The early, rapid growth of winter cereal rye in the springtime can be challenging to manage before planting corn or soybean. There are different methods of terminating the rye cover crop. It can be killed 2 or more weeks before no-till crop establishment with herbicides, incorporated by tillage, harvested for forage, or flattened with a roller crimper unit.
Tilling rye when it is less than 12 inches tall is a good way to terminate the stand. Plowing or disking rye after it is over 20 inches tall ties up soil nitrogen, takes moisture from the soil and is sometimes difficult to incorporate into the soil.
In no-till corn, glyphosate (Roundup) is the preferred product of choice for burning down cereal rye. Paraquat (Gramoxone) can also be used to burndown cereal rye before planting corn. Remember, paraquat is a non-selective, contact herbicide and will requires good spray coverage for optimum control of the rye. Glyphosate is a translocated, non-selective herbicide that is less dependent on spray coverage. Air temperature before, during and after glyphosate application can also influence control. Cold nights (<40°F) will reduce glyphosate activity, especially when followed by cool (<55°F) days. Cool weather (below 55°F) will slow the activity of paraquat, as will cloudy, overcast weather, but will not affect performance.
The glyphosate rate will depend on the stage of growth of the rye at the time of application. However, in most cases it is only necessary to use the .75 pounds acid equivalent rate of glyphosate (22 oz./ac Roundup PowerMax). Glyphosate formulations will contain 3 to 5 pounds acid equivalent per gallon. With glyphosate, include appropriate adjuvants (if required) plus spray grade ammonium sulfate (AMS) at 8.5 to 17 lbs/100 gallons of water.
If you have a limited supply of glyphosate, consider using reduced rates of glyphosate (.38 to .56 lb a.e./ac) plus 1 ounce Sharpen per acre with methylated seed oil (MSO) at one gallon per 100 gallons of water plus spray grade AMS at 8.5 to 17 lbs/100 gallons of water. For best results, do not substitute crop oil concentrate for the MSO.
Paraquat works well on smaller cereal rye before it reaches the boot stage. Add a nonionic surfactant to the spray tank to enhance penetration and total kill. If you will be planting corn and choose to use paraquat, consider adding atrazine in the tank mix to improve control of the rye. In 2009, research by Bill Curran at Penn State University, found that the additional of 1 quart of atrazine per acre, when used with paraquat, provided 99% control of 8-10 inch tall rye. Only 70% control of the rye was achieved when paraquat was used alone in this study. If you will be planting soybean and choose to use paraquat, consider adding 6 to 8 ounces metribuzin per acre to improve control of the rye.