NDSU Extension - Mercer County


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Maximizing Glyphosate Efficacy - Best Management Practices

glyphosate, weed control

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

Planting has finished across the county. With the rainfall last week plant development is rapidly occurring, on the other side so is weed development. Spraying season will be in full swing in the next few weeks and one of the most popular chemicals being used for weed control will be glyphosate. Glyphosate comes in many different types of formulations so producers need to understand the type of glyphosate product they are using. The article below provides information on how to use the product correctly.

Most crops are planted and growers will now shift their attention to controlling weeds. Understanding the factors that influence glyphosate performance, especially with glyphosate resistant weeds, will maximize efficacy.

Glyphosate concentration in formulation: Glyphosate products are formulated in many different acid-equivalent concentrations. Concentration, measured as acid equivalent, will determine your use rate.

Use full-labeled rates: the rate to use is determined by the size and type of weed species in the field. In general, the bigger the weed species, the higher the use rate needed for control. Annual weeds are best controlled when they are in an early growth stage, actively growing, and less than four inches tall.

Larger and older weeds are more difficult to control: More mature or hardened-off annual weeds may require full rates, even if they are smaller. Environmental stress, such as dry weather, can cause weeds to be short for their age, requiring a higher rate for good control.

Be aware of glyphosate resistant weed species: Weed species differ in their sensitivity to glyphosate. Some weed species have natural tolerance to glyphosate, while others are resistant and control is unlikely regardless of the application rate. Tank-mixing herbicides with different modes of actions along with weed resistance management practices can help to provide consistent control of tolerant or resistant weeds. Using lower than labeled rates can lead to poor weed control and potentially select for resistant weeds.

Always add nonionic surfactant at 0.25 percent v/v to fully loaded formulations (unless the label prohibits), especially to improve common lambs quarters control, at 0.25 to 0.50 percent v/v to partially loaded formulations, and at 0.5 to 1.0 percent v/v to non-loaded formulations. Surfactants increase spray solution spreading on leaves, improving plant uptake and translocation of glyphosate. Addition of crop oil concentrate or methylated seed oil is not recommended with glyphosate.

Always add ammonium sulfate (AMS) at 8 lb. /100 gallon, or liquid AMS at 2.5 gallon/100 gallon water to increase penetration into the plant for weed control and to condition hard water. AMS reduces the antagonistic effects of hard water.

Spray volume and droplet size matter: Glyphosate alone spray volumes of 5-10 gallons per acre (GPA) provides adequate coverage of weeds. Higher volumes (10-20 GPA) can be beneficial in situations with dense weed infestations, well-developed crop canopies, large weeds and when applying in combination with contact or soil residual herbicides. Coverage can also be optimized by nozzle selection.

Source: Tom Peters - Extension Sugarbeet Agronomist - NDSU & U of MN

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