PROJECT RESULTS

Development of Bacterial and Fungal Bioherbicides for Control of Herbicide-Resistant Wild Oat and Green Foxtail

Applicant: 

Dr. Susan M. Boyetchko

Saskatoon Research Centre

Agriculture and Agri-Food Canada

Saskatoon, SK  S7N 0X2  Canada

Table of Contents:

• Background and Objective
• Results and Discussion
• Conclusion

ARDI Project:

#99-320

Project Status:

Completed January, 2003

Background and Objective:

Wild oat (Avena fatua L.) and green foxtail (Setaria viridis [L.] Beauv.) rank as the two most abundant and economically important grass weeds in the Canadian prairies (#3, #6).  Recent surveys rank wild oat as the second most abundant weed in the northern Great Plains, where it was found in 64% of fields surveyed causing annual yield losses of $120 to $500 million.  Surveys for green foxtail indicated it was present in 46% of fields in the Canadian prairies, and its relative abundance in Saskatchewan and Manitoba remains unchanged (i.e. ranked #1), despite the number of herbicides used over the last 20 years.

In 1998, over $980 million was spent on herbicides in western Canada.   Both pre- and post-emergent chemical herbicides for control of these grass weeds include trifluralin, propanil, diclofop, sethoxydim, and atrazine;  however resistance to acetyl-CoA carboxylase (ACCase) inhibitors (Group 1), dinitroanilines (Group 3) and triallate (Group 8) herbicides have been documented.  It has been estimated that it costs producers $4 million annually to manage herbicide-resistant (HR) wild oat in Saskatchewan and Manitoba and $0.7 million in canola and pea, with costs increasing in wheat (1,2,4,5).  Moreover, the surveys also reported multiple-resistance of wild oat and green foxtail to more than one herbicide group, indicating the urgency for finding methods for managing HR weed populations.

Research on biological control of weeds has led to the discovery and development of several bacterial and fungal agents that suppress or inhibit wild oat and green foxtail.  These biocontrol agents have either been applied as a pre-emergent (granular formulation) or post-emergent (foliar) bioherbicide.  The proposed research will focus on the evaluation of microbial agents from the culture collection established in the Weed Biocontrol program at Saskatoon. Preliminary screening has demonstrated that several HR wild oat populations can be controlled with a bacterial agent (far right) compared to a control (left).  Furthermore, preliminary research on 3 bacterial strains indicates that their mode of action is novel and different from existing chemical herbicides.  Integration of biological control into current practices will enhance growers’ ability to manage HR weeds.  Biological control will be used as part of an integrated weed management strategy and can complement herbicide rotations by providing new modes of action into the system.  In addition, biological control may potentially reduce the use of chemical herbicides, thereby delaying the development of HR weeds and alleviate the pesticide load into the environment.  To specialty crop producers who have limited choice of herbicide options, biological control will provide them with new tools in an integrated weed management program.

The objective of this project was to build on current research activities for developing bioherbicides and/or biocontrol products against wild oat and green foxtail, but with the main focus on HR weed populations.  A screening program will be developed to identify the most efficaceous bacterial agents against HR wild oat and green foxtail.  The most promising agents will be selected and efficacy will be evaluated in laboratory and greenhouse trials using appropriate application rates and formulation.  Seed increases of HR wild oat (Group 1, 3, 8, multiple resistant [Group 1, 2, + 25]) and green foxtail (Group 1, 3, and multiple resistant [Group 1 +3]) populations were conducted in Agriculture and Agri-Food Canada greenhouses for use in this project.

