January 2018 Weed of the Month: Torching Noxious Weeds

There are many management tools/strategies that can be used to halt the spread of invasive plants. One tool that is often associated with gardening is the propane weed torch. It kills weeds organically, effectively, and selectively. Watching the plant burn to a crisp using a torch can also be satisfying! Torching will kill most annual weeds, but for perennial and woody vegetation, repeated torching is often needed to control regrowth.

In addition to managing weeds, there are ecological benefits of torching noxious weeds. Charcoal resulting from the charred weeds returns nitrogen back to the soil. The removal of noxious weeds stimulates new growth and allows native plants to return. There is also little soil disturbance and no left-over chemical residues.

Most weed torches produce up to 2,000 degrees F which is enough heat to kill most weeds and their propagating parts. Conservation Corps of Minnesota and Iowa (CCMI) uses weed torches to control naturalizing Asian bush honeysuckle, barberry, buckthorn, and other woody invasive plants. Torching Palmer amaranth has been an effective way to control this weed in conservation plantings. Zach Dieterman of CCMI says, “The weed torch is a great tool because it enables versatile and efficient control of invasive species. We can torch when weather conditions prohibit the use of herbicides or running fire. Also, we can precisely control individual plants... .”

Many safety precautions must be taken before considering any kind of controlled burn for weed control. Please contact the Minnesota Department of Natural Resources (DNR), local Forestry Office and your local police and fire authorities to inquire about requirements, legalities, and safety measures to consider before planning to weed torch. Other factors to consider include the following:

• Is a burn permit needed? The permit has basic instructions for conducting and controlling a burn, along with how to contact local emergency dispatch when you plan to weed torch.
• Vegetation moisture levels – is the vegetation very dry? If so, consider timing the torching when the vegetation is green or very wet.
• Is there a readily available source of water nearby for fire suppression?
• What are the environmental conditions? Consider wind direction and smoke hazards.
• What type of protective clothing and personal safety equipment are necessary? CCMI and other agencies such as the DNR and Minnesota Department of Transportation are required to wear fire retardant clothes along with boots, safety glasses/goggles, fire gloves, and a safety helmet. If you do not have access to fire retardant clothes, use cotton or wool. Avoid wearing polyester, because if hot enough it could melt to your skin. When in heavy smoke, use a dust mask, bandana, or approved respirator.