ASK THE AGRONOMIST BLOG

The last several weeks we’ve seen soybean fields throughout the Midwest under assault. Indiana and Illinois are dealing with historic levels of phytophthora and fusarium (sudden death syndrome). The southern Corn Belt has been dealing with soybean cyst nematodes and dry weather. The central Corn Belt is experiencing extremely wet, saturated conditions that have created difficult growing conditions.

With all of these issues, how should growers approach the challenges that this year brings to produce a viable, healthy crop?

The first step is to spend time in fields observing exactly what is happening with the crop. One mistake growers make is when they see their neighbors spraying and automatically think that they should jump in the sprayer as well. Not all issues can be addressed through chemical means, and knowing the condition of one’s own crop is paramount in designing a course of action.

The second step is to rely on research and not marketing. It is tempting to see a problem and want to apply the newest, greatest product to promote pod fill and retention; however, those products are not always warranted and certainly not always financially feasible. Understanding thresholds for insects and diseases can provide just as much return on investment as spraying the right insecticide or fungicide in a timely manner.

The third step should always be experimentation. I think it is always a good idea to leave an untreated check, or a treated check, in a field and mark the check and then harvest separately. This will provide you with on-farm knowledge about the rescue treatment and how the practice actually worked on your farm. Having this information can prove to be invaluable in subsequent years when the decision needs to be made on a larger scale.

The final thing I encourage is to remember these issues to help make decisions for next year’s crop. For example, a field that had SDS in 2018 should become a candidate for rotation in 2019 and late planting in 2020. Recognize that some issues are dependent on weather. However, water mold type issues and SCN are field-level problems that do not go away with the passing of time. Learn how to better manage these soils to mitigate the annual problems of these types of pests.

If you need help in this process, contact your Stine regional sales agronomist for strategies that can help you maximize this year’s crop and plan for a bigger harvest in the future.

A recent article published by Purdue University Extension titled “Soil Applied Herbicides and Rainfall for Activation” reminds farmers about how soil-applied chemistries can either work or fail depending on the amount of rainfall fields receive after application.  

Much of the Corn Belt is busy planting corn and even soybeans, so sprayers are not far behind with pre-emerge-type chemistries to control weeds during the early growing season. Residual herbicides (soil-applied or pre-type chemistries) work the same way; they require moisture for full activation and then act on emerging weed seedlings in some way. What really needs to happen for the herbicides to be successful is for the chemistry to be mixed with water in the soil and spread out to form a blanket of protection that weed seedlings must grow through. However, sometimes they fail to work.

Consider these contributing factors:

1. How much water does it take for the active ingredient to mix into the soil solution and become the barrier it is intended to be? We refer to this as water solubility. Not all chemicals react the same, so you need to know and understand the solubility of your particular chemistry.
2. How sensitive are weeds to the active ingredient? Again, not all chemicals are the same; some are better at controlling grasses, while others specialize in broadleaves. Knowing this simple characteristic about your chemistry is important.
3. What is the lethal dosage for my particular active ingredient? While this factor is not widely known and published, weeds grow so fast in certain conditions, or soil is moved because of erosion, that weeds do not take in a lethal dose or enough of the active ingredient to kill the seedling.

Purdue University Extension created a table referencing known water required for activation of soil-applied chemistries. I recommend growers take a look at this table before getting the sprayer out this growing season. Growers can also reach out to their local Stine agronomist for additional guidance.