Controlling Noxious Weeds

April 8, 2016

Controlling Noxious Weeds

            The weather hasn’t seemed like it lately, but we are coming into the window of time for controlling noxious weeds this spring. Fall may be the best time to control noxious weeds, but don’t neglect your opportunities this spring. Besides, many weeds require consecutive treatments in fall and spring to get good control. Here are some tips to help you get on top of these weeds.

            April, May or June is the best time to treat our three most common noxious weeds, depending on which species. We could have a weed of the month, because the timing is different for each of these three noxious weeds.  I’ll 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.

            APRIL: Musk thistle is the noxious weed easiest to control in the spring... but don’t wait too long! Musk thistles formed a rosette, much like a big, prickly 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 more difficult to control.

            With rain and warmer weather in April, musk thistle rosettes are fairly easy to control with several different herbicides. Once they bolt, many herbicides will not give adequate control and the ones that do provide some control are more expensive.

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

            MAY: The normal time to control leafy spurge in the spring is in early to mid-May when the spurge buds or starts to bloom. It appears to have a distinct pale yellow flower on an upright stem. Often wild mustards 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 don’t have this kind of sap.

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

            JUNE: Canada thistle is the last perennial problem weed you 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 plants you see around the edges of the patches.

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

•                  First, fall (mid-September to mid-October) is the best time to control them when the plants are storing nutrients in the roots for growth the following spring. The plants move herbicides applied in the fall to the roots which gives 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. Then you should come back in the fall to control the ones you missed or that came up from seed over the summer.

•                  Second, none of these weeds will be completely controlled with any single herbicide application. One reason 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 back from seeds or roots.

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