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Appendix I: Best Management Practice Program for the CLEARFIELD® Brassica juncea Production System

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Best Management Practice (BMP) Program for the  CLEARFIELD® Brassica juncea Production System

Developed by  BASF Canada

Table of Contents

  1. CLEARFIELD Production System
    1. Introduction
    2. Key Sustainability Issues
  2. CLEARFIELD Production System - Guiding Principles
  3. Resistance Management in the CLEARFIELD Production System
    1. Herbicide Resistance Management using an Integrated Weed Management (IWM) Approach
    2. Development of Resistance
    3. Identifying Weed Resistance
    4. General Recommendations to Minimize Development of Weed Resistance
    5. Chemical Control
    6. Cultural Control/Crop Management
  4. Integrated Weed Management (IWM) in the CLEARFIELD Production System
  5. Controlling Volunteers from CLEARFIELD Brassica juncea
    1. Summary
    2. Important Reasons for Control of Volunteers
    3. Cultural and Chemical Options for Volunteer Management
    4. Management of Volunteer CLEARFIELD B. juncea
  6. Managing Out-cCossing to Non-CLEARFIELD Crops and Weeds
    1. What is Out-Crossing and gene flow?
    2. Description of Brassica juncea Varieties with Clearfield Technology
    3. Potential for Out-Crossing in Clearfield Brassica juncea
    4. Potential for Out-crossing to Species related to Brassica juncea
    5. Potential for Out-Crossing to Canola
  7. Managing Out-Crossing of CLEARFIELD Brassica juncea to Related Species
  8. References

CLEARFIELD Production System

Introduction

The CLEARFIELD Production System for Brassica juncea is an innovative cropping system that offers broad-spectrum weed control. It creates a number of new opportunities for western Canadian producers:

Brassica juncea (L.) Czern. species is drought and heat tolerant and therefore naturally suited to the southern prairies. This is the main reason that traditionally mustard has been produced in the southern prairies, while canola was grown in the northern grainbelt. In recent times, economic pressure for crop diversification and precipitation patterns have led to increased canola production in the brown and dark brown soil zones. However, based on a three year study conducted by Agriculture and Agri-Food Canada (AAFC) in Swift Current, scientists concluded that oriental mustard (B. juncea) is better adapted to semiarid conditions than canola.

There are two additional agronomic characteristics of B. juncea that are attractive to producers. Firstly, it has very good resistance to blackleg disease, which is now wide spread in Saskatchewan. One of the other important agronomic features of B. juncea is its shattering resistance. The pods of B. juncea do not shatter as easily as B. napus, therefore it has greater potential for straight combining. Saskatchewan Wheat Pool and AAFC conducted experiments from 1998 to 2001 to test whether juncea canola had as much potential to be straight combined as B. rapa or mustard. Over the four year study, there was no significant difference in yield between swathing and straight combining juncea canola.

Canola quality juncea has the same agronomic advantages and suitability to the southern prairies as does oriental or brown mustard varieties, without the limited market and price volatility associated with the mustard market. However, broad spectrum weed control in conventional juncea remains an issue. The development of CLEARFIELD juncea canola will give producers an effective broad spectrum weed control tool while allowing canola juncea to retain its status as non GMO in international markets.

Key Sustainability Issues

The users, developers and marketers of herbicide tolerant cropping systems are responsible for sustaining the production system and must address the key issues of:

These key sustainability issues form the basis for our stewardship plans for crops grown using the CLEARFIELD Production System. The CLEARFIELD Brassica juncea Stewardship Plan, like those for other CLEARFIELD crops, can be summarized by the following guiding principles:

CLEARFIELD Production System - GUIDING PRINCIPLES

There are a number of GUIDELINES that must be understood and followed by Agronomists and Growers when using CLEARFIELD Production Systems.

