To Clip or Not to Clip – The Age-Old Question for Pasture Managers

June 18, 2024 4:47 PM
Blog Post

As we enter summer, most of our cool-season dominant pastures have headed out, or the grasses have started producing seed heads. The common question of whether to mow the seed heads arises. The decision to mow or not is site-specific. Mowing can remove seed heads, stimulate even grazing, and provide some weed control, but these benefits do not always outweigh the labor and fuel costs.

Cool-season grass pasture producing seed heads.
Cool-season grass pasture producing seed heads. Photo Credit: Shelby Gruss

Mowing your pastures helps divert plant growth from reproductive to vegetative growth. Cool-season perennials only produce seed heads once in the spring. Removing the stems and seed heads puts the grasses back into vegetative growth, increasing their quality. As the plant matures, quality declines; removing reproductive growth leaves us with new vegetative growth of higher quality. Additionally, it maintains a higher growth rate and stimulates tillering and regrowth.

However, to be cost-effective, assess the density of seed heads present by walking through the pasture. From a distance, there may appear to be more seed heads than there are. If you have grazed this field multiple times already, there are probably only a few seed heads. A high density of seed heads is needed to justify mowing. If you are short on forage, grazing the seed heads with animals that have lower nutritional requirements can help meet your needs without compromising the performance of higher-value animals. Particularly as we enter the summer slump, plant growth will slow due to high heat. Grazing management strategies should be implemented to ensure the animals are eating the seed heads and not selectively grazing around them.

Mowing the seed heads can even out the pasture. Besides being more aesthetically appealing, this promotes better forage utilization. Livestock typically graze around more mature plants if given the opportunity, leading to uneven grazing. Removing the seed heads helps reduce selective grazing. Uneven grazing occurs more often in continuous grazing systems. Implementing a rotational grazing system leads to more even pastures and better utilization without mowers. Rotational grazing also reduces the number of seed heads if animals graze the tops off the plants, particularly when grasses are in the boot stage.

Mowing also helps with weed control, particularly for perennial weed species. Mowing once may not be effective, but multiple mowings can reduce perennial weed persistence by depleting the plant's root reserves. The presence of annuals indicates declining stand density.

These are general guidelines for most of our cool-season perennial forages. However, if you have toxic endophyte tall fescue, mowing may be a better option even when it is not ideal for other cool-season grasses. Tall fescue has been spreading north and is present in many pastures across the state, particularly in the southern half of Iowa.

We manage tall fescue pastures differently due to the toxic endophyte. The toxic endophyte typically stays in the lower portion of the plant throughout vegetative growth but moves up the stem and into the seed head during reproductive growth, increasing the risk of fescue toxicosis in the herd. Mowing tall fescue helps avoid higher levels of the toxic endophyte as seed heads tend to have the highest concentration of the endophyte than any other plant part, which is particularly important as we enter the warmer months. High heat can exacerbate symptoms of fescue toxicosis.

In conclusion, the decision to mow or not to mow your pastures should be based on specific conditions and needs. While mowing can improve forage quality and control weeds, it must be balanced against costs and labor. Assess your pasture conditions, grazing needs, and the presence of toxic endophyte tall fescue to make an informed decision that best supports your livestock and pasture health.


Aaron Saeugling Field Agronomist in SW Iowa

Aaron Saeugling is a field agronomist in southwest Iowa for Iowa State University Extension and Outreach.