Widespread root rot found in Alta. pea fields

The severity found in surveys conducted last year reached levels at which the disease can become an economic threat

The Alberta team tasked with surveying for root rot in pea fields last year were rewarded, if you can call it that. They found root rot in every field visited on an estimated 66 percent of roots examined.

“Root rots continue to be a real issue in peas,” said Alberta Agriculture crop pathologist Michael Harding during the recent Agronomy Update webinars organized by the Alberta wheat and barley commissions.

“Mycosphaerella and ascochyta were by far the most commonly observed pathogen. We saw it in every field and almost on every plant, at least in one or two spots, and with a severity getting close to that 40 percent. So ascochyta and mycosphaerella were very, very common on peas in 2020.”

Disease severity above 42 percent is likely an economic threat to pea production, said Harding, and given the survey averages, that means some fields were above that threshold in 2020.

Field peas made up the lion’s share of pulse crops grown in Alberta last year, said Alberta Agriculture pulse crop researcher Robyne Bowness Davidson.

The crop was grown on 1.47 million acres, far above lentils, the next closest pulse crop in terms of acres, at 449,600 acres.

The ravages of ascochyta blight on a pea plant in Alberta. | Barb Glen photo

Among other pulse crops, Alberta farmers grew 57,000 acres of dry beans, 39,460 acres of fababeans, 38,125 acres of chickpeas and 1,000 acres of soybeans. Last year was a wet year compared to most, allowing moisture-loving root rots to flourish. Seed treatments can provide protection for some but not all problems.

Root rot diseases are characterized by poor emergence, stunted growth, yellowing of plants and root discolouration, said Bowness Davidson. Among the whole root rot complex, fusarium and aphanomyces are of greatest concern.

“The problem is that they occur together more often than not and can be very difficult to distinguish from each other,” she said.

Crop surveys proved challenging this year due to pandemic restrictions, although Alberta Agriculture staff, unlike those with Agriculture Canada, were able to conduct some of their usual surveys though they had fewer people at their disposal.

In wetter parts of the province, Bowness Davidson said it was difficult to tell on site whether sickly looking crops were due to disease or drowning. That’s an added complication to the fusarium versus aphanomyces issue.

Aphanomyces identification requires a DNA test, which is done at the Agriculture Canada lab operated by researcher Syama Chatterton. The lab was closed in March due to the pandemic and opened in November at reduced capacity. That has slowed the pace of testing, said Bowness Davidson.

However, there is likely a lot of root rot inoculum in fields, raising the threat of root diseases in 2021, depending on moisture and other conditions this spring. Aphanomyces is aggressive, is spreading and travels with other pathogens, so it continues to be a concern.

“I think the message is changing a little bit.… The really strong message we’re trying to send is that we’re going to really have to start knowing our fields. We’re going to have to pay attention to what is going on.… What did your pea or lentil field look like this year, in a wet year, and what did those pea and lentil fields look like the last time there was that crop in that field?”

She suggested a pulse rotation of six to eight years might be needed to avoid it.

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