By John Schoenhals, Pioneer Field Agronomist, Northern Ohio
Springtime in Ohio is an exciting time — color returns to fields, lawns, and landscapes, outdoor activities (with appropriate social distancing) can begin, and the sound of birds fills the early morning air. When it comes to fieldwork, spring is a pivotal time for setting corn and soybean yield potential.
While seed genetics, weather, planter calibration, and overall uniformity have a high impact on yield, it is important not to lose sight of the challenges of weeds to a grower’s operation.
The challenges that weeds pose to growing crops has increased drastically in recent years, and 2020 will bring even more challenges. Large amounts of prevent plant ground in 2019 allowed tough-to-control weeds such as marestail, ragweed, and waterhemp to produce enormous amounts of seeds. These seeds can very quickly be spread to new areas.
Waterhemp is the newest weed threat in many parts of the state, especially in soybean production. Waterhemp is an aggressive weed, growing up to 2 inches per day. It is also a prolific seed producer, and has resistance to multiple herbicides, with the ability to continue developing resistance.
Everyone wants an “easy button” when it comes to soybean weed control; however, it has becoming increasingly clear that an easy button does not exist. Rather than an easy button, growers should consider “three keys for weed control success.” These keys are essential regardless of the herbicide trait system used; whether that be conventional soybeans, value-added products such as Plenish, or stacked traits such as those found in the RoundUp Ready 2 Xtend or Enlist E3 systems.
The first key to weed control success in soybeans is to start clean. The easiest and cheapest time to control weeds such as marestail is before soybeans are planted. If weeds are not controlled at this time, the rest of the season will be spent performing “revenge” applications of herbicides, often with unsatisfactory results.
Starting clean can be accomplished through conventional tillage or burndown chemicals. When using chemicals such as dicamba or 2,4-D, take care to follow the labeled Plant Back Restrictions specific to the product and soybean technology being used. When using tillage to control early-season weeds, it is important to fully work the soil to kill emerged weeds — some vertical tillage tools may not move enough soil to un-root weeds in the spring.
The second key to successful weed control is to use a quality preemergent residual herbicide. A preemergent residual herbicide is applied to the soil prior to soybean emergence. These herbicides provide extended control of germinating and newly emerged weeds. Residual activity remains for several weeks before beginning to decline. Any residual herbicide program must include multiple modes of action, and for waterhemp control, should include a group 14 PPO herbicide ingredient.
When steps 1 and 2 are accomplished, step 3, in-crop herbicide applications, becomes much easier to manage. Most yield reduction due to weed competition occurs during the first six weeks after planting, so in-crop herbicide application timing should target weeds no more than 4 to 6 inches tall. These applications are limited by the soybean herbicide trait used in the field, but good application options exist for each technology.
In areas with known waterhemp issues, an “overlapping residual” may be applied with the POST herbicide. When this overlapping residual is applied about 3 weeks after planting, weed emergence can be prevented much deeper into the growing season. Since waterhemp can emerge through mid and late summer, these overlapping residual applications of products that contain s-metolachlor or acetochlor provide significant value.
Amid the hustle and bustle of the spring planting rush, make sure to take time to ensure that your soybean weed control program is in place to maximize yield potential. Be prepared to prioritize chemical applications to allow timely planting of soybeans and to set up a season of weed control success.