Project Code: PRR07-360
Mark Goodwin - Pulse Canada
To develop an early disease warning system and improve the delivery of a management decision tree as a basis for control recommendations and timing of fungicide applications
Summary of Results
Ascochyta blight, caused by the pathogenic fungus Ascochyta rabiei, is the most damaging disease of chickpea in Western Canada. When conditions for this disease are favourable, yield losses can reach up to 70% even in the most resistant varieties. In early 2000, severe outbreaks of the disease caused chickpea acreage to collapse by 90%. Since then, with the introduction of new fungicides (strobilurins) and more tolerant varieties, chickpea acreage has begun to recover again. However, concerns about the recurrence of severe outbreaks of Ascochyta blight have been on the rise because of emerging reports of pathogen resistance to strobilurins.
The goal of this project was to develop and validate tools which could help chickpea growers to make informed management decisions about the necessity and proper timing of fungicide applications, to avoid unnecessary sprays. These tools would allow growers to use near real-time field information for integrated disease control which, in turn may help to manage risk of fungicide resistance within the pathogen population.
Two complementary spray decision support tools were developed which make use of i) presence of pathogen inoculum (e.g. spores) in the field and, ii) best disease management practices available, respectively.
First a ‘sentinel’ system was developed to track the dynamics and quantify occurrence of pathogen spores in the chickpea fields. The system consisted of placing pre-grown (4-5 weeks old) potted chickpea ‘sentinel plants’ in the field twice a week through the growing season to act as spore traps. After 3 days of exposure in the field, these plants were taken back to the lab, incubated in growth cabinets for 3-5 days and then assessed for the presence and number of Ascochyta blight lesions. Email and/or fax alerts were sent to growers who had volunteered to participate in the project, to provide resulting information on inoculum estimates within specific testing periods. It usually took 5 days from the collection of sentinel plants from the field to the alerts being sent to growers. This was set up as an ‘early warning’ system to inform growers when spores become prevalent in fields in a given region, so that they could decide whether or not to spray. The goal was guiding growers to ‘hold off’ on spraying until the spores were actually present in the fields.
Secondly, an illustrated field guide was developed as a decision making resource to help growers determine the timing and choice of control measures. The decision process took into consideration the disease cycle, proper scouting and diagnostic techniques and best management options available.
The field guide was written by a team led by experts from the Saskatchewan Department of Agriculture, with assistance from the University of Saskatchewan researchers, Agriculture and AgriFood Canada scientists and crop protection experts. While the content was already available online through a CD-ROM, this hardcopy booklet aimed to make the information available in a format that was easier to use and more accessible by growers and agronomists. Moreover, the guide placed an emphasis on integrated disease management approaches to allow for targeted applications and prevent unnecessary sprays.
The ‘sentinel’ system was established at the beginning of the 2007 season and was also used in 2008. Alerts were disseminated twice a week directly to growers and crop advisors becoming, according to surveys conducted as part of this study, the single most important piece of information for decision making on Ascochyta blight management. This system helped to determine that Ascochyta spore numbers were much higher and arrived in fields much earlier in the season than previously thought. For instance, significant spore numbers were present in fields even when chickpea seedlings were emerging, during May and early June. Consequently, there was no opportunity to reduce the number of fungicide sprays or to delay the onset of scheduled spraying in these fields. It was concluded that under high pest pressure, the potential for achieving pesticide risk reduction would be very limited.
The new recommendation developed as a result of the sentinel project states that ‘Growers should be cognisant that spores are likely present as the crop is emerging and progressing through early stages. Therefore, plan your first application of fungicide (a) when the seedlings are at the 7-node stage and (b) when rainfall is in the forecast’.
The field guide booklet presents information pertaining to various agronomic and environmental factors impacting Ascochyta blight management including chickpea variety, crop stage, crop rotation, density of the crop, and rainfall received and forecasted. Since its publication in 2008 it has been disseminated for use to many chickpea growers and has become a preferred source of information for growers. High demand led to the publication of a revised version of the booklet in 2010 which was upgraded with new information resulting from this project. The booklet Scouting and Management of Ascochyta Blight in Chickpea (PDF, 1,548 KB) (available in English only) was printed on high quality, durable stock so that it would stand up well under field use conditions.
For more information on this project, please contact Mark Goodwin.