Originally published by Badger Crop Network, University of Wisconsin

With temperatures expected to be very hot in Wisconsin this week (week of June 29, 2026), several questions have come in regarding POST herbicide applications in soybean.

Based on what we are seeing in our research trials and hearing from consultants and growers across the state, I would not delay applications because of the heat. While these conditions are not ideal for spraying due to crop safety concerns, waiting too long can create even greater challenges. Waterhemp will continue to grow rapidly, crop canopies are advancing quickly, and many fields will soon move out of labeled application windows if they haven't already.

• Apply herbicides mid-morning after the sun is up and the dew has dried, wind conditions allowing.

• Fields previously treated with Liberty + Enlist One where waterhemp regrowth is being observed can be retreated. Liberty (glufosinate) would be my go-to option for these fields. Remember that Liberty requires a minimum 5-day interval between applications and must be applied before soybean reaches R1. Don't forget to add AMS with Liberty and apply when the sun is up.

• Minimize oils in the spray tank whenever possible. Increased oil loading generally increases the likelihood and severity of soybean injury under hot conditions.

• Include crop oil concentrate (COC) only when necessary, such as when clethodim is included for volunteer corn control.

• Include a Group 15 residual herbicide only where continued waterhemp emergence is expected and additional residual control is needed. Group 15 herbicides can increase soybean response, particularly under stressful environmental conditions.

For additional guidance on Group 15 herbicides with POST applications, see: "To Spray or Not to Spray a Group 15 Herbicide with Your POST Pass of Enlist One and Liberty?"

Some crop injury should be expected when applying herbicides during periods of elevated temperatures and relative humidity. However, soybean typically grow out of this injury. The risk of delaying applications is currently greater than the risk of temporary crop response. Delaying applications too long can allow waterhemp to become more difficult to control, crops to exceed labeled growth stages, and larger crop canopies to intercept more of the spray before it reaches target weeds.