Resistance Management in the CLEARFIELD Production System

Herbicides have been grouped based on their mode of action. Herbicides that are in Group 2 are those classed as ALS/AHAS inhibitors. BASF markets herbicides that are in the imidazolinone chemical family and they are members of Group 2. Herbicides such as ABSOLUTE, ODYSSEY SOLO and ADRENALIN used in the CLEARFIELD Production System are examples of Group 2 herbicides. BASF is therefore a key stakeholder in resistance management of ALS resistant weeds.

BASF is committed to maintaining the efficacy of all of its herbicides in order to provide growers with effective, high performance, environmentally sound products for many years. The key to the performance of CLEARFIELD Production Systems is effective weed resistance management. BASF is committed to delivering sustainable cropping systems that incorporate best practice principles. The CLEARFIELD Production System provides alternative options for growers within a well-managed rotation.

Herbicide Resistance Management using an Integrated Weed Management (IWM) Approach

The objectives of herbicide resistance management are to achieve weed control while preserving the value of each herbicide and each herbicide group for the longer term. An integrated approach to weed control is the Best Management Practice to delay the onset of weed resistance to herbicides. Integrated weed management involves the use of a range of methods available to the grower in order to provide effective weed control in crop. The use of herbicides is one of a number of useful tools available to growers.

Development of Resistance

Herbicide Resistance Action Committee (HRAC) is an industry initiative which fosters co-operation between plant protection manufactures, government, researchers, advisors and farmers. The objective of the working group is to facilitate the effective management of herbicide resistance. HRAC has identified a number of factors to consider when evaluating herbicide resistance risk. The most important factors influencing a plant's potential to develop resistance are:

Many exceptions to these generalizations exist, and this makes it difficult to predict which species will develop a resistant population. The time required for a weed population to develop resistance will vary, and depends on many factors, including:

Based on these factors, models have been developed to predict the development of resistance in a weed population. Current models provide an indication of the development of resistance; these indications are an essential input to the development of resistance management strategies and practices.

Identifying Weed Resistance

It is important to avoid confusing herbicide failure caused by weed resistance with herbicide failure caused by other factors. All other possible reasons for poor herbicide performance should be ruled out before considering the possibility of resistance. These include application error and poor environmental conditions at the time of herbicide application. Shifts in weed populations from susceptible species to species that are less sensitive can also cause weed control problems. Herbicide resistance should be suspected under the following conditions:

General Recommendations to Minimize Development of Weed Resistance

Following is a discussion and proposed strategies for managing ALS herbicide resistance in weed populations under the CLEARFIELD Production System. The guidelines for managing the development of weed resistance presented here are consistent with recommendations put forward in provincial crop protection guides and WREAP.

Development of herbicide resistant weeds can be avoided or delayed through good management practices. The recommendations listed below take into consideration many of the points discussed so far and are designed to provide an integrated approach to weed management in order to prevent or delay the onset of weed resistance. Three key areas of integrated weed management are chemical control, cultural practices and crop management.

Chemical Control

Know your herbicide groups.

Keep records of herbicide application.

Always read and follow herbicide label recommendations.

Use tank mixes or sequential applications of herbicides that have different modes of action.

Rotate among herbicide groups.

Utilize non-selective herbicides.

Cultural Control/Crop Management

Cultural (non-chemical) weed control practices do not exert any chemical selection pressure and can help to reduce the level of weeds in the soil seed bank. These practices are important components of an integrated weed control strategy.

Use crop rotations, notably rotations from broadleaf crops to grass crops, winter seeded and spring seeded crops, perennial and annual crops.

Plant competitive crops.

Seed early.

Plant quality seed/Increase your seeding rate

Combine tillage and/or timely cultivation with herbicide treatments, if practical.

Integrated Weed Management (IWM) in the CLEARFIELD Production System

CLEARFIELD Production System crops are tolerant to the imidazolinones, which are Group 2 herbicides. Group 2 herbicides work by inhibiting acetolactate synthase, an enzyme that is required for the production of the amino acids leucine, isoleucine and valine in plants. Group 2 herbicides are known as "ALS inhibitors".

