Harvest provides a great opportunity to give a final grade to our weed control program and take note of what we might need to adjust next season. Weeds continue to evolve and adapt to current herbicides and practices, and we also must learn how to evolve as to what tweaks we can employ to achieve our goal of weed-free fields at harvest. As you assess your current technology and strategy, below are some key learnings from our Practical Farm Research (PFR)® sites this past season to keep in mind as you make decisions for 2022.

1. DICAMBA VS. 2,4-D SOIL ACTIVITY AND BURNDOWN

The most consistent management practice associated with high-yielding soybeans is to plant early. However, planting early also requires early weed control. Not only are existing weeds typically more difficult to kill when temperatures are cool, but preventing weed emergence is also more challenging because soybeans are often not growing vegetatively as rapidly to create shade and provide competition to weeds within the seed bank.

Dicamba-containing herbicides will provide significantly more soil activity than 2,4-D-containing herbicides. Intuition tells us weeds provide competition for sunlight, nutrients, and water. However, recent research has found the most critical period for weed control is the earliest days, before “competition” exists. Dicambacontaining products, such as Engenia® or XtendiMax®, can provide up to 14 days of soil activity but must be paired with an approved residual herbicide for seasonlong weed control. This soil activity is also an important element as to why many successful fall herbicide recommendations include dicamba-containing herbicides such as Weedmaster®, Brash®, etc. Many residual herbicides have very limited burndown activity. Engenia® or XtendiMax® will help to increase burndown efficacy, especially on marestail. While Enlist® herbicides may not provide the burndown consistency of dicamba, the inclusion of an additional SOA (site of action), such as Sharpen® or Gramaxone®, will provide more complete marestail burndown.

2. CEREAL RYE: SEEDING RATE IMPACT ON WEED SUPPRESSION

Arguably, the most effective herbicide on the market today is not one that comes from a jug; it’s shade. Cereal rye and cover crops provide numerous soil benefits at various seeding rates. However, higher seeding rates lead to increased shade or competition to more effectively minimize weed emergence and thus reduce pressure on the post-emergence herbicide. By increasing from 30 to 60 lb./A. of cereal rye, waterhemp emergence was reduced by 64%. This shading will similarly impact other weeds as well, particularly marestail. However, increasing from 60 to 90 lb./A. did not further reduce weed emergence. Cover crops require a systems approachbalancing crop stand establishment, minimizing pests, as well as weed control. While lower seeding rates can positively impact soil health, more moderate rates will further impede weed emergence.

3. 2022 LIBERTY® SUPPLY

As Liberty continues to replace or supplement glyphosate in many postemergence programs, demand grows. 2021 brought about supply challenges for numerous products for various reasons. However, BASF has made significant changes in an attempt to meet the growing demand for Liberty herbicide.

• Increased the number of suppliers of inert ingredients
• Increasing storage of inert ingredients
  • Transportation and the late Texas freeze made for a shortage of the inert ingredients
• Increasing overall production as well as the number of production sites

Please communicate your usage intentions to your supplier as soon as your 2022 plan is developed.

~ Luke Schulte, CCA – Field Agronomist