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Submodule 8: How Invasive Plants Are Controlled

Chemical Control

Chemical control of plants usually involves the use of herbicides. Since about 1940, these chemicals have been part of weed management on rangelands. Herbicides are chemicals that interfere with weeds’ growth and/or seed production, thus reducing or eliminating their competitive edge over native plants. These effects can lead to weed death, or simply a decrease in vigor, which can lead to reduced seed production and/or winter survival. Many of these chemicals can be dangerous to the environment and to those applying them if label restrictions are ignored. For this reason, it is critical that you understand the capabilities and limitations of the herbicide you are planning to use. There are many different chemicals available so it is critical to know how herbicides kill plants, how they are applied, and how they interact with the environment. Knowing these things can help you determine if herbicides are an appropriate tool to help you accomplish your weed management goals.

 

Following are some of the things you need to consider when choosing a herbicide:

• Degree of response
• Does it control some or all species? Plants have species specific metabolic pathways that can make them more or less susceptible to certain chemicals. This is one of the main reasons why some herbicides work for some plants and not for others.
• Method of application
• Is it applied to leaves (foliar uptake) or soil? To be effective, herbicides are applied to the leaves and other vegetative parts of the plant and must be applied when the plant is actively growing. The chemical must remain in contact with the plant surface for a specific length of time so it can be absorbed into the plant. In addition, herbicides must be able to pass through the waxy cuticle layer found on the surface of most plant leaves and herbaceous stems.
• Is it applied to a specific area of the plant, broadcast over an area, or applied in bands throughout an infestation?
• Length of soil persistence
• Do its effects remain in the soil for an extended period of time, or only for one season?
• Systemic or contact
• Is the herbicide transported throughout the plant, or does it remain at the point of application? Some herbicides are “systemically” translocated throughout the plant, while others remain at the “contact” site.

• Mode of Action
• Does it inhibit the production of essential plant compounds?
• Does it have auxin-like properties? Auxin is a plant growth regulator – a plant hormone. Plants make this hormone to regulate their own growth and development, and then break it down when its effects are no longer needed. Some herbicides mimic the affects of auxin and literally cause the plants to grow themselves to death because they cannot break down the auxin-like herbicide.
• Does it inhibit photosynthesis? Photosynthesis is how plants produce their food. If this very complicated process is disrupted, the plants starve to death. Many herbicides have this effect.
• Does it inhibit cell division and therefore plant growth? All growth is first initiated by increasing the number of cells present in an organism, cell division. If this process stops, growth stops.
• Does it stop the synthesis of lipids in the plant? Lipids are critical for the cell membranes of all plant cells and for many other processes, including food storage in seeds. Disruption of the manufacturing of lipids in the plant can seriously reduce growth and development.

• Formulation
• Is it soluble in liquid, or does it need to be emulsified (suspended in water)?
• Is it in the form of granules, powder, or pellets?
• Is the use of an adjuvant (chemical to help the herbicide do its work) necessary?

Once you have chosen the correct herbicide, the biggest key to success in controlling your target weed is to apply the chemical according to label directions.

 

 

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