Last season brought record drought across most of the southern United States. As crops suffered, few producers worried about weed control. More than 90 percent of Texas was in one of the two most extreme stages of drought from June 2011 through the winter months, according to the National Oceanic and Atmospheric Administration’s U.S. Drought Monitor.
Eventually moisture will return to the badly scorched southern states, and when it does, weeds will be first to grow. Controlling those weeds quickly is critical to giving pasture grasses a chance to recover, says Texas A&M University forage specialist Larry Redmon.
“Drought-stressed pasture grasses have such limited root systems that they won’t be able to recover if weeds get a chance to form a canopy. Even with good early weed control, most pastures will take at least a year to recover from this drought.
“There is a lot of bare ground in pastures, with a lot of weed seeds near the surface,” he continues. “As soon as we get measureable rainfall, we can expect to see a flush of weeds. Producers should be watching closely come March, and should be ready to hit that first flush of annual weeds with well-timed herbicide applications.”
Farther east, where drought conditions were less intense last season, most pastures still experienced above-average weed pressures, notes Rocky Lemus, extension forage specialist, Mississippi State University. “Smutgrass is a real problem in the southwestern part of the state, and cogongrass has been very invasive the last few years. But weeds like woolly croton, horsenettle and cypress weed (dogfennel) were much worse last year than we normally see here in Mississippi. We also saw johnsongrass in new areas.”
Because of the dry conditions, producers avoided herbicide applications last summer. That was prudent, since herbicides would probably not have been very effective, and some may have further stressed pasture grasses, Lemus says. “But following rain in late August, some growers did apply herbicides. Unfortunately, by then many weeds were already in reproductive stages with mature seeds, so the treatment wasn’t very successful.”
Some much-needed rain in October and November helped alleviate some of the drought stress in pastures, he adds, supporting regrowth in tall fescue and helping establish seeded ryegrass. “That should allow those grasses to better compete with weeds.”
Looking ahead, making a herbicide application in late March or early April will be the most economical strategy this year, says Lemus. “About three weeks after winter annuals emerge, when weeds are three to four inches tall, is the best time for a herbicide application.”
He recommends growers watch weed populations closely this spring and summer, and make a second herbicide application, if necessary. “It doesn’t take much moisture for weed seeds to germinate. After last season, there could be a lot of weed seeds out there.”
Weed Challenges in Wet Conditions
Too much moisture presents growers with a separate set of weed-control challenges. Where spring and summer flooding was most severe—including areas of north-central and northwestern North Dakota—pasture grasses simply didn’t survive, says Kevin Sedivec, extension rangeland specialist, North Dakota State University. “Many growers will have to start over and reseed this spring.”
In pastures where flood waters came and left within a few days, weeds were very heavy last summer, he says, adding the biggest weed increase due to flooding was in the Canada thistle population.
“We usually get good thistle control with a fall herbicide application. But many growers didn’t have time for that before the first freeze in mid-September,” he says. “So they will need to track weed development closely this year and make a timely application in late spring.”
For growers facing reseeding, a burndown treatment is critical prior to drilling in any pasture grass, he says. “We recommend seeding straight grasses, since that will increase a grower’s herbicide options. Take the time to do a good job when drilling, making sure the seeds are planted at the right depth to get good, even emergence. That’s the best defense against early weed pressure.
“You’re always going to have some annual weeds,” he adds, “so follow up on the new pasture during the first month to see which weeds are coming through, then apply a herbicide if necessary to keep the new pasture as clean as possible during establishment.”
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