By Darren Hefty
Whether you got a pre-emerge herbicide on or not, you may need a tankmix partner for Roundup in your soybeans. I’ll list your main non-premix choices and the weeds they really help with. I’ll rank these products in terms of popularity, although this varies by region:
Flexstar is your best choice for pigweeds including waterhemp and Palmer pigweed. It’s also decent on ragweed and other small-seeded broadleaves. Plus, it has a little bit of residual. Flexstar is not labeled in all areas due to carryover concerns. That’s why we recommend a maximum of 12 ounces per acre, even where more is labeled.
Cobra has no soil residual, but it is the alternative product if you can’t use Flexstar in your area or if you’ve already used Flexstar once in the season. At 12.5 ounces per acre, Cobra will burn the leaves on your soybeans. The leaf burn rarely hurts yield, and it does decrease the incidence of sclerotinia white mold, so that’s a bonus. Cobra is not bad at suppressing kochia, pigweeds, ragweeds and other broadleaves, especially if they are under four inches tall.
Cadet and Resource are fairly similar products. Both are excellent at controlling velvetleaf at almost any growth stage. They also both help on pigweed control and many other broadleaves.
Harass is the generic version of the old Pinnacle. It is the best post-emerge helper for lambsquarters control, and it gives added kick on many non-ALS resistant weeds. It is only about $1 per acre.
FirstRate is the most popular tankmix partner if you have giant or common ragweed that is not ALS-resistant. It’s also my favorite choice for help on marestail, although nothing is perfect on a winter annual weed that’s probably now 2 feet tall.
Pursuit and Raptor are pretty similar products. They are the most broad-spectrum herbicides for soybeans. In terms of tough-to-control weeds, they work as well as anything on wild buckwheat in soybeans. Otherwise, cocklebur, sunflower, morningglory, velvetleaf and a number of other weeds including small annual grasses can be controlled with Pursuit or Raptor.
Finally, the residual herbicides like Warrant, Outlook and Dual deserve mention, even though they will not kill any weeds that have emerged. They are used for late-season residual activity only, as they kill grasses and small-seeded broadleaves. One caution is that they can heat up tankmixes, especially if you’re using higher rates of MSO or crop oil.
When it comes to post-emerge soybean tankmix partners for Roundup, all of them are best when weeds are 2 to 4 inches tall. Even then, don’t expect perfect control in one pass.