Continuous use of Group 2 herbicides may result in the selection of weed biotypes with a resistance to this Group of herbicides. Preservation of the effectiveness of this Group of herbicides is vital for efficient and cost-effective agricultural production in Canada. Therefore effective management strategies for weed control delay or avoid the potential for the development of resistant weeds is an important focus of the CLEARFIELD production system.

In addition to the general chemical and cultural control recommendations outlined in the previous section, a number of specific management strategies outlined below, should be followed when using the CLEARFIELD Production System. Growers and agronomists should give consideration to each of the following points, in order to develop an integrated weed management system when using CLEARFIELD crops as part of their production system.

Crop rotation and CLEARFIELD Brassica juncea

The wait period between canola crops recommended is three years (Source: 2003 Canola Growers Manual). This one in four year cropping rotation is recommended to help manage build up of weeds, disease, and insect pests that are common to canola. The same management issues that lead to a recommended three year wait period between canola crops also are pertinent to juncea canola. Brassica juncea has the same recommended cropping interval as canola.

Studies have demonstrated that crop rotations with high canola frequency have more cruciferous weeds such as stinkweed. Proper crop rotation will allow different herbicides to be used for weed control. For example, a much wider range of herbicides are recommended for use on cereal crops compared to canola. This is especially true for juncea canola that has even fewer herbicides than canola recommended for in crop use. Rotating crops allows for the possibility of rotating herbicide groups and therefore helps delay the development of weed resistance.

Brassica oilseed crops such as canola grown in a short rotation tend to have more problems with diseases such as blackleg and seedling root rot. Other common canola diseases include sclerotinia stem rot and to a lesser extent alternaria black spot. The current juncea canola varieties available are susceptible to sclerotinia. Recommended waiting periods between canola crops to help manage these diseases range from 2-4 years. The intervening cropping years will allow producers to rotate herbicide groups to help manage the build up of herbicide resistant weeds.

Similarly, crop rotation is the cultural control practice recommended for a number of insect pests of canola that are common on the prairies. Production of alternate crops such as cereals will again create the opportunity for the producer to rotate herbicide groups used in his weed management program.

The yield benefit of crop rotation has been demonstrated in each of the three prairie provinces. In studies where yield of canola planted in various stubble types was examined, canola yield was higher on cereal stubble compared to canola stubble (2003 Canola Growers Manual). Numerous factors including climatic conditions, management practices and soil productivity all have an impact on the yield benefit associated with crop rotation. However, the benefits of crop rotation for management of weeds, diseases and insect pests is well documented. The ability to rotate herbicide groups in a more diverse crop rotation associated with canola production will delay the onset of herbicide resistance.

Controlling Volunteers from CLEARFIELD Brassica juncea

Objective: control of all volunteers from CLEARFIELD crops before flowering.

Summary

Important Reasons for Control of Volunteers

Cultural and Chemical Options for Volunteer Management

A number of cultural and chemical control options are available to control volunteers including:

Management of volunteer CLEARFIELD B. juncea

The small seed size and large number of seeds produced by each B. juncea plant make juncea canola a crop that potentially may produce a large amount of volunteer plants. However, weed survey results indicate Brassica juncea is not a serious volunteer weed problem (Leeson et al., 2005). In the weed surveys conducted during 2001-2003, Indian mustard (Brassica juncea) was ranked 131st most common with a frequency of <0.1% of fields. In contrast, canola/rapeseed ranked 14th and wild mustard was ranked 24th most commonly occurring weed. Seed dormancy and farm management practices are the two most significant factors influencing the persistence of volunteer Brassica juncea.

Despite a long history of cultivation in western Canada, B. juncea has not become an abundant weed, and therefore there is good reason to conclude that it does not have the weedy characteristics of wild mustard and may be less prone than B.napus and B.rapa to become a problem as a volunteer weed. Dormancy has been studied more extensively in B.napus than in either B. juncea or B.rapa. Mature seed of B.napus has virtually no primary dormancy (Lutman, 1993). The vast majority of either Brassica juncea or Brassica napus will germinate within the year after crop harvest. Gulden, et al., (2003) found where canola was followed in rotation by wheat for three consecutive years that after 1, 2 and 3 winters, maximum persistence of 44, 1.4 and 0.2% of the original seedbank was observed, respectively.

