Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
We have been looking at delaying rye termination to gain more weed control benefits from the cover crop. We have worked mostly with cereal rye cover crops and have seen benefits in terms of fewer weeds emerging and those weeds that do emerge grow slower. Slower weed growth means cereal rye provides a wider window for when weeds are still susceptible to postemergence herbicides. When I began working on cereal rye for weed control a number of years ago, the conventional wisdom was that we needed a dense stand of rye (over 4,000 lbs of dry material) to provide weed control. However, over numerous studies we have found that even modest levels of rye (1500 to 2500 lbs) are helping us provide better overall weed control. Okay, let us be honest and acknowledge almost no one knows how many pounds of cover crop are in their fields. My point is, even if your stand is nothing to brag about, it is still providing you with weed control benefits. And there are very few situations when rye cover crop is a negative. Negative experiences typically center around soil moisture depletion by rye prior to planting.
When researchers discuss planting green, they often mean planting when the rye is in the heading stage. Last year we had a trial with planting into three cover crop scenarios. The first was killing the cereal rye two weeks before planting, second was planting into a living cereal rye cover crop when the rye was at the boot stage (roughly May 1) our last approach was planting green at the heading stage (May 14). We saw better weed control with the planting green early (May 1) compared to the rye terminated 2 weeks prior to planting. So, planting green can occur at any point, it does not mean that you must wait for the rye to head to experience weed control benefits.
We have found successful planting with cover crops for either a green cover crop (not sprayed prior to planting) or after the cover crop is completely dead. Planting into a “dying” cover crop when the stems are not stiff is the most challenging. That also goes for trying to plant when the rye is under moisture stress.
If you have a field with cereal rye, and thought about planting green but do not want to wait for the rye to head out, consider planting green earlier. You are still going to see benefits.