Impact, Armezon carryover injury observed in northwest Iowa

June 25, 2020 10:01 PM
Blog Post

There have been a few fields where topramezone – the active ingredient in Impact and Armezon – carried over from an application last June – and is injuring this year’s soybean crop. Other agronomists have reported carryover of other Group 27 herbicides on soybean this year (mesotrione, isoxaflutole).

This was observed this in 2013, but it did not affect a lot of acres that year.  However, that was following the drought year of 2012 and the lack of summer rainfall in 2012 somewhat explained this problem.

This year – the fields that have been observed have an irregular pattern of injury , stunting of soybean plants, bleaching of soybean leaves and browning of soybean leaves.  Herbicide drift from Group 27 herbicides was ruled out because of the pattern of injury across the field. 

Some of the possible reasons for this topramezone carryover include a delayed 2019 corn planting date, a delayed 2019 postemergence corn herbicide application date and an extended period of cool,wet weather in mid-May 2020.  However, rainfall amounts in 2019 and 2020 could be considered at least normal if not above normal.     

These affected soybean fields have regrowth at the leaf axils.  However, this recovery – to date – has been slow. 

Replanting the field to a soybean crop was considered – but since there were many unknowns – this was not considered a good option. 

Carryover symptoms did not follow any particular field pattern

Impact herbicide carryover in Palo Alto county.



Paul Kassel Field Agronomist in NW Iowa

Paul Kassel provides research based crop production information to area farmers and agribusiness. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include soil survey, crop production, soil ferti...

Bob Hartzler Professor of Agronomy

Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio...