PPDL Picture of the Week for
May 23, 2016
Fomesafen Carryover on Corn
Travis Legleiter, Weed Science Professional Assistant, Botany & Plant Pathology Department
As suspected from last year’s delay in postemergence herbicide applications due to a saturated June, there have been reports of fomesafen carryover onto corn this spring. Fomesafen is the active ingredient in a number of postemergence soybean herbicides, most recognizably Reflex and Flexstar although there are several others. Fomesafen is a PPO-inhibiting herbicide that is used widely in soybean because of its ability to effectively control many of our glyphosate resistant weeds including waterhemp, Palmer, and giant ragweed.
The drawback of fomesafen is its carryover potential to corn with a labeled 10 month replant interval. The saturated conditions of last June caused many postemergence applications to be pushed back until late June and July with even some reports of applications occurring in August. A little quick math and you will see that late July and August applications are very unlikely to meet the 10 month interval.
The likely hood of carryover has been decreased simply due to continued moisture in the soil in late fall and timely rainfalls this spring. Most herbicides are degraded by microbes that are only active in moist conditions, thus the increased fear of carryover during drought years. In the case of fomesafen it is degraded even more rapidly in saturated soils (anaerobic conditions) which is an oddity for a herbicide, so those producers in southern Indiana who have experience a month of saturated soils likely have a lower risk if they did make late fomesafen applications last year.
The soil conditions are of less concern for carryover to corn this spring, but rather the high number of late season applications last summer are why it is likely we will continue to see cases of carryover on corn this spring.
The injury symptoms of fomesafen carryover on corn are unique in that it causes veinal chlorosis or yellowing and clearing of the leaf veins. This is in contrast to what we see in many other striped corn symptoms in which we see interveinal chlorosis.
Often injury to corn from fomesafen carryover is only minor and rarely requires replants unless there is significant stand loss. The corn will typically grow out of the injury within a week or two.