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
Preventive measures include planting weed-free seed in
pastures and working toward eliminating bare spots around areas such as
“When we have bare spots, we’re going to have weeds,”
“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
It is important to correctly identify the weeds present in a
“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
“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
“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.”