Infectious pulse disease requires caution

It’s a bad idea to grow peas and lentils on a field where Aphanomyces euteitches infection has become too extreme, scientists and crop experts heard during the Tenth Canadian Pulse Workshop.

“Keep susceptible crops out of fields with high risk unless you’re a riverboat gambler,” said Agriculture Canada researcher Bruce Gossen in an interview during the event.

“You’re going to lose substantial yield in a highly infested field, even in a dry year.”

Millions of pulse acres suffered serious yield loss in 2016 due to wet conditions, which allowed root rots to run rampant. For many root rots, seed treatments and good rotations provide good protection except in very bad years, such as this one.

However, that doesn’t seem to apply to A. euteiches, Gossen said.

Seed treatments don’t prevent its widespread impact and there are no good resistant varieties to the disease.

The inoculum can sit in the soil for years, reducing the effectiveness of rotations.

“Once you get the inoculum ramped up, you continue to have problems, even if it’s dry,” said Gossen.

“If it gets wet, then they really become unglued.”

Gossen compared A. euteiches to clubroot, which he also studies, and said many of the same approaches should be followed.

“I would not be planting that (field) first and dragging soil into other sites,” said Gossen.

“I’d be trying to isolate that problem.”

Resistant varieties are at least a few years away, so avoiding creating newly infected fields is essential. When resistance is developed, it can’t be overused or it will also fail quickly.

“Even when we have them, if you plant them in a heavily infested field where the inoculum potential is really high, you’re going to blow up the resistance just like we have blown up the resistance to clubroot in a lot of places,” said Gossen.

Researchers believe A. euteiches has probably always been present in Western Canada, but pulse crops have been grown in large scales for only a couple of decades. After early years of few problems, root rots have become more widespread, including A. euteiches.

As the general problem with root rots have grown, the ability of researchers to separate A. euteiches has developed with molecular marker testing.

The good news is that this allows farmers to find out what kind of root rot they have. The bad news is that A. euiteiches is widespread and severe in some places.

Wet conditions have allowed root rots to become a much more serious problem for growers in recent years, but Gossen said drier years might not eliminate the problem. The impact of wet years lingers because so much inoculum is produced and left behind.

“The potential for disease is going to stay high.”

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