Fall Noxious Weed Control

October 23, 2015

Fall Noxious Weed Control

As harvest winds down, there is another important task that many folks need to remember. Fall is a perfect time of the year to control our three most common noxious weeds, leafy spurge, Canada thistle and musk thistle. This fall is setting up to be excellent for weed control because of moderate temperatures, some rainfall, and the lack of a hard killing frost have weeds actively growing which makes the more susceptible to herbicide treatments.

This is the time of year when these plants build up food reserves in their roots for next year’s growth. Herbicides applied at this time are also translocated to the roots, providing better control than when applied in the spring. Another advantage is many plants that might be injured by drift, but not noxious weeds, will be killed by a light frost.

On any of these weeds, you will never get complete control with a single application, but fall is a good time to start your noxious weed control program. This may allow you to cut out or spot treat individual plants with a herbicide next spring. Even if you do a good job of controlling noxious weeds between a fall and spring treatment, it is important to monitor the areas where they were a problem because the seed may remain viable in the soil for several years.

Of the three noxious weeds mentioned, you need to treat leafy spurge right away. You’ve already missed part of the time when controls are effective in the fall (September), but can still get good control if treated in October. Leafy spurge is not as tolerant of frost, so you need to be sure you treat it while there is still healthy green growth to absorb any herbicides you apply.

Next on your list for controlling should be Canada thistle. This perennial weed is the most difficult of the three to control. It may take repeated fall and spring applications. Canada thistle usually is found in patches because it spreads by underground “roots” called rhizomes as well as by seed. So when you spray a patch of Canada thistles, be sure to spray another 15-20 feet beyond the last plants in the patch you see to get any new shoots just coming up through the grass.

Musk thistle is the easiest of these three noxious weeds to control. It is easier to control because it has a two-year life cycle instead of coming up from roots year after year like leafy spurge or Canada thistle. The first year in its life cycle, musk thistles form a rosette that looks like a big prickly dandelion. In the second year, the rosette grows a little more in early spring and then it bolts, or sends up a flower stalk. After it is done flowering and the seed has been produced, the plant dies.

It is best if you control the rosettes in the fall and then treat any that survived next spring. It is harder to see the rosettes because they may be hidden by the grass. But if you had musk thistles last year, go back to the same areas and look for them. If they were allowed to mature, you may still find some dead flowering stalks to help you identify where rosettes might be growing. You can treat musk thistles now and on into early November before the ground freezes. If you wait until later in the fall, your choice of herbicides becomes more limited.

Different products are more effective on each of these weeds and even the time of application may make a difference on which product will work best for you.

Controlling noxious weeds is not a pleasant task and may take several years to really see a lot of improvement. However, the sooner you start, the sooner you will see success. So if you have noxious weeds on your farm, this fall would be a great time to start bringing them under control.

For more information on controlling noxious weeds, contact your local Nebraska Extension office or your county weed control superintendent.