The information in this blog post was submitted by Marty Williams, USDA-ARS  (217-244-5476; martin.williams@usda.gov).

Severe sensitivity to a relatively new postemergence herbicide, tolpyralate (trade name Shieldex), has been documented in certain inbred lines of field corn and sweet corn.  Tolpyralate sensitivity is a new genetic vulnerability in corn; hybrid response to other HPPD-inhibiting herbicides (e.g. mesotrione) applied postemergence has no bearing on response to tolpyralate.  The issue was brought to the attention of my lab in late 2021 based on the response of a single sweet corn inbred.  We have since documented severe sensitivity in 49 inbred lines of corn.  The source of the sugary enhancer (se) trait in sweet corn, IL677A is highly sensitive to tolpyralate.  Symptoms include leaf bleaching 7-10 days after herbicide application.  Preliminary results indicate the sensitivity trait is recessive and I have heard anecdotal reports of injury in corn hybrids.  If you plan to use tolpyralate for weed control, I encourage you to contact the herbicide manufacturer (SummitAgro USA) and the seed company of your corn hybrid(s) to confirm the combination is safe.

Watch this video for a brief interview on the topic with Stu Ellis, AgricultureReporting.com: Some new corn hybrids and corn herbicides won't mix. (youtube.com). 

For the detailed journal article: First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to a herbicide - Williams - 2024 - Pest Management Science - Wiley Online Library