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University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

Alternative Weed Control Strategies and Pesticide Free Production: Brandon MB

Background

Pesticide Free Production (PFP) was developed by Canadian farmers and researchers as a practical means of reducing pesticide use in certain years. PFP is a production system in which non-genetically modified crops are grown without the use of pesticide, including chemical seed treatments, from the time of crop emergence until the time of marketing (learn more about Pesticide Free Production). Residual activity of pesticides used prior to the PFP crop must have ceased, but use of non-residual pre-emergent pesticides such as Roundup is permissible. In addition to this, there are no restrictions on the use of fertilizer.

Study Objectives

The objective of this experiment was to determine the success of PFP oat production in a four year rotation of pea-wheat-canola-oat. The utility of chaff removal, strategic tillage, and intensive herbicide usage in non-PFP years is compared to a conventional rotation and a PFP rotation that was identical to the conventional system except that pesticides were not applied.

Experiment Description

Research was conducted Northwest of Brandon on a Newdale clay loam soil. The field experiment utilizes commercially available farm equipment and large plots to ensure that the results are applicable to field scale production. The experiment compares five PFP rotations to a conventional pesticide rotation. Oat is the target PFP crop. Given the extensive usage of zero tillage in western Manitoba, this experiment was conducted in zero tillage and is a complimentary study to the zero tillage PFP experiment conducted at Carman by the University of Manitoba.

The treatments are as follows:

 
Year 1
Year 2
Year 3
Year 4
 
 
 
 
 
Pea
Wheat
Canola
Oat
 

Treatments

 

Conventional

pesticide*

pesticide

pesticide

pesticide

 

Standard PFP

pesticide

pesticide

pesticide

PFP

 

PFP+Chaff Collection (CC)

pesticide + chaff collection

pesticide + chaff collection

pesticide + chaff collection

PFP+ chaff collection

 

PFP + Strategic Tillage (ST)

pesticide

pesticide

pesticide + fall harrows

PFP

 

PFP + CC+ ST

pesticide + chaff collection

pesticide + chaff collection

pesticide + chaff collection + fall harrows

PFP + chaff collection

 

PFP + Intensive Weed Management (IWM)

pesticide + chaff collection

pesticide + chaff collection

pesticide + chaff collection

PFP + chaff collection + trifluralin after oat harvest

 

* "pesticide" refers to in-crop pesticide; glyphosate is used on all treatments before crop-emergence

This experiment is fully-phased, meaning that every treatment occurs every year to avoid weather effects. Plots were established in 2000, therefore rotational data and comparisons of PFP approaches could not be made in this year. However, comparisons between PFP and non-PFP oat were possible as was the impact of oat PFP production on subsequent pea yields. In 2003 the rotations have still not gone through a complete cycle of the rotation.

Results

The following are a summary of results from 2000 to 2003. Note that all crops appeared in all years of the rotation to remove weather effects from any one year.

Oat Yield

In 2003 the average PFP oat yields were 11% greater than the non PFP yields. In 2002 some PFP oat treatments had a 4% yield advantage over conventionally grown oats, this differs from 2001 where the yields were the same. It is possible that herbicide damage in the conventional oat production system reduced oat yields. Damage from Stampede is greater under conditions of high temperature and moisture such as 2003. Likewise there may have been some physical crop damage from herbicide application, although this is considered unlikely. In 2002 and 2003 yields in all crops were greater where the chaff cart had been used. Seed size in oat was not impacted by weed management (data not shown). No explanation for the improved crop yields can be offered as the numbers of volunteer grain did not appear to be altered significantly indicating that much of the volunteer grain was shattered prior to the crop entering the combine.

Dockage

Dockage in PFP oat were generally the same as conventionally grown oat. The chaff collection and disturbance treatments had very little impact on dockage in PFP oat with the lowest dockage occurring in the plots with standard PFP. This number, while numerically the lowest, did not differ significantly from conventionally produced oat and most other treatments. Dockage levels vary greatly between years and appear to reflect harvesting conditions more than weed numbers.

Pea Yield

Pea yields in 2003 were 19% higher in plots where intensive weed management had occurred. However, pea yields were equal where PFP oat and standard weed management PFP oat were produced. PFP oat can be grown without yield reductions in the subsequent pea crop. Pea yields in chaff cart & strategic tillage (PFP + CC +ST), strategic tillage (PFP + ST) and trifluralin (PFP + IWM) were higher than other PFP and conventional planting in 2003. This differs from previous seasons when pea yield was equal after all oat crops. Dockage in pea was less than 2.5% in all crop rotations and while the rotation where trifluralin was added had slightly lower dockage this was similar to several other treatments (data not shown). Pea seed size was slightly affected by weed management in the PFP year (data not shown). This difference was only 2.5% and was while seed size was lowest in treatments where chaff collection occurred it is doubtful that chaff collection was causal.

Weed Density

When taken across all crops weed density was similar for all management systems except for the PFP with intensive weed management in pea after oat and in canola after wheat (only pea data shown). Weed densities prior to in crop spraying varied from an average of 7/m2 prior to in crop spraying in wheat to 99 prior to spraying canola. Almost all of the weeds in dry pea were oat species and were likely volunteer oat . Volunteer oat numbers were not consistently reduced by the use of the chaff cart. The low weed densities, prior to incrop spraying of the non PFP oat crop, were similar in 2001 and 2002. Mustard/canola species were low and with the exception of PFP+intensive weed management did not differ between treatments in 2002.

Weed Biomass

Weed biomass in the oat crop in 2003 was less than in 2002. Variability in weed biomass between the PFP treatments was not consistent between seasons and the total biomass was less than 1% of the seed yield indicating excellent weed management had been obtained. Weed biomass in the pea crop where surface applied trifluralin was applied was less than 3 g/m2 which was 10% of where non PFP oat had been grown or any of the other PFP treatments. This low level would indicate that most of the dockage in dry pea was pods and broken seed rather than weeds.

Recommendations

  • Oat is a superior PFP crop. Regardless of PFP management, PFP oat yielded the same as or better than sprayed oat.
  • PFP oat can be grown without yield reductions or weed problems in the subsequent pea crop.
  • Weed density was less when trifluralin was used after PFP oat, however, herbicide use was not reduced in this treatment when compared to the conventional treatment.
  • The key to this PFP production system is the application of preharvest Roundup to prevent the build up of perennial weeds and the use of direct seeding.
  • It should be noted that the excellent weed control in the PFP oat crop is due in part to delaying seeding of this crop until after many weeds have emerged.
  • Likewise it should be noted that this trial was begun on land which had very few perennial weeds and had been where weed numbers were reduced by the harvest of the preceding crop for green feed.

Further Information:
Producing PFP Oats - Reducing Pesticide Risk (CD-ROM available free of charge)

Copyright and Liability

This page created August 2004.
Updated March 2005.