Graziers may learn helpful information about their pastures by observing the weeds that become prominent in autumn.

That’s according to Fred Fishel, director of the University of Missouri Integrated Pest Management program. He says weeds aren’t necessarily more prevalent in fall, but they tend to stand out because they grow fast under less-than-ideal conditions.

"Some of these weed species are indicative of soil conditions such as low pH and fertility, poor drainage and soil compaction," Fishel says.

Among the most frequently reported fall weeds in Missouri pastures are broom-sedge, goldenrod, ironweed, common mullein, red sorrel and milkweed.

Broomsedge is a bunchgrass that turns rust-colored in fall. Growing up to 3’ tall with leaves up to a foot long, it has flattened stems and fluffy, bearded seeds.

"Broomsedge is a good indicator plant of low soil fertility," he says.

Red sorrel is a red-stemmed perennial that reaches a height of about 18". Its leaves are arrowhead-shaped. Flowers are yellow on male plants and red on female plants.

"It is indicative of acid soil conditions," says Fishel.

"We see these weeds in a lot of abandoned or rundown pastures," he adds. "They’re a good sign producers need to take soil tests and get their fertility and liming needs up to par."

Other "indicator" weeds in pastures might include yellow nutsedge. Recognizable from its three-sided stems, it thrives "in wet conditions, especially in low-lying areas that don’t drain well."

Summer annuals such as prostrate knotweed and goosegrass are good indicators of compaction.

"Around driveways and sidewalk cracks, you see a lot of goosegrass," says Fishel. "I’ve seen a lot of it in hard, compacted, trodden-down pastures."