Effect of variety selection, herbicides, and tillage on Michigan sugarbeet (Beta vulgaris) production

Michigan sugarbeet growers have two additional options for residual control of late-emerging weeds, with the recent registrations of s-metolachlor and dimethenamid-P. Applications of these herbicides can cause sugarbeet injury. Previous research has shown that sugarbeet varieties differ in their response to herbicides. Reduced sugarbeet growth from herbicide injury can impact sugarbeet's competitiveness with late-emerging weeds and sugarbeet yield. To reduce the potential for sugarbeet injury, s-metolachlor should be applied after the first micro-rate application or when sugarbeets are at the 2-leaf stage or larger, with the exception of applying one-fourth of the s-metolachlor rate in each of four micro-rate applications. Dimethenamid-P applications should be applied after the second micro-rate application or once sugarbeets are at the 4-leaf stage. The addition of either s -metolachlor or dimethenamid-P to micro-rate herbicide applications improved giant foxtail, common lambsquarters, and pigweed (redroot pigweed and Powell amaranth) control compared with the base micro-rate treatment. None of the treatments reduced recoverable white sucrose yield. Results from field and greenhouse experiments indicate that the residual activity of s-metolachlor was greater than that of dimethenamid-P. Split-applications of both herbicides provided similar residual control of giant foxtail compared with full-application rates.; Sugarbeet varieties varied in their response to s-metolachlor and dimethenamid-P in field and greenhouse experiments. Greenhouse results indicated the greatest sugarbeet injury from s-metolachlor and dimethenamid-P occurred from applications directly to the soil compared with applications to the leaf surface, indicating that herbicide absorption is primarily through the roots and/or hypocotyls of the sugarbeet plant. Under hydroponic conditions, there were no differences in sugarbeet tolerance between s-metolachlor and dimethenamid-P, indicating that differences in herbicide solubility and adsorption to the soil contributed to the differences in the magnitude of injury between the herbicides in the field. 'Beta 5833R' was the most tolerant sugarbeet variety and 'Hilleshog 7172RZ' was the most susceptible sugarbeet variety to s-metolachlor and dimethenamid-P. Slower metabolism of 14C-herbicides in sugarbeet shoots was likely the most significant factor contributing to differences in sugarbeet variety tolerance to both s-metolachlor and dimethenamid-P.; Fields trials were conducted to determine if tillage and soil-applied herbicides had an effect on sugarbeet injury and weed control from micro-rate herbicide applications. Sugarbeets emerged earlier in the moldboard plow system compared with the chisel plowed system. However, under dry conditions sugarbeet emergence was later in the moldboard plowed system. PRE treatments of s-metolachlor, ethofumesate, and ethofumesate plus pyrazon followed by four micro-rate applications increased sugarbeet injury compared with the no-PRE treatment. Common lambsquarters, pigweed (redroot pigweed and Powell amaranth), and giant foxtail control in mid-August was consistently higher when a PRE herbicide was applied prior to the micro-rate herbicide treatments. Recoverable white sucrose yield was greater in the moldboard plowed treatments compared with the chisel plowed treatments in three out of four sites tested.