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Managing aphanomyces and root rot

2017 survey results showed a high prevalence of root rot in Prairie pulse crops

Root rot is a soil-borne disease that affects the roots of developing peas and lentils. Root rot can infect crops at any stage, and once it sets in there is no way of stopping the infection. Saskatchewan Pulse crop advisor Sherrilyn Phelps advises growers on best prevention practices.

Disease prevention

Proper rotation is important. Peas and lentils, Phelps said, should be rotated every three to four years. Once the pathogen is present, though, producers need to move to longer rotations of six to eight years between pea and lentil crops.

Even rotation can’t stop disease from occurring, which means regular scouting is important. “Being able to detect patches or areas of a field that are showing symptoms is important for early detection,” said Phelps.

Yellowing and stunting are pretty common early symptoms, typically in June or July. However, later season infections can also occur and often go unnoticed. In later infections, said Phelps, plants tend to lodge and flatten.

“Areas of a field that are lodged more or fields showing bad lodging where other fields are okay could be cause for concern,” she said.

Get confirmation

No matter when the symptoms first arise, the next step is to confirm the pathogen or pathogens involved. Producers can do so by sending soil samples and plant roots to labs for diagnostics. If the samples are positive for aphanomyces, producers should move to six-year rotation at minimum.

Phelps notes that healthy, vigorous seedlings and plants are better equipped to fight disease. “This starts with good seed, seeding into warm soils, ensuring good nutrition, and using seed treatments to provide some level of protection against root rots,” she said.

Research shows that a combination of root rot pathogens with aphanomyces is more problematic than aphanomyces alone. “Seed treatments can provide early protection against other root rot pathogens, which may help alleviate some stress early in the season,” said Phelps. “Seeding into warm soils also speeds up germination and can reduce stress.”

Phelps warns growers not to seed too deep as deep seeding can cause plants to struggle to emerge, adding unnecessary stress. She also warns growers to watch their timing for rolling. “Avoid rolling when the soil is wet as it can be compacted more easily and lead to increased stress on the plant,” she said. “Peas and lentils can be rolled after they emerge, so the window for rolling is quite wide and should be done when the soil conditions are favourable to avoid addition stress to the seedlings.”

2017 survey results

Researchers in Alberta, Saskatchewan and Manitoba have been conducting annual surveys to assess the presence of root rot and levels of severity. (2017 will be the final year of this federally sponsored survey, now that researchers have a better understanding of the problem.) While this year’s results show that prevalence is high (presence in fields), for the most part incidence (percentage of plants infected within fields) remained fairly average.

Agriculture and Agri-Food Canada researcher Syama Chatterton analyzed this year’s results. In peas, she says she found root rot in every field, making prevalence an alarming 100 per cent. “As for the percentage of roots that have disease within a field, we’re looking at about 70 per cent,” she said.

In terms of severity, roots are rated on a scale of 1 to 7 with 1 being healthy and 7 being the most diseased. Peas, said Chatterton, were at about 3 to 3.3 average severity across all roots in Alberta, Saskatchewan and Manitoba with little variations in some regions.

Lentils provided a much different story. Chatterton saw a lot less root rot. She saw about 20 to 30 per cent incidence, even though prevalence was at 100 per cent. Severity came in at 2 on average.

“That’s a lot lower than what we had seen in previous years,” said Chatterton. “I think that was due to some of those drier conditions that we saw in the lentil growing areas in 2017.”

Chatterton also calculated the number of fields that were positive for aphanomyces. Very few, she said, were actually positive. In lentils, roughly 10 per cent. In peas, roughly 40 per cent were positive for aphanomyces.

About the author

Columnist

Melanie Epp is a freelance farm writer.

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