By: Eric Yu, Graduate Research Assistant; Liz Stahl, Extension Educator - Crops; & Debalin Sarangi, Extension Weed Specialist
 |
Fig. 1. Cereal rye cover crop at the tillering stage in
Rosemount, MN, on May 5, 2022. |
When managed properly, a fall-planted cereal rye cover crop can provide several soil health and weed management benefits. However, adequate termination of cereal rye in the spring is important for proper cash crop establishment and to prevent the cover crop from becoming an unwanted plant in the field. Inadequate termination can lead to unwanted competition with the cash crop for moisture, nutrients, and/or sunlight, which can ultimately lead to yield reductions of the cash crops.
Evaluating mechanical and chemical options
Field experiments were conducted at Lamberton and Rosemount, MN, in 2022 to evaluate various mechanical and chemical options for cereal rye cover crop termination in the spring. The mechanical treatments included mowing the cereal rye at ground level and a tillage treatment of rototilling to a 10-inch depth. The herbicide treatments included Roundup PowerMax, Liberty, Gramoxone, Select Max, and Reviton alone, as well as a Roundup PowerMax with various tank-mix partners and Gramoxone + 2,4-D (see Table 1 for the full list of treatments and rates). Herbicides were applied at a 15 gal/A carrier volume using AIXR 110015 nozzles.
Cereal rye was drilled at a rate of 60 lbs/A after soybean harvest in 2021. In the following spring of 2022, the cover crop was terminated at either the tillering (early) or heading (late) growth stage. This corresponded to a date of May 9 and May 16 for the early termination timing at Rosemount and Lamberton, respectively, and June 1 for the late timing at both locations.
Table 1. Cereal rye cover crop termination treatments, applied at two timings: Early (the tillering stage of cereal rye), or late (the heading stage).
| Treatment |
Rate |
|
fl oz/acre |
|
|
|
|
| Mowing |
-- |
| Tillage (rototiller) |
-- |
| Roundup PowerMax |
32 |
| Liberty |
29 |
| Select Max |
12 |
| Reviton |
2 |
| Roundup PowerMax + Liberty |
32 + 29 |
| Roundup PowerMax + Select Max |
32 + 12 |
| Reoundup PowerMax +Reviton |
32 + 2 |
| Roundup PowerMax + 2,4-D LV6 |
32 + 12 |
| Roundup PowerMax + Valor SX |
32 + 3 |
| Roundup PowerMax + Verdict |
32 + 5 |
| Gramoxone |
32 |
| Gramoxone + 2,4-D LV6 |
32 + 12 |
Termination results
Cereal rye percent control was assessed visually 21 days after treatment by comparing treatments to the untreated control. Figure 2 shows the percent control of cereal rye as a result of the termination treatments at each termination timing.
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| Figure 2. Cereal rye control/ (%) 21 days after treatment when treatments were applied at the (A) tillering stage, and (B) heading stage. Bars with no common letter(s) on the top are statistically different at Ī± = 0.05. |
Mechanical control options
For the mechanical options, tillage (rototiller) and mowing worked better when termination was delayed to the heading stage. Cereal rye control reached 98% with tillage at this stage, while mowing only resulted in 45% control at the later timing.
Herbicide control options
Roundup PowerMax (glyphosate) applied alone or with other herbicides provided maximum (> 95%) cereal rye control regardless of growth stage at termination. The efficacy of Select Max (clethodim) was growth stage dependent with
better control (88%) at the tillering stage than at heading (7%). Liberty
(glufosinate) and Reviton (tiafenacil) did not provide adequate control at
either the tillering or heading stages. Treatments that included Gramoxone
(paraquat) provided total control when termination was delayed to the heading stage, but control was less than the Roundup PowerMax treatments at tillering.
 |
| Figure 3. Cereal rye termination 14 days after treatment in Rosemount, MN in 2022. The treatments were applied at the tillering stage of cereal rye. |
Take-home messages
- Best cereal rye termination option - Glyphosate was the best option for terminating cereal rye in the spring. If there are concerns that glyphosate-resistant weeds are present in the field at the time of termination, add a tank-mix partner that will bring an alternate site of action for control of those weeds. Effectiveness and rapidity of termination improves when applications are made on a warm, sunny day.
- Glufosinate considerations - Like this research, previous studies conducted in the Midwest also reported that control of a cereal rye cover crop in the spring with glufosinate was less effective and more inconsistent than control with glyphosate. Glufosinate works best when applied on warm, sunny days with enough humidity in the air. Spray coverage should be maximized to get the best results from contact herbicide (e.g., Liberty and Gramoxone) applications.
- Paraquat considerations - It is important to note that if a person is considering using paraquat as an alternative to glyphosate, it is a restricted use pesticide, so the applicator must be certified at the time of application. Additional training is also required every three years for anyone who will be mixing, loading, and/or applying paraquat due to this product’s toxicity (see more details at https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators).
- Final thoughts - For organic producers, the timing of cereal rye termination is important. Mowing did not provide adequate control in this trial, but tillage was a viable option if termination was delayed until heading. However, if dry conditions prevail in the spring, termination delays may lead to moisture stress for the cash crops. If cereal rye is used as forage or for grazing, it should be harvested multiple times for total control.
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