Impact of 2,4-D Micro-Rates on non-2,4-D Tolerant Soybean

Abstract

Auxin type herbicides (eg. dicamba, 2,4-D) are an integral component of major cropping systems in North America. With the recent launching of Enlist E3 soybean in the U.S., in-season application of 2,4-D to soybean fields is expected to increase. This will enable use of Enlist One and Enlist Duo herbicides thus broadening farmers’ flexibility in controlling tough-to-control broadleaf and grass weeds including glyphosate-resistant biotypes. Despite the availability of new Enlist herbicides with low volatility potential, their potential off-target movement represents a major threat to non 2,4-D tolerant soybean as well as other broadleaf crops. Furthermore, the negative impact of 2,4-D drift on non-2,4-D tolerant crops may vary with the rate of the herbicide, crop type and/or growth stage at time of drift occurrence. Given its total acreage, this negative impact is likely to be more pronounced in the U.S. soybean belt. Of the approximately 240 million acres planted to the four major crops (i.e. corn, soybean, wheat and cotton) in the U.S. in 2018, corn and soybean accounted for 75% of the planted acreage and 90 million acres each (USDA Ag Outlook Forum for 2018 U.S. crop acreage, yield, production, and price projections for major U.S. crops). Although Enlist E3 soybean was available for planting in 2019 season, it will not be available in commercial quantities until the 2020 season. Since the majority of soybeans are still non-2,4-D tolerant soybean, it is important to understand the potential impact of 2,4-D drift. Therefore, field study was initiated in 2019 (and will be repeated in 2020) to measure the impact of 2,4-D micro-rates on four soybean types (Dicamba-Tolerant, Roundup Ready, Liberty-Link and Conventional soybean).