First there are brand names for herbicides. Many or you know those, although as more names come out, it's even harder to even keep up with brand names. Which ones are for corn? Which ones are for soybeans? Which ones work on grass? Which ones only work on broadleaves? When can they be applied? The questions are endless.

Dealers and specialists went from talking brand names to talking active ingredients. Maybe you're still struggling with that step. Some are easier to learn, like glyphosate, since it is off patent and many companies make glyphosate and sell it under various names.

Related: Fight Resistant Weeds by Knowing Modes of Action

Three modes of action: The message at this stop from the Bayer expert was clear --- use three effective modes of action each season in your weed control program.

"Now you need to go one step further and talk about modes of action," says Dave Lamore, senior technical service rep for Bayer Chemicals. "It's not enough anymore to just know the active ingredient."

He was talking about corn specifically at a recent field day, but he says the same concept also applies to soybeans. The driving force behind needing to know modes of action is to help prevent weed resistance, he says.

Various chemicals are now classified by their mode of action in killing weeds. Numbers are assigned to chemicals that all work on certain sites within the plant. Companies are now printing these numbers on product labels.

"You really need to get used to them, and pay attention to them," Lamore says. Otherwise even if you bought chemistry from different companies, you could end up with herbicides that have the same mode of action, which means the same way of killing weeds.

When you use only one or even two modes of action to kill a weed, it is easier for the species to develop resistance, he says. The mutations which have resistance to that chemistry can be 'moved to the front of the reproductive line' faster because they survive at a higher rate.

"You need to be using three modes of action against a weed to help prevent future resistance," Lamore says. And if the weed is glyphosate resistant, then if you have glyphosate in the program, it doesn't count as one of the modes of action.

Related: Know herbicide mode of action and control resistant weeds with online tool

You may have it in there to get other non-resistant weeds, which is fine, just don't count on it to have any effect on resistant weeds, the specialist concludes.