Whip Weeds in 2018
As you enter the 2018 growing season, weed management will be top of mind if you are a soybean grower. As previous seasons have shown, it’s going to take the entire toolbox – and maybe the addition of a few new tools – to stay a step ahead of evolving herbicide-resistant weeds.
Kevin Bradley, University of Missouri Extension weed specialist, looks to a combination of cultural practices and the use of smart herbicides to keep fields clean.
While new, promising systems are available, Bradley wants to remind you that no system will ever provide a silver bullet for weed control.
It will be necessary to look beyond herbicides, even with the new low-volatility dicamba formulations and other chemistries entering the market, he says.
No matter which system you decide to adopt, you can’t view it as the solution to all your problems, says Bradley.
Instead of relying on herbicides to take care of 100% of the weeds, Bradley wants you to lean on a combination of chemical and cultural practices to control herbicide-resistant weeds.
Following are his recommendations if you are looking to best harness the different tools available.
Control the weed seed
Destroying the weed seed is one way to prevent the weeds from becoming troublesome. One practice Bradley is researching is windrow burning.
“We don’t know if it’s a good idea or not yet, but it’s an option worth investigating,” says Bradley.
This mechanical option comes at a relatively inexpensive cost compared with other practices.
“For $50 or less, you can make a chute on the back of your combine, windrow the chaff and weed seed into a row behind the combine, and then burn it,” explains Bradley. “We’re investigating this practice and whether it will be sufficient to kill weed seed.”
So far, his research indicates that it is likely to do the job.
“We’ve got a whole lot more work to do, and you need to think about all the implications of that, but it is another way to think about weed control rather than just going out there with herbicides only,” he says.
Another mechanical option is to grind up the weed seed with weed seed destructors. Machine prototypes that attach to the combine are being developed, says Bradley.
Another nonherbicidal technique for weed control is adding cover crops. Cover crops can suppress weed germination and provide competition for weeds.
“We have plenty of data that show a cover crop can match certain weeds,” says Bradley. “We have examples where cereal rye didn’t allow marestail to germinate.”
He points out that some cover crops can suppress early-season waterhemp emergence, as well.
Again, it won’t be a silver bullet.
“We also have data that show it’s not a home run – it may not even be a triple,” says Bradley.
He expects there will be times when flushes of waterhemp push through the cover crop. Yet, data show cover crops can be helpful in controlling weeds early in the season.
make a Last-ditch effort
Tillage is a practice that, when push comes to shove, may be helpful in nightmare fields.
“I’m certainly not saying we should all go out and till all our acres, but we had a study a couple of years ago that showed you can turn a really bad field around in a hurry, if you do a drastic tillage operation – not by using a vertical tillage tool or a chisel plow – that’s not going to bury those seeds deep enough to make much of a difference,” says Bradley.
Instead, a moldboard plow has to be used to bury the seed deep enough.
In worst-case scenarios, which have happened in Missouri, a moldboard plow can help, says Bradley.
“I’ve dealt with some farmers who have turned it around pretty quickly by just moldboard plowing one time,” he says.
After the moldboard plow pass, he recommends that growers implement no-till or cover crops, or both, and good weed management. This will take advantage of the weakness of weeds, like waterhemp, in being unable to emerge from deep soil depths.
Moldboard plowing won’t be ideal for everybody, but it is an option he wants you to know is available.
In addition to destroying weed seed, planting cover crops, and adding tillage passes when necessary, Bradley suggests that you consider adjusting row spacing, plant populations, and planting dates. Manipulating these factors can allow crops to reach canopy sooner and shade out weeds early in the season.
mix up the chemistry
In addition to cultural practices, Bradley says herbicides will have to be used effectively to manage weeds.
In Missouri, Bradley points to the following practices for turning around weed-management issues.
- Use preemergent herbicides and postemergent herbicides at full label rates.
- Use multiple modes of action.
- Make applications as close to the time of planting as possible.
Bradley believes that implementing the previous strategies has resulted in the cleanest fields they’ve had statewide in the past two to three years.
“You have to mix modes of actions, no matter which system you are going to plant,” says Bradley. “You need group 14 and group 15 herbicides for preemergence applications in soybeans.”
The other thing that has really turned the trouble fields around for Bradley is using a preemergence herbicide and then following it with an effective postemergence application with a residual included in the postapplication.
“That’s your best chance of success and your least risk of having late-season waterhemp flushes,” Bradley explains. “Our growers who have had the best-looking, cleanest fields are usually the ones who are adopting this recommendation. There are numerous products that work.”