By Roy A. Ulrich, Technical Agronomist, DEKALB and Asgrow, Southern Ohio
At the mid-point of the 2023 growing season, we have the opportunity to look back at the spring to evaluate the management practices left to employ during the remainder of the growing season. Did the weather put in jeopardy the success of this crop by raining too much? Not raining enough? Can we mitigate the potential impact of those stresses? And, weed control and nutrient deficiencies are timely topics regardless of how the weather has impacted your plans.
Over the last several years, tall waterhemp has continued to expand across the state. There has been more tall waterhemp visually evident late in the growing season poking out of the canopy in soybean fields. Tall waterhemp, like most other weeds in the pigweed family, requires warmer soil temperatures to germinate, so the weeds aren’t present until after our spring-applied residuals start to break down. Once emerged, tall waterhemp has an extremely fast growth rate, so a delayed post-application due to wet weather or an equipment breakdown can quickly take a plant from a controllable size to one that is off-label and too big in relatively a short amount of time. So, as we move into the time of year when post-applications are being made, we need to consider adding in another residual product that is strong against the pig weed family to increase our success of clean fields later in the growing season. While the last several herbicide tolerant trait releases in soybeans allow for more options to control tall waterhemp, relying solely on those modes of action isn’t the best approach to having a successful herbicide program. Utilizing those modes of action, along with a residual product applied to the crop, will lengthen the control window and increase the success rate. While this isn’t at all a new concept, many times an in-season residual product is in the plans, but a relatively clean field will make people remove the product in favor of saving some costs, only to have waterhemp show up later in the summer to reduce yields and add to the weed seed bank.
Another opportunity to adjust a management practice would be to look at tissue samples from the previous growing season to see if a key secondary or micronutrient is consistently deficient later in the growing season. This is the most efficient way to look at tissue samples, as it shows a longer trend deficiency and a need for a nutrient versus the reactively using tissue samples are to “fix” a deficiency. For example, if tissue samples in the early reproductive stages of a corn or soybean crop have consistently shown your crop is short a key nutrient, then applying that nutrient now allows for it to be applied, but also moved into the crop and readily available for when it historically has been short. In contrast, waiting until after the crop reaches that deficiency level and then trying to counteract that after the fact with an application of a nutrient can be less effective.
Why focus only on secondary or micronutrients and not the macronutrients? The explanation is in the name of the nutrient macro. Macro nutrients for corn (nitrogen, phosphorus, and potassium) are needed in substantial amounts and should be applied to the soil ahead of planting to ensure adequate levels of those nutrients are available for uptake when the crop is in need. While there are still nitrogen applications being made via sidedress, applying potassium or phosphorus at this point of the growing season isn’t cost-effective on a per unit basis. However, applying secondary or micronutrients that are needed in smaller amounts can be a very effective and efficient way to address fertility needs. Nutrients that commonly are low in tissue test that can be managed this way would be sulfur, zinc, and manganese. Applying these nutrients now ahead of when tissue tests historically show they are deficient can keep this year’s crop from becoming short on key nutrients in the growing season.
Maximizing the key available nutrients to a crop and minimizing the competitive pressure from weeds such as tall waterhemp will increase chances of a successful crop and the opportunity to utilize the tools like fungicides for disease protection and insecticides to improve seed number and weight in soybeans.