Volunteer canola has been shown to persist for at least 4 years in rotation in western Canada (Legere et al. 2001). The duration of persistence is dependent on a number of factors and may be linked to canola genotypes varying in the potential for induction into secondary dormancy. Gulden, et al., (2003) classified 6 canola genotypes on the basis for potential for the development of secondary seed dormancy. Canola genotypes classified as high potential for secondary dormancy exhibited 6 to 12 fold greater persistence then those classified as having medium potential. Large seed size was also found to be associated with secondary dormancy.

To date we are not aware of these types of studies being initiated with B. juncea or B. rapa. However, B. juncea has some attributes that may reduce its volunteer weed potential in comparison with B. napus, such as shatter resistance, smaller seed size and thin seed coat in yellow-seeded varieties. Brassica rapa has had a reputation for being more persistent in the soil than B. napus.

Farm management practices will have a significant impact on volunteer weed problems. Starting in the fall after a crop of B. juncea has been produced and into the next cropping season, there are numerous opportunities to successfully manage volunteer B. juncea. Volunteer B. juncea is easily controlled by several common herbicides, and can be controlled through normal weed control practices commonly used by western Canadian producers.

The first opportunity is in the fall of the year the crop is grown. Practising good stubble management after harvest and leaving B. juncea seed on the surface will increase seed mortality and help to reduce the seed bank population in the soil. Depending on moisture conditions, a significant amount of volunteer B. juncea may germinate in the fall immediately after harvest. These volunteers will be effectively managed with freezing temperatures prior to winter.

The following season there are a number of options available to control volunteer CLEARFIELD B. juncea. Pre-seed control with glyphosate or other non-selective products is a common practice in western Canada for the control of early germinating grass and broadleaf weeds as well as winter annuals. Volunteer CLEARFIELD Brassica juncea that has emerged in the spring will be controlled during this common weed control operation.

As indicated earlier, cereal crops are one of the most common rotational crops with canola or Brassica juncea. Volunteer CLEARFIELD B. juncea will be effectively controlled by a whole range of Group 4 (growth regulator) and Group 6 (photosynthetic inhibitors) herbicides that are commonly used in wheat and barley for annual broadleaf weed control. The following list highlights options for volunteer CLEARFIELD B. juncea control in cereal crops. The herbicides are listed by active ingredient and herbicide Group, not trade name. The list of commercial products available to control volunteer Brassica juncea would actually be larger.

Active Ingredient Herbicide Group
2,4-D 4
Bentazon + 2,4-D 6, 4
Bromoxynil + MCPA 6, 4
Bromoxynil + 2,4-D 6, 4
Clopyralid + MCPA 4
Dicamba + MCPA/2,4-D 4
Dicamba + MCPA K+ 4
Dicamba + 2,4-D amine + Mecoprop 4
Dicamba + Mecoprop + MCPA 4
Diclorprop + 2,4-D 4
Florasulam + 2,4-D 4
Florasulam + Clopyralid + MCPA 4
Fluroxypyr + MCPA 4
Fluroxypyr + Clopyralid + MCPA 4
Metribuzin 5

If CLEARFIELD wheat is grown as part of the 4 year crop rotation with CLEARFIELD juncea (Group 2 herbicide use recommended in only 2 out of 4 year rotation), the herbicides available for use on CLEARFIELD wheat will effectively control volunteer CLEARFIELD juncea. The two CLEARFIELD wheat herbicides commercially available are ADRENALIN SC and ALTITUDE FX. Both of these herbicides combine herbicides with different modes of action (Herbicide Group 2 + Group 4). ADRENALIN SC is a pre-mix of imazamox + 2,4-D. ALTITUDE FX is a co-pack of imazamox + fluroxypyr + MCPA. Consideration of herbicide resistance management and volunteer CLEARFIELD crop control was an integral part of our commercial decision on CLEARFIELD wheat herbicide offers.

