Tips on fall weed management

As Mother Nature continues to threaten snow, you may be thinking about cleaning up around your property. Spraying weeds probably doesn’t come to mind as a fall chore; usually you think of spraying weeds in the spring or summer when they are actively growing.

Fall is an ideal time to control many weeds with herbicides. Perennial weeds with extensive root systems are beginning to prepare for “winter hibernation.” To survive the long winter they need to store a bunch of carbohydrates in the roots and root crowns to feed on through winter. They also need something to jump start growth in the spring before leaves open and plants start photosynthesizing.

Herbicides that work by translocating the chemical to other parts of the plant work especially well in late fall. The chemicals are transported, along with the carbohydrates, to the root and root crown which kills or severely weakens the plant. If the plant is just weakened, the next hard frost or a long winter will help to kill even those super tough weeds. The protective waxy leaf coating is also thinner in the fall so herbicide absorption is better.

Russian knapweed is best controlled really late in the fall because of this process. The plant can look completely shut down for the winter and as long as the ground isn’t frozen, it can still be controlled with herbicides.

Field bindweed is another tough perennial weed that is a source of irritation for many landowners. A late fall, preferably just before a hard frost, treatment with a strong glyphosate solution can be effective.

Cheatgrass is another invader in the Big Horn Basin. Pre-emergent herbicides can be applied in the fall to prevent cheatgrass from germinating. Timing and application rates are crucial. Contact your local county Weed & Pest for specific treatment options and always read the herbicide label for control rates and timing.

The key to controlling annual and biennial weeds is limiting seed dispersal. Small patches can be controlled by digging plants. If you have a mower that catches the plant material, mow those weeds and dispose of the weed seeds by burning or bagging and taking to a trash disposal area. These steps will keep the seeds from becoming next year’s problem.

Now that you’ve controlled the bad weeds, you want something desirable to take their place. Fall is also a great time to plant cool-season grasses. These grasses will provide competition for undesirable weeds and hopefully reduce need for weed control in the future. Again, if you are spraying herbicides in the fall, check the label to see how long you need to wait before planting into the treated areas.

Fall is a great time for weed control so add it to your list of chores before winter arrives. As always, feel free to contact me with questions – [email protected].