Despite more options for 2017, Brandon Monebrake and his grandfather Dean Petry of Preble County are staying with the corn herbicide program they have been using.

A look at weed control in 2017: Corn

While having more weed control options than ever before can be an exciting opportunity for farms to tackle problem weeds, it can also be confusing, which can lead to expensive problems down the road.

For now Dean Petry and grandson Brandon Monebrake in Preble County are planning to continue what has already been working for their corn herbicide program.

“We are sticking with what we are doing. We don’t really have an issue with marestail. Giant ragweed is the big issue for us,” Petry said. “We use Lexar. Then we use HERBIMAX crop oil with Roundup for spot spraying in the corn. Sometimes Johnsongrass can be a problem in the corn, but Lexar holds it down pretty good.”

The farm has been in no-till for 25 years and the corn burndown is done shortly after planting.

“We do a burndown for corn in the spring after we plant,” Monebrake said. “We spray when we put 28% on when the corn is six inches or a foot tall.”

The warm winter is the source of some concern as planting season draws near. Fields were looking a bit too green earlier than normal.

“The fields were already greening up in March when it was way too early to see the weed pressure,” Petry said. “There were some people spraying up around here during the warm spell in February.”

As far as the new technology, they are planning to wait and see how things go.

Petry Farms2“I am letting everyone else experiment with the 2,4-D and Dicamba stuff and see how it goes. It makes me a little nervous,” Petry said. “They say it doesn’t move readily but they’ll have to prove it to me. There are some grapes around here and it is easy to kill them.”

In terms of corn herbicides, there are plenty of excellent options to select from, said Mark Loux, Ohio State University Extension herbicide specialist.

“Corn growers currently have many effective preemergence and postemergence herbicides and herbicide tolerance traits to choose from, and there can be considerable competition between manufacturers, which works to reduce costs. There are a number of broad-spectrum preemergence premix products and tank-mixes that we rate as an 8 or 9 across the board in the ‘2017 Weed Control Guide for Ohio, Indiana, and Illinois,’” Loux said. “These include Acuron, Lexar, Resicore, Corvus/atrazine, Cinch ATZ/Instigate, and combinations of any of several atrazine premix products with Balance PRO. These herbicides will be more effective then two-component atrazine premix products such as Bicep II Magnum, Harness Xtra, etc. on certain weeds. Many growers prefer a total preemergence approach in corn since they have their hands full with postemergence applications on their soybean acres. And in some cases growers opt for an early postemergence approach in corn from spike to V2, which can be effective with some of these same herbicides. Keep in mind that taking a one-pass early postemergence approach on a substantial number of acres can be difficult to manage in certain years.”

As in the case of the Petry Farms, post- decisions in corn need to be carefully made on a field-by-field basis.

“It is possible to make these one-pass approaches work in some fields, but it’s also important to recognize where it’s necessary to use a combination of preemergence and postemergence applications. Not every field lends itself to a total preemergence approach, and continuing to use more and more residual herbicide won’t solve every problem,” Loux said. “Keep in mind that getting effective control of problem herbicide-resistant weeds in corn makes control easier in next year’s soybeans, so take advantage of all of the tools that are available for corn. A combination of preemergence and postemergence herbicide applications will be more effective than a total preemergence approach in fields with heavy annual grass pressure, perennial weeds, and moderate to high populations of large-seeded annual broadleaf weeds such as giant ragweed, cocklebur, burcucumber, and morningglories. Palmer amaranth and waterhemp often require a postemergence follow up also, due to their ability to emerge well into the growing season.”

The post- applications in corn are particularly important on those breakouts of giant ragweed that can plague fields.

“Giant ragweed is one of the primary reasons that a postemergence herbicide application is needed in many corn fields. The most effective preemergence herbicide programs may provide adequate control of low-density giant ragweed infestations, but usually start to break as the population increases. Giant ragweed populations are often concentrated in certain areas of the field at a higher density, so that preemergence herbicides just cannot provide enough control in these areas,” Loux said. “This same logic can be applied to the other annual weeds — once populations reach a certain level of infestation or have exhibited a pattern of continued emergence into mid-season, trying to get by without postemergence herbicides is a mistake. Burcucumber is probably the biggest offender with regard to late emergence. Use of herbicides with residual activity in both the preemergence and postemergence application is essential for this weed, and it is still capable of emerging in great numbers in mid-July and causing problems with harvest.”

With more options now available for weed control, the importance of a long-term multi-year weed control strategy has increased, Loux said.

“It’s important to consider the longer-range view when deciding on which technology and herbicides to use in corn, and to avoid overlap of herbicide sites of action between corn and soybeans as much as possible. The use of different sites of action, and the effectiveness of corn herbicides on certain weeds that are problematic in soybeans, have prevented us from having more severe and more widespread herbicide resistance issues than we currently have,” he said. “Evolving technologies are making it more likely that manufacturers will promote use of the same products in both crops, and it will fall on growers and their advisors to avoid this. Until now we have used dicamba and HPPD inhibitors (Balance, Callisto, etc.) only in corn, and 2,4-D primarily in burndown programs. The current or pending availability of Xtend soybeans and the Balance Bean, and Enlist corn and soybeans result in the ability to apply dicamba, 2,4-D, and Balance in both crops, and doing so will increase the selection for weeds resistant to these herbicides.”

For planning purposes Loux suggests:

1. See how often the same herbicide site of action is being used for control of the same weed problems in burndown and postemergence treatments; and then

2. Rotate these herbicides frequently and employ mixtures of two effective herbicide sites of action.

Loux provided this example of diversity for postemergence control of giant ragweed over a four-year period with two years of corn and two years of soybeans (following a preemergence program): Year 1: Roundup Ready soybeans — glyphosate + fomesafen (Flexstar, etc.); Year 2: Roundup Ready corn — glyphosate + Status; Year 3: LibertyLink soybeans — glufosinate (Liberty, etc.); Year 4: corn — Laudis + atrazine.

“Where a grower starts to use dicamba POST in Roundup Ready Xtend soybeans, this program should probably be changed to deemphasize use of Status in corn,” Loux said. “Growers and advisors with questions about long-term strategies to avoid resistance should feel free to contact us for help.”

Loux can be reached at loux.1@osu.edu and also suggests reviewing the “Problem Weed” section of the “Weed Control Guide for specific strategies on the tougher weeds. For more visit OSU Weed Management.

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