Likewise, some of the SU herbicide offers on the market are co-packed with Group 4 herbicides. Harmony K and Refine M are two examples of SU product offers that will control volunteer CLEARFIELD juncea. As with our CLEARFIELD wheat herbicides, use of these products on a cereal crop following juncea should only be done in 2 out of 4 cropping years. The use of an SU herbicide without the addition of a Group 4 tank mix partner is not recommended for volunteer CLEARFIELD Brassica juncea control in cereals; Volunteer weed control will not be satisfactory to manage this CLEARFIELD plant.

Peas are a much less common rotational crop following Brassica juncea. In peas a number of options are available for control of volunteer CLEARFIELD Brassica juncea. Basagran Forte (Group 6) can be used at low rates in-crop for volunteer CLEARFIELD Brassica juncea control. Additional in-crop options available to control volunteer CLEARFIELD Brassica juncea include: MCPA sodium salt (Group 4) or Sencor (Group 5).

In summary, Brassica juncea does not pose a serious threat as a volunteer weed. Numerous weed management tools, cultural and chemical are available to effectively control volunteer CLEARFIELD Brassica juncea. These tools are part of the normal weed control practices commonly used currently by western Canadian producers. Management of volunteer CLEARFIELD Brassica juncea will not require any significant change in weed control practices.

Managing out-crossing to non-CLEARFIELD crops and weeds

What is Out-crossing and Gene Flow?

Gene flow is the movement of gametes, zygotes (seeds), individuals, or groups of individuals from one place to another and their subsequent incorporation in the gene pool of the new locality (Slatkin, 1987). Gene flow is a natural biological process and in plants it primarily occurs via pollen or seed dispersal (Levin and Kerster, 1974). The relative importance of gene flow to population genetic structure depends on the distance between donor and recipient populations, population size, how long the process has been in effect, and whether the new gene confers any fitness advantage to the recipient population (Waines and Hegde, 2003).

Out-crossing (or cross-pollination) is a type of mating in plants in which a male gamete of one individual fertilizes a female gamete of another individual (Waines and Hegde, 2003). The term out-crossing generally refers to mating within a species and the term has been used synonymously with gene flow (Gleaves, 1973; Handel, 1983). However, as defined earlier, gene flow can occur through means other then cross-pollination. We will restrict this discussion to pollen-mediated gene flow (out-crossing).

A wide range of factors influence the ability of a given plant to out-cross with others, including synchrony of flowering, stigma receptivity, pollen production, pollen dispersal, pollen viability and environmental factors. The likelihood of out-crossing varies greatly from species to species and variety to variety. Successful out-crossing may result in the offspring displaying characteristics of both parent plants.

The risk of out-crossing can vary between crop and weed species. The focus for management must be on the control of volunteers and managing herbicide tolerant crops and related species.

Description of B. juncea Varieties with CLEARFIELD Technology

There are both vegetable and oilseed types of B. juncea, possibly of different origins. Both types are considered to be natural amphidiploids (AABB genome, 2n=36). It is believed to have derived from natural interspecific hybridization between B. rapa (AA genome, 2n=20) by B. nigra (BB genome, 2n=16) crosses.

CLEARFIELD Brassica juncea was developed by mutagenesis and inter-specific crossing with CLEARFIELD B. napus, followed by backcrossing to B.juncea. It was not derived from recombinant DNA technology, i.e. it is not genetically engineered (GE)". These varieties have been bred to have tolerance to the BASF imidazolinone herbicides, ODYSSEY and SOLO.

Potential for Out-crossing in CLEARFIELD Brassica juncea

All B. juncea varieties have an annual growth habit. Fertilization of ovules usually results from self pollination, although interplant outcrossing rates of 20 - 30% have been reported (Rakow and Woods, 1987). Bees are the primary pollen vector, because the pollen is heavy and sticky and it is not carried great distances by the wind. Cross pollination of neighbours can also result from physical contact of the flowering racemes. Successive generations of B.juncea arise from seed from previous generations.

