Menu

Pre-emergent Herbicides: Will They Still Work as Normal?

With the nice spring, some farmers worked the ground ahead of time but were waiting to plant corn. Then considerable portions of South Dakota received some much needed moisture this past weekend. In many cases some weeds germinated before the pre-emergent product was applied after planting. Most pre-emergent products need about ½ to ¾ inch of moisture to be activated once they are applied. Once this happens, the product is able to kill the weeds.

Effectiveness on early emerging weeds
If weeds germinated before the pre-emergent was activated there may be some weeds that will continue to grow and will need a post-emergent treatment to control them before they get too large. Some pre-emergent products do have the ability to kill some small emerged weeds (kick back). Atrazine is the active ingredient with the largest window to control emerged weeds.

To see if your product does have kick back control check the product label. If not, consider applying a burndown with the pre-emergent to take out emerged weeds, or consider doing one more tillage pass before planting.

Post-activation considerations
Remember that once the product has been activated it will start to control germinating weeds and should work as normal from this time forward. In most cases no chemical is lost waiting for activation, and even if the field had temporary flooding the product is usually still present. In all cases read the label for more information on how your product works. Do not add more of the same product to the field unless it is recommended as this may cause crop injury.

Pest Management Guides

For more information on herbicides labeled for use in South Dakota, consult the following resources:

Source: Paul O. Johnson, South Dakota State University 

Recent News

Managing Corn Tar Spot in 2020
6/4/2020

It’s early in the season, but before we know it, corn will be chest high and we will be thinking about if in season management is needed.  Last year I mentioned that you should “avoid the cosmic freakout” around tar spot.  I again emphasize this statement this season.  Tar spot is endemic to the state […]

Prevent Plant 2020
6/3/2020

Some Illinois corn acres are still unplanted due to wet weather. The final plant date for crop insurance has passed for extreme southern Illinois (May 28) and is rapidly approaching for the rest of Illinois (June 5). After the final plant date for corn, farmers who purchased the COMBO crop insurance product can take a […]

Soil Residual Herbicide Options after Corn Emergence
6/2/2020

Application of soil residual herbicides is important because they deliver a few weeks of residual weed control and aid in weed resistance management by incorporating additional site(s) of action in herbicide program. Several residual herbicides can be applied after corn emergence without injury to corn. A Few important factors should be considered when addressing weed […]

Your browser is out-of-date!

Update your browser to view this website correctly. Update my browser now