The Green Solutions - Healthy Trees and Shrubs



Last updated : January 10, 2002

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Healthy Trees and Shrubs

Newly planted trees and shrubs need care. By checking them daily, you can guard against insects and diseases. Natural methods of control are easy to use and require little effort. Nevertheless, some trees need more attention than others and have very specific soil requirements. Flowering shrubs and ornamental crab apple trees are very popular. The drawback to crab apple and other fruit trees, however, is that they attract birds and require more maintenance. Therefore, they are not a good choice for people who go away on vacation for a month or two every year.

Insects common to trees and shrubs

It is important to learn about insects and diseases and ways to repel or eliminate them. Green solutions provide a means of handling such problems without using pesticides, thereby enhancing the wonderful contribution that your trees make to a healthy environment.

Dormant oil is one of the natural, environmentally safe substances that you should use to control insects. This product, which is sold at garden centres, smothers insects. Shrubs and trees, including fruit trees and evergreens, can be treated with dormant oil. Read the label before applying the oil: its dehydrating action is harmful to certain trees. The oil must be applied before the buds swell and are ready to open. Dormant oil is available at garden centres beginning in February.

Many shrubs are vulnerable to diseases such as mildew, black spot or rust. Good air circulation is important. Overly dense planting reduces air circulation and favours disease. Avoid overwatering because it promotes fungus diseases. Remove leaves and branches infected with mould, spot, rust or canker. Sulphur applications can be effective against fungi.

Image: Codling Moth
Codling Moth

Image: Apple Maggot
Apple Maggot

Insects and diseases that affect fruit trees

Excluding berry bushes, the most popular fruit tree in city gardens is undoubtedly the apple tree. Here are a few suggestions for combatting insects and diseases. Watch out for codling moths andapple maggots; they attack the apples directly. Applying dormant oil in the spring helps to control these insects. For other insects, you can use the same controls as for common tree and shrub pests, as well as traps.

Piece of cardboard coated with sticky material

There are a number of methods you can use to trap insects that crawl up tree trunks, such as eastern and forest tent caterpillars or fall and spring cankerworms. One way is to wrap a 15 to 21 cm wide band of corrugated cardboard or cloth around the trunk and smear it with natural resin. Make sure that insects cannot crawl under the bands. Remove and burn the bands regularly. Use this treatment in early spring and early fall, and scrape the trunk with a stiff brush to remove any larvae that may have taken shelter there.

Sticky yellow panel

To control tarnished plant bugs, in the spring, fold a piece of cardboard in half, coat of the inner sides with a sticky substance, and attach it 1 m above the ground. Apple maggots can be trapped in late June after the apple blossoms have fallen, by hanging red balls covered with glue or natural resin 1.5 m above the ground.

You can place sticky yellow panels in trees to determine the degree of infestation and the type of insects involved. Also, removing any fruit and leaves that have fallen on the ground is a good way to reduce the spread of disease and insect attacks.

A number of plants repel apple maggots and other insects that attack apple trees. You can plant aromatic herbs (mint, lavender, sage), nasturtiums or marigolds under the trees. Chives reduce apple scab infestations.

To control mildew and apple scab, spray undiluted human urine on the foliage before the buds open. Three weeks later, repeat the treatment using a solution of one part urine and four parts water. In fall, repeat again with a solution of equal parts urine and water.

Aphids

Insects	Solutions	Remarks
Aphids	Dormant oil	Apply in April after the risk of severe frost is over and before the buds open.
	Cutt off infested branches and spray with soapy water	Repeat regularly. Rinse with clean water before the foliage is dry.

Thrips

Insects	Solutions	Remarks
Thrips	Dormant oil	Apply in late March, early April before the buds swell and are ready to open.

Leafminers

Insects	Solutions	Remarks
Leafminers	Remove all infested leaves and crush them to kill the bugs	They live inside the leaves

Caterpillars

Insects	Solutions	Remarks
Caterpillars	Plant nasturtiums at the base of trees Roll up leaves containing caterpillars and remove	Leafminers are repelled by nasturtiums
	Bacillus thurigiensis (B.t.)	thes bacteria can be used to kill types of caterpillars.
	Diatomaceous earth Lime	Apply on caterpillars directly

Forest tent caterpillars

Insects	Solutions	Remarks
Forest tent caterpillars	Destroy eggs and cocoons with a broom or rag soaked in rubbing alcohol	Caterpillars attack deciduous trees.
	Apply treatment from early spring through fall.
	Bt, lime and diatomaceous earth

Leafhoppers

Insects	Solutions	Remarks
Leafhoppers	Plant petunias or geraniums at the base of trees	These plants repel leafhoppers.

