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Glyphosate 101: Everything Farmers Need to Know About Glyphosate

Sep 29, 2023

This guide includes the following sections:

What Is Glyphosate?

Glyphosate is a non-selective, systemic herbicide that controls grasses and broadleaf weeds. It is an extremely important herbicide in crop production systems because it has high efficacy on non-resistant weeds and is a cost-effective weed control solution for farmers.

Glyphosate is a foliar-applied herbicide that can be applied pre-emergence to most crops or post-emergence to glyphosate-tolerant crops to control emerged weeds. It must contact growing leaf tissue to translocate within a weed effectively; it has no activity on non-emerged weeds.

Mixing glyphosate with effective residual herbicides that control non-emerged weeds can help ensure clean fields for planting and early crop development.

Glyphosate is a weak acid available in different salt formulations, including isopropylamine, ammonium, trimesium and potassium salts. Different glyphosate salts have different molecular weights and acid-to-salt ratios, influencing how concentrated the herbicide can be in the formulated product.

There are also variations in solubility among the various glyphosate salt formulations. Solubility characteristics may impact formulation stability, absorption and translocation in weeds, although there isn’t sufficient research to support a superior glyphosate-salt formulation.

How Does Glyphosate Work?

Glyphosate is a Group 9 amino acid synthesis inhibitor herbicide. It controls weeds by inhibiting a single plant enzyme: 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS). Because this enzyme is crucial for amino acid formation, glyphosate effectively kills weeds by disrupting key protein production pathways required for plant growth and development.

How Long Does Glyphosate Take to Work?

Glyphosate moves through the plant from the point of foliage contact and into the root system. Visible effects on most annual weeds occur within two to four days, but for most perennial weeds such effects may not appear for seven days or more.

Extremely cool or cloudy weather following treatment may slow the activity of glyphosate and delay the development of visual symptoms. Visible effects often include a gradual wilting and yellowing of the plant, which advances to complete browning of above-ground growth and deterioration of underground plant parts.

Generally, weeds will begin to respond to a glyphosate application in days, but it may take weeks depending on the environmental conditions and application practices. Variables affecting how quickly glyphosate is taken up and translocated throughout the target weed can include:

Temperature
Relative humidity
Rainfall following application
Soil moisture
Plant stress
Light availability

University research reports that midday glyphosate applications may improve product performance compared to early morning or evening applications.

Glyphosate Application Best Practices

Glyphosate is only effective on actively growing weeds, so the product works best under conditions that favor healthy plant growth. Heavy rainfall soon after glyphosate application can wash the product off foliage, potentially necessitating a repeat application. The rainfastness interval required will vary depending on environmental conditions, but allowing six hours between an application and a rainfall event is generally a good guideline.

Although glyphosate may persist in the soil for several months, it is tightly bound to soil molecules. Therefore, it has no soil residual activity to control non-emerged weeds.

For long-lasting weed control, glyphosate may be tank-mixed with residual herbicides. Consult the product label for specific tank-mixing best practices.

Glyphosate can be applied before planting, at planting or after planting in most crops, but applications must be made prior to crop emergence. For glyphosate-tolerant crops, applications may be made postemergence up to the V8 growth stage in corn and through the R2 stage in soybeans. Consult the product label for postemergence application guidance for other glyphosate-tolerant crops.

Glyphosate application rates will vary depending on the:

Product
Soil type
Tillage method
Crop
Targeted weed species
Environmental conditions

For example, for AgSaver™ Glyphosate 53.8% broadcast ground applications, general use rate recommendations are 1.5 to 3 pints per acre for annual weeds, 3 to 7.5 pints per acre for perennial weeds and 3 to 7.5 pints per acre for woody brush and trees. A carrier volume of 3 to 40 gallons of water per acre is suggested for broadcast spray applications. Consult the product label for specific application rate guidance.

Adding ammonium sulfate to the tank mix may increase glyphosate performance, particularly when using hard water as a herbicide carrier, under drought conditions or when tank-mixed with certain residual herbicides. Non-ionic surfactants may also improve glyphosate performance, especially for high-water volume applications, tough-to-control weeds, adverse environmental condition applications and managing weeds under stress.

