109 What’s Up? Preliminary Results from the 2002 Manitoba Survey of Weeds in Cereal and Oilseed Crops Rene Van Acker, Dept. of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2 [email protected] Gordon Thomas and Julia Leeson, Agriculture and Agri-Food Canada, Saskatoon, SK Todd Andrews and Kim Brown, Manitoba Agriculture and Food, Carman, MB. Introduction Weed surveys in arable crops are valuable for establishing the extent and nature of weed infestations. This information can be used by researchers, by extension and industry specialists, and by producers to establish priorities for weed management strategies within a region. With a series of surveys over time, tracking the rise or decline of species is also possible, indicating potential problems, and the impact of changes in agricultural practice and policy on weed infestations. In Manitoba, provincial weed surveys of residual weed populations in major cereal and oilseed crops were conducted in 1978-81 (Thomas and Wise 1984) in 1986 (Thomas and Wise 1988) and in 1997 (Van Acker et al. 2000). On average, cereals accounted for 79%, canola (Brassica napus L.) 9% and flax (Linum usitatissimum L.)12% of the fields included in these surveys. The purpose of the 2002 survey was to establish a Asnapshot@ of the nature and extent of weed infestations within Manitoba fields seeded to the major cereal and oilseed crops. This survey project was part of a program of the Research Branch of Agriculture and Agri-Food Canada to document relative abundance and geographic distribution of weed problems across Canada. The 2002 survey was organized by ecodistricts within the ecoregions of the province (Smith et al. 1998) (Figure 1). This approach allowed for an investigation of the relationship of weed infestations to ecologically-based divisions within the province. Methods In 2002 a post control (mid-summer) survey of weed species was conducted in fields of spring wheat, barley, oats, flax and canola using stratified random sampling to select fields within agroecoregions in Manitoba. A total of 631 fields were surveyed. Weed data was summarized on the basis of relative abundance (RA) which is an integrated measure of frequency, density and uniformity. Weeds within chosen fields were counted within twenty 0.25 m2 quadrats placed within an inverted “W” pattern in an area within the field that was considered representative of the field and at least 100 m from any field margin (Leeson et al. 2002). For annual, biennial, simple perennial and winter annual species, individuals were counted. For spreading perennials, above ground shoots were counted as individuals. Surveys were coordinated by Agriculture and Agri-Food Canada and Manitoba Agriculture. Surveys were conducted by Manitoba Agriculture staff, Agriculture and Agri-food Canada staff from Saskatoon, Manitoba weed supervisors, and graduate students from the University of Manitoba. Results From the 1978-81 surveys, a hierarchy of weed species was established within the province. Nine weed species accounted for 77% of the relative abundance of the 152 weed species observed in the survey (Thomas 1991). Green foxtail (Setaria viridis (L.) Beauv.), wild oats (Avena fatua L.) and wild buckwheat (Polygonum convoluvulus L.) were ranked first, second and third in relative abundance in the 1978-81, 1986 , 1997 and 2002 surveys. Canada thistle (Cirsium arvense L.) was the most abundant perennial species, ranking fifth in 1978-81, eighth in 1986, fourth in 1997 and fourth in the 2002 survey. On the basis of RA the top 10 weed species in field crops in Manitoba in 2002 were (in order from most to least abundant); green foxtail, wild oat, wild buckwheat, barnyardgrass (Echinochloa crus-galli L.), Canada thistle (Cirsium arvense L.), redroot pigweed (Amaranthus retroflexus L.), lamb’s quarters

110 (Chenopodium album L.), pale smartweed (Polygonum lapathifolium L.), dandelion (Taraxacum officinale G. H. Weber ex Wiggers) and volunteer canola (B. napus) (Figure 2). When compared to past surveys, we noticed that a number of weed species were becoming more abundant in the province. Of note are annual sowthistle (Sonchus asper (L.) Hill & S. oleraceus L.), dandelion, volunteer canola, volunteer wheat (Triticum aestivum L.), barnyardgrass and kochia (Kochia scoparia (L.) Schrad.), which have risen in RA ranking by 22, 13, 9, 9, 8 and 7 positions respectively, when compared to the 1997 survey. Other weed species have become much less abundant, including Russian thistle (Salsola kali L. subsp. ruthenica (Iljin) Soó), bluebur (Lappula squarrosa (Retz.) Dumort). shepherd’s purse (Capsella bursa-pastoris L.) and chickweed (Stellaria media (L.) Vill.) which have fallen in RA ranking by 21, 15, 14 and 11 positions respectively, when compared to the 1997 survey (Table 1). The top three species, in terms of RA, have not changed since broad surveys began in Manitoba in the 1970’s. Generally, post control weed densities have been declining in field crops in Manitoba since the 1970’s. This pattern has been consistent across all weed life form groups (winter annuals, perennials, annuals). These results show that our overall weed management efforts may be effectively reducing weed density in field crops in Manitoba, generally. Area surveyed in agricultural regions and districts included in the weed survey.

