Habitat & Conservation  |  11/16/2022

Fall Herbicide Site Prep


Get a head start on next year's unwanted broadleafs

By Michael Retterer, Rights-of-Way & Energy Program Manager

Late fall is a great time to chase roosters, quail, grouse and big game, but it’s also the ideal time for habitat site preparation.

Come late October, most native herbaceous plants have pulled nutrients into their deep root systems and gone dormant, awaiting the warm soil temperatures that signal another spring. In this state, they’re much less vulnerable to contact herbicides, many of which provide residual control that may prevent germination from seed or suppress growth. Residual herbicides are a great tool when used correctly and offer long term control of target species. If using a residual herbicide be sure to read the label and understand the potential impact on non-target species. Herbicide labels include information about the target species controlled (aka weeds) and those species not affected (at a specific rate, time, etc). If your non-target species isn’t listed as a safe-to-use on species, assume the herbicide will have detrimental effects.

Confident your actions will have minimal impact on your favorite natives, you are free to aggressively target a handful of undesirable species like brome, fescue and many broadleaf weeds that are still actively photosynthesizing, and thus vulnerable. Additionally, fall is a great time to control some of the invasives found in many woodlands like bush honeysuckle, autumn olive and garlic mustard rosettes. As cool temperatures turn cold, these species enter senescence, switching from producing food for growth to producing food that’s stored in their roots. Applying herbicide at this stage ensures the highest degree of control as the herbicide is translocated into the roots, and the plant is killed. An ideal application time would be following the first hard freeze (temperature 27 degrees for at least 3 hours) when the following days temperatures are at least in the mid-50s.   

Using herbicides to kill target species in the fall also provides a significant window through winter and into spring for the vegetative material of the “weed” to break down, releasing nutrients back into the soil and providing the opportunity for improved seed-to-soil contact for seeding projects. 

Late season herbicide site preparations also coincides with a time when most plants are naturally dying back, so aesthetically there isn’t a significant difference from what’s normally observed.

Glyphosate (aka Roundup) is the herbicide most used for fall chemical site preparation. Remember to always follow the label for herbicides. Generally, for spot spray applications, mixing 2-3 ounces of glyphosate (41%) with a gallon of water and 1 ounce of surfactant is appropriate for most herbaceous plant control. The spray should completely coat the plant material but not runoff. For broadcast applications, many managers recommend 2 quarts per acre (25 gallons of water) for fall applications.     

On a side note, a similar, albeit smaller, attack window is also available in the spring before non-target native species break dormancy, but target weeds have started growing. Control is less effective since translocation is moving from roots to buds. Also, in open winters when temperatures warm into the 40s or 50s for a few days, contact herbicides can be effective on actively growing forbs.

Poor site preparation is the best predictor of project failure so take a day off chasing birds to ready your next habitat project. It’ll be more successful, the birds will be more productive, and so will your next hunt.