Disease levels in next year’s pea crop can be managed by making the right decisions when it comes to seed choice, rotation and fungicide application
Knowledge is power in the fight against two common pea diseases.
“The more you know about these things that are trying to take a bite out of your crop and your wallet, the better off you’ll be when it comes to trying to manage them,” Alberta Agriculture plant pathologist Michael Harding said at the recent Alberta Pulse Growers/Alberta Barley Growers joint meeting in Acme.
“Anyone who’s grown peas probably knows as well as anyone about what root rots look like and what ascochyta mycosphaerella looks like in the field. They’re very commonly occurring.”
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Ascochyta
Of the two diseases, ascochyta is most common — and most devastating.
“Twenty to 50 per cent yield losses are not that uncommon in pea fields in Alberta due to this disease,” said Harding.
“Because it’s so commonly occurring and causes such significant losses, this is really one of our No. 1 production constraints for peas.”
The foliage disease is both seed- and airborne, and appears as tan or grey lesions on the leaf and stems that can turn black as they grow. These lesions reduce photosynthetic capacity, resulting in reduced seed weight, size and number. Sometimes, the disease affects the lower part of the canopy as well.
“When that happens, you might not see a direct improvement in the actual seed yield from a fungicide application,” said Harding. “But if the disease is causing a lot of problems low in the canopy, it causes lodging, which reduces the harvestability of the crop.”
Because ascochyta can survive in the soil and infected crop residues, managing stubble and having an adequate crop rotation is critical.
“A three- to four-year break of susceptible crops is really a foundational principle of management for this disease,” said Harding. “The organism can survive in the soil, but the levels of inoculum that exist in the soil are going to drop with time.”
Using disease-free, treated seed will also reduce the impact of ascochyta, said Harding.
“If we’re using bin-run pea grain seed and it has a lot of ascochyta on it, we’re increasing the risk of seeing that disease show up early. The earlier it shows up, the more difficult it is to manage.”
A timely fungicide application can keep the disease pressure down, as well. Harding looks at four factors to help determine if a fungicide application is warranted: the canopy, the humidity, the symptoms and the weather. But even if producers do everything right, the risk of ascochyta outbreaks remains high.
“It’s pretty rare that we’re ever going to see a season in Alberta where we don’t have this showing up in pea fields,” he said.
Root rots
Root rots are becoming more of a problem.
“There are pea fields in Alberta now that are becoming absolutely devastated by root rots,” said Harding.
The disease limits the ability of roots to take up nutrients and water, causing yellowing and wilting in the canopy and discolouration of the main tap root and feeder roots.
Yield loss can be difficult to estimate but can be extreme in some cases, particularly in warm, wet soils.
“Any time where we get prolonged moisture and warm soil conditions, that really is just stoking the fire for these organisms to cause serious damage on roots,” said Harding.
Choosing fields that have low incidence of disease reduces the risk.
“If you have a significant amount of root rot on a pulse crop in a field, I wouldn’t put peas in there the next year. That would be asking for trouble.”
It’s also wise to not plant peas in fields that are heavy clay, heavily compacted or have poor drainage, he said.
Rotation can only reduce, not prevent, issues with root rot.
“Rotation only gets us so far because these organisms exist everywhere regardless of what crops we grow,” said Harding. “But by rotating away, the really aggressive pathogens will fall back down to a basal level.”
Choosing high-quality, high-vigour seed helps as well.
“There really isn’t anything we can do once the seed is put in the ground to protect that seed, so using good-quality, high-vigour seed is important,” said Harding, adding seed treatments can also help plants maintain their vigour.
Regardless of whether producers are seeing root rots or ascochyta in their fields, promoting good plant health is essential to reducing the risk of these diseases in Alberta pea fields.
“The healthier the crop, the more likely we are to be able to weather the storm and manage the disease situation in pea crops,” he said.