Tarnished plant bugs

Insects	Solutions	Remarks
Tarnished plant bugs	Apply rotenone or pyrethrum	Spread only at night in order to avoid killing honey bees

Mealybugs

Insects	Solutions	Remarks
Mealybugs	Allpy rubbing alcohol or camphor directly on the insects	Repeat daily for a few weeks

Red mites

Insects	Solutions	Remarks
Red mites	Spray with cold soapy water	They reproduce in hot, dry weather
	Sprinkle wood ash, lime, rye flour, diatomaceous earth or pyrethrum on plants
	Dormant oil	Dormant oil is sold at garden centres

Maintaining fruit trees

Apple trees do not produce fruit until their third year. You should plant two or three different varieties of apple trees to ensure that you have apples to harvest. Ornamental crab apple trees are good pollinators. Apple trees must be planted in a sunny area protected from prevailing winds, and the soil must be rich in nitrogen and fertilized with compost or fish emulsion.

Pruning

For a complete description of pruning, you should buy a good reference book. A tree that is pruned regularly will produce fruit; one that is neglected will remain barren. Good pruning stimulates growth and makes trees more resistant to disease. Pruning should be done in March or April, on a calm, sunny day. Over the first few years, you must cut back the main branches to shape the tree. In addition, branches that are damaged, that intertwine, or that block light must be pruned.

General care

In Québec, it is best to plant trees, shrubs and evergreens in spring, because in the fall they may not have enough time to put down new roots before the first frost. Planting should be done before growth begins, when the ground has thawed and the soil is dry enough.

During the first few years of growth, new trees need a lot of water. When they are older, thorough watering once a week during the hot spells in July is sufficient. To prevent fungus disease, never water the trunk or foliage.

In the summer, avoid placing the barbecue under trees, since the smoke and heat can harm them. Do not nurse tree injuries. There is a popular fallacy that trees suffer like humans when they are injured. However, like a bandage left on a wound too long, a protective dressing may favour infection in a tree, since it can crack and let water seep in. Never use paint to dress a tree wound. You should call a tree specialist to prune large trees, since this work may be dangerous. If any tree roots are exposed, cover them with wet peat moss to prevent dehydration.

Dig holes at the foliage limit

Deciduous trees and shrubs

In the spring, remove any winter protection from shrubs and cut back dead or damaged branches. Fertilize older trees in early spring or late fall when growth has stopped. After heavy rainfall, water trees thoroughly to soften the soil before applying fertilizer. Dig holes at the foliage limit, and place some fertilizer rich in nitrogen and potassium (bone meal, seaweed, fish emulsion) into each hole, then fill them with sand and compost. This helps to aerate compacted soil.

Prune leafy shrubs and hedges in spring before the buds open. Flowering shrubs must be pruned after they have bloomed in the spring. In fall, wrap spiral protectors around the trunks of young trees to keep mice away. Remove dead leaves and branches.

Evergreens

In spring, remove winter protection from small evergreens and apply a fertilizer rich in nitrogen and potassium. Evergreens prefer slightly acid soil, so it is important to add humus. In fall, an application of potassium, such as seaweed, increases evergreens' resistance to the cold. Cedar hedges must be pruned in June and August. Make sure to cut the top back more than the base so that enough light reaches the lower branches. In fall, wrap burlap or another type of protective covering around your evergreens and water them thoroughly. When the ground is frozen, place a mulch under the hedges to conserve moisture over the winter.

Long-term investments

Unlike flower gardens, trees and shrubs are often neglected: they may suffer from nutrient deficiency, insect infestations and diseases. Trees and shrubs are long-lasting investments. They enhance the beauty of our homes, provide shade, conserve moisture, prevent soil erosion and provide habitats for birds. They therefore deserve all the care we can give them.

Recommended reading

Kourik, Robert. 1986. Designing and Maintaining Your Edible Landscape Naturally. Santa Rosa, CA: Metamorphic Press. 370 p.

Turner, KB, CS Kirby and BW Dance. 1975. Common Pests of Trees and Shrubs. Publication PC, 3. Ontario Ministry of Natural Resources.

Yepsen, Roger B, Jr. 1976. Organic Plant Protection: A Comprehensive Reference on Controlling Insects and Diseases in the Garden, Orchard and Yard without Using Chemicals. Emmaus, PA: Rodale Press. 688 p.

Collaborators : Sylvie Deslauriers, agronomist. Département de santé communautaire de Lanaudière

Fore more informations contact :
Environment Canada
Inquiry Centre
105 McGill Street, 2nd Floor
Montréal QC
H2Y 2E7
(514) 496-6851
1-800-463-4311

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