Porcupine Provincial Forest

Swan River

Duck Mountain Provincial Park

Northwest Region

Ethelbert

Roblin Dauphin Riding Mountain National Park

Russell

Shoal Lake Hamiota Virden

Ste. Rose

Souris

Carberry

Teulon

Boissevain

Stonewall

Portage La Prairie Treherne

Somerset

Melita

Killarney Pilot Mound

Southwest Region Central Region

Ashern Fisher Branch Arborg Lundar

MinneNee- Gladdosa pawa stone

Brandon

EasternInterlake Region

Selkirk

Winnipeg

Ecoregions Beausejour

Dugald

SteinSt. bach Pierre Carman Morris Starbuck

Morden

Dominion City Altona

Interlake Plain & Lake of the Woods Boreal Transition Mid-Boreal Uplands Lake Manitoba Plain Aspen Parkland Southwest Manitoba Uplands Agricultural Region Boundary

Vita

Leeson, J. Y., A. G. Thomas, T. Andrews, K. R. Brown and R. C. Van Acker. 2002. Weed survey of Manitoba cereal and oilseed crops in 2002. Agriculture and Agri-Food Canada Weed Survey Series Publication 02-2. Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan.

Figure 1. Area surveyed in 2002, showing ecoregions and agricultural regions and districts. Volunteer wheat has increased in relative abundance since the 1997 survey rising in rank from 21st in 1997 to 12th in 2002 (Table 1). Volunteer wheat frequency increased from 10.2% of fields surveyed in 1997 to 15.8% of fields surveyed in 2002. Average occurrence density remained relatively unchanged at 2.4 and 2.1 plants m-2 in 1997 and 2002, respectively. The rise in abundance of volunteer wheat may be related to the steep rise in incidence and severity of fusarium infection of wheat in Manitoba over the past decade. With fusarium infection, more grain is passed through the combine, and although this grain is diseased much of it will remain adequately viable to recruit as volunteer seedlings.

111 Barnyardgrass has risen in relative abundance moving from 12th position in 1997 to 4th in 2002. Barnyardgrass was found in 24.1% of fields in 2002, compared to 18.1% in 1997 (Table 1). The area of infestation remains similar to the 1997 survey where barnyardgrass was found mostly in the Lake Manitoba plain and Interlake ecoregions. Barnyardgrass is a warm season grass which prefers moist soils for recruitment (Maun and Barrett 1986). The rise in abundance of this species over the past 5 years may be related to above average rainfall levels in the Lake Manitoba plain and Interlake ecoregions during this period (Paul Bullock, personal communication). Volunteer canola (Brassica napus L.) has increased in rank from 31st in 1978-81 to 28th in 1986, to 19th in 1997 and to 10th in 2002, based on relative abundance (Table 1). This rapid and steady increase was due, in part to the increase in canola acreage in the province, but between the years of 1997 and 2002 canola acreage has not increased and so the most recent rise in relative abundance of this species must be due to other factors. Controlling glyphosate resistant volunteer canola requires the addition of 2,4-D or MCPA to pre-seeding glyphosate treatments and this may not always be entirely effective (Simard et al. 2003). In addition, glyphosate tolerant volunteer canola has been found to contaminate pedigreed certified canola seedlots and this can lead to unexpected control problems for producers who choose to grow nonglyphosate tolerant canola in direct-seeded cropping systems (Friesen et al. 2003). Relative Abundance Index

