Monday, June 17, 2024
Alberta GardenerPlantsTrees & Shrubs

A troubleshooting guide for evergreens

Tree showing dead branches from cytospora.
Spruce spider mite damage
A close up view of spruce bud scale


What’s wrong with my evergreen trees?

This is a question I hear daily during the spring, summer and, especially, the fall. That question is very important. It is the very first signal that a property owner is aware his or her trees no longer look “normal”. A great number of people do not see adverse changes occurring in their trees until they look dead, or nearly so.

The discolouration and dropping of evergreen needles is a natural phenomenon, and the main cause of needle loss in the wild. Evergreen needles and leaves do not survive for a lengthy period, and in fact usually have a life span of only five to seven years on healthy trees. The needles first start to die in the central and lower part of the tree, and this change progresses upward over time.

Though the brown needles and leaves may have developed slowly, the problem is often recognized only when something dramatic occurs. What usually catches the tree owner’s attention is the sudden fall of a very large number of brown needles and leaves.

The question, “What is wrong with my evergreen trees?” should have been asked when the tree first lost part of its greenness. This can happen as early as a year or two after a tree is planted. This is especially true in southern Manitoba where heavy clay soils predominate. Spruce trees, for example, do not grow well on clay soils.

Walk through an indigenous coniferous evergreen forest where trees of the same species – say spruce – and various ages are growing. You will see these spruce trees naturally lose needles as they get older. Age is an important factor here in causing needle loss and branch death, but so are diseases and pests. In landscape plantings of coniferous evergreen trees, however, pests and disease are the major cause of needle loss and dying branches.

Needle and branch loss are not the only symptoms signaling you have a troubled tree. After noting the symptoms, you can begin to deal with your tree’s problem. You will need answers to two key questions: “What is the problem?” and “How can it be treated?’

The cause of the affliction will vary depending on the type of tree. Here are some of the more common problems, apart from natural aging,that afflict spruce trees, the probable causes and ways of treating the problem. Unfortunately, these majestic trees, the most popular evergreen planted on our residential properties, incur many other pest and disease problems not dealt with here.

Sympton: Rusty brown needles that eventually fall.
Likely causes:

1. Internal fungus disease (called Cytospora or white blister canker).This creates cracks in the bark causing resin to drip and leave grey-white dripping streaks on the bark. The fungus also causes open wounds or blisters on tops of branches. These wounds can be greyish white or greyish blue in colour, eventually turning brown and black.

2. Feeding by spider mites which leave fine, poorly formed webs in the needles, especially near the ends of the twigs.

Best treatments:

1. Properly aerate and fertilize tree out to a distance of half its height in all directions, where possible.

2. Pressure wash thoroughly once a month with water only all needles and branches as high as possible on the tree. Water pressure dislodges spider mites.

Sympton: Curled twig ends denuded of needles, especially on one side of the twig.
Likely cause:

Tip blight (Sirococcus) fungal disease.

Best treatment:

Spray approved fungicide on the entire tree in lateMay or June.

Sympton: Chewed up ends of twigs in June. The culprits, green and later brown caterpillars, are easy to spot. Bud caps may be stuck on the ends of the developing needles causing them to bow out like a spindle.
Likely cause:

Spruce bud worms which develop in the needle cluster that arises from a bud.

Best treatment:

Spray the pesticide, Btk (for example, the biological Dipel brand), onto the entire tree when feeding is first noticed in early spring, to kill the young caterpillars.

Sympton: Black sooty mold covering twigs and needles especially near the junction of two opposite twigs on the branch.
Likely cause:

1. Spruce bud scales, ball-shaped insects, initially light brown in colour but eventually turning black. Often two to five scale balls cluster in one location on the twig; honey dew excretions from scales become infected with sooty mold.

2. An overhanging shade tree such as oak, maple or elm may have heavily infested leaves with aphids whose honey dew secretions become infected with sooty mold.

Best treatment:

1.Pressure wash tree using water only to dislodge young scales (called nymphs) in May and early June while they are in the crawling stage. Scale nymphs fall to the ground where they cease to be a threat to the tree.

2. Spray shade tree in early spring with Btk to control aphids. The problems of other coniferous evergreens such as pines, firs, cedars and junipers can usually be treated with correct diagnosis, though some diseases are lethal. A future article will discuss the symptoms, causes and treatments of the most common problems affecting this group of coniferous evergreens.

Mike Allen is a consulting urban forester, certified ISA arborist and owner of Viburnum Tree Experts in Winnipeg.

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