Potential for Out-crossing to Species Related to B. juncea

Interspecific and intergeneric crosses have been made between B. juncea and its relatives, however, many have been made artificially through ovary culture, ovule culture, embryo rescue and protoplast fusion. Warwick et al. (2000b) have done an extensive review of the interspecific and intergeneric hybrids of B. juncea and related species that have been obtained sexually.

Wild mustard (Sinapis arvensis) is the most abundant of the B. juncea weedy relatives in western Canada. A plant from the cross between B. juncea and S. arvensis was backcrossed into B. juncea and into S. arvensis (Bing et al., 1991). The resulting plants were weak or sterile and produced no seed on open pollination suggesting that this cross would not result in the natural transfer of traits from either species being stably inserted into the other species.

Warwick (2004) also demonstrated that gene flow from B. juncea to S. arvensis is possible. However, the hybrids formed have reduced pollen fertility and do not produce seed when back-crossed with either parent. In the rare situation where hybrids form with the unreduced genome of B. juncea, and have the potential to back-cross to S. arvensis, the herbicide tolerant trait is not stably incorporated into the S. arvensis genome. No interspecific hybrids involving S. arvensis have been confirmed in nature (Warwick et al., 2000a).

Lefol et al. (1997) investigated the production of hybrid seeds between B. juncea and dog mustard (Erucastrum gallicum) or wild radish (Raphanus raphanistrum) using reciprocal crosses. They did not use embryo rescue, so that their measurements referred to seed production which might occur under natural conditions. The R. raphanistrum x B. juncea cross failed to produce any seed, and the viable seed produced from all the other crosses was not considered to be hybrid. Thus the probability of intergeneric crosses between these two weedy species and B. juncea seems to be low.

Potential for Out-crossing to Canola

Numerous studies have been conducted with canola that demonstrate the amount of pollen movement decreases dramatically as the distance from the pollen source increases (Stringham and Downey, 1978, Downey, 1999, Scheffler et al. 1995). In other experiments, less than 0.03% cross pollination was observed when the pollen source was 30 meters away (Staniland et al., 2000). This work on pollen dispersal was done primarily with small scale field trials. Others have suggested that pollen moved over greater distances (Hall et al., 2000).

In terms of related crops, Bing et al. (1991) reported that, there was potential for hybrids between B. juncea, B. napus and B. rapa to produce viable seed that could survive to the next generations.

Warwick (2007) summarized results of ongoing pollen flow studies from transgenic Brassica napus to Brassica juncea. These studies have documented gene flow of 0.005% at distances of up to 200 meters.

Managing out-crossing of CLEARFIELD Brassica juncea canola to related species

Evidence indicates that the herbicide tolerant gene does not confer any competitive advantage to plants unless specific herbicides are used. It does not result in increased weediness or invasiveness of the species. Herbicide tolerant plants created through out-crossing can be managed in the same fashion as herbicide tolerant volunteers.

As discussed in the section titled "Management of volunteer CLEARFIELD B. juncea," the combination of crop rotation, farm management practices and the numerous chemical and cultural methods of weed control available for volunteer B. juncea control will all contribute to effective control of both B. juncea volunteers or any hybrid created through out-crossing.

The following practices should be followed to help in minimize the potential for out-crossing to occur.

References

Bing, D.J., Downey, R.K. and Rakow, G.F.W. 1991. Potential of gene transfer among oilseed Brassica and their weedy relatives. GCIRC 1991 Congress. pp. 1022-1027.

Downey, R.K. 1999a. Gene flow and rape - the Canadian experience. Gene Flow and Agriculture:Relevance for Transgenic Crops, BCPC Symposium Proceedings No. 72, April 1999, Keele, Staffordshire, UK, pp. 109-116.

Gleaves, J.T. 1973. Gene flow mediated by wind-borne pollen. Heredity 31:355-366.

Gulden, R. H., Thomas, A. G. and Shirtliffe, S. J. 2003b. Secondary seed dormancy prolongs persistence of volunteer canola (Brassica napus) in western Canada. Weed Sci. 51: 904-913.

