Don’t Let Deceptive Weeds Compromise Your Customers’ Herbicide Control

A primary directive for effective postemergence control has long been to spray when weeds are small: 4 inches or less.

This is especially true when targeting fast-growing, hard-to-control weeds like waterhemp, Palmer amaranth and giant ragweed. 

When the weather is favorable, waterhemp can grow 1 inch per day and can reach 4 inches in height very quickly. Palmer amaranth can grow up to 2.5 inches per day and quickly become difficult to control. Early season scouting is vital, so the weeds can be sprayed with postemergence herbicides before they reach the recommended height for effective control. Weeds can go from manageable to out of control in a few short days. Sometimes the window to identify and spray it is only about a week, which can be hard to manage during the busy spring season.

Not only do weeds grow quickly but also their heights can be deceptive. A weed that measures 8 inches in the field could, in fact, be much larger from the herbicide point of view.

“Once weeds reach 6 inches in height, they begin to branch out,” explains Dennis Holland, market development specialist for Corteva Agriscience. “Each side branch has multiple growing points, and the more growing points, the greater the potential for the weeds to survive a herbicide application.

“A single branch may have eight or 12 growing points. When you break the branches of an 8-inch weed and lay them end to end, you and your herbicide are facing a 30-inch or even larger weed. That makes control more difficult.”

Weeds larger than 3 to 4 inches are more likely to survive a herbicide application, especially when conditions are less than ideal during application (e.g., issues with rate, coverage, temperature, time of day). 

Holland reiterates the importance of controlling weeds when they are small and shares these reminders for successful in-season weed control:

1. Scout Early and Often
   Rapidly growing weeds can quickly become out of control, particularly during the busy early planting and application season.
2. Use Full, Labeled Herbicide Rates
   It’s important to use full, labeled herbicide rates for effective weed control. Skimping on herbicide rates gives weeds a chance to survive and increases the potential for resistance to develop. By following the labeled herbicide rate and making timely applications, you’ll be able to better control the most difficult weeds.
3. Control Weeds When They’re Small and Actively Growing
   Weeds grow fast. When they’re less than 6 inches tall, they have fewer growing points for herbicides to target and control. Weeds growing actively are absorbing moisture and other nutrients from the soil and systemic herbicides will be able to translocate to the targeted growing points, which is another reason spraying when weeds are small is important. Enlist^® herbicides are systemic herbicides, which means they are absorbed and work to kill the entire weed.
   
   Weed seeds are always present in the soil, and seedlings are easier to control compared to emerged weeds.  So be sure to include residual products in your post-pass.  Herbicides with residual soil activity will allow fewer weeds to emerge and will keep the field weed free until crop canopy.
4. Follow Label Directions to Achieve Optimum Coverage
   Successful weed control requires quality, on-target application. Review the label or product use guide when setting up the sprayer for details on the right nozzles, pressure and boom height. To help minimize spray drift potential, maintain the boom height specified by the nozzle manufacturer — usually 24 inches or less above the crop canopy.

Following burndown, Enlist Duo^® and Enlist One^® herbicides with Colex-D^® technology are the only herbicides containing 2,4-D that are authorized for preemergence and postemergence use with Enlist^® crops. Consult Enlist^® herbicide labels for weed species controlled. Enlist Duo and Enlist One herbicides are not registered for use or sale in all states and counties; are not registered in AK, CA, CT, HI, ID, MA, ME, MT, NH, NV, OR, RI, UT, VT, WA and WY; and have additional subcounty restrictions in AL, GA, TN and TX, while existing county restrictions still remain in FL. All users must check “Bulletins Live! Two” no earlier than six months before using Enlist One or Enlist Duo. To obtain “Bulletins,” consult epa.gov/espp/, call 1-844-447-3813, or email ESPP@epa.gov. You must use the “Bulletin” valid for the month and state and county in which Enlist One or Enlist Duo are being applied. Contact your state pesticide regulatory agency if you have questions about the registration status of Enlist^® herbicides in your area. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. IT IS A VIOLATION OF FEDERAL AND STATE LAW TO USE ANY PESTICIDE PRODUCT OTHER THAN IN ACCORDANCE WITH ITS LABELING. ONLY USE FORMULATIONS THAT ARE SPECIFICALLY LABELED FOR SUCH USE IN THE STATE OF APPLICATION. USE OF PESTICIDE PRODUCTS, INCLUDING, WITHOUT LIMITATION, 2,4-D-CONTAINING PRODUCTS NOT AUTHORIZED FOR USE WITH ENLIST CROPS, MAY RESULT IN OFF-TARGET DAMAGE TO SENSITIVE CROPS/AREAS AND/OR SUSCEPTIBLE PLANTS, IN ADDITION TO CIVIL AND/OR CRIMINAL PENALTIES. Additional product-specific stewardship requirements for Enlist crops, including the Enlist Product Use Guide, can be found at www.traitstewardship.com.