Field research at four locations established in early April each year will investigate PRE herbicide application rate and timing and POST applications with and without layered residual.
Advances in soybean seed treatments, planting equipment and perceptibly subtle climate change have spurred interest in planting soybean weeks earlier compared with long-term averages. Reports of soybean planting as early as April 6 in 2020 were well in advance of corn planting progress reports. The potential of increased soybean yields as an outcome of early planting, however, can be offset by environmental and pest-related factors, some of which could actually reduce yield potential. The adage “You can’t control the weather” highlights the risks associated with the uncertainties (such as frost after soybean emergence, excessive precipitation leading to replanting, etc.) of weather, but many pest management uncertainties also are relevant.
Weed control is of paramount importance in allowing a soybean crop to express its genetic yield potential. Yet, scant data exist to guide weed management recommendations in early-planted soybean. For instance, should the application of a soil-residual herbicide occur at planting, split between at-planting and at-post application timings, or even needed in early-planted soybean? Are there data to support the hypothesis that some level of soil-residual herbicide is necessary several weeks in advance of soybean and weed emergence? Soybean seedling emergence will be dictated by accumulation of growing degree days and soil moisture, but when will soybean emergence occur in relation to emergence of summer annual weed species? Soybean canopy development is an important weed management component, so how important is soybean row spacing in early-planted soybean for weed management?
The idea for this research originated when the XtendiMax and Engenia herbicide labels required foliar applications to occur within 45 days of soybean planting. Although that label requirement no longer exists, the necessity to generate data on weed management in early-planted soybean persists. We propose to initiate an experiment in 2021 as part of a M.S. graduate student research project and repeat the experiment in 2022. Obviously, there is risk that weather might not facilitate the early establishment of this research, so we further propose to establish multiple locations (University-managed locations and locations with industry cooperators) to increase the probability of successful establishment. Our a priori assumptions and uncertainties are:
Soil-residual herbicides will be necessary – we simply have no data to suggest when the application should occur and at what application rate
Foliar-applied herbicides will be necessary – the concept of layered residuals is gaining momentum, but are they needed in very early planted soybean and if so, at what rate should they be applied?
Waterhemp will continue to be a driver weed species that emerges throughout most of the growing season