Spring green up and growth of cover crops is occurring and has been for several weeks in some areas. You should consider terminating cover crop stands sooner rather than later, especially if the soil and environmental conditions allow.
Even though cover crops reduce soil erosion, improve nutrient capturing and benefit residue management, THEY ARE NOW WEEDS! Complete control of cover crops during the early spring is critical for future crop yield.
There are two main types of cover crops, broadleaves and grasses, and we need to distinguish the best way to manage these different types.
Broadleaf Cover Crops: While most of the broadleaf cover crops do go through winterkill, do not assume that has happened this year. Cold winters generally mean more winter kill, but some of the cover crop may remain in the spring and will interfere with the planted crop.
It is now time to scout to see if winter has allowed for some survival. Some species, such as Crimson clover and Austrian winter peas, consistently survive winterkill to some extent. To be successful in managing these broadleaf cover crops, it is important to consider other chemical controls, in addition to glyphosate. Incorporating a growth regulator may provide more consistent control and another effective site of action for resistance management.
Grass Cover Crops: We can further split grass cover crops into two groups—annual ryegrass and not annual ryegrass. While glyphosate is probably the most used herbicide to manage all of these grass species, herbicide rate and timing may be different.
If annual ryegrass has any significant growth, it can become very difficult to manage. The standard recommendation for annual ryegrass is to apply glyphosate at 1.13 lb. ae/acre (Roundup PowerMAX® @ 32 fl oz) with the appropriate adjuvants to plants less than 6” in height. If annual ryegrass is taller than 6”, increasing the rate of glyphosate may be warranted.
We have a little more flexibility with other grass species, cereal rye included. The standard glyphosate recommendation would be to apply at a rate of 1.13 lb. ae/acre with the appropriate adjuvants to stands less than 18” tall. Again, if the cover crop is taller, we may need to increase the glyphosate rate. A cool environment may also necessitate an increased glyphosate rate, regardless of plant height.
The key to successfully terminating our cover crops is to manage them with the right herbicide while they are still small. While some of these standard recommendations allow for termination to occur after significant spring growth, that would be a worst-case scenario and not one of our BMPs for a standard growing season. Cover crops have provided their benefits, and now is the time to consider termination to ensure maximum yield of the following cash crop.
- Chemical control and rate should be dependent on cover crop species and growth stage
- Glyphosate is many times the best solution, or may be used in conjunction with other herbicides to gain complete control
- Complete termination is the key to starting off a successful cropping season