Why and when are herbicides used in forestry operations?

Oregon is one of the best tree-growing regions in the world, but even our fast-growing, native species such as Douglas-fir can be smothered by weeds and other broadleaf plants. Both native and invasive species such as vine maple, Scotch broom and blackberry can quickly overcome seedlings.

New trees need to outgrow the faster-growing weeds and brush around them in order to survive their first few years. In fact, landowners are required by law to make sure this happens. That’s why private forest landowners use herbicides to control competing plants and let the trees get a head start. After the trees are 8 to 10 feet tall they will shade the ground, and the weeds will die off naturally due to lack of sunlight.

Herbicides are typically applied on any piece of ground just two to four times within 40 or 50 years. By the time young trees enter their second or third year, they are usually outgrowing the other vegetation. At that point, there’s no need to apply herbicides until the next harvest several decades later.

In some dry-forest types in eastern Oregon, herbicides are rarely if ever used.

Forest protection laws limit the use of chemicals.

Lots of rules to know. Foresters want to use herbicides as sparingly and safely as possible. The chemicals are the same or similar to chemicals available to consumers. However, foresters must follow strict rules laid out by a variety of state and federal regulations, as well as the Oregon Forest Practices Act. It’s a lot of rules, but they’re all important and must be followed responsibly for the health and safety of people, aquatic life and drinking water. The rules include:

  • Never spray near streams with fish or around municipal water supplies.
  • Complete a mandatory written plan for any chemical application within 100 feet of fish-bearing streams.
  • Dispose of waste and chemical containers properly.
  • Keep daily application records.
  • Follow stringent rules for aerial applications.
  • Follow all label restrictions, along with the rules of the Environmental Protection Agency, the Oregon Department of Agriculture, the Oregon Department of Environmental Quality, the Oregon Water Resource Department and the federal Occupational Safety and Health Administration.
"Forest chemicals help us raise a healthy forest faster and more economically. They are just one tool we use, and most forest managers use chemicals only when needed, just two or three times in the first couple years of a new forest's life."
Nancy Hathaway Retired schoolteacher and forest landowner, Corvallis
A Day in the Woods: Chemicals and the Forest

Two extension foresters explain why chemicals are sometimes used in Oregon’s working forests

A Day in the Woods: Chemicals and the Forest

Two extension foresters explain why chemicals are sometimes used in Oregon’s working forests