The Titan Blog

Optimizing Post-Emergence Weed Management

Al Erickson
April 27, 2018

Recognizing the Threat of Yield Loss
Weeds compete for yield at early stages of development in corn and soybeans, stealing dollars at harvest. Money spent on the highest-yielding varieties of corn and soybeans is essentially wasted if weed infestations can’t be controlled timely throughout the season. In fact, yield hits stemming from poorly-timed weed control can be largely invisible. You never even know you lost those bushels.

Understanding Your Weed Resistance
Rotating a single site of action is no longer an effective strategy. Tank mixing herbicides with different sites of action is the best management tool in fighting resistance. In continuous crop systems with two applications and one site of action, resistance can lead to weed control failure in as little as two years. By comparison, the addition of a herbicide with two effective sites of action can delay resistance for 18 to 20 years. Weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides. Understanding your weed resistance will narrow herbicide choices to build confidence in product performance and maximize your return on investment. The challenge is, which herbicide is the most effective for my weed spectrum without knowing the state of my weed resistance? 

The International Survey of Herbicide Resistant Weeds is a collaborative effort between weed scientists in over 80 countries. Their purpose is to maintain scientific accuracy in the reporting of herbicide resistant weeds globally. This collaborative effort is supported by government, academic, and industry weed scientists worldwide. As resistance continues to evolve, check the website periodically for new cases added to your states’ log. Go to the International Survey of Herbicide Resistant Weeds and follow these easy steps to provide information for your region:

#1. Click on the drop down menu to list your state.
#2. Click on GO to generate a chronological list of cases validated by local weed scientists.

If a herbicide premix has two active ingredients with two different sites of action, but your target weed is resistant to one of the active ingredients, you no longer have two effective sites of action. Furthermore, you’re not realizing maximum return on investment on that premium valued tank mix combination. Once you’ve determined the state of weed resistance for your region, go to the Herbicide Classification Chart for more information on matching herbicides to the most effective sites of action.

Selecting the Best Performing Herbicides for My Weeds
Once you’ve identified herbicides with the most effective sites of action, use weed guides to find herbicide performance ratings by crop, product, and weed species. The 2018 Weed, Disease, and Insect Management Guide is a result of replicated and randomized trials across multiple locations and years of data. These herbicide ratings do not include the current status of weed resistance for each state or your region. However, ratings combined with confirmed cases of weed resistance can give you the most effective herbicide options to protect your yield for maximum ROI.

Optimizing Herbicide Application
Adding herbicides into the tank in the correct order is critical to ensure herbicide compatibility isn’t compromised. Generally, following the WALES acronym is a good way to remember the mixing order of products. Review adjuvant recommendations when tank mixing. Usually, a maximum corn size is specified which can be based on growth stage or corn height. Herbicides should be applied when weeds are less than four inches tall to ensure that risk of yield loss from early weed interference is minimized. Use a residual tank mix partner and remember to always read the label and follow directions.

Tank mixing herbicides with different sites of action is the best management tool in fighting resistance.