denuded of their needles except on one side. All ages and sizes of Spruce trees are affected. This is a potentially lethal tree disease that can be treated with a fungicide such as fixed copper spray or Daconil. Usually two spray treatments of copper 10 to 14 days apart are necessary in the Spring and early Summer. Normally only one Daconil spray is required. On very heavily infected larger trees, often White Spruce, a third treatment will likely be necessary. Copper sprays are often added to other pesticides.

• Spruce Rhizosphaera needle cast disease: This is a common needle disease of Spruce trees. Typically the needles have a grey-green shade to their colour. With a hand lens there should be two distinct rows of black dots (minute fungus growth growing inside the breathing pores) on the underside of the needles. It is controlled with copper fungicides in a similar manner as tip blight disease.

• Cytospora canker (white blister) fungus disease: There is no known cure for this canker disease which is the most common and most widely spread disease of ornamental Spruce trees in southern Manitoba. Look for resinous white blisters on the lower or upper branches and/or resin bleeding from cracks in the bark of the trunk. Timely removal of the dead and significantly infected branches (a sanitation process) on all Spruce trees is the first action that should be taken.

• Keeping the Spruce trees healthy through regular aeration, fertilization and watering willsignificantly slow the rate of expansion of Cytospora canker disease, tip blight disease, and most spider mite and insect infestations.

• FERTILIZATION: Pest infestations can be significantly reduced by following a regular annual program of fertilization and aeration. Unless you recently or regularly add nutrients to the soil around your trees they are definitely nutrient deficient Trees in their natural forest setting get nutrients from the decomposing leaf and litter of the forest floor. In the landscape, leaf litter and grass clippings are usually raked up and removed so there are no naturally available nutrients. Nutrients must be applied or your trees will live in a very weakened state, susceptible to disease, insects and storm damage. Fertilizing your trees is the best preventative medicine for a valuable investment – Your Trees!

• All trees will benefit from aeration and fertilization treatments. It is recommended that these treatments be done annually for large Spruce trees for at least the next 3 to 4 years. It will take some time for the treatments to reveal positive results in these trees. There are virtually no feeding roots directly beneath the Spruce branches. Eventually older needles on Spruce trees fall due to age; so some needle drop in these trees will be natural. In recent years, Spider Mites have significantly
advanced the timing of Spruce needle fall in southern Manitoba.

• WATERING: Hot dry summers create stressful situations for coniferous evergreens especially Colorado Blue Spruce growing on heavy clay soils. Detailed watering information for these trees is available upon request.

Limitations

• Spring-flowering shrubs will not bloom the year of rejuvenation.

• On shrubs with a rock and weed fabric mulch, rejuvenation may not be successful due to decreased root vigor and interference of the mulch with growth from the base.

• Extremely overgrown shrubs with large woody bases may not respondwell to rejuvenation pruning.

• Shrubs with many dead branches will not respond well to rejuvenation pruning. As a rule of thumb, if more than one-third of the branches are woody, without healthy foliage, the shrub will probably not respond.

Replacement

Shrubs that have been repeatedly sheared often become woody and filled with dead twigs. The best option may be to replace them. On many commercial sites, labor issues prohibit routine pruning. When shrubs become overgrown, they are simply replaced as a low-maintenance alternative. Shrubs can also be overwhelmed by weedy invaders. If routine clearing of these invading woody species is not done, the original shrubs may be compromised or lost. Replacement may again be needed.