A Look at Spruce and Cedar in the Spring

March-April 2003

THE TEMPERATURE IS BECOMING BEARABLE, the days are longer and you can start to visualize new growth on the trees. However, winter has been really tough on white spruce (Picea glauca) and white cedar (Thuja occidentalis), as it is every year. This discussion will examine the symptoms that show up on these trees in early spring so that differences can be highlighted and the correct diagnosis can be made. Correct treatment (if any) can then be explored.

Symptoms on White Cedar

  • individual brown tips, which can range from a few tips to most tips over entire tree (see Cedar Leaf Miner)
  • brown blotch with a blackish tinge, low to the ground (see Dog Urine)
  • large areas of browning, which include multiple years of growth, usually on one side (see Salt Injury)

Symptoms on White Spruce

  • off colour needles of various ages which fall off the tree when touched or by spring (see Salt Injury, Spider Mites, Dehydration)

Cedar Leaf Minor (Argyresthia sp.) attacks the newly formed tips of white cedar. Larvae mine out the needle tissue and cause adjacent tissue to brown. Infestation can be light (few tips) to very heavy (when almost every tip has browned off). Diagnose this insect by picking off the brown tip and looking for a mined hole in the tissue (uninfected tissue is solid – check this by pulling off a green tip). Do the same to green tissue and realize that the tissue should be solid. The caterpillars overwinter in the tissue so occasionally you may find a caterpillar inside the mined tissue (Warning: the caterpillars are tougher to find than you would think).

Dog Urine is a problem on cedars when the tree is within a fenced area with dogs or along a walking path. Dogs love to urinate on evergreens and once a tree has been marked, every dog has to add to the spot. I expect that salts within urine may draw moisture out of the tissue or build up in toxic amounts. Look for a blackish tinge on the brown foliage. (Note: it is possible that any animal urine will cause the same symptoms. Think humans if the blackish spot is two or three feet from grade, too high for a dog).

Salt Injury is a severe problem on cedars and white spruce that are in the direct path of salt spray (along a major highway or road where speeds and salt usage is high). Salt absorption into the ground is usually not a problem as most salty water drains away in the spring before soil thaws. The book Diseases of Trees and Shrubs lists white cedar and white spruce as having a low tolerance to salt. Other spruces listed include Colorado with a high tolerance and Norway with a moderate tolerance.

Look at the pattern of injury to help with diagnosis as the symptoms of browning are vague. Browning should be heaviest on the roadside, especially on the angle which would catch the salt spray and prevailing winds. Damage will be minimal where fencing or other vegetation provides protection. If the tree is tall, damage may be minimal above a certain height (height depends on distance of tree from the road, amount of salt applied and speed of vehicles on the road).

Spider Mites are a problem on both cedars and spruce (especially white spruce). Mites that attack cedars are usually most active during the hot summer months and the symptom of foliar bronzing (the killing of individual cells which blend together as dead cells increase in number) turn up in August and September. Spruce are attacked by cool weather mites, which are active in spring and fall; the mites usually attack older, interior foliage. When there is a heavy infestation of mites in the fall, symptoms of bronzing usually are not apparent until early spring. The tree will drop damaged foliage. Browning foliage on white spruce should be examined closely with a magnifying lens. Spider mites leave lots of microscopic evidence – tiny, tiny webbing; white broken eggshells; cast-off skins; and dirt buildup on the honeydew (mite excrement). Don’t expect to see a mite walking around; they are difficult to spot unless populations are very large.

Dehydration is a serious problem for white spruce that are growing in poor soils (soils that are compacted, in urban areas, have a low % of organic matter, high wind and sun exposure). We are experiencing extended summer and fall droughts on a yearly basis. The soil around the spruce may not be able to absorb water adequately when water conditions are good. Roots may dehydrate and the aboveground parts may enter winter dehydrated. If winter temperatures rise above 0 degrees Celsius, needles may attempt photosynthesis and use up water within the needle tissue. As the soil moisture is in a frozen state, replacement water is not available and needle tissue will dehydrate. Add a wee bit of salt spray and the single problems of salt or dehydration are compounded. Newly transplanted trees are often victims of dehydration, especially if planted in the fall, due to inadequate numbers of absorbing roots. The symptoms of browning needles due to dehydration may occur over the entire tree but may be less on the new tips as scarce water sources seem to be concentrated in new tissues. The symptoms should be heaviest in the interior (same as mites).

As always, the place to look for control methods for the biotic pests (miner and mites) is within OMAFRA’s Publication 383 – Nursery and Landscape Plant Production, which outlines non-chemical and chemical controls registered for use in Ontario. For the abiotic problems, use common sense and the basic health care management steps of proper watering, mulching, aeration and protection from salt and urine producers. Working to prevent these problems from occurring will be more successful than attempting to "fix" the problem come spring.

— Patricia Thomson, B.Sc.F. Consulting Arborist, Kelly’s Tree Care Ltd. with thanks to Alex Bykov, City of Toronto Forestry, for his help in fact-checking my observations. Photos from: Trees of Ontario, Lone Pine Publishing, 2001.

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