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.
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- Retired Weed Scientist and Professor of Agronomy