Saturday, April 20, 2024

Impregnating Fertilizers With Herbicide


In Mid-South cotton, Palmer amaranth and grasses are major concerns when it comes to weed control. Cotton Incorporated is utilizing core funding, as well as Tennessee and Arkansas State Support Program funding, to develop weed control strategies that will benefit Mid-South cotton producers.

One method that is gaining traction in the Mid-South is impregnating fertilizers with herbicide for in-season weed control. Impregnating fertilizer is the act of coating granular fertilizer with an herbicide pesticide with the goal to manage targeted weeds. This practice is nothing new to the cotton industry but has recently found new life in the Mid-South as a practical and efficient weed control method. In this article, we are going to cover a few herbicides that work well within this practice and explore the effectiveness researchers have seen for this weed control practice.

Drs. Larry Steckel, Tennessee Extension weed specialist, and Tom Barber, Arkansas Extension weed specialist, are both looking for ways to control Palmer amaranth and other Mid-South grasses. Their research is exploring impregnating fertilizers rather than using conventional over-the-top spraying or post-directed methods, thus freeing up sprayers for other applications, potentially cutting out a trip across the fields, decreasing crop injury and possibly opening-up new herbicide options for cotton in the future.

New Herbicide Options

Arkansas’ Tom Barber recommends the impregnated fertilizer application method, especially on acres struggling with pigweed control.

Barber has been evaluating impregnated fertilizers for years and said, “I recommend this application method, especially on the acres that struggle so much with pigweed control. Pyroxasulfone needs to be on those acres one way or the other to manage the multi-herbicide resistant pigweed populations.”

Additionally, Barber and other weed specialists across the Cotton Belt have researched numerous herbicides without a current label in cotton for both weed control and crop injury. Although no new modes of action are currently available, this impregnation application could lead to new herbicide options in cotton in the future.   

Steckel has also been researching Pyroxasulfone products (Zidua and Anthem Flex) for several years and has had very good results. He evaluated applying Pyroxasulfone via impregnated fertilizer at 1-2 leaf, 5-7 leaf, as well as the labeled post direct spray at 5-7 leaf with each of these treatments at two different rates, 3.25 fl oz/a + 250 lb/a and 6.5 fl oz/a + 250 lb/a. His overall conclusion was that applying Pyroxasulfone via impregnated fertilizer provides residual control of Palmer amaranth with minimal injury to cotton. He concluded that application at the 1-2 leaf stage or the 5-7 leaf stage are the best options moving forward for increased control of Palmer amaranth.

Best Practices To Follow

Although the Pyroxasulfone-impregnated fertilizer does provide some additional flexibility for applying an effective residual herbicide, Steckel points out several practices need to be followed to ensure a uniform application and effective weed control. First, per the label, a minimum amount of 200 lbs/a is required and a maximum of 700 lbs/a. Steckel observed the 500 lbs/a fertilizer performed better than the 250 lbs/a due to better distribution of the Pyroxasulfone.

Second, the uniformity of the application is critical. Factors that can detrimentally impact the uniform application are wind speed and wind direction, especially wind perpendicular to the row direction. Additionally, the granular spreaders need to be properly calibrated for application rate and uniform distribution.   

Cotton Incorporated’s Director of Agricultural and Environmental Research, Dr. Gaylon Morgan, stated “Cotton Incorporated’s core and state support funding in weed management research and outreach is critical to ensuring balanced and unbiased evaluation of products and application methods. The practice of impregnating fertilizers with herbicides, while proven effective in other regions of the Cotton Belt, is now proving to be a viable strategy for weed control in the Mid-South,” said Morgan.

For more on Cotton Incorporated’s efforts in weed management strategies, visit

Grant Saum is The Cotton Board’s Mid-South Regional Communication Manager. Email him at

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