Do you remember those herbicide commercials where the weeds would sneer and smirk at the farmer? They drove him crazy until he was able to knock them out and have some peace. Well, most Indiana farmers are experiencing that first part with waterhemp right now, hoping to find some peace.

That’s because waterhemp herbicide resistance is no longer just an issue in soybeans. With resistance to dicamba and HPPD herbicides, and inconsistency or suspected resistance to glufosinate and 2,4-D, there is cause for concern.

“Those are concerning because that impacts corn now,” says Bryan Young, a professor of weed science at Purdue University. “The HPPD resistance, for years, used to be a central Illinois and Iowa issue, and parts of Nebraska and Kansas. So, in other words, here in Indiana, who cares? But in the last few years, we’re hearing of more issues with HPPD herbicides not working postemergence on waterhemp.”

Some examples of those HPPD herbicides are Callisto, Laudis and Halex GT.

Young says that adding atrazine to the mix can help some, but atrazine resistance also has been intensifying.

Possible solutions

Relying on a post-application to control waterhemp is the last thing you should do, Young says. Instead, he recommends applying a preemerge soil residual herbicide and following that up three weeks later with an overlapping soil residual herbicide application. Herbicide cost is always an issue, Young says, but new targeted spray technology using boom-mounted cameras may be an option to reduce costs for the foliar active herbicides in the postemergence pass.

Related:7 factors that affect spot-spraying efficiency

Additionally, Young recommends throwing an effective combination of herbicides at waterhemp instead of a single mode of action. If you plan to use a group 15 herbicide, such as acetochlor in Warrant or S-metolachlor in Dual, in back-to-back applications and years, Young says to use another herbicide with it.

“I think any herbicide we use these days is going to select for some type of resistance because we have resistance to almost all of them,” Young adds. “So, the best thing we can do is apply a strategic combination of herbicides each time we make a preemergence or postemergence pass.”

Effective soil residual applications

Spending the extra money to have a soil residual herbicide in that first post-application could contribute to better waterhemp control. Young sees that as the next logical step to getting ahead of waterhemp.

Marcelo Zimmer, a weed science program specialist at Purdue, says that it’s key to overlap soil residual herbicides to make the most of them. However, if you’ve waited until weeds have emerged before making that second pass, then you’ve missed the window for control.

Related:Weeds survive spraying in wacky ways

“If your weeds have already emerged when you’re making the post-application, are you really overlapping residuals?” Zimmer says. “For overlapping residuals, you need to make that application before the pre-herbicide starts to break. So, maybe bringing that post-application a little bit earlier will help us utilize soil residual herbicides a little bit better.”

Again, this is where Young emphasizes that it is key to use the calendar method and follow your first soil residual application with an overlapping soil residual three weeks later. If you wait too long and see some weeds popping up, then it is not an overlapping application. These applications will be expensive, but Young says that they’re necessary to avoid issues later in the season. He advises against cutting costs by skimping on your pre-application.

“We have to stay one step ahead of the weeds,” Young says. “We have failed at doing that thus far.”