Weed management discussed

There are many noxious weeds plaguing producers in the West, including common mullein and cheatgrass. In a recent University of Nebraska-Lincoln (UNL) Beefwatch podcast, dated Nov. 27, UNL Extension Integrated Weed Management Specialist Nevin Lawrence explains common control measures for the two weeds on rangelands. 

Common mullein

“Common mullein is an invasive weed, non-native to the U.S., and it has been a priority weed in Colorado, Wyoming and Montana,” says Lawrence. “Like a lot of the invasive weeds we deal with, it tends to take a foothold in disturbed areas.” 

Lawrence shares mullein typically spreads from right-of-ways and roadsides into Crop Reserve Program (CRP) pastures after farming and into rangelands. The corresponding Beefwatch newsletter, written by Lawrence and UNL Extension Range and Forage Management Specialist Mitch Stephenson, says previous winters have favored overwintering weed species, like common mullein and cheatgrass. 

“Some seeds, not necessarily mullein, can be viable in the soil for up to 50 years or longer, so this kind of issue takes a long time to get a hold of and manage,” Lawrence notes. “After mullein germinates, it spends the rest of the first year in a vegetative growth form and doesn’t produce seeds. It dies down to the crown in the winter, and comes back the next spring, producing flower structures with seeds.”

The life cycle and trademark velvety, soft leaves of mullein make it a difficult plant to eradicate with herbicide. However, Lawrence and Stephenson have conducted research to find which herbicide products and application times work best to control the weed. 

Mullein control

After testing seven different herbicide products, along with an added crop oil concentrate to penetrate the fuzzy leaves, the duo found all of the herbicides used to be effective in controlling mullein. 

“In our study, we found everything we used, including 2-4,D and dicamba, which are not labeled for mullein control, worked,” shares Lawrence. “However, all herbicides labeled for use on common mullein specify the best timing of herbicide application is before the plant bolts and sets seed.”

Lawrence shares the timing of herbicide application is often more important than the product itself. He recommends applying herbicide in the spring while the plant has ample water supply and before it goes to seed. 

“If producers miss the spring herbicide application, the next best time is the fall before any hard freezes,” he adds. “Although, a fall application won’t control any plants in the second year of growth, especially those which have set seed.”

Another consideration for those looking to control mullein or any weed chemically, is herbicides work best when targeted plants are healthy, says Lawrence. Plants readily absorb herbicide in the spring, but after summer heat and water stress, plants take up less water so herbicides will be less effective.

Cheatgrass control

“Grazing has been recommended as a control option for cheatgrass,” says Lawrence. “In my opinion, producers aren’t going to eliminate cheatgrass through grazing, but they can reduce seed production, and if grazed during the right time of year, cheatgrass can be good forage.” 

In terms of herbicides to control cheatgrass, Lawrence says two herbicides have been used effectively for years. Rimsulfuron and imazapic both have good activity on cheatgrass, typically controlling around 90 percent of cheatgrass. But, they can injure desirable grasses and the control is variable from year to year. 

“There is a new product called Rejuvra, made by Bayer,” Lawrence notes. “It doesn’t work like a traditional cheatgrass herbicide, and it has no control over cheatgrass once it is germinated. But, it controls cheatgrass as it germinates and emerges from the soil.” 

Lawrence explains most cheatgrass seeds are viable in soils for up to two years, and Rejuvra applications have seen up to two years of cheatgrass control. 

“It is hard to get out in a time where cheatgrass isn’t up, so often Rejuvra will have to be mixed with rimsulfuron, imazapic or glyphosate,” he says. “These combinations lead to residual control.” 

Rejuvra is also a product safe for use on rangelands and grazed lands, notes Lawrence. A similar product, Esplanade, is marketed for industrial applications but has not been approved for range and pasture. 

Lawrence also shares Rejuvra could be an option for restoring desirable plant populations on rangelands. While there are economics to take into consideration, the cost of Rejuvra might not be an option for most producers. 

“Will removing cheatgrass from a pasture pay for greater production, more cattle per acre or better yields? Probably not,” says Lawrence. “There is evidence reducing cheatgrass will reduce wildfire risk, lead to more diverse plant communities and may impact land value.” 

For both species, Lawrence shares he and Stephenson plan to continue weed management research to help growers. 

Averi Hales is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.