Glyphosate Resistance Management

Because of glyphosate’s wide use in agricultural production for several decades, some weed populations have developed herbicide resistance. This happens when weed populations with natural genetic tolerance to glyphosate are not effectively managed with non-glyphosate herbicides, allowing the herbicide-tolerant weed populations to multiply in fields over time.

The International Herbicide-Resistant Weed Database reports that worldwide, 58 weed species are resistant to glyphosate.

Glyphosate herbicide-resistant weed populations will continue to expand. You must be thoughtful in your weed management strategy to get effective weed control if resistance is a problem in your fields.

Here are a few tips to help manage glyphosate weed resistance:

Make timely herbicide applications when weeds are 4” or smaller
Use multiple modes of action
Use layered residuals to extend the window of weed control
Add effective adjuvants to improve spray performance and plant uptake
Scout fields after applications to verify the application was effective
Add cultural or mechanical weed control practices, including tillage

Glyphosate Safety Guidelines

While glyphosate is relatively safe from a toxicity standpoint, applicators should still use best safety practices when using the product.

Do not enter treated areas during the four-hour restricted entry interval (REI) or until the spray solution has dried.
Wear appropriate personal protective equipment, including a long shirt, pants, and close-toed shoes when handling glyphosate.
Wash your hands after handling the herbicide and remove clothing and PPE immediately if the product gets inside.
Follow all label instructions to ensure the safe use of glyphosate.

Keep glyphosate containers closed to prevent spills and contamination. Store above 5°F

to keep the product from crystallizing while in storage. Crystals will settle to the bottom; if you observe crystallization, place the product in a warm room (68°F) for several days to redissolve and roll or shake the container to mix well before using.

Dispose of glyphosate waste in a landfill approved for pesticide disposal or in accordance with applicable federal, state or local procedures. Emptied containers retain vapor and product residue. Observe all labeled safeguards until containers are cleaned, reconditioned, or destroyed.

Branded vs. Generic Glyphosate Products

The initial patent on glyphosate (Roundup^®) has expired, so many generic glyphosate alternatives are available that come with substantial cost savings.

A generic crop protection product is manufactured and sold by a company other than the original manufacturer but contains the same active ingredient(s) (A.I.). Generic chemicals usually enter the market 12 -20 years after the initial discovery of the active ingredient(s) once the original product’s patent expires. From a regulatory standpoint, generic versions of branded products must have the same A.I. components to be registered by the government regulator.

Whether you’re purchasing branded or generic glyphosate products, it’s important to consider each formulation's acid equivalent (a.e.). Acid equivalent information should be visible on the herbicide label in the ingredient statement section. A higher acid equivalent formulated product will require lower application rates, impacting storage requirements and application efficiency.

Some products may also contain additives, such as surfactants or other adjuvants, that can help increase spray efficacy. So, even if active ingredients are identical between two products, inert additives in a formulation may improve product performance.

While Roundup^® is a brand-name glyphosate product, there are also many generic alternatives, including AgSaver™ Glyphosate 53.8% and Willowood Glypho 6.

For more information, read the blog post “Understanding Branded vs. Generic Crop Protection Products.”

Generic Glyphosate Quality Assurance

To ensure FBN^® product efficacy and performance is as good or better than branded glyphosate, we invest millions of dollars every year conducting laboratory (stability studies, physico-chemical testing like viscosity, pH, density, etc.), formulation testing (e.g., emulsion stability, persistent foaming, pourability, suspensibility, etc.) and field trials comparing an FBN product to its branded counterpart.

You can trust you’ll get comparable field performance compared to name-brand glyphosate alternatives at a fraction of the cost.

Buy Glyphosate from FBN Direct^®

Interested in purchasing glyphosate at a cost savings? FBN Direct carries AgSaver™ Glyphosate 53.8%, an isopropylamine salt formulation and Willowood Glypho 6, a potassium salt formulation available in bulk tote sizes.

For a complete weed control solution, you can purchase common glyphosate tank mix partners, including residual herbicides and AMS water conditioners, through FBN Direct for even more cost savings.

With a convenient online platform, transparent pricing and direct-to-farm delivery available on your schedule, FBN Direct puts Farmers First^®.

Related Resources

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FBN Network

Sep 29, 2023