ORLANDO, Fla. – When Valent’s new Valor herbicide receives an in-season label for cotton, which Valent expects in time for the 2004 use season, it will provide growers with another option in their weed control arsenal.
At a recent Valor product launch event in Orlando, weed scientists from three land-grant universities gave their take on how to best use this new herbicide alone and in combination with other herbicides.
Ed Murdock, a retired weed scientist with Clemson University, says the biggest benefit he sees with Valor is the residual activity it provides for pigweed control, even several weeks after treatment. He hasn’t seen the same residual activity on pitted morningglories, coffeebean or nutsedge.
Even so, Murdock says, the residual pigweed control Valor provides is a “major plus” for those producers battling the hard-to-control weed. “Our number one problem is pigweed, everything else is secondary,” Murdock says. “Growers must-control weeds prior to, or at planting, are pigweed, Carolina geranium, horseweed, chickweed and henbit.”
In his studies of burndown herbicides, a stand-alone treatment of glyphosate controlled 50 percent of the pigweed population. Adding Valor to the mix increased pigweed control to 100 percent.
Murdock recommends adding 2 ounces of Valor with a glyphosate burndown treatment for the control of Palmer Amaranth, commonly known as pigweed.
“If you go into reduced tillage, you’ve got to be a good manager because you are 100 percent dependent on your herbicide program working,” Murdock says.
However, Murdock sees little residual benefit with Valor if Palmer Amaranth is not a problem. The new herbicide does provide residual activity on prickly sida and common lambsquarters at the 2-ounce application rate. “You can pick up more weeds including morninglory and coffee senna if you up the Valor rate to 3 ounces per acre.”
A preplant burndown tank mix with Valor is probably not needed, he cautions, if 2,4-D is applied early in the season.
Alan York, a weed scientist at North Carolina State University, says, “Traditionally, burndown tankmixes of 2,4-D plus glyphosate have been extremely efficient in controlling cutleaf evening primrose. But, a lot of growers don’t want to use it because of worries about washing it out of their tanks.
Up until now, York says, there haven’t been many alternatives available to cotton growers. “Clarity provides adequate control, but isn’t a player because of the product’s cost. Resistant horseweed populations may change our minds about the economic benefits of that product, however.”
York does not recommend Valor applied as a stand-alone product. While he has seen mixed results, he says Valor alone “just didn’t do it,” on many problem weeds.
“A tank mix of glyphosate and Valor looks extremely good early on, or at about 18 days after treatment. Stretching out farther into the season, we do see some weed re-growth, but my gut feeling is that the weed control provided is probably good enough,” he says. “Adding 2,4-D to that tank mix provides extremely good control and eliminates re-growth.”
In addition, York says he hasn’t seen any antagonism on the weed species controlled with Valor. “You can help on some species without tanking away control of other species,” he says.
A late April application, following a mid-December application of glyphosate plus Valor, picks up some residual control of several weed species, he says. “Having this residual control provides the growers with insurance against early season weed competition in cotton.”
York does caution growers on potential “splash up” injury when using Valor herbicide. If Valor is applied to bare ground and little to no rainfall occurs after treatment, then the potential is there for an irrigation treatment at the time the cotton plants are emerging to cause the previously applied product to “splash up” onto the cotton plant causing plant injury, he says.
To avoid splash-up injury, York recommends carefully following the labeled application specifications for Valor.
Stanley Culpepper, a weed scientist with the University of Georgia in Tifton, has undertaken comparison studies of post-directed layby weed control treatments following good early-season weed control.
Culpepper compared the “standard treatment” of glyphosate as a stand-alone product versus a tank mix of glyphosate and Valor at the 1 ounce rate, and a treatment of 2 ounces of Valor plus MSMA.
Adding Valor to the glyphosate provided acceptable control to both entireleaf and pitted morningglories, as well as yellow nutsedge and palmer amaranth. “Ask yourself when the Palmer Amaranth is coming up, before or after layby, before spending the money on Valor,” he says. “Some other weeds, like annual grasses, aren’t helped with the addition of Valor, and are often best controlled by a stand-alone treatment of glyphosate.”
Deciding which Valor rate to use, Culpepper says, is based on the amount of residual weed control desired.
Because the tank mix of Valor and MSMA performed similarly to the Valor-glyphosate mix in his tests, Culpepper suggests using whichever tank mix best fits your production system.
Culpepper says he is concerned about potential herbicide injury caused by applying Valor to young, small green cotton. “It’s also very important to remember to use a nonionic surfactant, and not a crop oil concentrate. Crop oil concentrates will certainly heat up the Valor, and can cause crop injury,” he says.
“Cotton growers are going to have to make a precise application no matter how you apply a Valor tank mix. You’ll know quickly if you mistakenly apply the tank mix 5 or 6 inches up the plant, because your cotton leaves will be down on the ground.”