Researchers have determined that aphanomyces, a root rot pathogen, can live in the soil for more than 10 years
Rotation is the key management strategy to control aphanomyces, but even that might not eliminate the pathogen from the soil.
Producers attending pulse meetings this winter heard that the root rot pathogen can live in the soil for more than 10 years.
Sherrilyn Phelps, agronomy manager at Saskatchewan Pulse Growers, said moving to longer rotations is the only tool growers have.
“I hate recommending that we need to go to a six- to eight-year rotation in peas and lentils, because just from a management perspective how do you set up an eight-year rotation when you’re used to doing a two-, three-, or four-year rotation?” she said at a Regina meeting. “It’s going to take some challenging discussions and a lot of evaluations on an individual farm on how we’re actually going to get to those rotations.”
Aphanomyces wasn’t identified in Saskatchewan until 2012 but has likely been present longer.
University of Saskatchewan pulse pathologist Sabine Banniza told a different meeting that the pathogen is native to the Prairies and is probably everywhere.
Recent wet years have increased its presence but she noted that even in the extremely dry conditions of 2018 a lot of aphanomyces was reported.
The pathogen can be detected in soil samples mostly in the top 20 centimetres, but can be found as deep as 60 cm, she said.
It also affects peas and lentils at any growth stage.
Alone, aphanomyces is an aggressive pathogen, but when combined with fusarium, as it usually is, the two become like dynamite, Phelps said.
Fusarium avenaceum is the most aggressive of the fusarium pathogens in peas and lentils. Phelps said it’s easier to isolate and research these pathogens. They are most susceptible at the seedling stage and that’s why seed treatments work.
Research has found that there is a strong interaction between pea leaf weevil and fusarium root rot.
While the SPG recommends not planting peas or lentils on fields that test positive for aphanomyces for at least six and preferably eight years, Phelps said growers could look at other pulses — fababeans, soybeans or chickpeas may be options.
Several years of non-host crops are required to reduce inoculum levels.
Studies have found that oat green manure can suppress aphanomyces by causing the oospores to germinate without a host plant present. Research is examining how mustard can do the same.
Other management strategies include choosing fields with lighter soil to better manage moisture, maximizing the health and vigour of seedlings and avoiding stress on the plants.
Banniza said resistance breeding is underway based on two main lines from the USDA that should be in co-op trials by 2022.
She said lots of work has been done in France but varieties haven’t yet been widely released to prevent resistance from breaking down.
Choosing healthy seed is critical to try to delay infection as long as possible, she said.