Fall is the best time to control some noxious weeds, but we should not neglect our opportunities this spring. Besides, many weeds require consecutive treatments in fall and spring to get them down to manageable levels. I am very familiar with these noxious weeds because I have personally dealt with all three of these on my acreage.
I will touch on each of our three major noxious weeds. I will go in the normal order we would control these in the spring, earliest to latest, which also happens to be from the easiest to hardest to control.
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. The optimum treatment timing will also vary with your location. These dates are based on my location in eastern Nebraska, just north of Omaha. As you go further north or west, the timing will be later.
This noxious weed may be easiest of the three to control in the spring... but we 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. In early May it bolts, or sends up a flower stalk, and is much more difficult to control.
When we 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 we waited too long and they've started to flower, a hoe or shovel is your best method of control, but it is important to clip 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, even if it isn't fully open, some seeds will mature on the dead plant and perpetuate your battle with this weed.
Our normal timing of spring control is in mid-May when the spurge buds or starts to bloom. It has a distinct yellow flower on an upright stem. Often some of our wild mustards are confused with leafy spurge. The easiest way to distinguish between the two is to break the stem or leaves. Leafy spurge has a milky sap (like a milkweed) while mustards do not have this kind of 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 weed 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.
This perennial problem weed would be the last one we would normally control in the spring. Unlike other thistles, we want to wait until flower buds form which typically occurs in mid- to late June. Getting good coverage with our 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 we normally would treat them, but I think the control was just as good with better coverage before the grass got tall. I still needed to go back and spot treat those that I missed later in the summer.
There are two important things to remember when trying to control these noxious weeds...
First- fall is the best time to control them when plants are sending nutrients to the roots for
growth the following spring. Treatments then will move the herbicides to the roots and give us better control.
However, if we have these weeds this spring, that means we missed controlling them last fall or we didn't get complete control. We need to treat them now rather than waiting until fall. Then we should come back in the fall and control the ones we missed or that came up from seed over the summer.
Second- 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 we 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 less than a couple acres... but you can be sure I'll be out there with my backpack sprayer this spring treating those little patches that keep coming back.