By Darren Hefty
To achieve top yields in corn, there is a lot of focus on fertility, seed placement, aggressive plant population management, and more. However, you can throw all of those things out the window if you mess up and don’t get your weeds under control right from the start. The foundation to a good weed control program for corn is the pre-emerge herbicide.
Let’s look at a few of the most popular questions we’ve been receiving on the Ag PhD Radio program about corn pre-emerge herbicide plans.
Which pre-emerge herbicides work best for conventional corn?
If you are planting conventional corn (not resistant to non-selective herbicides like Roundup or Liberty), the biggest concern you have is GRASS control. Since corn is a grass crop, it makes sense that it would be tougher to knock out grass weeds as compared to broadleaf weeds. However, most of us have switched from grass herbicides to combination grass + broadleaf weed control products in the pre program over the last 5 to 10 years. Here’s why grass control is really the most important thing in conventional corn: your limited rescue options. I should mention there is actually only one product that can rescue grass control if you can’t use Liberty or Roundup – Accent Q. Accent Q has a safener, so it is easier on corn than the old Accent. The other two things you need to know about Accent Q are it costs over $22 per acre and it only controls grasses less than 2 inches tall. It’s much cheaper and more effective to control the grasses pre-emerge. If a few broadleaf weeds escape, there are plenty of options to wipe them out later. The products of choice for conventional corn are: Dual II Magnum, Harness, Outlook, and Surpass NXT. Just be sure to use the full rate.
What pre-emerge herbicides for corn work best in no-till?
The pre-emerge base products for grass control all work well in no-till situations. The big issues to deal with in no-till are:
- Weed spectrum
- Residue tie-up
- Rainfall incorporation since tillage won’t be used
The no-till weed spectrum is different in that there are often winter annuals present in the early spring (e.g. marestail, pennycress, mustards, etc.). Also, weeds like dandelion can be more of a problem. Adding dicamba or Roundup to almost any of the pre herbicides helps if weeds are already emerged. I really like Verdict because it contains a high rate of Sharpen (Kixor) and adds a lot to a burndown program. Of course, Gramoxone is a good alternative to Roundup where resistant weeds are an issue.
Which pre-emerge corn herbicide program works best at controlling Roundup-resistant weeds?
The combination grass + broadleaf herbicides are typically best where resistant weeds are a problem. The aforementioned Verdict works very well when pigweeds, ragweeds, winter annuals, and kochia are the predominant species. SureStart and TripleFLEX are popular options where ragweed and pigweed are among the weeds present. Corvus, which contains Balance Flexx, is a solid choice in states where it’s labeled. The Balance Flexx product is very good on pigweeds, ragweeds, kochia, and more.
The real key for success in corn weed control and overall yields is to get a good pre-emerge herbicide out there early. Focus on grass control in conventional corn, winter annuals in no-till, and broadleaf weeds where resistance to Roundup is an issue.