Biological Control for Weed Management

Most successful weed management plans use a number of methods: herbicides, mechanical, cultural, and when appropriate biological control. Use of multiple methods at the same time is called Integrated Pest Management - or IPM.

Biological control of weeds is the use of one organism to control another. Classical biological control is the introduction of control agents - usually insects - into a region that is not part of their natural range, to permanently reduce the populations of selected weeds. They are used to reduce, not get rid of the weeds.

Biological control may be an option for your weed problem if.....

  • You don't expect the weed to be totally eradicated
  • You don't need instant gratification
  • You are willing to check release sites for establishment and impact
  • You are willing to give the agents the time they need to work (two to five plus years) before resorting to other weed management options (spray, mechanical, cultural)

Biological Agents

Peruse pictures of biological control agents. For a complete list of weeds and their biocontrol agents, visit the Nez Perce Bio-Control Center website.

Spotted Knapweed

Spotted knapweed in bloom

Spotted Knapweed Agents

Thirteen insects have been released
that will attack knapweed species. Some prefer other
knapweed species over spotted. The most effective
established agents preferring spotted knapweed are
A.zoegana, C. achates, Larinus spp., and Urophora
spp. Work in Canada shows the best control if seed head
feeders and root feeders are combined. View the full list (PDF).

Leafy Spurge

Leafy spurge in bloom

Leafy Spurge

Beetles (Aphthona spp.) that eat the leaves and seed
have been the most visible and effective so far. Grazing
by sheep, goats, llamas or hogs is an effective way to
keep the plants from blooming. View the full list of agents (PDF) for weeds.

Dalmation Toadflax

Dalmatain toadflax in bloom


Flower feeding beetles (Brachypterolus pulicarius)
are likely already in your yellow toadflax. A stem-boring
weevil (Mecinus janthinus) that attacks Dalmatian
toadflax is showing promise.View the full list of agents (PDF).

Prescription Grazing

Prescription grazing - is carefully controlled grazing to meet land management objectives. It can reduce weeds in crop systems, control weeds in tree crops, remove weeds in sensitive areas, and control weeds on range lands.

Keys to Prescription Grazing

  • Timing of grazing - when weeds are most susceptible and taste the best to the animal, generally early spring in North Idaho.
  • Frequency of grazing - Depends on the weed species; life span, reproduction, longevity of seeds in the soil, and how it reacts to grazing.
  • Stocking rate - How many animals do you need on how much acreage? It depends on the density of the weed infestation, the palatability of the weed, and your specific goals.
  • Pick the right animal for the job - Pick the correct species and breed for your weed. It is a myth that any old goat (or sheep, or cow) will do.

Learn more from the Targeted Grazing website with grazing guidelines for weed control.

Sheep looking into camera
Three white goats

Local Programs

Contact your State Department of Agriculture, County Noxious Weed Office, Local Cooperative Weed Management Area (CWMA) or Extension Agent.