Optimizing Post-Emergence Weed Management

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.

Value of a Pre-emerge Herbicide

Dr. Aaron Hager, Weed Science – University of Illinois states, “The key to winning the battle of the weeds is not looking for another herbicide to spray on it after it’s emerged. We’ve lost that battle. We will continue to lose that battle. We need to focus all of our attention on targeting the weakest stage of the life cycle of plants. That’s the seed.”

Weed Competition to Yield

University of Minnesota trials in 2014 showed corn yields suffered by 40 bu./acre when weed control was delayed by just five days beyond the optimum time for removal. In 2015, trials at the University of Nebraska, a broad-spectrum, soil-applied herbicide pushed the post weed control timing in soybeans to V5, a gain of three to four leaf stages for effective post-emergence weed control. The pre-emerge herbicide bought 16 to 21 days.

Understanding weed physiology and timing of emergence is important to stage the proper pre-emerge herbicide. The following resource, Weed Emergence Sequences, indicates giant ragweed emerges several weeks before the average corn planting date. Field history of giant ragweed without a pre-emerge herbicide could reduce corn and soybean yields due to early competition. In Ohio, a single giant ragweed plant every 3 ft. caused approximately 65% yield loss in corn and an 80% yield loss in soybeans. A well-targeted pre-emerge herbicide cuts down the density and variety of weeds that have to be controlled later. They will also be smaller and more uniform in size, allowing them to be targeted at a vulnerable seedling stage. Without a pre-emerge, a wider range of weed sizes and species make it difficult to get consistent weed control. In fact, yield losses stemming from poorly-timed weed control can be largely invisible. To buy more days for profitable weed control, apply a pre-emerge residual herbicide.

Selecting Effective Pre-emerge Herbicides

Initial weed resistance began with individual populations becoming resistant to the frequent use of specific herbicides at the population level. Without changes in herbicide use patterns, weeds became resistant to multiple herbicide groups at the individual level. This is called stacked resistance. The challenge is, which herbicide is the most effective for my weed spectrum without knowing the state of my weed resistance? To identify herbicides with weed resistance, use the International Survey of Herbicide Resistant Weeds. The following easy steps will provide information for your region:

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

This list of individual cases of weed resistance is essential to narrow herbicide options to the most effective choices. Weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides. The purpose of this survey is to monitor the evolution of herbicide-resistant weeds and assess their impact. The site is a global collaboration between weed scientists with a common goal of understanding, preventing, and managing the occurrence of herbicide-resistant weeds. There are currently 559 cases of herbicide resistant weeds in the United States.

Once weed resistance for specific herbicides is identified in your region, use the Herbicide Classification Chart, to select an effective pre-emerge herbicide for your weed spectrum for maximum return on investment. Always read the label and follow directions.

Summary

Profitable crop production begins with a pre-emergence herbicide to start clean and protect yield. While unsteady commodity prices may tempt your customers to lower their investment in weed control, allowing crops to compete with weeds will steal dollars at harvest. Once weeds rob yield, growers can’t get it back. Don’t delay weed control with a post only herbicide plan. 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.

To Use Dicamba or Not To Use Dicamba

Even if you are planting RR2 Xtend® soybeans, the answer to this could be “I’m undecided.” Some growers are planting RR2 Xtend® soybeans in 2017 and using their existing herbicide plan without dicamba. These growers are willing to let first year experiences improve their knowledge base for dicamba use in 2018. However, there are good reasons to use dicamba in a preplant or postemergence program. The increasing spread of herbicide-resistant weeds have lowered the performance of many herbicide programs.

