In the last 2 days, many locations in south Georgia received lots of rain (Figure 1). Thus, I have been getting many texts and telephone calls about what might happen to any PRE herbicides that were applied to field corn. In general, I would say that if runoff/washing was minimal, there is a good chance that the herbicides are still in the field, especially if the PRE treatments were watered in soon after application. Research in Georgia has shown that runoff of Dual II Magnum and Prowl EC in conventional tillage systems was reduced 1.2-2X when irrigation occurred shortly after application (Potter et al. 2008. Herbicide incorporation by irrigation and tillage impact on runoff loss. Journal of Environmental Quality 37:839-847).
In 2022, a very similar weather event occurred in my research plots during the first 7 days after planting (3.84″ of irrigation/rainfall). All my PRE herbicides worked just fine (Figures 2, 3, 4). Note in Figure 2 that there are some wild radish plants in the plot but no pigweed or grasses. In general, all of the Group 15 herbicides (Anthem Maxx, Dual Magnum, Outlook, Warrant, Zidua) do not provide adequate residual control of wild radish so this should not be a surprise. FYI, Anthem Maxx/Zidua are slightly better on wild radish than the other Group 15’s.
Bottom line, no way to know for certain how much herbicide will be left in the field. My best advice would be to keep eyes on/feet in the field and pull the trigger earlier on POST treatments when/if needed.
