By: Clark Brenzil, PAg., Provincial Specialist Weed Control
The Saskatchewan Weed Survey was conducted in 2014 and 2015. As part of it, a survey of herbicide resistance (HR) was also conducted on a subset of the same fields across the province. This survey indicated that Group 1 and 2 HR is increasing across the province.
The results are concerning, with 57 per cent of surveyed fields showing the presence of at least one HR weed biotype. This is a substantial increase when compared to 31 per cent of fields in 2009 and 10 per cent of fields in 2003.
Based on this survey, it is estimated that nearly 12 million acres in Saskatchewan are infested with weeds resistant to Group 1 and Group 2 herbicides, representing a total field area of 21.5 million acres of farmland. Based on survey responses from affected farmers, the estimated additional cost to manage HR weeds in Saskatchewan is estimated at $258 million annually.
When looking at survey specifics:
Wild oat (Avena fatua L.)
- Forty-nine per cent of the surveyed fields had either Group 1 or Group 2 resistant wild oat, compared with 35 per cent of sampled fields in 2009.
- Group 1-HR wild oat was found in 45 per cent of all surveyed fields (67 per cent per cent of wild oat populations), compared with 24 per cent of surveyed fields (32 per cent of wild oat populations) in 2009. This is a rough doubling in five to six years.
- Group 2-HR wild oat was found in 21 per cent of all surveyed fields (32 per cent of wild oat populations), compared with 7 per cent of sampled fields in 2009.
- Wild oats testing resistant to both Group 1 and Group 2 herbicides was found in 16 per cent of all surveyed fields (25 per cent of wild oat populations), compared with 5 per cent of fields sampled in 2009. Wild oats in these fields would only be manageable with Group 3 herbicides, triallate (Group 8), glyphosate, Liberty and suppression with Focus (Group 15).
- In an elevator survey conducted across Saskatchewan in 1997 (Beckie and Juras 1998; Beckie et al. 1999a, 1999b), roughly one quarter of elevators had wild oat seeds that were resistant to Group 8. There were also wild oats that were resistant to all of Groups 1, 2 and 8. Presumably the proportion of these populations has increased over time as well.
- Wild oats are also ranked second in their likelihood of acquire glyphosate resistance in models developed by Dr. Hugh Beckie at Agriculture and Agri-Food Canada in Saskatoon.
- Resistance to Group 15 in wild oat has recently been documented in Manitoba, which has a longer history of Group 15 use in corn and soybeans.
- The highest levels of Group 1 resistance were found in the Brown soil zone with 60 per cent of fields tested; the highest level of Group 2 resistance was found in the Dark Brown soil zone with 30 per cent of fields.
Green foxtail (Setaria viridis (L.) P. Beauv. = wild millet)
- Thirty-one per cent of the surveyed fields had either Group 1- or Group 2-resistant green foxtail, compared with 14 per cent of sampled fields in 2009.
- Group 1-HR green foxtail was found in 17 per cent of fields where the weed was sampled.
- Group 2-HR green foxtail was found in 15 per cent of fields; this is the first survey in Saskatchewan to document Group 2 resistance in this weed.
- Two fields had Group 1+2 HR green foxtail.
Broadleaf weeds (Group 2 only):
- Six broadleaf weed species were found to have Group 2 herbicide resistant populations:
- Chickweed in 20 per cent of fields sampled. Chickweed resistant to Group 2 herbicides was not found in the 2009 or 2003 surveys.
- Cleavers in 20 per cent of fields sampled. This level is roughly the same as the 21 per cent of fields Group 2-HR cleavers was found in 2009.
- Redroot pigweed* in 10 per cent of fields sampled.
- Shepherd’s-purse* in 23 per cent of fields sampled.
- Stinkweed* in 14 per cent of fields sampled.
- Wild mustard in 25 per cent of fields sampled.
*This is the first Saskatchewan survey to document redroot pigweed, shepherd’s-purse and stinkweed with populations resistant to Group 2 herbicides.