80

60

40

20

Life form Annual grass Annual broad-leaved Facultative winter annual Perennial

Weed Species

Frequency Uniformity Density

0 Green foxtail Wild oats Wild buckwheat Barnyard grass Canada thistle Redroot pigweed Lamb's-quarters Pale smartweed Dandelion Volunteer canola (Argentine) Wild mustard Volunteer wheat Annual sow-thistle spp. Quack grass Cleavers Kochia Round-leaved mallow Night-flowering catchfly Perennial sow-thistle Stinkweed

(%)

(%)

(m-2)

65.0 56.6 57.7 24.1 41.4 27.9 24.6 27.1 20.6 16.6 16.5 15.8 16.8 12.7 10.8 8.6 11.6 10.1 12.0 8.4

27.7 20.2 15.1 6.0 7.3 5.9 5.2 5.1 3.3 3.3 2.9 2.9 2.3 1.9 2.7 1.6 2.0 1.7 1.2 1.3

23.8 11.7 2.8 12.0 1.8 3.4 2.9 1.9 1.5 2.7 2.1 2.1 1.1 4.1 3.8 6.2 1.5 1.5 0.9 3.2

Figure 2. From the 2002 weed survey in Manitoba, the top 20 weed species ranked according to relative abundance. Uniformity and density measures are occurrence measures. Annual sowthistle was much more abundant in the 2002 survey compared to the 1997 survey and perennial sowthistle abundance fell (Table 1). This is an artifact of the 2002 survey method where particular attention was paid to identifying annual and perennial sowthistle as separate species in the 2002 survey. Annual sowthistle, however, remains a significant weed species in Manitoba appearing in 15.8% of fields in 2002. It is interesting that annual sowthistle is found in greatest abundance concisely in the Swan River and Grandview ecodistricts which are classified as cold sub-humid to humid ecodistricts (Smith et al. 1998). The distinction in abundance is acute between the Swan River and Hamiota ecodistricts where there is much less abundance of annual sowthistle in the latter. The Hamiota

112 ecodistrict has a significantly greater soil water deficit (180 mm) than the Swan River (150 mm) or Grandview (130 mm) ecodistricts (Smith et al. 1998). The difference in abundance may be linked to greater soil moisture levels and annual sowthistle’s propensity to recruitment in soil with greater moisture levels (Boyd and Van Acker 2003). The abundance in these regions may also result from windborne seed movement from nearby ecodistricts in Saskatchewan. In the 1995 weed survey in Saskatchewan it was shown that sowthistle was most abundant in the Swan River Plain, St. Lazare Plain, Yorkton Plain and Melville Plain ecodistricts (Thomas et al 1996) which sit to the immediate west and northwest of the Swan River ecodistrict. Table 1. Weed species shifts in rank among surveys from 1979-81 to 2002. Rankings based on relative abundance.

Annual grass Barnyard grass Volunteer wheat Green foxtail Wild oats Volunteer barley Annual broad-leaved Annual sow-thistle spp. Volunteer canola Cleavers Kochia Round-leaved mallow Chickweed Redroot pigweed Wild buckwheat Lamb's-quarters Thyme-leaved spurge Wild mustard Pale smartweed Hemp-nettle Volunteer flax Dog mustard Russian thistle

Change in Relative Abundance Rank 1970’s 1986 1997 1970’s to to to to 1986 1997 2002 2002

-14 3 0 0 7

15 -3 0 0 -12

8 9 0 0 2

9 9 0 0 -3

16 3 13 1 2 13 2 0 0 -6 3 -1 3 5 8 -7

40 9 6 8 4 4 2 0 -3 1 -2 -2 -2 -9 -18 -11

22 9 0 7 3 -11 -1 0 2 3 -5 -1 -8 -7 -5 -21

78 21 19 16 9 6 3 0 -1 -2 -4 -4 -7 -11 -15 -39

3 -2 1 -7

4 -2 -7 -26

-14 -4 -3 -15

-7 -8 -9 -48

-11 -3 -1 -2 -3

14 4 3 -5 3

13 -1 -4 2 -11

16 0 -2 -5 -11

Facultative winter annual Shepherd's-purse Night-flowering catchfly Stinkweed Bluebur Perennial Dandelion Canada thistle Quack grass Field horsetail Perennial sow-thistle

Kochia has risen significantly in rank since 1997, rising to 16th position in 2002 from 23rd position in 1997 (Table 1). Although kochia was found in only 8.6% of fields in 2002, infestations of kochia are concentrated in the Oaklake and Killarney ecodistricts in the southwest of the province and the Melville ecodistrict west of Brandon, which are within the Aspen Parkland ecoregion. It is also found in high

