Bruce Anderson’s Forage Advice: Damage from Disc Mowers and Fall Control of Winter Annual Bromes


I like mixing alfalfa with grasses like orchardgrass, fescue, and festulolium.  Disc mowers are complicating my plans, however.

Disc mowers are fantastic machines.  Compared to sickle bar mowers, they cut faster, have less maintenance and repairs, and rarely plug.  They can cut the crop shorter and keep going even if they occasionally scalp the surface.  And that’s the problem!

With alfalfa, regrowth comes from crown buds using nutrients stored underground in the taproot.  It doesn’t matter if you leave a 1-inch or a 4-inch stubble, alfalfa regrowth rate will be the same.

Grasses are different.  Grasses depend on nutrients stored in the lower stem for early regrowth.  And some grasses, like orchardgrass, fescue, and festulolium that have very low basal leaves, they also use energy produced by photosynthesis in those basal leaves for regrowth energy.  So, cutting these grasses short results in much slower regrowth and a weakening of the plant because the source of energy to support regrowth has been removed.

In a grass-alfalfa mixture, the short stubble left by a disc mower delays and slows the regrowth of the grass while the alfalfa recovers at its usual rate. Pretty soon alfalfa gets several inches taller than the grass, forms a tight canopy, and shades out the grass growing underneath.  Before long the grass dies out and disappears.

Clearly, the solution is to raise the cutting height to around 3 to 4 inches like happens naturally with a sickle bar.  This is easier said than done, however.  First, you need to remember to leave a taller stubble.  And if working with a custom operator, it probably will require reminding that person of your stubble height demands.

Keeping grass in alfalfa when cutting with a disc mower is challenging, but it can be done.


Did you have downy brome, cheatgrass, or wild oats in your pasture this spring?  Although difficult, they can be controlled and your pasture revitalized.

Winter annual bromes often invade thin or overgrazed pastures in fall and early spring.  Livestock dislike grazing them, so over time they can take over and make large patches of pasture nearly worthless.

By far the most effective control method is to spray six to eight ounces per acre of an imazapic herbicide like Plateau as soon as possible this month.  This pre-emerge treatment will prevent most annual bromes from developing.

As we move into October, however, it is likely that some, or maybe a lot of these grass seedlings will have already emerged.  When this situation exists, add an adjuvant like a non-ionic surfactant or methylated seed oil to the spray mix for better control of emerged seedlings.

In warm-season grass pastures and rangeland, there is another option.  You can use glyphosate herbicides after top growth of these grasses has died due to a hard freeze or two.  This can kill emerged annual brome seedlings without harming the desirable grasses.  However, do not use glyphosate in cool-season pastures because it will injure or kill the pasture grasses as well.

These treatments may need to be repeated for a couple years to prevent reoccurrence of these weedy grasses.  But with proper grazing management and other practices, your pastures can develop thicker stands of the more desirable grasses.

It takes a long, dedicated process to recover pastures overtaken by winter annual bromes.  There are no shortcuts!


These tips are from  Bruce Anderson, Extension Forage Specialist, University of Nebraska-Lincoln, Phone 402-472-6237


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