Cedars, pines and shrubs have own problems

Hey there, time traveller!
This article was published 16/11/2003 (8174 days ago), so information in it may no longer be current.

THIS year has seen far more problems affecting all varieties of coniferous evergreen trees than any other previous year within the last 10 years. I have discussed the pests and diseases affecting the spruce trees several times this year in this column. In this article I want to focus on cedar and pine trees and shrubs. Fall and winter are excellent times of the year to assess coniferous evergreen problems and plan for their treatment next year.

Many varieties of globe and columnar eastern white cedars are infested with Fletcher scale insects. The scale insects are present if there are clear droplets of sticky liquid (honey dew) on the leaves in late spring and summer. The newly hatched very tiny, scale nymphs or crawlers (pale yellow to light brown in colour) emerge from the brown blobs (adult females) in late May to early June. The blobs are brown domes that protect the developing young inside. If you wrap sticky tape sticky side up around a portion of the leaves and the twiglets, you should be able to see the young scales on the tape. These crawlers can be knocked off the leaves and twigs with a concentrated jet of water from a garden hose or power washer. Dormant oil can be sprayed on the leaves after the heavy frost period in early spring but before the opening of the buds. This period is usually in mid-April to early May. However this period can vary from year to year. Late season infestations can be controlled with stronger pesticides. Often the honey dew becomes infected with sooty mould disease leaving a greasy, blackish-green cast to the leaves. When the scales are controlled, the mould is no longer a problem. Lime sulfur spray can be applied to the foliage after spraying dormant oil in April. The leaves will die if the mould infection is severe enough.

On older cedars I have noticed the presence of spruce spider mites. Typically, the leaves have a stippled look to them. Heavy snow fall will sometimes cause cedars to bend over. Be sure to carefully brush off the snow afterwards. If the stems of upright cedars have separated from their normal close knit pattern, simply tie the stems together loosely with sturdy twine. They should be fine by next spring.

I am often asked about pruning cedars. How much can I prune? When can I prune? As with all pruning the rule of thumb is to prune no more than one-third of the living green growth. If you cut deep into a cedar and expose the inside you will notice it is devoid of leaves. If you do prune too hard that is what you are going to end up with: very little green growth. New growth will not start from bare stems. New growth starts from living leaves and adjacent twiglets. Early June is the best time to prune cedars as this will allow the plant to recover from pruning through the growing season. Never prune any evergreen when it is wet. Wet periods are often the time when diseases are spread, especially in the spring.

Dehydrating leaves

Winter burn commonly affects the south and south-west facing sides of cedars, junipers and other coniferous evergreens by dehydrating the leaves and turning them rusty brown. Thoroughly water the plants before the ground freezes. Usually late fall watering will prevent serious winter burn, but not always. The plants should also be watered during dry spring and summer periods. Placing a burlap screen around the south and south-west sides of the cedars provides an ideal protection against winter burning if the cedars are not too high. Do not wrap burlap directly onto the cedar as this is no guarantee that the leaves will not be burned. The reason why so many cedars and junipers “burn” is related to their sensitivity to southern Manitoba’s severe winters. Many of these plants originate in B.C. or Minnesota where the climate is not as harsh. The genetics of the plant are the prevailing factor that allows a plant to be acclimatized to a colder area or not. Genetically, a cedar in central Okanogan, B.C. is different than a cedar from Sandilands in Manitoba.

Many people have called me about what they believe to be excessive dropping of needles from their pine trees especially Scotch pine. Both Scotch and Mugo pines have incurred higher than normal needle losses.

Both Scotch pine and Mugo pine trees are susceptible to a serious fungus disease that has become much more active in 2003 than in previous years. The disease is called Sirococcus tip blight of pine. The tips of the twigs are usually slightly curled or may be very prominently curled. The needles closest to the tips start out as a yellowish-green colour and then turn a straw brown in colour before falling off. Often the discoloured needles are in the same area as green healthy appearing needles. As with most tree diseases, tip blight disease favours pines that are in some stage of growing stress such as limited root systems and growing on nutritionally impoverish soils. Older pines are often more susceptible than younger ones.

Prune off the infected areas on the tree before doing any spraying. Never prune when the tree branches are wet. Always sterilize the pruning tools after each cut with diluted bleach or methyl hydrate as the tools will spread the microscopic spores of this disease to healthy areas of the tree. A dormant fungicide such as lime sulfur spray can be applied to the foliage in April before the buds open. There is no guarantee that this spray will work, but it has been effective in the early control of some tree diseases. This should be tried for smaller trees such as Mugo pines, as the actual spraying can be done fairly easily. Advanced stages of the disease can be treated with a fungicide such as copper spray or Daconil. Usually two or three spray treatments are necessary in the spring and early summer. An assessment of the effectiveness of the spraying should be done in August or early September to determine if further control will be necessary in the following year.

Fertilize and water the roots of both the cedars and the pines to promote their vigour and to restore their source of nutrition. Clay soils are very poor in nitrogen and iron which all evergreens require. The feeding or absorbing root system of trees is not confined to the drip line of their crowns as many fertilizer products suggest. The roots extend at least half the height of the tree in all directions unless blocked by buildings, driveways and the like.

Mike Allen is a consulting urban forester and certified I.S.A. arborist with Viburnum Tree Experts. He makes house calls for consultation on problems with trees and woody shrubs. He can be contacted by calling 831-6503 or on e-mail at viburnumtrees@shaw.ca . You can also mail questions to him c/0 Newsroom, Winnipeg Free Press, 1355 Mountain Ave., Winnipeg, MB, R2X 3B6.