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Reducing Risk of Crop Injury from Herbicide Applications

July 9, 2024

Weed control in sweet corn can be a challenging prospect. Reduced plant height and slower canopy cover compared to field corn reduces overall crop tolerance to weeds. While cultivation can be part of a weed management strategy, most growers rely on pre and/or post-applied herbicides for weed control. Herbicides may come with the risk of crop injury, and understanding these concerns is important to the prevention of this injury and, ultimately, the success of that delicious sweet corn. Below is a review of pre- and post-emergence applications, as well as some concerns to be aware of relating to specific chemistries and potential varietal differences. Also, an explanation of how the IFSI breeding program screens for crop tolerance to multiple groups of herbicides and where a grower can find information on varietal responses to these herbicides.

This is not meant to be a complete weed control guide for sweet corn. Also, it is always important to closely read and follow the herbicide label directions. Herbicide labels have key information on worker and environmental safety, application rates and instructions (including crop safety considerations), crop rotation, and harvest interval information.

Preplant or Preemergence Applications

There are numerous options for pre-plant and preemergence applications that provide residual control of both grass and broad-leaf weeds. The important item to note is that the crop safety to these pre-applied herbicides is generally very good. Many products rely on chloroacetamides in combination with atrazine and/or Callisto. These pre-emerge options include Atrazine, Acuron, Acuron Flexi, Harness, Harness Xtra, Armezon, Armezon PRO, Anthem Maxx, Bicep Lite II Magnum, and Zidua .1 There are instances where Dual (s-metolachlor) or other Group 15 herbicides can cause injury to seedlings. Seedlings may appear buggy-whipped, where the leaves do not unfurl.2 The risk for crop injury is greatest in cool, wet weather and with shallow planted corn.3

Post-emergent Applications

For post-emergence control, common choices include an HPPD inhibitor, such as Callisto (mesotrione), in combination with Atrazine. HPPD inhibitors are often called bleachers as their mode of action disrupts carotenoid biosynthesis and leave susceptible plants white.4 Some examples of HPPD inhibitors include Callisto (mesotrione), Laudis (tembotrione), and Impact/Aremzon (topramezone). ALS inhibitors are also commonly used for post-emergent control of grasses in sweet corn. Common ALS inhibitors include nicosulfuron (Accent Q), foramsulfuron, and primisulfuron.

Reducing Risk of Crop Injury

Both of these herbicide classes, HPPD and ALS, can significantly injure sweet corn when applied post. Growers have options to minimize these risks of crop injury. One option is to choose an HPPD inhibitor that has better crop safety, such as Imapct/Armezon or Shield X (tolpyralate). These products have less crop injury, even on more sensitive genotypes. Also, avoiding application during extreme weather conditions and applying according to label directions. Following application directions is particularly important with the ALS inhibitors. See below for directions directly from the Accent Q label:

“Applications of ACCENT® Q may be applied broadcast or with drop nozzles (post-directed) on sweet corn up to 12 inches tall or up to and including 5 leaf-collars (V5). For sweet corn 12 - 18 inches tall, apply only with drop nozzles. DO NOT apply to sweet corn taller than 18 inches or those which exhibit 6 or more leaf- collars (V6) and make only one application of ACCENT® Q per year.”

If applied outside of those restrictions, significant crop injury can occur even with tolerant varieties. See image below for an example of a mis-applied late application of Accent without the use of drop nozzles and the characteristic bottle necking symptom of the ear.

Bottlenecking injury from a late application of Accent (nicosulfuron) applied without the use of drop nozzles.

The last factor for reducing crop injury is to understand the herbicide reaction of the varieties that will be planted. On IFSI’s product page, an herbicide classification of Tolerant (T), Intermediate (I), or Sensitive (S) is provided.


Note that there are no fully sensitive commercial varieties within the IFSI portfolio. Varieties indicated as tolerant would be unlikely to show injury when these herbicides are applied according to label directions. Varieties labeled as Intermediate require additional explanation and consideration. When considering applying HPPD inhibitors to Intermediate hybrids, there is some risk of bleaching, although the plants likely grow out of this injury with little to no effect. See the graph from Meyer (2010), where the striped bar would be equivalent to intermediate hybrids; while there is bleaching injury, yield loss was only 0-4% and not significantly different from the nontreated control.5 For ALS inhibitors, additional caution should be exercised on intermediate hybrids because of the severity of injury. It is not recommended to apply ALS inhibitors on intermediate hybrids, but if grass control is a necessity and application is the only means for control, then apply a product with a safener such as Accent Q, utilize drop nozzles to reduce chemicals from getting into the whorl, and follow crop growth stage restrictions as stated on the label.

Image from Meyer (2010)5, intermediate hybrids are the striped bars, while tolerant are the solid black.

IFSI’s breeding program routinely screens for herbicide tolerance throughout the inbred development process. This eliminates sensitive parents for future products. It is an important step to provide growers with the information they need on existing hybrids as well as preserve the tools of these herbicides in future products.

Herbicide screening in the IFSI breeding nursery. Clear distinction between tolerant and sensitive responses to nicosulfuron. Some sensitive responses to nicosulfuron result in complete plant death.


  4. Pallett, K. E. “The mode of action of isoxaflutole: a case study of an emerging target site.” Herbicides and their mechanism of action (2000).
  5. Meyer, Michael D., Jerald K. Pataky, and Martin M. Williams. “Genetic factors influencing adverse effects of mesotrione and nicosulfuron on sweet corn yield.” Agronomy Journal 102.4 (2010): 1138-1144.
Author's Image

About the Author

Charlie Thompson      Vice President – Director of Research

Charlie heads the breeding and product development team in IFSI’s vegetable division, catering to a worldwide network of seed dealers, growers, and consumers. Armed with a master’s degree in plant breeding and genetics from the University of Illinois and over 13 years of experience, Charlie is driven by a fervor to provide products and expertise that significantly influence stakeholders in the vegetable seed market. He is dedicated to advancing the legacy of IFSI and bringing forth solutions through cutting-edge genetics.

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