Hall, L., K. Topinka, J. Huffman, and L. Davis. 2000. Pollen flow between herbicide-resistant Brassica napus is the cause of multiple-resistant B. napus volunteers. Weed Science 48: 688-694.

Handel, S.N. 1983. Pollination ecology, plant population structure, and gene flow. P. 163-211. In L. Real (ed.) Pollination biology. Academic Press, Orlando, FL.

Heyn, F.W. 1977. Analysis of unreduced gametes in the Brassiceae by crosses between species and ploidy levels. Z. Pflanzenzuchtg. 78: 13-30.

Leeson, J.Y., Thomas, A.G., Hall, L.M., Brenzil, C.A., Andrews, T., Brown, K.R. and Van Acker, R.C. 2005. Prairie Weed Survey, Cereal, Oilseed and Pulse Crops 1970s to the 2000s. Weed Survey Series Publ. 05-01. Agriculture Canada, Saskatoon, Saskatchewan. 406 pp.

Lefol, E., Seguin-Swartz, G. and Downey, R.K. 1997. Sexual hybridization in crosses of cultivated Brassica species with crucifers Erucastrum gallicum and Raphanus raphanistrum: Potential for gene introgression. Euphytica 95: 127-139.

Leger, A., Simard, M.J., Thomas, A.G., Pageau, D., Lajeunesse, J. Warwick, S.I. and Derksen, D.A. 2001. Presence and persistence of volunteer canola in Canadian cropping systems. Pages 143-148 in Proceedings of the Brighton British Crop Protection Conference-Weeds. Farnham, Great Britain: British Crop Protection Council.

Levin, D.A., and H.W. Kerster. 1974. Gene flow in seed plants. Evol. Biol. 7:139-220.

Lutman, P.J.W. 1993. The occurrence and persistence of volunteer oilseed rape (Brassica napus). Aspects of Applied Biology 35, Volunteer Crops as Weeds, 29-36.

Rakow, G. and D. Woods. 1987. Outcrossing in rape and mustard under Saskatchewan prairie conditions. Can. J. Plant Sci. 67: 147-151.

Scheffler, J.A., Parkinson, R. and Dale, P.J. 1995. Evaluating the effectiveness of isolation distances for field plots of oilseed rape (Brassica napus) using a herbicide-resistance transgene as a selectable marker. Plant Breeding 144:317-321.

Slatkin, M. 1987. Gene flow and the geographic structure of natural populations. Science (Washington, DC) 236:787-792.

Staniland, B.K., McVetty, P.B.E., Friesen, L.F., Yarrow, S., Freyssinet, G., & Freyssinet, M. 2000. Effectiveness of border areas in confining the spread of transgenic Brassica napus pollen. Canadian Journal of Plant Science 80: 521-526.

Stringam, G.R., and Downey, R.K. 1978. Effectiveness of isolation distance in turnip rape. Can. J. Plant Sci. 58:427-434.

Waines, J. G., and S.G. Hegde. 2003. Review and Interpretation. Intraspecific gene flow in bread wheat as affected by reproductive biology and pollination ecology of wheat flowers. Crop Sci. 43:451-463.

Warwick, S.I., Beckie, H.J., Thomas, A.G. and McDonald, T. 2000a. The biology of Canadian weeds. 8. Sinapis arvensis. L. (updated). Can. J. Pl. Sci. 80:939-961.

Warwick, S.I., Francis, A. and La Fleche, J. 2000b. Guide to the Wild Germplasm of Brassica and Allied Crops (tribe Brassiceae, Brassicaceae) 2nd Edition. Electronic publication. [http://www.brassica.info/resources/crucifer_genetics/guidewild.htm]

Warwick, S. I. 2004. Gene flow risk assessment from herbicide-resistant Brassica crops to related weed species. Report to the Canadian Food Inspection Agency.

Warwick, S. I. 2007. Gene flow between GM crops and related species in Canada. In: The first decade of herbicide resistant crops in Canada. Edited by C. Swanton and R. Gulden. Topics in Canadian Weed Science, Vol. 4. Published by the Canadian Weed Science Society. "In Press".

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