113 relative abundance in the Alonsa ecodistrict within the Lake Manitoba Plain ecoregion. All of these ecodistricts have large areas with salinity problems (Smith et al. 1998) and this may help to explain the abundance of kochia in these districts because it is a species which can establish in saline soils. Kochia abundance is also rising within the Winkler and Emerson ecodistricts within the Lake Manitoba Plain ecoregion. The rise in abundance in these latter ecodistricts may be related to the great increase in dry bean (Phaseolus vulgaris L.) acreage in these ecodistricts within the past 5 years, and the association of increased soil salinization with the frequency of shallow rooted, low water use crops such as dry beans in rotation. There has also been an increase in group 2 (acetolactate synthesis inhibitor) herbicide use in Manitoba over the past 10 years (Thomas et al. 1997) and group 2 resistant kochia biotypes exist in Manitoba, and their incidence may be rising, although this has not been confirmed. Facultative winter annual species have fallen greatly in relative abundance since 1997 (Table 1). This is somewhat surprising given the low levels of tillage commonly practiced in Manitoba (Thomas et al. 1999). The decline in abundance of this species group may reflect an increased awareness of these species by producers who practice reduced-tillage cropping and a concomitant increase in their skill in effectively managing this group of species. Among perennial species, dandelion abundance has risen greatly since 1997 (Table 1). This increase in abundance may be related both to a decline in tillage and to above average rainfall, generally, in Manitoba over the past 5 years. Dandelion is a simple perennial. Seedling recruitment for this species is favoured in moist soils (Froese and Van Acker 2003, Boyd and Van Acker 2003) and recent years of above average precipitation, coupled with a reduction in tillage in Manitoba may be contributing to the rise in abundance of this species. The Dandelion infestation is highly abundant in the Hamiota ecodistrict where annual sowthislte is less abundant and Boyd and Van Acker (2003) have shown that although dandelion recruitment is favoured in moist soils it will still recruit to a significant level in dry soils, and to a greater extent than sowthistle. The increase of abundance of both Dandelion and annual sowthistle into ecodistricts within the upper Aspen Parkland and Lower Boreal Transition ecoregions may also be related to the ability of both of these species to recruit from the surface and to recruit throughout the season which allows these species to successfully invade reduced tillage fields and gaps within forage hay production fields (Stewart-Wade et al. 2002; Hutchinson et al. 1984). Forage hay production fields are relatively common within these ecodistrict (Martin Entz, personal communication). A number of species have fallen in relative abundance since 1997. Wild mustard was found in only 16.5% of fields in 2002 versus 37.4% of fields in 1997. This decline suggests a significant improvement in management of this species, and this improvement must be in in-crop treatments because wild mustard maintains a very long-lived seedbank, and eradication from given sites in 5 years is unlikely. The introduction of herbicide tolerant canola and an increase in use of highly efficacious group 2 products in cereals (Thomas et al. 1999) may have facilitated the management of wild mustard in canola and cereal crops, respectively. In 2002, hempnettle was found in only 6.8% of fields, down from 13.9% of fields in 1997. Hempnettle is not well controlled with group 4 (auxinic) herbicides (O’Donovan and Sharma 1987) and the recent decline in abundance may be related to a rise in use of herbicides in groups other than group 4 in cereal and oilseed crops, generally, in Manitoba (Thomas et al. 1999). Conclusions The 2002 weed survey results, and comparisons to former surveys, show us that certain weed species are emerging as new weed problems, including volunteer canola, volunteer wheat, barnyardgrass and annual sowthistle. These species require focused management attention in the future. The survey also shows us that some species are declining in abundance and that these declines may be management related. The reasons for an increase or decrease in abundance of given species is facilitated by stratification of the survey on the basis of ecodistricts. However, there is still considerable speculation required in developing explanations for species abundance shifts. Management information from surveyed fields is being

