Controlling Weeds


Biological Control Agents to Control Invasive Species

Field Bindweed Mite Damage Biological control (biocontrol) is the introduction and use of an insect, disease, or other pathogen to control a non-native plant species, while not impacting native plants. Biocontrol can be a viable option for dealing with some large infestation of noxious weeds. If the infestation is still small or just getting started, biocontrol is not the best solution.

The Colorado Department of Agriculture sponsors the Colorado Insectary in Palisade, Colorado. At the Insectary they are conducting research to find organisms to help in the control of specific noxious weeds and troublesome insects. On these pages they discuss the biocontrol agents that are available for the different weed species as well as allow for ordering.

Musk Thistle Seed Feeding Beetle Over the years, in Weld County, we have released the Field Bindweed mites, the Leafy Spurge flea beetles, the Diffuse Knapweed seed feeding weevil, the Dalmatian Toadflax stem feeding weevils, and the Russian Knapweed gall wasp. We have also partnered with local landowners to aid in the distribution of the Canada Thistle rust. Some landowners have tried the Puncturevine seed feeding weevils. Mixed success has been seen with these agents. If you release any biocontrol agents, please contact the Weed Division office at 970-400-3770. So together we can monitor the progress and success of the agents used.

Grazing to Control Invasive Species

Horse grazing in Russian Knapweed Using livestock to graze noxious weeds can be an effective option if done correctly. The goal when grazing noxious weeds with livestock is to target the noxious weed(s) while leaving as much of the native vegetation not grazed as possible so that it can compete with the weeds, filling in the voids left behind.

Plant Toxicity Concerns with Grazing

Calf born with crooked legs Before beginning a grazing program identify what weeds (noxious and otherwise) the livestock will be consuming. Most plants have the potential to be toxic at some point during the plant’s growth cycle. The toxicity may depend on the plant species, the growth stage of the plant, the time of year, weather and on the animal’s physiology (species, reproduction status, age, etc.). Therefore, do your research and determine if grazing the noxious weeds and other plants on your property is the best choice for you and your animals.


When grazing noxious weeds with livestock it is important to monitor the body condition of the animals, as well as their physical development. Some toxicities are accumulative in nature and may end in death. Some toxicity’s only cause chronic illnesses. Additional supplementation with grain, micronutrients or other forage maybe needed as well as veterinary treatment. Continue to monitor their body condition even after they are removed from an area.

Using Fire To Control Invasive Species

Fire is a tool that farmers have used for centuries. Most of the time fire is used to clear old, dead vegetation so that weed re-growth is readily visible for chemical treatment. The fire also stimulates some grasses to green up sooner by warming the ground. However, fire can also open the door to more or new noxious weed infestations be stressing existing vegetation that may not have evolved with fire.

Spring burned ditch Care needs to be taken when using fire. Contact Health and Environment at 970-304-6410 to ask if a burn permit is needed for your situation and to learn if there are any burn bans in place. Always give your local fire department a call before you start a fire.

Organic Farming Practices

More and more people are taking their operations organic. The Weed Division understands this philosophy and encourages the use of organic principles and methods if conducted appropriately. Landowner Specialists are available to help you identify the weeds on your property and develop a management plan that meets your needs as well as fulfills the obligation to control noxious weeds.

Field of red lettuce row crop The biggest issue that still needs to be addressed for the Weed Division is the control of noxious weeds on the lands certified as organic and on the roadside shoulders. Using Weld County's ROW as the buffer zone is not the best choice for commercial organic production. These buffer zones need to be on your property. Even if the property is organic, the landowner is still required to control all noxious weeds and stop their spread to neighboring lands per Colorado State Law and Weld County Code Chapter 15.