The derecho left many Iowa farmers with significant volunteer corn this growing season, and unfortunately some may be facing a similar situation for 2022 after late August storms flattened fields.
As it has started to warm up, folks are ready to implement early-spring weed management programs, especially in fields with infestations of winter annuals like field pennycress and marestail (horseweed). Spring burndown (preplant) herbicide programs should target winter annual plants at the rosette stage, prior to stem elongation (bolting), for consistent control. Cold nights (<40°F) will reduce activity of herbicides, particularly for glyphosate. With cool weather conditions, it is recommended to wait for a few days until it warms up before applying herbicides.
Volunteer corn remains high on many minds this spring and one of the biggest questions is how much of those corn seed will germinate this spring. In an effort to learn more about the challenge we’re facing, Bob Hartzler collected soil and corn ears from the same fields he collected from last fall. To remind the reader, soil was collected and sifted from several 12” by 12” by 6” depth areas in mid-October to determine how many ungerminated corn kernels were left in the soil in a field that was disked under in late August and early September.
Due to extensive damage to corn fields last year from the derecho, volunteer corn is a looming threat for many fields this spring. Farmers intending to plant corn in these derecho-affected fields have limited options for managing volunteer corn, thus thoughtful planning is critical. I asked a collective of weed scientists their thoughts on best management practices for controlling volunteer corn prior to planting corn. I received responses from University colleagues in 8 states and Canada. The following is a summary of their thoughts and some resources that you may find helpful.
A concern for corn fields damaged by this year's Derecho is how best to manage volunteer corn in 2021. Our recommendation is to rotate to soybean or some other crop if at all possible since additional control options are available in soybean (Sept 3, 2020 article). There have been questions regarding how much viable corn seed is left in these fields after abundant corn germination in September (Figure 1).
August's derecho left many Iowans with unharvestable corn. For operations that left their corn in the field, decisions should be made to reduce the problem of volunteer corn next planting season.
In this video, Field Agronomist Meaghan Anderson and Weed Specialist Bob Hartzler discuss the unique situation many farmers face with volunteer and options for encouraging germination this fall and reducing the number of volunteer plants you may have to deal with next year.
Downed corn from the August 10 Derecho, which affected millions of acres in Iowa, will contribute to significant volunteer corn populations in crop fields in 2021. Volunteer corn ranging from 800 to 13,000 plants per acre can cause yield losses up to 54% in soybean and up to 13% in corn, according to the research conducted at SDSU, UMN, and UNL. In unharvested corn fields, establishment of 1% of the corn seed present would result in volunteer corn populations of more than 100,000 plants per acre.
Iowa fields have significant volunteer corn problems this spring. If dry conditions continue, farmers will need to adjust combines to minimize harvest losses.
Volunteer corn is giving recently planted and yet-to-be planted corn and soybean fields a splash of green color. Manage volunteer corn early to avoid yield losses.