114 gathered and this information will provide valuable opportunity for additional insight into why given weed species are more or less prevalent within given ecodistricts. The deductive power of this information is even greater now that we can compare trends in management using the 1997 questionnaire data. Deducing whether management changes have contributed to a rise or decline in abundance of a given species will be of great value. This analysis will proceed in the coming year. Acknowledgments Direct financial assistance to conduct the survey was provided by the Matching Investment Initiative (MII) of Agriculture and Agri-Food Canada and by the following herbicide manufacturers and distributors: Aventis Crop Science Canada Co., BASF Canada, Bayer Inc., Dow AgroSciences Canada Inc., Dupont Canada Inc., Monsanto Canada Inc., Nufarm Agriculture Inc., WestCo Fertilizers Limited References: Boyd, N.S. and R.C. Van Acker. 2003. The effects of depth and fluctuating soil moisture on the emergence of ten annual and five perennial weed species. Weed Sci: 51 (in press). Friesen, L.F., A.G. Nelson and R.C. Van Acker. 2003. Evidence of contamination of pedigreed canola (Brassica napus) seedlots in western Canada with genetically engineered herbicide resistant traits. Poster abstract. Proceedings of the Canadian Weed Science Society annual meeting, Saskatoon, SK. (in press). Froese, N. T., and R. C. Van Acker. 2003. Distribution and interference of dandelion (Taraxacum officinale G.H. Weber in Wiggers) in spring canola. Weed Science 51: (in press) Hutchinson, I., J. Colsi, and R.A. Lewin. 1984. The biology of Canadian weeds. 63. Sonchus asper (L.) Hill and S. oleraceus L. Can J. Plant Sci. 64:731-744. Leeson, J. Y., A. G. Thomas, T. Andrews, K. R. Brown and R. C. Van Acker. 2002. Manitoba weed survey of cereal and oilseed crops in 2002. Weed Survey Series Publication 02-2. Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan. Maun, M.A., and S.C.H. Barrett. 1986. The biology of Canadian weeds. 77. Echinochloa crus-galli (L.) beauv. Can. J. Plant. Sci. 66:739-759. O’Donovan, J.T., and M.P. Sharma. 1987. The biology of Canadian weeds. 78. Galeopsis tetrahit L. Can. J. Plant Sci. 67:787-796. Simard, M., and A. Legere. 2003. Control of volunteer canola with auxinic herbicides. Poster abstract. Proceedings of the Canadian Weed Science Society annual meeting, Saskatoon, SK. (in press). Smith, R. E., Veldhuis, H., Mills, G. F., Eilers, R. G., Fraser, W. R. and Lelyk, G. W. 1998. Terrestrial Ecozones, Ecoregions, and Ecodistricts of Manitoba, An Ecological Stratification of Manitoba's Natural Landscapes. Technical Bulletin 1998-9E. Land Resource Unit, Brandon Research Centre, Research Branch, Agriculture and Agri-Food Canada, Winnipeg, Manitoba. Report and map at 1: 1 500 000 scale. Stewart-Wade, S.M., S. Neumann, L.L. Collins and G.J. Boland. 2002. The biology of Canadian weeds. 117. Taraxacum officinale G.H. Weber ex Wiggers. Can J. Plant Sci. 82: 825-853. Thomas, A. G. 1985. Weed survey system used in Saskatchewan for cereal and oilseed crops. Weed Sci. 33: 34-43. Thomas, A. G. 1991. Floristic composition and relative abundance of weeds in annual crops of Manitoba. Can. J. Plant Sci. 71: 831-839.

115 Thomas, A. G., R.F. Wise, B.L. Frick and L.T. Juras. 1996. Saskatchewan weed survey of cereal and oilseed crops in 1995. Weed Survey Series Publ. 96-1. Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan. 419 pp. and maps. Thomas, A. G., Frick, B. L., Van Acker, R. C., Knezevic, S. Z. and Joosse, D. 1998. Manitoba weed survey of cereal and oilseed crops in 1997. Weed Survey Series Publ. 98-1. Agriculture and AgriFood Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan. 192 pp. and maps. Thomas, A. G., Frick, B. L., Van Acker, R. C., Knezevic, S. Z. and Joosse, D. 1999. Farm Management

practices in Manitoba, 1997 Manitoba weed survey questionnaire results. AAFC Weed survey series 99-3. Agriculture and Agri- Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan. 297 pp. Van Acker, R. C., Thomas, A. G., Leeson, J. Y., Knezevic, S. Z. and Frick, B. L. 2000. Comparison of weed communities in Manitoba ecoregions and crops. Can. J. Plant Sci. 80:963-972