Control Noxious Weeds

April 3, 2015

Control Noxious Weeds This Spring

I'm going to talk about noxious weeds a little bit early, as recent rains and warm temperatures may move up the time to control them this year. If you are not ready, you can miss the window when you can most effectively control noxious weeds... in the spring.

Fall is the best time to control some noxious weeds, but you should not neglect your opportunities this spring. Besides, many weeds require consecutive treatments, fall and spring, to get them to manageable levels. Here are some tips to help you control these weeds before you get one of those dreaded letters from the weed control superintendent or FSA office. They have no sense of humor!

I will touch on each of our three most common noxious weeds. The timing of control I mention on each of these might vary a week or more earlier or later, depending on the weather. Early spring, move up the control time... later spring, move it back. I will go in the normal order you would control these in the spring, earliest to latest, which also happens to be from the easiest to hardest to control.

Musk Thistle: This noxious weed may be easiest to control in the spring... but you can't wait too long! Musk thistles formed a rosette, much like a big dandelion, last summer and fall. It continues to grow in this form this spring. Around the first of May it bolts, or sends up a flower stalk, and is much more difficult to control.

When you have good growing conditions, adequate soil moisture and warm days, musk thistle rosettes are fairly easy to control with several different herbicides. Once they bolt, many of these herbicides will not give adequate control, and the ones that will give some control are more expensive.

If you waited too long and they started to flower, a hoe or shovel is probably your best method of control. However, it is important to clip and destroy those flowers to prevent them from going to seed. If you cut off a plant and can see the distinct purple color in the flower bud, even if it isn't fully open, some seeds will mature on the dead plant and perpetuate your battle with this weed.

Leafy spurge: The normal time to control leafy spurge in the spring is in mid-May when the spurge forms flower buds or starts to bloom. It has a distinct yellow flower, actually modified leaves that look like petals on a flower, on an upright stem. Wild mustards often are confused with leafy spurge. The easiest way to distinguish between the two is to break the stem or leaves. Leafy spurge will have a milky sap (like a milkweed) while mustards have a clear sap.

In spring, you should treat leafy spurge just as the tops start to turn yellow. This weed generally grows in patches and you should spray 20 to 30 feet beyond any plants you see to get those coming up from the roots. This perennial has an extensive root system, and you may need to come back a couple of weeks after your initial application to treat the weeds that escaped.

Canada Thistle: This perennial problem weed would be the last one you would normally control in the spring. Unlike other thistles, you want to wait until flower buds form, which typically occurs in mid to late June. Getting good coverage with your sprayer is the biggest challenge because grass may be as tall or taller than the thistles. As with leafy spurge, Canada thistle is usually found in dense patches, and it is important to spray beyond the edges of the patches.

Even though it is earlier than we normally recommend, I can tell you from personal experience that you can get good control earlier in the spring if the Canada thistle are in CRP. I burned off my grass in April and then sprayed the thistles when they greened up in mid-May. This is about a month earlier than you normally would treat them, but I got just as good control with better coverage before the grass got tall. However, I still needed to go back later in the summer and spot treat those I missed.

There are two important things to remember when trying to control these noxious weeds...

#1 - Fall is the best time to control them when the plants are sending nutrients to the roots and storing them for growth the following spring. Treatments then will move the herbicides to the roots and give you better control. However, if you have these weeds this spring, that means you missed controlling them last fall or you didn't get complete control. You need to treat them now rather than waiting until fall. Also treat in the fall and control the ones you missed or that came up from seed over the summer.

#2 - None of these weeds can be completely controlled with a single application of any herbicide. One of the reasons they are classified as noxious weeds is because of the difficulty of control. Even if you control all the top growth of any of these weeds, there will likely be some that come up from seeds or roots.

Again from personal experience, I've dealt with all three of these weeds on my place. By keeping after them each year, I've reduced the area they infest from over 100 acres to just isolated patches... but you can be sure I'll be out there with my ATV sprayer this spring treating any noxious weeds I can find. My goal is to someday be able to say I don't have a noxious weed on my place. I think I have a better chance of winning the Powerball, but that won't keep me from trying!

For more information on controlling noxious weeds, contact your local Nebraska Extension office.