Skip to content

Herbicides and cover crops for improved corn establishment

Principal Investigator: Francois Tardif

Research Institution: University of Guelph

Timeline: April 2020 – March 2022


  • Determine the best timing of fall rye cover crop termination prior to planting corn.
  • Determine if termination of fall rye cover crop with herbicide providing fast burn would reduce negative impact of planting green.
  • Determine if separating fall rye from corn when planted in twin rows would help improve corn establishment.
  • Determine the impact of residual corn herbicides on interseeded cover crops based on soil type and timing.


  • Ontario grain farmers will benefit by knowing which combination of termination timing, herbicide type and cover crop planting pattern will allow maximization of both fall rye biomass and corn establishment and yield.
  • The development of guidelines on the effect of PRE and early POST residual corn herbicides on interseeded cover crops will allow growers to select cover crop species with the lowest probability of injury, ensuring increased establishment success.

Scientific Summary:

Cover crops are beneficial to cropping systems as they help improve soil health and contribute to crop protection. One challenge with cover crops is to maximise their growth without reducing the yield of the main crops. For example, delaying termination of a fall rye cover crop and planting green would maximize biomass production but may affect corn establishment. This may lead to variable results which have been attributed to various causes such as rye allelopathy, N capture or increased root diseases. Another factor that has not been considered is the possibility that corn plants emerging in the presence of a green rye cover crop may see their growth impacted because of altered light being reflected by the green tissues. Another approach to cover crops that warrants examination is the variable establishment of various species when interseeded into corn, which may be due to the use of residual herbicides in PRE- or early POST-emergence. Knowing which corn herbicides have enough residual to impact cover crops and determining species’ sensitivity to specific products would allow for optimisation of interseeding.

Part 1

In order to try to improve the establishment of corn into a rye cover crop, we propose to manipulate the system so as to isolate factors that have the strongest impact.

Timing of termination: Comparing termination at 2 wks, 1 wk, 1 day before planting and 1 week after planting will determine the impact of time; Termination with glyphosate alone or mixed with a fast-acting herbicide (Liberty) would determine if a more rapid kill would reduce the negative light signal that is perceived by corn compared to the slow kill due to glyphosate alone.

Planting pattern: Rye planted in twin rows vs full coverage. Twin rows would allow corn to be planted away from the rye, presumably reducing any negative impacts this cover crop may have.

Part 2

To determine which corn herbicides have enough residual to impact cover crops, various soil residual corn herbicides will be applied PRE to corn prior to interseeding various cover crop species. The twelve herbicide treatments are: Acuron, Atrazine, Callisto, Converge XT, Dual II Magnum, Engarde, Frontier MAX, Integrity, Primextra II Magnum, Prowl H2O, XtendiMax, and Zidua SC. Six cover crop species will be seeded at the V5-V6 stage of corn and are fall rye, oats, fall triticale, red clover, white radish and oilseed radish.

External Funding Partners:

OMAFRA Alliance Tier 1

The project was funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the government of Ontario and the University of Guelph.