Termination Options for Cover Crops and Winter Cereal Forages

Best management practices for terminating winter cereal forages and cover crops with pre-plant burndown programs.

As planting season approaches, here are a few best management practices for starting clean in fields with winter cereals that will be harvested for forage or cover crops that will be terminated ahead of planting.

Terminating winter cereals harvested for spring forage.

Chopping cereal rye or triticale prior to anthesis is generally not an effective method of termination. Previous Penn State field trials have demonstrated that chopping rye at the late-boot stage can result in up to 80% regrowth and chopping at the mid-heading stage can result in up to 50% regrowth. Spraying cereal rye with common burndown products (glyphosate, paraquat, etc) prior to ryelage harvest is illegal. Consequently, termination of cereal rye that has been harvested for forage is best managed with post-harvest herbicide applications. Glyphosate (1.13 lb ae/ac) is generally a more effective burndown option than contact herbicides like paraquat for post-harvest termination of cereal rye. It is likely not necessary to delay termination after harvest to allow for regrowth when using glyphosate as long as the harvest height results in enough green leaf tissue at the base of plants to absorb the systemic herbicide and weather conditions (> 55°F) are optimal for uptake and translocation.

Cover crop termination strategies.

When terminating cover crops, consider the need for additional tank-mix partners in glyphosate- or paraquat-based burndown programs to control emerged weed populations and to optimize control of grass, legume, and brassica cover crop species. Based on field trials within this region, we recommend three keys for developing cover crop burndown programs:

1. Know which weeds are present in your cover crop stand. A well-established cover crop stand suppresses many fall- and spring-emerging weed species. But some species, such as glyphosate-resistant horseweed, may also be present in the understory of cover crop stands. Consequently, it may be necessary to adjust your cover crop burndown program or application timing to achieve effective weed control.
2. Tank-mix synthetic auxins for legumes and brassicas. Though both glyphosate and paraquat have activity on broadleaf cover crops, Mid-Atlantic field trials consistently showed including dicamba or 2,4-D LVE in the tank improved control of legumes and brassicas (Table 1).
3. Understand pre-plant application restrictions for tank-mix partners. Make sure to check herbicide labels to understand restrictions in both corn and soybean (Table 2). For example, cover crop termination timing and soybean seed trait technology (i.e., Enlist 3, Xtend, XtendFlex, LibertyLink) will determine which herbicide formulations and rates that can be used.

Table 1. Effectiveness of burndown herbicides and tank-mixtures for control of overwintering grass, legume, and brassica cover crops. Control ratings (1-10) based on Mid-Atlantic field trials. Control ratings of 9 or greater should be selected to optimize control of cover crops.

^† winter wheat, triticale, cereal rye; ^†† overwintering brassica spp; winter canola, rapeseed

Table 2. Herbicide restrictions and BMPs in cover crop termination scenarios within field crops.