As far as the corn weed control programs currently being used in Georgia, they basically boil down to five things, says Eric Prostko, University of Georgia Extension weed specialist.
“Of course we’re using a lot of Roundup on Roundup Ready corn, but we’re also seeing other materials being used such as Steadfast Q, Liberty, Capreno or Halex GT. Most growers are probably going to be using one of these, and generally in our research I have found no major differences in the programs. There are slight differences but not enough for me to tell you that one program is better than another. Rarely do we see yield differences, and slight differences in weed control really don’t result in big differences in yield.”
Many of the corn hybrids, especially from Pioneer, have multiple resistances, he adds. “We have glyphosate resistance as well as resistance to Liberty or glufosinate. That gives us another option from which to choose if we need to depending on the weed species that is present.”
Occasionally and especially in recent years, Prostko says he has received calls from growers who do not want to use Roundup or Liberty.
“If you’ve been a corn grower for a while then you know there were numerous products we used before Roundup, and Steadfast Q is one we’re using in Georgia. If you think back to before Roundup Ready, one of the biggest issues we had was with hybrid tolerance to herbicides. We were using a lot of Accent, and we knew there were a lot of hybrid issues with doing that. In the last several years, we’ve seen a change in the formulations of some of those old materials, and they now include a crop safener.
“We looked at two sensitive DeKalb corn hybrids and sprayed at the one and two times rate of some products, and we didn’t see any problems with the exception of Capreno. So we feel there shouldn’t be a problem if you want to use Steadfast Q on these sensitive hybrids.”
Atrazine still the backbone
Atrazine, says Prostko, was first registered in 1959 and remains the backbone to weed control in corn.
“It’s very cheap, and it’s effective. I encourage all of our growers to use atrazine, for many reasons. However, we have discovered atrazine resistance in Georgia. We originally thought it might be restricted to regions where corn was grown for dairy production, and that perhaps it was due to a certain rotation, but we have since found resistance in a couple of non-dairy rotations. We’ve now found atrazine-resistant Palmer amaranth pigweed in three Georgia counties.”
The good news, he says, is if farmers were to lose atrazine today, for whatever reason, they still could do a reasonable job of controlling weeds in corn. The downside would be cost, he adds, because any material now available would cost more than an atrazine-based program.
“That’s especially a problem with lower corn prices. Efficacy-wise, we could do a good job controlling most of our weed problems without atrazine, but we’d prefer to have it.”
There’s a lot buzz in the farming community about dicamba-resistant cotton and soybeans, says Prostko, and 2,4-D-resistant crops also are coming in the future.
“Enlist herbicide corn and soybeans – resistant to 2,4-D – will be available for the Midwest. We will see this technology at some point in the future in the Southeast but not for 2015. If you grow corn, you already know you can use 2,4-D, but you’re restricted in the amount and how you use it. This technology will allow for more flexibility, but we won’t have it for at least a year and probably longer than that.”
Prostko asks producers to use caution whenever they’re using herbicide tank-mixes. “Most growers want to put everything in the spray tank to avoid going over a field more than once. But if you use tank-mixes, be cautious. If you’re using a dry formulation, make sure you pre-mix it in water before mixing it in the tank.”
A couple of new herbicide products available to field corn growers this year, says Prostko, include the residuals Anthem and Anthem ATZ.
“These products are not superior to currently available ones, but sometimes they offer a different mode of action. Dow is promoting a couple of pre-mixes, FulTime and Keystone, and they contain atrazine and acetochlor. Syngenta has a new product called Acuron, which is a four-way mix. It looks good in our tests but not significantly better than what we’re already using.”