You’ve committed to second-year soybeans because the economics looked more promising. Will it turn out to be a wise decision? Experts believe the devil is in the details. One detail is handling weeds. Will weed pressure shift and intensify in fields where you grew soybeans last year?

The Indiana Certified Crop Advisers panel answering that question includes: Jesse Grogan, agronomist, LG Seeds, Lafayette; Greg Kneubuhler, G&K Concepts, Harlan; and Tom Stein, manager of the Boswell and Templeton branches for Ceres Solutions.

Stein: You can expect a shift in weed pressure in second-year beans, and control will become more difficult. If you’ve had weed escapes before, expect even larger problems in beans after beans. The pigweed species are more likely to proliferate in this cropping system. They include smooth and redroot pigweed, tall waterhemp, and Palmer amaranth. Products that work well applied postemergence on pigweed species, outside of glyphosate, include Group 14 PPO inhibitors such as Flexstar, Flexstar GT, Reflex, Cobra and Avalanche Ultra.

Kneubuhler: I would highly favor a good residual program ahead of planting, particularly due to our current problems with marestail, Palmer amaranth and tall waterhemp. Don’t rely only on post products. For marestail in particular, there is documented resistance to both glyphosate and ALS chemistries. If you don’t control marestail with a solid residual program, your post options are very weak. There are several solid residual options. Get with your CCA to work them out if you have questions.

Stein: The key to success controlling weeds with PPO inhibitors (postemergence) is good coverage. To me that means 20 gallons per acre minimum as a carrier. Use a medium droplet size, and spray when weeds are small, say the size of a coffee cup. The best way to control these weeds in your Roundup Ready 2 platform is with layered herbicide applications. This typically means burndown, premergence and postemergence applications. All should be tank-mixed with residuals from group 3, 14 or 15 herbicides. These numbers are on the label. 

Grogan: It’s possible for weed shifts to occur. Many weed shifts have already begun. Weeds most often identified are glyphosate-resistant marestail and pigweeds, like waterhemp and Palmer amaranth. Giant ragweed fits in this category, too. Some waterhemp is resistant to multiple post herbicides in addition to glyphosate, including PPO and ALS chemistries.

Effective weed control programs are package mixes of products representing different sites of action. Look for a clean burndown of existing weeds applied with a full rate of residual herbicides at planting. It’s best to prevent weed emergence from planting to full canopy development. Some people use post programs as a rescue for weed breaks in the program.

Post herbicide treatments of glyphosate can be mixed with products like Flexstar and Cobra, but those are losing effectiveness in a few areas. If you planted LibertyLink soybeans, you have the option to use glufosinate as a post-applied product. It has no known weed resistance. Control emerged weeds when they are 4 to 6 inches tall.