Pesticide Free Production

The study site is located at the Ian N. Morrison research farm in Carman, Manitoba on Treaty 1 territory. The soil is an Orthic Black Hochfeld fine loam.

Original Experiment

There were two fully phased rotations and the treatments were:

Control - in-crop herbicides were applied on all annual crops.

PFP1 - in-crop herbicides not applied to oats.

PFP2 - in-crop herbicides not applied to oats and flax.

Key Findings

Weed Population

• Over the long term, weed seedbank populations were greater in rotations where in-crop herbicides were omitted, but significant yield reductions only occurred in some PFP2 crops.
• After ten years, the weed community composition in the seedbank of the control and PFP1 rotations were similar. In the PFP2 rotation there was a species shift toward lambsquarters, Canada thistle, buckwheat, and foxtail species, and away from redroot pigweed and yellow woodsorrel.
• The weed seedbank density in the tallgrass prairie was about 7 times less than the annual control rotations and was dominated by lambsquarters and foxtail species.
• The continuous chemical fallow treatment had the lowest weed seedbank density—almost 40 times lower than the control annual rotations—and was predominantly redroot pigweed and yellow woodsorrel.

Crop yield

• When looking at the yield of all annual crops over four years, there was only a reduction in yield in the PFP2 rotation.
• The PFP1 rotations had higher weed seedbank densities than the control but this did not negatively impact the yields of any of the annual crops.
• There was no yield reduction in wheat or canola, even in the PFP2 annual rotation where the seedbank population was doubled. This is due to their competitiveness with weeds and the effective in-crop herbicides that are available for these crops.

Economics

• Over 10 years, a crude economic analysis suggests that occasional in-crop herbicide omissions, particularly in competitive crops, may increase net revenues by saving the costs of herbicide while having no major impact on weed populations and crop grain yield.

Summary

Herbicide applications are often used to reduce future weed populations. In the first ten years, this study demonstrated that increases in the densities of weed seeds in the seedbank have small negative impacts, if any, on grain yields in competitive crops. Not applying in-crop herbicides in highly competitive crops resulted in slightly higher economic returns over the long term.

In 2010 the rotation sequence was changed and in 2017 the study was modified to reflect modern crop rotation and weed management techniques in Manitoba.

The study now uses row spacing and seeding density to reduce the weed seedbank and herbicide-resistant green foxtail. The rotations have been updated to grow the most common crops grown in Manitoba (wheat, canola, and soybean) in 3 and 4-year rotations.

Gulden, R. 2012. Long-term Pesticide Free Production Study at Carman, MB (2000). Prairie Soils & Crops. 5: 30-35.

Gulden, R.H., Lewis. D.W., Froese, J.C., Van Acker, R.C., Martens, G.B., Entz, M.H., Derksen, D.A., and Bell, L.W. 2011. The effect of rotation and in-crop weed management on the germinable weed seedbank after 10 years. Weed Science. 59: 553-561.

Schoofs, A. Entz, M. H., Van Acker, R., Thiessen Martens, J., and Derksen, D.A. 2005. Agronomic performance of Pesticide Free Production under two crop rotations. Renewable Agriculture and Food Systems. 20: 91-100.

Nazarko, O., Van Acker, R., Entz, M.H., Schoofs, A., and Martens, G. 2004. Pesticide Free Production: Characteristics of farms and farmers participating in a pesticide use reduction pilot project in Manitoba, Canada. Renewable Agriculture and Food Systems. 19: 4-14.

Nazarko, O.M., Van Acker, R.C., Entz, M.H., Schoofs, A., Martens, G. 2003. Pesticide Free Production of Field Crops: Results of an On‐Farm Pilot Project. Agronomy journal 95(5): 1262-1273.

Magnusson, J.E. 2002. Consumer interest in and willingness-to-pay for Pesticide Free Production food products: a probit analysis. MSc thesis, University of Manitoba, Winnipeg.