Russ Higgins, University of Illinois Extension commercial agriculture educator, speaks during the Illinois Forage Institute. The event was sponsored by the Illinois Forage and Grassland Council and Black Hawk College.
Russ Higgins, University of Illinois Extension commercial agriculture educator, speaks during the Illinois Forage Institute. The event was sponsored by the Illinois Forage and Grassland Council and Black Hawk College.

GALVA, Ill. — An integrated approach is important for weed control in pastures.

“I am here to talk about weed control, but really for a pasture we want to talk about weed management,” said Russ Higgins, University of Illinois Extension commercial agriculture educator. “Herbicides are just a small portion of what we can do to control weeds.”

A dense stand in a pasture can outcompete the weeds.

“Pastures in the Midwest don’t always get the level of management that some of our other crops do, but if we have a dense stand, that will go a long way to prevent weeds,” Higgins said during the Illinois Forage Institute, sponsored by the Illinois Forage and Grassland Council and Black Hawk College.

Preventive measures include planting weed-free seed in pastures and working toward eliminating bare spots around areas such as waterers.

“When we have bare spots, we’re going to have weeds,” Higgins said.

“If we have weeds in pastures instead of forages that means we have a problem. The proper pH, drainage and fertility will go a long way to prevent a weed problem.”

Grazing management also is critical. It is important to avoid overgrazing a pasture.

“I know this is difficult because livestock may be there a little longer than they should be because you don’t have anywhere else to put them,” Higgins said.

Timing is important to control pasture weeds with mowing.

“Make sure you mow the weeds before they produce a seed head,” Higgins said. “And you probably will have to mow several times, and remember as you mow common ragweed, it will set the head lower and lower.”

It is important to correctly identify the weeds present in a pasture.

“We have to know what weed species we have present in the stand, and we need to be aware of the grazing restrictions if we choose to use an herbicide,” Higgins said.

Once the weed species is identified, the next step is to determine the lifecycle of the weeds. The weeds will be winter annuals, summer annuals, biennials or perennials.

Winter annuals emerge in late summer, fall or early winter. These weeds emerge from seed, produce a small rosette, overwinter and start growing early in the spring.

“They will take off when the soil temperature is consistently 40 to 45 degrees, quickly finish their vegetative growth, go to reproductive stage, produce seeds and die,” Higgins explained. “These are the weeds that give us all the purple, yellow and white colors, including shepherd’s purse and mustards.”

Since winter annuals are actively growing when most of the pastures are dormant, these are the easiest of the weeds to kill.

Summer annuals have the same growth as most pasture grasses. Summer annuals emerge in the spring, go through vegetative growth, produce seeds and die during the summer. Ragweeds, lambsquarters and pigweeds are examples of summer annuals.

“Perilla mint and Japanese hops are summer annual weeds that are moving into southern Illinois,” Higgins said. “Perilla mint is a fairly toxic weed that we don’t want in our pastures, and Japanese hops is a vine that looks similar to wild cucumber.”

The best time to control summer annuals is when they are in the young, vegetative stage.

“It is really important to walk your pastures, because it is hard to see a 2- to 4-inch weed when you’re in your truck,” Higgins said.

Biennial weeds have a two-year lifecycle. They will emerge from seed the first year, produce a rosette and overwinter. The second year, the biennial weeds go through a quick growth stage, bolt and produce seeds.

“These weeds are much harder to kill chemically the second year, so we want try to control them the first year,” Higgins said. “If we can get about 1 inch below the soil surface with a thistle fork, that does a good job of killing them.”

The greatest weed control challenge in pastures is perennial weeds.

“They come back year after year because they have the ability to store nutrients in their underground structure such as rhizomes, stolons or bulbs,” Higgins said.

“If we try to control weeds like Canada thistle or dandelion chemically, we have to be careful with timing. You should make an application just before bud stage or in the fall when the weeds are taking nutrients down into the root system.”

Higgins advised farmers to avoid trying to kill a Canada thistle patch by disking up the weeds.

“If you do that, you’ve cut up the rhizomes underground and probably doubled the size of your patch,” he said.

“We don’t have a lot of new chemistries for herbicides. Instead, we have a lot of remixing. And we have several issues with herbicides for pastures — they are effective, but fairly short term. Most will injure or kill legumes, and some have haying restrictions. Therefore, you need to take the time to read the label.”