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The rise of Aphanomyces in peas and lentils across Western Canada.

Best management practices to reduce risk of infection of aphanomyces root rot.

Written by: Allison Friesen


Introduction

Seed- and soil-borne diseases are common occurrences for Canadian pulse growers, especially with the wet weather patterns and tightened pulse rotations of the past few years. But there’s one disease in particular that has recently caught the attention of growers and agronomists alike. Root rot caused by Aphanomyces euteiches is a disease that has been identified across Western Canada and can be quite detrimental in peas and lentils. There is a concern that the growing prevalence and incidence of this disease could potentially have a dramatic impact on pulse acres throughout most of Saskatchewan and parts of Alberta.


Aphanomyces is part of the oomycete family of fungal-like pathogens and is one of the most difficult root rots to control because of its insensitivity to chemical treatments. The pathogen thrives in wet, waterlogged soils where it produces both motile zoospores and sexual oospores. The zoospores “swim” through the soil towards susceptible plants and oospores can survive in the soil for 10 to 20 years, acting as a continuous source of inoculum. Belowground, some of the first symptoms to appear are lower nodulation levels, decreased root masses, and girdled, honey-brown coloured roots. Aboveground symptoms appear 1 to 2 weeks after infection and include yellowing and chlorosis of leaves, stunted growth and seedling death (Figure 1).


Figure 1: Above and below ground symptoms of Aphanomyces Root Rot. A. Stunting and yellowing of leaves, B. Caramel colouring of the roots, C. Girdling of the stem.

Source: U of S Cheryl Cho, Dr. Sabine Banniza Lab


Regional considerations

The 2015 growing season was much drier compared to 2014 in Western Canada, which fooled growers into thinking that disease pressure in pulse fields would be lower in 2016. But pulse prices continued to soar and more and more growers are deciding to push their limits with rotations and grow pulses in non-traditional regions. Combined with this, in 2015 we saw a warm fall, a mild winter and an early spring, producing conditions that were conducive for disease development. To top it all off, this past July was an extremely wet month (Figure 2) and as the rain continues, aphanomyces is becoming a very real issue.


Figure 2: 7-day precipitation map for the Prairie region, July 13-19 – Environment Canada 2016


Consequences

Aphanomyces can cause devastating crop losses on entire growing regions where field peas, lentils and alfalfa are common rotational crops. This is especially true since there is no effective seed treatment available. It’s been estimated that this disease can cause yield losses of 50 percent or more. We’ve seen examples of this kind of impact in France and the Great Lake Regions of the United States. Inoculum levels have become so high in these regions, that pea production and the processing facilities around them have been relocated to drier areas with better growing conditions.


Best Practices

Despite some seed treatments being introduced to the market for suppression, there is still no effective chemical solution to completely control this disease. However, there are several other steps growers can take to minimize risk in their fields, including lengthening rotations between susceptible crops.


Field choice

  • Choose fields with lighter textured soils and good drainage
  • Take peas/lentils out of rotation for 3 years, up to 8 years if aphanomyces is positively identified
  • Manage or avoid compacted fields

Soil testing and fertility

  • Use starter nitrogen if soils have less than 15 lbs available N per acre in the top 12 inches of soil/li>
  • Use phosphorus if seeding early into cool soils
  • Test seed quality to ensure best seed lots possible

Seeding decisions

  • Use appropriate inoculant to promote nodulation
  • Apply seed treatments for other fungal pathogens or if planting early into cool soils
  • Choose more resistant crops such as faba beans, chickpeas and soybeans
  • Minimize seed damage and watch airspeed of the seeder
  • Seed into warm moist soil for quicker emergence and more vigorous seedlings

After seeding

  • Scout crop for signs of stress
  • Follow herbicide labels as increased injury can occur when plants are stressed

Expert opinion

Aphanomyces has been found worldwide in several pulse growing regions. It was first reported in Canada in the 1930s, but only positively identified in Saskatchewan in 2012. This is supported by Dr. Sabine Banniza from the Department of Plant Sciences at the University of Saskatchewan, who believes the pathogen has only been present for a little over 3 years in Canada. Its impact was not substantial which is why the pathogen went undetected until now. If aphanomyces does develop into a major disease in Western Canada, Dr. Banniza believes it could become a big problem for pea production. Her recommendations include relying on alternative crops that have natural tolerances to aphanomyces. For example, planting chickpeas in lighter, drier soils and using cultivars like CDC Frontier that have partial resistance to the disease.


Future Innovations

There are currently no pea or lentil cultivars available with complete resistance to aphanomyces. However, Dr. Banniza is working with labs in both the US and France to breed lines with resistant traits. Research is being conducted at the University of Saskatchewan and Agriculture and Agri-Food Canada on the infection process and pathogen survival, along with the development of an accurate quantification method from soil samples. BASF is currently working on a seed solution for aphanomyces and it is our top priority to have a product registered as soon as possible to mitigate this disease.

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