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Winning the war on pea problems

Weeds, disease and pests will all steal yield from less-competitive pea crops

A crop of field peas in saskatchewan

Disease and pests pose a big risk for growers. A little planning can go a long way to limiting the damage.

Peas are somewhat less competitive than some other crops like barley, canola or wheat because their canopy is open a bit longer, so weeds get a better start,” said Dr. Neil Harker, research scientist, weed ecology and crop management with Agriculture and Agri-Food Canada.

Adding to the difficulty is that the main weed culprits have changed over the years, making them a bit of a moving target.

“For example, a few years ago in central Alberta the main focus in peas was annual sow thistle,” said Harker. “But in terms of relative abundance, the most recent surveys show cleavers, volunteer wheat and wild buckwheat as the chief weed issues.”

Cleavers in particular are a growing problem for peas.

“Cleavers numbers are increasing and they are moving out of the black soil zone where they were well-adapted and are appearing more in dark brown soils than in the past.”

The cleavers challenge is further complicated by the issue of herbicide resistance. Since the most common herbicides applied to peas are Group 2 ALS inhibitors, cleavers have developed considerable resistance to these chemicals.

“That resistance means we can’t treat cleavers as easily which limits our options with peas compared to other crops. Cleavers are an important weed threat in peas that we will have to deal with in the future.”

The fact that peas are less competitive puts a premium on weed prevention. Grower planning for a pea crop should pay more attention to difficult weeds like Canada thistle, getting them under control pre-harvest.

The strain of the disease

Pea disease threats have increased sharply over the last five or six years due to weather conditions.

“We’ve been seeing severe root rot that affects crop yield, standability and harvestability,” said Sherrilyn Phelps, agronomy and seed program manager with Saskatchewan Pulse Growers. “White mould (sclerotinia) has also been prevalent, especially in 2016.”

And because there is no fungicide or chemical that will go down into the root system and control the diseases affecting peas, Phelps said prevention is vital.

“With root rot it’s all about management. There are four pathogens that can cause problems for peas: rhizoctonia, pythium, fusarium and aphanomyces.”

The approach for the four pathogens differs slightly, but for the most part they are soil-borne diseases that appear when plants are stressed and excess moisture is present.

Because aphanomyces is more specific to peas and lentils, rotation is a prime management tool.

“Where a field has tested positive for aphanomyces, we recommend abstaining from pea and lentil production for six years.”

Since aphanomyces can affect the plant at any point in its life cycle, Phelps notes that you can get later infection, for which seed treatment is ineffective.

“It’s more aggressive, longer lived in the soil and more devastating when it does infect the plant.”

In battling the other three pathogens, there are seed treatments available to help with early season control. Additional factors include field choice (choosing fields lighter in soil texture to improve drainage), managing fertility, staying on label with herbicide application and managing seed carefully so as not to damage it.

“You should do everything possible to have a healthy, vigorous plant to minimize stress and equip it to better combat disease.”

Pesky pests

The other threat to peas comes from insect pests. One of the most problematic is pea leaf weevil, which gives the leaves a scalloped appearance where the adult insects have chewed on the leaf edges.

“The problem is that those adults lay eggs in the soil and the larvae eat the nodules,” said Phelps. “That impacts the amount of nitrogen fixed. We’re still trying to understand the yield implications and how to manage this pest.”

Seed treatments with insecticides can help. In-crop foliar applications can control the adults, which appear in late May to early June in most areas.

Over the last couple of years, pea aphides have also been an issue, especially in drier conditions as they suck the sap out of plants and cause considerable stress.

“If these insects are sucking on the petioles at flowering time, they can affect the number of pods that form or fertilization of the flower, so it’s something to keep an eye on.”

Know the economic thresholds before applying insecticide, as there are a lot of beneficial insects that help keep pea aphides under control.

Keeping peas healthy is not easy. But by taking a calculated approach and staying on top of the problem, you may keep your peas growing strong.

About the author


Geoff Geoff Geddes is a freelance agriculture and business writer based in Edmonton. Find him online at or email [email protected]

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