With the wet weather we have experienced this spring, we are seeing herbicide injury particularly in corn from PRE applications. Although, various herbicides can cause injury during prolonged cool or wet periods, ALS inhibitor herbicides in particular can be evident in fields. Much of this injury appears as stunted somewhat chlorotic corn with injury ratings ranging from 10 to 25%.
The primary ALS-inhibitor corn herbicides used PRE in our region include products that contain rimsulfuron (Basis Blend, Instigate, Prequel and Resolve products), thiencarbazone (Corvus), and flumetsulam (Hornet and Surestart II/TripleFlex II). The potential for ALS injury increases with rapid uptake of the herbicides during warm wet weather conditions.
We suspect that the abundant frequent rainfall during May followed by hot weather stimulate herbicide uptake above the tolerance level for corn. The injury also tends to be worse where poor soil properties and less than ideal planting conditions exist such as on clay knobs, areas planted when wet producing compaction and cloddiness, shallower planted corn, etc.
Hopefully good growing conditions and sunlight over the next few weeks will allow the corn to recover leaving little if any impact on grain yields.