Aggressive root rot pathogens could cross over from faba beans to field peas, creating a potentially disastrous situation
More acres mean more disease pressure, and faba bean growers are being urged to be on the lookout for two diseases.
“Faba beans appear to be an emerging crop once again in the province, and any time acres of a crop increase, we’re alert to see what’s going to happen with them,” provincial plant pathologist Michael Harding told a recent joint meeting of Alberta Pulse Growers and the Alberta Barley Commission.
“If there’s more faba bean stubble out there, more acres adjacent to one another, and more faba bean in rotation, what’s that going to do to some of these diseases? It will be interesting to see.”
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The two diseases to keep watch for are chocolate spot (a fungus formally known as botrytis) and root rot, he said.
“These are the usual suspects, and they tend to cause significant losses in some fields each year,” Harding said.
Chocolate spot
Chocolate spot is a common pathogen in Alberta and it’s “not going to go away,” he said.
“It’s going to be here year in and year out, and the environment is going to be one of the factors that will really drive this.”
Characterized by reddish-brown lesions that often turn black, chocolate spot spreads in warm, moist conditions, and severely reduce yields. Because it’s seed-borne, using high-quality, high-vigour seed is important, said Harding.
“If the seed lot has a lot of botrytis on it, we could be introducing more severe problems than would normally exist,” he noted.
Seed treatment can also help.
“Fungicidal seed treatments can help minimize the effects on seeds, but fungicidal seed treatments won’t rescue heavily infested seed lots,” said Harding, adding there are no fungicides specifically labelled for chocolate spot in faba bean.
He recommends a four-year crop rotation and using high-quality seed to reduce the risk of a serious outbreak.
Root rot
Root rot has also caused problems in faba beans over the past growing season.
“With root rot, we’ve got those usual suspects that are always present in our Alberta soils, like fusarium and rhizoctonia, and they will cause similar symptoms and similar problems in faba beans as those in pea,” said Harding.
Because it’s a soil-borne disease, you have to choose your rotation carefully.
“There are at least three or four diseases that could build up as a result of having peas and faba beans in close rotation,” he said. “With root rots, any time you have a crop in there that will host these really aggressive root rot pathogens, those will pass over from faba beans to pea.”
Although growing peas on faba beans is less risky than growing peas on peas, don’t take chances, Harding said.
“It’s still a high-risk situation when you’re growing crops that share that disease-causing organism,” he said. “To have peas in close rotation with faba beans would be potentially disastrous for the root rot situation.”
Burying your trash
Burying crop residue is one way producers can reduce some types of faba bean diseases — although not root rots.
“The organisms that are causing root rot are surviving under the soil regardless of whether there’s a lot of crop residue there,” said Harding. “You’re not really adding to the root rot problem by burying trash, but you’re not preventing it either.”
Foliar diseases like chocolate spot, however, can spread rapidly in the right conditions if crop residues aren’t buried.
“If you leave those infected residues sitting on the surface of the field and then bring a susceptible crop in, all you need is some wetness and you’re going to have a bad disease problem,” Harding said.
While burying crop residue helps, a four-year crop rotation is really the cornerstone to any strong disease management plan.
“If I was going to create a foundational principle for managing diseases, burying crop residue wouldn’t be the foundation,” said Harding. “Crop rotation would be the foundation.”
