AMES, Iowa – While the popularity of sudangrass has fluctuated over the years, cattle producers have shown a renewed interest in its use as pasture acres have decreased and drought issues have impacted perennial pasture quality, according to Grant Dewell, Iowa State University (ISU) associate professor of veterinary medicine and beef extension veterinarian.

In fact, he said the use of sudangrass and similar sorghum-sudangrass hybrids in pastures to add nutrition and feed volume for cattle has been around for a long time.

“Sudangrass was introduced into the U.S. in the early 1900s, and became a common pasture crop,” he said. “Sudangrass grows in warm and hot conditions, and is fairly drought-tolerant and can produce large quantities of forage.”

According to ISU, sudangrass is a fast-growing, warm-season annual grass of the sorghum family used primarily for forage (i.e., hay, pasture, silage), and as a cover crop for nutrient scavenging and weed suppression. It’s also known for its rapid growth, high biomass production and ability to regrow after cutting or grazing, ISU added.

Shelby Gruss, ISU assistant professor of agronomy and forage extension specialist, said, “There has definitely been more interest in the last few years, but I would not limit it to sudangrass. Producers are showing increased interest in summer annuals in general as a way to boost productivity.

“This practice is especially useful in sacrifice lots (or dry lots that are non-grazing, small, enclosed areas for livestock used to protect pastures from overgrazing, damage from mud, or during renovation), or calving pastures where the perennial stand is weaker and less productive,” she said.

Gruss added the practice involves planting a summer annual like sudangrass following the spring flush of cool-season growth, typically in early to mid-June.

She said the general steps of sudangrass management are: grazing or mowing the perennial stand low just prior to planting to open the canopy for seedling establishment; drilling (the practice of planting summer annual forage crops like sorghum-sudangrass by sowing their seeds directly into the soil) the summer annual (sudangrass); allowing about 40 days of growth (depending on species and environmental conditions) before grazing; and evaluating the stand after grazing.

“Nitrogen application will likely improve summer annual productivity, but timing is critical,” Gruss said. “Since the perennial stand already has an established root system, nitrogen should be applied when the summer annual is actively growing and cool-season perennials are slowing down. Research on this is limited, so current recommendations are more hypothetical than proven.”

Dewell said, “As a fairly rapidly growing forage crop, sudangrass can be grazed. It’s generally safer to use a rotational grazing system with fairly high stocking rates so cattle graze all the sudangrass down and then move off.

“If you leave cattle on too long where parts of the pasture are starting to regrow, cattle will prefer the new lush forage, which can have higher levels of prussic acid (a highly poisonous and rapidly acting chemical compound that can be released from certain plants and is lethal to livestock and humans),” he said, adding that farmers should “increase stocking density and (move) off in a few days to minimize toxicity (from high levels of prussic acid) and allow the plant to regrow.

“Prussic acid toxicity is a concern, but it can be managed,” he said. “Generally, sudangrass is safer than forage sorghums, but good management is still important. Once the forage is at least 18 inches tall, it is safe to graze during summer grazing season. Be mindful of regrowth when managing pastures. In the fall when frost conditions exist, cattle should be removed from sudangrass pastures for seven days to allow the prussic acid to dissipate.”

Andrew P. Griffith, University of Tennessee professor of agricultural and resource economics, said, “One good time to use a sudangrass hybrid is when a pasture is going to be renovated in the fall. A person can chemically control a good portion of the weeds and then plant sudangrass hybrids that will provide enough competition to kill a lot of what was not controlled chemically.

“It is also appropriate to use it when there will be a need for a large quantity of high-quality forage in a short time span,” he added. “It has the ability to produce a lot of high-quality feedstuff at a high quantity, if fertilized correctly. This does require some input, but it can be beneficial.”

He said, “In my mind, it is another tool in the tool kit. I would not call it a specialty tool, but it also is not a tool that is used every day. There are some risks as they tend to collect nitrates when moisture is not adequate. They do take capital and labor as they have to be seeded every year.”

Gruss said, “Adding summer annuals (like sudangrass) can help boost forage production during the summer slump. However, it’s important to also plan for what comes next, whether that involves weed management, over-seeding, or other stand improvements.”

Griffith said, “They (sudangrass) are most successful being planted into a clean seedbed whether that be no-tilled in a field that the competition was chemically controlled, or in a tilled field with no weed competition.

“There are people who interseed (plant seeds of a cover crop or forage into an existing crop or pasture), but I have never experienced a situation where this was the best method to accumulate the best production from a quantity standpoint,” he said.

“Thus, planting into a clean seedbed is the environment where production can be maximized, but these hybrids also require appropriate fertilization to produce well,” he added. “In most cases, most grazing operations would be better off with a warm-season perennial (like switchgrass, which possesses mechanisms that allow it to tolerate cold temperatures during winter as dormant plants), but there are situations where these warm-season annuals (like sudangrass) can be beneficial.”