Bob Hartzler has received several calls regarding suspected fomesafen carryover injury to corn. Fomesafen is a group 14 herbicide (PPO inhibitor), and the active ingredient in Reflex, Flexstar, Prefix, Marvel and other products.
Carryover is typically associated with applications made after late June and/or when the season turns dry following application. Labels of most products containing fomesafen specify a 10-month rotation interval for planting corn.
The primary symptom of fomesafen injury is striped leaves due to chlorotic or necrotic veins on the leaves. Other factors can cause striping on leaves, but fomesafen is unique in that the veins are affected rather than interveinal tissue. Some of the leaves may fold over midway due to loss of integrity of the leaf midvein.
Frequently only two or three leaves are affected and injured plants recover quickly. However, at times there can be stand loss and the only way to determine the potential impact is to determine the percentage of plants affected and closely monitor the rate of recovery.
The spread of glyphosate resistant waterhemp has led to an increase in ‘rescue’ applications with group 14 herbicides such as fomesafen, lactofen (Cobra, etc.) and acifluorfen (UltraBlazer, etc.). Of these products, only fomesafen poses a threat to rotational corn. A switch to alternative herbicides later in the season can avoid this risk. However, keep in mind that late applications of group 14 herbicides usually are ineffective against the large waterhemp present at these times. Ideally, develop integrated strategies that minimize the need for mid-season rescue operations.