When cattle producers and forage experts in the southeastern United States talk about the toughest pasture weeds to control, smutgrass is always near the top of the list.
According to Brent Sellers, you can find smutgrass 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,” says the University of Florida extension weed specialist. 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 throughout the Southeast. “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 bunch grass 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.”
Timing Is Key
The key to effective control is taking action before weed density is too great, notes Sellers. “Once smutgrass covers more than 50 percent of the pasture, it’s often too late for spot-spraying. When an infestation gets up to 60 or 70 percent, you’re looking at pasture renovation.”
That can be a costly proposition, says Jason Tate, ranch manager for Sweet Lake Land and Oil, Sweet Lake, La. “The cost of tillage control alone could be upwards of $20 per acre at today’s fuel prices, plus the cost of a planting pass and seed. Then you have to wait at least six months for it to regrow. That all adds up, and it’s why we want to avoid mechanical renovation.”
Smutgrass Control in Bermudagrass
A few years ago, Tate worked with his retailer Verret to try a herbicide control approach for smutgrass in bermudagrass pastures. Verret recommended using DuPont™ Velpar® L herbicide. “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 in March 2011, that restriction was significantly reduced. Now pastures treated with Velpar® L 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 upperhand 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.”
Target Applications During Rainy Periods
For best smutgrass control, apply Velpar® L 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.”
Sellers has applied the herbicide with and without an adjuvant. “In general, there was no significant increase in control with the addition of a surfactant, and definitely not enough of an economic advantage to justify the added cost.
“We need to continue to evaluate that idea, though,” he continues. “While most of the activity with Velpar® L comes from root uptake, there is some foliar activity. So adding an adjuvant may aid in control if rain doesn’t fall within a week after application.”
Within three to four weeks after Velpar® L application, 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 continues. “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.”
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.”
It’s important to adjust the application rate of the herbicide 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.”
He adds that, while the herbicide is one of a grower’s limited options for controlling smutgrass, Velpar® L also controls other weed species, including barnyardgrass, dogfennel, fescue, lespedeza and pigweed.
According to Verret, who has worked with growers for many years to control smutgrass, the label change for Velpar® L is a significant opportunity for better pasture management. “Eliminating the grazing restriction lets cattle producers treat infested areas before smutgrass spreads, without having to give up a whole pasture.”