*This content was previously published by Corteva Agriscience.
Brad Burkhart, Market Development Specialist for Corteva Agriscience, says waterhemp is the number-one weed concern for most licensees. One reason is its rapid rate of growth, up to 2-3” a day under certain conditions. “That means you can’t afford to take the weekend off” when it comes to treating it, Burkhart says. Research shows that for every inch of weed growth, farmers lose 0.7 bu/A yield. So, 6” of waterhemp growth in $10 bu/A soybeans can cause a loss of $42 per acre! Waterhemp is also one of the toughest weeds to control because it’s resistant to six or more herbicide chemistries, including dicamba. This means growers must make preventing or treating waterhemp a priority.
Other weed threats include giant ragweed and marestail, plus some farms have pockets of Palmer amaranth. Burkhart says that if you have Palmer amaranth, that should be your primary concern since it can quickly take over a field. Luckily, the same approach he recommends for controlling waterhemp can be used on Palmer amaranth since they’re in the same weed class.
Burkhart recommends using a combination of herbicides for burndown, preemergent treatment and residual coverage. Group 14 (PPO) herbicides provide effective protection, especially when used in combination with a Group 5 chemistry. Keep in mind that this means a grower will need to commit to planting only soybeans on these acres. But Burkhart says it’s important to use a Group 14 product because there’s documented waterhemp resistance to so many other classes of chemistries.
Another combination Burkhart recommends is an Enlist One® herbicide-glufosinate tank-mix for treating waterhemp or Palmer amaranth in Enlist E3® soybean fields. “The beauty of those two in the tank is you get the best of both worlds,” he says. “Systemic control from Enlist One herbicide and contact control from glufosinate.”
Components of a program approach to soybean weed control
- Start clean with a burndown — in the fall if possible, or the spring as an alternative.
- Use multiple pre-planting sites of action (SOAs) — apply two weeks before or up to three days after planting.
- Use multiple post-planting SOAs — apply within 28 days of the pre-application and include a residual for extended control.
One key to successful waterhemp control is timely in-crop application — preemergent or, at a minimum, before plants reach 6” in height. Burkhart recommends using a pre-emergence product like Sonic® herbicide or Trivence® herbicide (Group 5 and Group 14 herbicides) for burndown and residual protection, followed by a Group 15 herbicide — EverpreX® herbicide or Enversa™ herbicide (coming in 2025) — 21 to 28 days later. This timing should prevent waterhemp germination. “Group 15 herbicides are essentially a soil barrier,” Burkhart says. “So, that chemistry can only control it if waterhemp hasn’t come up yet.” Burkhart warns that not using multiple MOAs or skipping the residual piece can increase the potential for herbicide resistance in the future.
“The tools we have today are our tools for the next three to five years, so we need to be good stewards of them,” Burkhart cautions. “Because if we’re not using multiple modes of action (MOAs), were going to find ourselves in a world of hurt in a few years.”
If waterhemp was a problem this year, document which fields had pressure and then make a plan for the fall and next season. Burkart says, “Combine the affected field last to prevent spread. Or look into rotation if you’re not using a Group 14.” It’s important to be good stewards of the technologies we have today and use multiple MOAs to protect their efficacy and help prevent the potential for resistance.
Burkhart has a number of tips for successfully treating waterhemp and similar weeds using Enlist® herbicide tank-mixes on Enlist E3 soybeans:
- Use a water volume of at least 15 gal/A for better herbicide coverage.
- Use AMS or an AMS replacement of at least 2 lbs./A.
- Use the right nozzle (check the list at Enlist.com) and spray in the upper third of the pressure range for consistent droplet size.
- Consider adding surfactants or adjuvants to the tank-mix depending on field conditions.
- If volunteer corn in soybeans is a concern, use a clethodim tank-mix with Enlist One herbicide, but be sure to increase the rate by a third to counteract any antagonism between the chemistries.
