When should I spray my cereal rye cover crop before soybeans?

Cereal rye is a versatile cover crop that can be seeded late into the fall in Ontario. Not to be confused with annual ryegrass – a grass that can be challenging to control – it is a winter cereal that overwinters reliably and grows rapidly in the spring. Delayed termination of rye by herbicide prior to soybean planting can enhance weed suppression and soil benefits. We have summarized the findings of on-farm and small plot research trials conducted with the Ontario Soil and Crop Improvement Association from 2017-2020 that evaluated the impacts of rye and its termination timing.

Read on to learn more or click below to view a short video on the project results.

The simple answer

Spray the cereal rye cover crop just prior to planting soybeans “green” into it. Delaying termination until planting maximizes cover crop benefits and poses minimal risk to the soybean crop.

young soybeans growing in field with rye residue

A little more information

Impact on soybean yield
Delaying termination of rye and planting soybeans “green” (day of planting) does not negatively impact crop yield compared to spraying it off two weeks before planting, based on 13 site-years of replicated Ontario trials. Average yield was within 1 bu/ac (Figure 1).

Graph showing two similar box and whisker plots

Why plant green?
Delaying termination until planting greatly increases aboveground cover crop growth (Figure 2). Cover crop biomass is positively associated with soil benefits such as increased soil organic matter and improved infiltration and soil structure. It also enhances weed suppression (Figure 3).

The full story

Replicated, randomized on-farm strip-trials were conducted in Brant, Wellington, Huron, Lambton and Stormont, Dundas and Glengarry United Counties from 2017 to 2020 (Figure 4). Cereal rye was seeded at rates ranging from 20 to 100 lb/acre, as early as August and as late as November 9. Existing farmer cooperator equipment was used to seed and terminate rye and to plant soybeans.

Effects of planting soybeans green vs. early termination
• Reduced final plant stand by ~10,000 plants/acre
• Delayed soybean growth and maturity when rye stand was thick (Figure 5)
• Lowered soil moisture in seed zone during dry spring conditions
• Reduced weed abundance during soybean critical weed free period, but not enough to reduce herbicide use

Take aways for planting green
• Less is more – aim for a modest cover crop stand
• Plant green or spray rye early (10-14 days before planting). Avoid planting into yellow, dying plant material.
• Ensure seeder can cut through plant material, place seed to depth and close slot – a well-maintained no-till drill is adequate in most cases
• Use a minimum seeding rate of 160,000 seeds/acre to ensure an adequate stand
• Don’t delay termination beyond date of soybean planting; under dry spring conditions, termination 1-2 weeks post-planting can lower soybean yields

For more detailed information:

See the full-length article on Field Crops News or contact:

Jake Munroe
Soil Management Specialist (Field Crops)
Ontario Ministry of Agriculture, Food and Rural Affairs

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This project was funded in part by the Ontario Ministry of Agriculture, Food and Rural Affairs through the Canadian Agricultural Partnership, a five-year federal-provincial-territorial initiative.
The views expressed in the publication are the views of the Recipient and do not necessarily reflect those of the Province or Canada.