Research was conducted to evaluate corn (Zea mays L.) and soybean (Glycine max L. Merr.) injury and weed control with pyroxasulfone applied preemergence (PRE) and postemergence (POST). In corn, pyroxasulfone applied both PRE at 150 g/ha and POST at 60 g/ha with glyphosate controlled barnyardgrass, Palmer amaranth, sicklepod, prickly sida, browntop millet, ivyleaf morningglory, and entireleaf morningglory 90 to 99% 30 days after the POST application. Weed control was no greater than when pyroxasulfone at 150 g/ha was applied only PRE. Control of barnyardgrass, Palmer amaranth, smooth pigweed, and browntop millet was greater for pyroxasulfone PRE compared with atrazine PRE and lower corn yield was observed for the atrazine treatment. In a second corn study, pyroxasulfone applied alone PRE controlled barnyardgrass, smooth pigweed, Palmer amaranth, hophornbeam copperleaf, sicklepod, ivyleaf morningglory, pitted morningglory, and prickly sida 83 to 100% 66 days after application. Equivalent weed control was obtained for pyroxasulfone plus atrazine and atrazine plus S-metolachlor applied PRE. Corn yield was lower when pyroxasulfone was applied only PRE compared with pyroxasulfone plus atrazine PRE and atrazine plus S-metolachlor PRE.
Soybean injury was observed when pyroxasulfone was applied at 60 to 300 g/ha, and at 10 days after application, injury was 2 to 5% when applied PRE and 15 to 21% when applied POST. Injury consisted of crinkling of leaflet surface, irregular leaflet margins, indentation of leaflet tips, and a drooping of leaf petioles (POST application only). Soybean yield was not negatively affected by pyroxasulfone regardless of application timing. In a second soybean study, pyroxasulfone applied alone PRE at 150 g/ha controlled, browntop millet an average of 99%, barnyardgrass 75%, hophornbeam copperleaf 99%, ivyleaf morningglory 86%, hemp sesbania 98%, sicklepod 95% and pitted morningglory 73% around 30 days after treatment. Compared with pyroxasulfone applied alone PRE at 150 g/ha, weed control was not improved when pyroxasulfone was applied PRE with saflufenacil, flumioxazin, fluthicet-methyl, or chlorimuron ethyl plus flumioxazin plus thifensulfuron methyl. Crop safety, consistency in weed control, and flexibility in application timing with pyroxasulfone suggests that it should have a fit in corn and soybean weed management programs in the mid-south.