Control Noxious Weeds NOW!

September 25, 2015

Control Noxious Weeds NOW!

Late September and October may be the best time of the year to control our three most common noxious weeds... leafy spurge, Canada thistle and musk thistle. These plants will be growing rapidly with recent rains and warm days this fall. Actively growing plants are more susceptible to herbicide applications.

At this time of year plants are building 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, as we move into October, 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 our noxious weed control program. This may allow us to cut out individual plants or spot treat with a herbicide next spring. Even if you do a good job of control between fall and spring treatments, it is important to monitor the areas where noxious weeds 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. 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. Leafy spurge can be distinguished from other similar looking weeds by the milky sap in the stem and leaves.

Next on our 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, but you usually get the best results in the fall, so start now.

Leafy spurge and Canada thistle are usually found in patches because they both spread by underground “roots” called rhizomes as well as by seed. So when you spray a patch of either of these weeds, 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 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. That’s what you would find right now. The following spring, the rosette grows a little more 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’s best to 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 products becomes more limited.

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. If you have noxious weeds on your farm, this fall would be a great time to start bringing them under control.

Different products are more effective on each of these weeds and even the time of application may make a difference in which product will work best for you. For more information on controlling noxious weeds, contact your county weed control superintendent or your local Nebraska Extension office.