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closeup of hands holding waterhemp
PROLIFIC PRODUCER: Waterhemp generally produces 250,000 seeds or more per plant — a good reason to kill this weed before it goes to seed.

Weed control: What went wrong and why?

Learn to correctly identify a herbicide application issue.

Farmers know the frustration and fear that comes with seeing weeds standing smugly in the field following herbicide application. It can be difficult to pinpoint what exactly went wrong. Was it something you did? Was it something you didn’t do? Could it be weed resistance?

Determining what caused weeds to escape a herbicide application can be challenging, but it is important to get to the bottom of it to ensure ultimate protection against weeds going forward, says Corey Klaphake, agronomy technical specialist with West Central Distribution.

The burndown timeline depends on which herbicides were applied, he says. Herbicides like glyphosate or contact herbicides typically end in plant death in seven to 14 days. Synthetic auxin herbicides, such as dicamba, can take two to four weeks for weeds to fully die. Often, weeds sprayed with translocated herbicides like dicamba may look alive, but symptoms such as twisting stems or no new growth can indicate that the application was successful.

Causes of escaped weeds
Many factors can play into herbicide efficacy. Environment and weather conditions can affect your herbicide applications negatively if they are not optimal for spraying, Klaphake says.

High humidity and temperatures between 65 to 85 degrees F are ideal for herbicide applications. Conditions that are too dry and too hot can lead to spray droplets drying before the chemical can be absorbed. If weeds are exposed to low moisture and humidity for an extended period, it can also reduce penetration if the weeds harden off.

Another consideration is the cold. Cold weather makes it difficult for weeds to absorb the herbicide. It also slows weed growth and hardens cell walls, decreasing both herbicide uptake and translocation and reducing weed control. When making early-season applications, it’s important to keep this in mind to ensure that it’s not too cold to be effective.

When using a contact herbicide, your risk of escaped weeds can be greater if the application is not done properly, Klaphake says. Since weeds will only be affected where the herbicide comes into contact, it’s crucial to target small weeds, as well as increase spray coverage by applying with spray volumes of 15 to 20 gallons per acre and using a nozzle recommended by the product label.

Improper herbicide and equipment use can hinder herbicide efficacy and lead to weed survival. When applicators go off label, it increases the possibility of an ineffective application. Factors such as weed size, spray volume, boom height, tank-mix partners and nozzle use all play a role in the success of the herbicide application.

Solutions for escaped weeds
“Determining your next move after seeing weeds in the field following herbicide application depends on what caused the plants to survive,” Klaphake notes. “Working with your agronomist to evaluate the situation will help identify factors that could have led to an ineffective herbicide application.”

If it seems to be caused by weed resistance, you should look into using herbicides that have different modes of action that are still effective on your particular weed species, he says. If no options are available or labeled for that timing, this may require cultivation or hand-weeding, as the most important response to weed escapes is preventing the weeds from going to seed. Once weeds begin to seed in your field, it could magnify the situation and lead to contamination of surrounding fields.

Weed presence could also be caused by weather conditions, equipment misuse or another environmental factor. A second application would be appropriate for this case.

Using multiple modes of action and correct adjuvants can optimize herbicide performance. West Central Distribution offers a high-efficacy adjuvant, called Last Chance, which can increase herbicide efficacy and help prevent escaped weeds in your field.

“Last Chance is a surfactant and deposition aid. This product works to improve herbicide performance by maximizing uniform coverage, increasing wetting and providing strength to penetrate through waxy or weather-hardened cuticles,” Klaphake says. “It’s important to make sure you’re getting the most out of your herbicides. Exploring the different tank-mix partners that can assist with that is well-worth it and can lead to great results.”

Proactively prevent escaped weeds

The best way to ensure herbicide efficacy is by working with your agronomist to find the product that best fits your needs and following the label.

The label helps you identify optimum conditions, equipment specs and approved adjuvants to get the most out of the herbicide and produce consistent results.

Depending on geography, it may be beneficial to apply herbicides in the fall to take care of winter annual weeds, especially in no-till situations, says Corey Klaphake, weed management specialist with West Central Distribution.

The other option to control these winter annuals is with a spring burndown. Attempting to control winter annual weeds with in-crop applications is not a recommended practice.

Preemerge residual herbicides should be used in all geographies to take pressure off the post-application, he adds. Layering another residual herbicide with your post-application is also recommended to prevent weeds from emerging until canopy closure.

“Doing your due diligence in choosing the best product for your field, following the herbicide label, using tank-mix partners to increase efficacy and considering conditions before making applications will maximize your herbicide applications and, in turn, increase weed control in the field,” Klaphake says.

Source: West Central Distribution

TAGS: Herbicide
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