One of the key aspects of growing a cover crop is to know when to kill it. You should have a cover crop control plan thought through before you plant in the fall. Obviously, some cover crops are terminated due to winter-kill and that takes this management component out of the equation. A lot of variables can go into this decision, but probably the most important one is assigned to what you are trying to accomplish with the cover crop. If it’s moisture uptake and drying out the soil is desired, you will want to leave it grow as long as possible and plant directly into it while still green. This practice has become known as “Planting Green” and is gaining acreage as farmers are learning to embrace this additional level of cover crop management. Some other benefits include maximizing the potential value of the cover crop, like nitrogen production in the case of legumes. Some farmers are even reporting less slug damage as those pesky critters seem to prefer a smorgasbord of cover crops for their diet over a corn or bean seedling. This practice requires a higher level of management, equipment modification, and diligence. We will discuss the concept of planting green in much greater detail in a few weeks.


The biggest risk in allowing cover crops to grow is a dry spell with no rain in sight. If this occurs near the outset of the planting window, a compromise is in order; you may have to spray earlier so that the cover crop does not use up moisture that will need to be available to the cash crop. Also, for rookies, terminating earlier is advised, as it’s simply easier.

Special Instructions

Annual ryegrass control has a specific set of guidelines. The deep roots, which accomplishes a lot for nitrogen scavenging, and the rather short top growth coupled with waxy leaves, make this cover crop a challenge to kill. But, if the termination rules are followed, many have found annual ryegrass to be their favorite cover crop. You need to make spray water first by adjusting the ph down to around 4.5 and a water hardness rating less than 3 grains per gallon. A spray grade ammonium sulfate must be added before adding glyphosate. Use a high rate of glyphosate sprayed between 9 a.m. and 3 p.m. and when the temperature is above 60 degrees. Avoid mixing with a residual herbicide; instead, only use water as a carrier and aim to apply between 8-12 gallons per acre. Rarely do those suggestions all align, but try to do what you can to get satisfactory results. Annual ryegrass is best controlled when the first node is visible; that requires “down on your knees” observation so you know the most susceptible maturity stage.


If maximum nitrogen production is desired, allow cover crops like hairy vetch or crimson clover to reach first flower. This may be into the middle of May for these popular legumes, but intentionally planting your corn into these fields last will make this a successful proposition.

Cereal Rye

Clearly the most used species of cover crops is cereal rye. There is no exact stage for termination, or height that is correct for everyone. Some farmers have killed at 12 inches and others have purposefully let it get over 6-feet tall. Aside from the moisture considerations listed above, cereal rye is easy to terminate and easy to plant into. If cereal rye is over 18 inches, planting equipment needs to be adjusted to account for the higher biomass. Cover crop roller crimpers may come into play — another topic coming soon. In addition, a spoked-type closing wheel or the new angle-pitch closing wheel bracket may be required to close the seed slot of the dense root mass.

Termination Takeaways

Before you plant a cover crop, having a strategic plan for termination is paramount. Following these guidelines and proven tips will enable you to achieve the goals you have for cover crop benefits on your farm.