With a distribution survey of Aphanomyces in pulses now complete – short answer: it’s everywhere – research has now turned to possible remedies, such as Brassica cover crops.

Some years back, pulse specialists began to hear more and more about the incidence of root rot in Alberta’s pea and lentil crops.

While researchers assumed it was caused by the usual suspect – Fusarium – this time, it wasn’t. The culprit was a root rot causal agent not seen in Alberta before: Aphanomyces. Researchers knew they needed to get a handle on this new problem as quickly as possible.

Syama Chatterton, Lethbridge-based Plant Pathologist with Agriculture and Agri-Food Canada, began a five-year survey in 2013 on the incidence and severity of Aphanomyces root rot in Alberta and Saskatchewan. She also wanted to know how environmental and weather patterns affected its distribution.

Chatterton and her team studied Aphanomyces root rot in peas, lentils, faba beans, dry beans and alfalfa. The weather cooperated nicely, providing both very wet and very dry years for comparative purposes during the survey’s growing seasons.

As expected, they found that rainfall/moisture was the biggest driver of Aphanomyces root rot. Aphanomyces root rot on peas was still present in dry years, with up to 40% of pea fields testing positive.  In wet years, however, the Aphanomyces level jumped up to 70% for peas. For lentils, Aphanomyces was virtually non-existent in dry years. In wet years, Aphanomyces was present in 40% to 50% of lentil fields.

“Something really interesting to look at, that came out of this survey project, is how moisture affects Aphanomyces and why it affects these two crops in a bit of a different way,” Chatterton said.

Testing Brassica cover crops

Inspired by greenhouse research showing that Brassica green manure crops could biofumigate the soil and break down spores of Aphanomyces, Chatterton began an APG-funded four-year project in 2017 to scale-up this concept.

“We wanted to take that from the greenhouse and see if it could be applied in the field and fit in with the agronomy practices of producers,” Chatterton said.

In 2018, researchers will seed cover crops in the spring and fall, including oriental and white mustard in combination with tillage radish. They’ll include a better-known Brassica – canola – in the trials. The expectation, however, is that canola won’t be as effective at breaking down Aphanomyces spores as mustards are, due to canola’s lower glucosinolate levels.

Using green manure crops to control soil-borne pests has been previously explored in potato production. Could this strategy work in peas and lentils? The production risk and confirmed wide distribution of Aphanomyces root rot in pulses give Chatterton’s work special urgency.

“When we started the Aphanomyces survey, we knew we’d find it,” she said. “What surprised us was just how widespread it was across the prairie provinces. Basically any field with a long history of growing peas or lentils had it.”