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Friend or Foe: When to Take Action Against Pests

How to tell when to treat for pests and when to wait

Insects and disease (collectively called “pests”) can cause harm to a tree. Some insects and disease are ordinary and part of a healthy ecosystem. But there is a point when they will impact the long-term health of your tree. That point is called threshold.

What is threshold?

Threshold is the point at which pests go from being a natural part of the ecosystem to being a threat to your plants. Arborists set thresholds so that they know when to take action and when to let nature do its job without human intervention.

Threshold will vary by plant species, plant size, type of pest, and so forth, but the general idea is to identify what percentage of the plant has sustained damage. Some pests are fine, but too many crosses the threshold. Once the plant reaches this point, it will need care.

What are some things to watch for?

Extensively chewed, yellow, or brown leaves at a time when they should be healthy and green

Holes in the bark, especially if there is material oozing out

Cracking or discoloration of bark

Swelling or unusual bumps under the bark

White spots, brown spots, and other extensive discoloration on leaves

These are just a few indications that the pest has possibly crossed the threshold and your plant needs further care.

What should you do if you see these signs of distress?

First, we suggest looking for possible underlying health issues that may be weakening the plant’s defense mechanisms. It is important to remember that a healthy, well cared for tree will not typically succumb to an insect attack.

Once the underlying health issue has been addressed, you may need to treat for the specific pest. But be careful – you do not want to inadvertently cause harm to other insects, plants, soil, or members of the ecosystem. You must first accurately identify the pest and research the best treatment that will cause the least amount of collateral damage to the rest of the ecosystem.

There are so many different kinds of pests, and often they need their own specific treatment, but there are several safe options, including:

  • Horticultural oil
  • Encouraging bugs that eat the pests to take residence
  • Foliar fungicides that do not include metal oxides
  • Tree banding
  • Using bacteria and fungi that interrupt pest life cycles or fend off other harmful pests

If you are having trouble identifying a pest or determining which treatment will be the most effective, you are always welcome to make an appointment with one of our Treecologists. They are trained in identifying pests and choosing the option that will have the smallest impact on the broader ecosystem.

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