Consider some of the following before integrating dicamba into your Xtend® soybean system:

Be sure to read and understand the dicamba labels and stewardship guidelines. Assess fields now to determine if some should not be treated with dicamba due to sensitive surroundings. Other fields may be at risk from frequent wind direction on the day of application.
While we use the term “dicamba” throughout this discussion, only three dicamba products are labeled for use in Xtend soybeans: XtendiMax, FeXapan, and Engenia. Use of other dicamba products is an off-label application.
Some growers will be planting non-Xtend and Xtend soybeans. If dicamba use is a planned program, ensure that planters are cleaned out before switching seed traits and dicamba is applied to the right fields.
Each of the labeled dicamba choices have frequently updated websites listing new approved tank mixes, adjuvants and nozzles. You are required to check the label within 7 days of application for any changes or updates.
If you’re planning to use a custom applicator for dicamba applications, be aware that some will not be spraying dicamba on soybeans this year. Other applicators may have higher rates for dicamba use.
Consider your weed spectrum and compare weed control ratings between dicamba and your current herbicide choices. Also, acknowledge weed resistance to certain herbicide groups in your area. Dicamba has excellent control ratings for marestail, giant ragweed, and waterhemp.
Your current herbicide program may be effective. However, using dicamba could reduce the selection pressure for resistance to certain herbicides due to their continuous use or overuse. An example of this is the reliance on HG14 herbicides (Valor, Flexstar, Cobra/Phoenix) for weeds that are resistant to glyphosate and ALS inhibitors. Continued use of HG14’s is pushing weeds to become resistant to 32 herbicides used in corn and soybeans. Substituting dicamba for fomesafen or Cobra in the postemergence treatment can sustain many of the other HG14’s.
Dicamba may be more cost effective versus postemergence combinations of glyphosate + fomesafen (Flexstar etc.).
Dicamba can be a better and more consistent herbicide in preplant burndown. There are no plant back restrictions if your using an approved dicamba on Xtend soybeans.
Keep in mind that failure to use any new technology judiciously can result in selection for resistance and possibly reduce their utility rapidly.

Protect Yield with a Crop Protection Plan for 2017

Knowing which seed and herbicide selections performed best this year will help you plan effectively for next year. You’ve evaluated seed choices and crop protection plans, scouted your fields, and kept a close eye on the yield monitor during harvest. Now you can record what you’ve learned and use that information to move forward to the decision-making process that lies ahead.

1) Observations at the end of the season are critical for 2017

Review the performance of this year’s herbicide and disease protection program in your fields. A well-planned crop protection program proves valuable at harvest. Each year brings different challenges. Observations over several years establishes potential for consistently higher yields. Many of the highest yielding soybeans are those that were planted into clean fields. Starting clean helped them overcome early season competition that resulted in lower yields.

Your weed, disease, and insect challenges from 2016 should connect to your seed choices for 2017. If you grow conventional corn and saw major weed escapes during harvest, a change in herbicide modes of action may be right for your system.

2) Know YOUR challenges and prepare for 2017

Today’s diversity of pest challenges between production systems demands a customized script for each grower. Proactive planning gives you the best chance of overcoming your competition on your farm in 2017. The pest influences that hindered your crop yield in 2016 are likely to return or intensify in 2017. Reacting to challenges as they happen can mean “too little too late” after bushels are lost and profitability is reduced. Your Trusted Advisor at Tian Pro can help you build a crop protection plan based on what’s right for YOUR acres.

An effective herbicide program includes layered residual control and multiple modes of action. This eliminates gaps in weed control and safeguards against resistance development. Foliar health programs should include a fungicide that provides broad-spectrum, residual control. A product that offers curative and preventive activity will provide maximum return on investment.

3) Work with Titan Pro as YOUR Premier Partner

Today’s grower realizes that seed selection and crop protection products are part of a comprehensive approach to higher yields. Your team at Tian Pro partners to provide unbiased broad based solutions tailored to your specific needs. The complexity of avoiding threats to increase yields demands the understanding of how one product selection affects another. Prioritizing yield potential during your seed selection may come at the expense of disease susceptibility. Titan Pro will collaborate on a disease control programs that maximizes return on investment and increases your crop potential.

4) Summary

Following through with the plans you make is just as important as making them to begin with. You can plant the best seeds on the market, but unless you are committed to safeguarding that genetic potential, you may not reap the benefits you expect.