Not so fast, johnsongrass!

By Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension

On Thursday, Sept. 17, Noble County hosted the East Central Grazing Alliance for a pasture walk at The Johnson Family Farm with a great turnout and conversation. Thank you to Mark Johnson and his family for hosting us at their farm!

The conversation centered on bale grazing during the winter months. We discussed what to consider and implement before, during, and after trying bale grazing; how to determine whether it is a feasible, labor-saving method for tending livestock on pasture; and how to choose what hay to feed and how to position it while the ground is solid. We talked about the importance of having your soil and hay tested to make the most effective, efficient, and economical choices about fertilizer and manure application, hay value (nutritional and monetary), and supplemental feed needs.

As a side note from the pasture walk, we also addressed johnsongrass creeping up on the Johnsons, who are trying to stop this weed in its tracks. With this year’s excessive rainfall and frequent flooding events, weed seed has been moving with water across the landscape. Throughout the county, we are seeing increased johnsongrass pressure all-around, especially along waterways and ditches.

Johnsongrass is a warm-season grass that is related to corn. Unlike its relatives — corn, sorghum, and sorghum-sudangrass, which are annual species commonly used for agronomic purposes, johnsongrass is a perennial that has naturalized itself in our environment. Johnsongrass begins actively growing when soil temperatures reach 70 degrees Fahrenheit, which makes it more prevalent in Ohio from mid-summer to fall.

Whether we classify johnsongrass as a weed or as a forage could be debated, but it is considered a noxious weed in Ohio, and therefore the debate is resolved: It is a weed. It is a non-native, aggressive, naturalized plant that provides some forage value, but it should not be purposefully planted or propagated because of the threats it poses to our native species and agronomic cropping systems.

Johnsongrass can be very challenging to control with herbicides in pastures and hayfields that are predominantly grass swards without harming beneficial grasses. There are a greater range of options for effective herbicide use in legume systems. The best news for pasture and hayfield managers is that although johnsongrass is aggressive and spreads by both seeds and rhizomes, it is not tolerant of close grazing or mowing.

Continually using animals to graze down johnsongrass or defoliating it with machinery can prevent the development of seedheads and weaken the root system over time, while also providing a source of feed for livestock, with the exception of equine animals. Horses should not be introduced to areas where they would have the opportunity to graze johnsongrass or other sorghum-type forages due to the risk of developing equine cystitis.

There are other concerns with grazing johnsongrass that stem from how the plant responds to environmental stress. Like other members of the sorghum family, johnsongrass can cause nitrate or prussic acid toxicity if plants are overfertilized with nitrogen, subjected to drought, and/or frost. During times of stress, nitrogen cannot be effectively metabolized by the plant and thus can accumulate at levels that are dangerous for animals to consume. In turn, prussic acid is produced by the plant in response to stress, which is also dangerous and can lead to animal distress or death. Both nitrate and prussic acid levels will dissipate over time after the stress event and can be fed again safely, but managers must be observant and responsive when growing conditions are inhibited by environmental stress. Nitrates and prussic acid do not dissipate to safe levels with the act of harvesting or ensiling. Therefore, managers cannot effectively speed up the time to safe consumption with mechanical harvest. Patience is the tool that is needed.

When you discover johnsongrass on your property, make a plan to address it. Spot treatment via repeated mowing, grazing, and/or grass effective herbicides should be employed as soon as johnsongrass encroachment is discovered. Glyphosate at a rate of 1-2 quarts per acre or a 2% solution for spot spraying is about 70% effective on johnsongrass. If you are applying herbicide along a waterway, you must make sure that the formulation you use is safe for aquatic use. Always read the label before applying any type of pesticide and reach out if instructions are unclear.