Fomesafen Carryover to Corn

Jun 16, 2021

By Meaghan Anderson

ISU Extension and Outreach Field Agronomists recently highlighted a significant number of phone calls related to fomesafen carryover injury to corn rotated from 2020 soybeans. In some cases, this injury has been misidentified as other issues, like boron deficiency. There are several factors resulting in this injury: 1) continued problems with waterhemp result in late-season applications in soybean, 2) fomesafen is relatively persistent, and 3) many areas of Iowa received less than average late-season rainfall in 2020. In most cases, this carryover injury has been limited to relatively small sprayer overlap areas, though some fields are showing injury on a more widespread area.

Characteristics of the primary products used postemergence to control waterhemp in Iowa are listed in Table 1. For a herbicide to pose carryover risks, it must persist at toxic concentrations into the following growing season and be biologically available. Both fomesafen and glyphosate are relatively persistent (longer half-life) compared to the some other herbicides. The K_OCis a measure of how tightly a chemical is held to soil colloids. As the K_OCvalue increases, less herbicide is available to be absorbed by plants. Whereas fomesafen can be readily absorbed by plants due to low adsorption to soil colloids, glyphosate is unavailable to plants due to tight binding to soil particles.

Table 1. Herbicide characteristics influencing carryover potential. Herbicide Handbook, 10th Edition. Weed Science Society of America.

Active ingredient	Trade name	Half-life	Availability (K_OC)
fomesafen	Flexstar	100 days	60
lactofen	Cobra	3 days	10,000
glufosinate	Liberty	7 days	100
dicamba	Xtendimax	14 days	2
glyphosate	Roundup	47 days	24,000

The relatively long half-life of fomesafen, combined with below average rainfall late-season rain in Iowa, is the reason for the increased issues with carryover in 2021. Much of the state received 4-6+ fewer inches of rain than normal during July and August of 2020 (Figure 1).

Fomesafen Carryover to Corn

The primary symptom of fomesafen injury is striped leaves due to chlorotic or necrotic veins on the leaves (Figures 2, 3, and 4). Other factors can cause striping on leaves, but fomesafen is unique in that the veins are affected rather than interveinal tissue. Some of the leaves may fold over midway due to loss of integrity of the leaf midvein. Frequently only two or three leaves are affected and injured plants recover quickly with no visible injury to subsequent leaves. However, at times there can be stand loss and the only way to determine the potential impact is to determine the percentage of plants affected and closely monitor the rate of recovery.

While this injury is sometimes unavoidable due to weather conditions, it is often exaggerated by late herbicide applications in soybean. Rather than focusing on the problem of corn injury due to fomesafen, it is more important to consider why late-season applications of postemergence herbicides are required. An integrated program relying on full rates of effective preemergence herbicides with multiple sites of action and early postemergence applications in conjunction with a soil residual herbicide (layered residual program) in soybean, and an increased emphasis on driving down the size of the weed seed bank, should reduce the need for the late-season applications and reduce the likelihood of seeing fomesafen carryover in future years.

Source : iastate.edu

Video: From Students to Solutions | On The Brink: Season 2, Episode 14

Ask Canada’s most decorated soybean breeder his favourite part of the job and he doesn’t name a single variety. He names the students.

Istvan Rajcan is a professor of soybean breeding and genetics in the Department of Plant Agriculture at the University of Guelph, where he has run the soybean breeding program for 28 and a half years. In that time he has developed 87 soybean cultivars, published 140 refereed papers and trained 51 graduate students. In 2025 he received the Public Sector Impact Award from the National Association for Plant Breeding.

He is also worried. In this episode he says Canada is at a crossroads, pointing to recent government cuts to plant breeding programs and to the facilities that support them. His prescription is structural. "Plant breeding funding formula has to be a long-term one," he says.

The formula he is defending is the public-private matching arrangement his program runs on. Private seed companies fund the work, provincial or federal money matches it, and the combined pool stretches each dollar further than either source could alone. At the National Association for Plant Breeding annual meeting in June, he says American public breeders were often surprised at how well that collaboration works in Canada.

He also describes how the people entering plant breeding have changed. His early graduate students came mostly from farms. More recently they include, in his words, "city kids who just became excited about genetics."

Topics covered:

Why public-private plant breeding funding in Canada needs a long-term

commitment rather than a larger one

How matching private seed company investment with provincial and federal

dollars multiplies research capacity

How the graduate student pipeline into plant breeding has shifted from

farm kids to city kids