Results and Discussion:

Wild Oat:  Growth Pouch Bioassay Screening 

A total of 40 bacterial strains were evaluated.  While the root suppression in the agar bioassays was relatively high, the results from the growth pouch bioassays represent a more “realistic” scenario as to the performance of the bacterial strains in the greenhouse and field.  In general, root suppression was lower in the growth pouch bioassays than in the agar bioassays (by comparing the same bacterial strains).  However, the top 3 bacterial strains were BRG100, OY4GFT28, and OY4GFT23 in their ability to suppress several wild oat populations.  By providing this information, we can further select these bacterial strains to enhance their bioherbicidal activity through fermentation studies and to encapsulate them in suitable granular formulations for application as preemergent (soil-applied) bioherbicides.  This is currently an ongoing research activity at Saskatoon in the weed biocontrol program.  An outstanding bacterial strain (OY3WO11) which is capable of providing over 90% root suppression of all 4 wild oat populations was also selected and tested in the field at Saskatoon in the 2001 and 2002 field season and shows great potential as a bioherbicide agent.   

Green Foxtail:  Growth Pouch Bioassay Screening

A total of 115 bacterial strains were evaluated.  Out of these 115 bacteria evaluated, 15 bacterial strains are considered the top candidates (including strains 189 and BRG100) that are capable of controlling all 3 populations of green foxtail evaluated (i.e. susceptible, and UMDEL [Grp 3] and UM8 [Grp 1] resistant populations). For the most part, these bacterial strains provided over 50% root suppression to two or more of the green foxtail populations.  Bacterial strain FWO2 provided excellent control of all HR green foxtail populations. Several other bacterial strains which ranked as the second group with intermediate activity, provided 30-50% reduction in root growth in two or more of the green foxtail populations. 

It should be noted that bacterial strains 189 and BRG100 have been evaluated over the last 5 years in field studies against susceptible green foxtail populations (as part of our major weed biocontrol activities at Saskatoon), providing 70 to 90% weed control in the field using two granular formulations (a peat prill and pesta formulation).  Bacterial strain FWO2 was tested in the field in 2002 for the first time and, despite record drought conditions, provided promising weed biocontrol against green foxtail.

Field Evaluations

As a result of previous testing of bacterial strains in growth pouches against wild oat during this ARDI project, we selected strain OY3WO11, which showed excellent potential against four wild oat populations (Susceptible, Bentley [Grp 8], UM1 [Grp 1], UMWO12 [Grp 1,2, 25]).  It provided up to 50% weed control using both a peat prill and pesta formulation at two sites:  Saskatoon and Scott, SK.  These results look extremely promising for this agent and further studies to formulate and mass-produce (i.e. ferment) this bacterial strain will continue.  Similar results were demonstrated for bacterial strain FWO2 against green foxtail during the 2002 field season.  Additional field tests with bacterial strains OY3WO11 and FWO2 are required in 2003.

Conclusion:

The following lists the potential economic impact to farmers:

• The key economic benefit of this project is the contribution of biological control to enhance effectiveness for managing herbicide-resistant (HR) populations of wild oat and green foxtail.  It is estimated that management of HR populations cost farmers well over $4 million annually in the Canadian prairies.

• The use of biological control may reduce the dependency on chemical herbicides, help delay the development of HR weed populations, and reduce the risk of pesticide contamination in the environment.

• The project provides an innovative management tool to some specialty crop producers such as organic growers.  Reduced use or no use of chemical pesticides will enable these producers to meet the need of specialty markets where profit margins are often much greater.

• Agriculture and Agri-Food Canada acquired an industry partner to collaborate on research and development to commercialize the technology to develop these soil bacteria as “pre-emergent biocontrol agents of annual grass weeds” (green foxtail and wild oat).  Over the next 4 to 5 years, in collaboration with our industry partner, we will continue to conduct fermentation and formulation experiments for scale-up production, and conduct field trials at several sites.  The industry partner will further evaluate the technology and negotiate a licensing agreement with Agriculture and Agri-Food Canada should they wish to pursue commercialization of this technology.  The continued support by ARDI has allowed us to identify the most promising bacterial agents for management of not only susceptible wild oat and green foxtail populations, but has allowed us to identify those bacterial strains that can be used in the management of herbicide-resistant weeds.    

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