Weed Burndown Before Soybean Planting

One of the many constants in crop production is this: weeds will be present before soybean planting, and those weeds will need to be controlled so that planting is done in a weed-free seedbed. Weed burndown before planting requires knowledge of the weed species present in a field, and which herbicide or herbicides will be required to eliminate those weeds.

The decision about which herbicide or herbicides to use is now more complex because of the resistance to herbicides that has developed in many of the common Midsouth weeds. Drs. Tom Barber and Tommy Butts, Univ. of Arkansas Ext. Weed Scientists, recently posted an article titled “Herbicide Selection for Winter Weed Burndown Amid High Prices and Product Shortages” that offers valuable guidelines for weed burndown options in the face of herbicide-resistant (HR) weeds, plus high herbicide prices and potential shortages. Major points covered in the article follow.

•   Use of a paraquat-based system when marestail is present;

•   Controlling glyphosate-resistant (GR) Italian ryegrass with clethodim (Select Max) as a major component [see “Management of Italian Ryegrass in Agronomic Crops” (Univ. of Arkansas publication FSA2191) for additional information];

•   Including a residual herbicide as a component of early burndown applications;

•   Use of Reviton herbicide as a component of a burndown mixture;

•   Keeping abreast of air temperature at time of application since most herbicides are not very effective when applied during a period with cold temperatures.

Dr. Jason Bond posted an article in Delta FarmPress titled “Managing Italian Ryegrass in Mississippi Soybeans”. Information in this article can be used to supplement that in the above-cited Univ. of Arkansas articles when dealing with GR Italian ryegrass in the fall and spring. This article is especially important pertaining to the development of Italian ryegrass populations that are resistant to clethodim, and the use of fall and spring tillage to control this weed prior to planting.

Knowledge of the plant-back interval following the use of particular herbicides must be considered where soybean will be planted following herbicide burndown of weeds. This information can be found in Univ. of Arkansas publication MP 519 and in the label for a particular herbicide.

As stated above, the choice of burndown herbicides for use in 2022 is confounded by both HR weeds and by high herbicide prices and potential shortages. Nevertheless, producers can still devise an effective weed burndown program using the information in the above articles and in consultation with Extension personnel and industry reps.

Composed by Larry G. Heatherly, Feb. 2022, larryh91746@gmail.com