Abstract
Field experiments were conducted in 2021 and 2022 to evaluate cereal cover crops and herbicide programs for weed control in sugar beet ( Beta vulgaris ). The experiment was set up in a split‐split‐plot randomized complete block design with four replications. The main plot was two fall‐planted cereal cover crops (cereal rye and winter wheat) and no cover crop; the split‐plot factor was five cover crop termination timings (14 and 7 days before planting, day of planting, and 14 and 7 days after planting), and the split‐split‐plot factor was three herbicide programs (dimethenamid‐p + glyphosate at four leaf sugar beet; dimethenamid‐p + glyphosate at four leaf sugar beet followed by glyphosate at 10 leaf stage; and glyphosate at four leaf sugar beet followed by glyphosate at 10 leaf stage). Cereal rye produced more biomass and thus provided up to 50% better weed suppression than winter wheat. Terminating cover crops after sugar beet was planted reduced common lambsquarters and kochia density by 28%–90% at the time of the first postemergence herbicide application. One‐time application of dimethenamid‐p + glyphosate had similar weed control as glyphosate applied twice. Delaying cover crop termination until 7 or 14 days after planting reduced sugar beet stand density and reduced root yield by 8%–28%. Terminating cereal cover crops with herbicides at planting or up to 7 days prior provided optimal sugar beet yield in this study.
Cereal rye cover crop provided up to 50% better weed suppression than winter wheat. Delaying cover crop termination beyond the day of sugar beet planting reduced sugar beet density and yield. The optimal timing to terminate cover crop was 7 days before sugar beet planting to the day sugar beet is planted.
Sugar beets do not grow very tall, so weeds are able to grow faster and outcompete the crop. Although weed control is very important for preventing sugar beet yield loss, very few chemical products can be used to effectively control weeds in sugar beets. One practice that can complement herbicides to control weeds is by planting grassy crops such as cereal rye and winter wheat in the fall before planting sugar beets the following spring. This study looked at the best time to kill cereal rye and winter wheat to ensure that they provide some weed suppression but do not reduce sugar beet yield. The results showed that cereal rye provided better weed control than winter wheat. Killing the cereal rye and winter wheat late may help provide better weed control but may also reduce sugar beet yield. Approximately 7 days before sugar beet is planted is the best time to kill the cereal rye or winter wheat to ensure they provide good weed control without reducing sugar beet yield.