The 5 Most Common Pest and Plant Plagues in Ontario

Nothing is more frustrating to the home gardener than the threat of an insect invasion or fast spreading plant disease destroying the beauty of your home landscape.

Adding to the anguish of possibly losing some of your favourite trees and shrubs is the difficulty of figuring out what the problem actually is and what to do about it.

Here are five of the most common plant disease and insect problems in southern Ontario and the first steps to take in treating them.

1. Canker

Cankers are fungal diseases that affect the bark of trees and shrubs. If canker is present, patches of bark in your backyard landscaping may split or peel away.

There is often a change in colour of affected areas along with orange or black ooze that contains spores.

Cankers are more likely to occur in times of stress when plants are not at optimum health.

Though most tree and shrub species are potentially susceptible, the following are most likely to be the victims in southern Ontario

  • Lombardy poplar
  • Colorado spruce
  • Norway spruce

What you should do: You should prune out and throw away infected branches, but in severe cases, the whole tree may have to be removed.

2. Leaf Blotches, Blight and Anthracnose

There are several variations of these bacterial diseases that affect leaves of trees and shrubs.

Numerous black or brown blotches on leaves are the most obvious symptoms.

They usually start in spring and are most likely to spread and become severe if there is cloudy, wet weather in late spring and early summer.

What you should do: Be sure to remove the fallen leaves to throw away or burn, limiting the spread of these diseases.

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3. Rusts

Rusts are somewhat similar to leaf blights, except they are caused by fungi. Spots on leaves are likely to be yellow, orange or brown.

Some types of rust such as cedar-apple rust, one of the most common, need two different species of host for the fungus to complete its life cycle.

Like leaf blotches, rusts can cause backyard and front yard landscaping leaves to die early and drop.

What you should do: Control is difficult; prune affected branches, and water only in the mornings.

Aphids4. Aphids

Aphids are one of the most common insect pests, attacking ornamental and vegetable plants.

Aphids may be green, yellow or black; most are not much bigger than a pin head, but they usually appear in clusters.

They secrete fluids that may attract ants and cause a black fungus to grow, multiplying the damage and annoyance. Aphids are usually on the underside of leaves.

What you should do: Spraying an insecticidal soap is a first step to take in hopes of getting rid of them.

5. ScaleScale

Scale insects are also commonly found on many ornamentals in Ontario.

The name comes from the waxy coating, usually whitish or brown in colour.

They are almost like small barnacles, attaching themselves to plant stems and branches.

Like aphids, a few scale are not a problem, but once they start to multiply, they can be difficult to get rid of.

What you should do: Dormant oil or lime sulphur can be used to control scale, in addition to pruning out heavily infested branches.

More things you should know about pest and plant plagues in Ontario

Note that some conditions may appear to be a pest or disease problem worthy of garden care when, in fact, they are a naturally occurring life cycle stage, such as autumn needle shed on conifer trees.

Plants that are stressed by lack of water or unusual weather may not be looking their best, but they are also more likely to develop pest problems.

Got a pest problem? Let us take care of it for you

If you are not sure how to diagnose or treat an insect invasion or plant disease, it is best to consult with the experts at Lawrence Park Complete Garden Care.

Contact us to talk to an experienced landscape designer about plant problems in your yard or garden.