When cattle producers and forage experts in the Southeast talk about the toughest pasture weeds to control, smutgrass is always near the top of the list.
According to Brent Sellers, University of Florida extension weed specialist, smutgrass can be found in almost any pasture in southern Florida.
“Smutgrass always ranks in the top three toughest weeds in the survey of county and state extension staff that we conduct every five years,” he says. The weed is also prevalent in Alabama, Georgia, Louisiana, Mississippi and Texas.
Smutgrass is aggressive, doesn’t need much moisture and produces seeds from May through the summer months. “And mowing smutgrass can actually increase its seed production, so mechanical control is not a good option,” notes Sellers.
In pastures, smutgrass spreads and competes with desirable perennial grasses, says Randy Verret, location manager for G & H Seed Co., Iowa, LA. “As smutgrass invades, it occupies more area in the pasture and eventually reduces carrying capacity. Animals overgraze the desirable, more palatable grasses, which gives smutgrass even more opportunity to spread.”
The invasive bunchgrass offers little nutritional value and reduces hay quality, Verret says. “In bermudagrass hayfields, total forage removal gives smutgrass a greater chance to spread and establish more seedlings before the bermudagrass can regrow,” he adds.
The key to effective control is taking action before weed density is too great, notes Sellers. “Once smutgrass covers more than 50% of the pasture, it’s often too late for spot spraying. When an infestation gets up to 60 or 70%, you’re looking at pasture renovation.”
A few years ago, Tate worked with Verret to try a herbicide control approach for smutgrass on bermudagrass. Verret recommended using DuPont Velpar L.
“We had a high infestation of smutgrass and were looking at tearing up the pasture. But the Velpar L application worked well,” says Tate. “I would have used it on other pastures if it weren’t for the grazing restriction the product used to have.”
But that restriction was significantly reduced in March 2011. Now pastures treated with the herbicide at 4.5 pints per acre or less can be grazed immediately and treated acres may be cut, dried and fed 38 days after application.
That’s good news for Tate, who says he wants to use the herbicide to get the upper hand on smutgrass invading a few other pastures among the more than 10,000 acres he manages in southwestern Louisiana. “Smutgrass works its way into a pasture one to two years after we improve it. I really want to get control of it before it takes over, which can happen in just three or four years.”
For best smutgrass control, apply the herbicide when weeds are actively growing, advises Craig Alford, range, pasture and invasives portfolio manager for DuPont Crop Protection. “For many areas in the Southeast, that’s in May and June, when rain is more frequent.”
In central and southern Florida, July and August have proven to be good application months, says Sellers. “But really it’s less about the specific month and more about when it rains more frequently. It’s best to time an application between rains or the day before rain is expected, since that timing seems to encourage maximum root uptake.”
Within three to four weeks after an application of Velpar L, there may be some yellowing of bermudagrass or bahiagrass, adds Sellers. “We have occasionally observed a little bit of crop stunting, as well. It depends largely on rainfall and how actively the pasture and weeds are growing at the time of application.
“In most cases we see that the bermudagrass or bahiagrass grows out of it fairly quickly,” he says. “Bahiagrass shows good tolerance to the herbicide and usually turns dark green again within about 40 days. Bermudagrass is a little less tolerant, but usually starts to exhibit new green growth within 30 to 40 days.”
It’s important to adjust the application rate based on soil texture, notes Alford. “You need to use a lower rate on coarse-textured sandy soils and a higher rate on fine-textured soils, such as clay loams.”
Sellers encourages fertilization after herbicide treatment. “Adding nutrients will increase forage production and allow the bahiagrass or bermudagrass to quickly fill in the open areas created by dying smutgrass,” he says.