Three years of fieldwork in field peas and faba beans will allow growers to sharpen their approach to this significant insect pest.

Pea leaf weevil is believed to cause two kinds of damage: first, this year; then, next year.

The first year’s damage is inflicted on its host crops of field pea and faba bean. Since pea leaf weevil feeds on root nodules that are essential to nitrogen fixation, immediate crop yields can suffer. With less nitrogen being fixed the first year, the following year’s crop (wheat, for example) could be under-nourished or would require added nitrogen.

In recent years, Dr. Hector Carcamo and his colleagues have added vital detail to this picture. In 2016-18, he led a study that examined pea leaf weevil management and produced important conclusions in several key areas.

Weevils prefer faba beans to peas. “One question we had going in was, does pea leaf weevil do more or less damage in faba beans compared to peas,” said Carcamo, Lethbridge-based Research Scientist, Insect Pest Management with Agriculture and Agri-Food Canada. “After all, faba beans have more nodules than field peas and of all the pulse crops, they are the best at fixing nitrogen. Our work found that pea leaf weevils fed more on faba beans.”

Faba bean threshold lower than peas. Having 15% of seedlings with damage on the clam leaf at the 2- to 3-node stage can result in economic yield losses. This threshold is lower than for peas, which is 30%. This shows the importance of managing the pest through seed treatment rather than foliar application, which the project found did not provide worthwhile protection.

“We found that the plots treated with a seed insecticide showed less damage compared to the plots treated with a foliar insecticide,” said team member Asha Wijerathna, PhD student at the University of Alberta.

Pea leaf weevil defense starts in the summer. Scouting the previous growing season can give growers an indication of how strong the following year’s weevil activity is likely to be.

“What is the population of pea leaf weevils at the end of the summer?” Carcamo said. “What are the conditions that might affect the mortality of the pea leaf weevil during the winter? Based on that, before they buy seed, growers need to decide whether or not to get the seed treated.”

Carcamo adds that seeding early could invite greater weevil damage; later-seeded crops tend to see less damage.

Nitrogen loss isn’t significant. Based on analysis of soil nitrogen and straw nitrogen of crops planted the next year, Carcamo now believes nitrogen loss caused by damaged nodules the previous year doesn’t significantly hurt yields.

Looking forward, he wants to understand how beneficial insects and spiders could play a role in managing pea leaf weevil. Carcamo’s final caution is that the environmental impact of chemical control should be carefully balanced with its yield protection benefits.

“The pesticides are not specific to the pea leaf weevil,” he said. “When you use an insecticide – either a seed treatment or a foliar – you can expect some negative effects on the beneficial insects.”

This researcher wants to make it easier to predict when white mould will occur, and know which cultivars and seed sources are the best match against bacterial blight.  

If disease was less of an issue, dry beans could be an even bigger crop than the 50,000 acres it’s averaged in recent years in southern Alberta. If this happened, more growers could enjoy the soil-building and economic benefits of the different market classes of dry bean.

With funding from the Canadian Agricultural Partnership AgriScience Program, AAFC Plant Pathologist Dr. Syama Chatterton is midway through a four-year effort aimed at the key bean diseases of white mould and bacterial blight, with the goal of adding management options and reducing risk.

For Chatterton’s team, 2019 was the second year of collecting white mould spores. Based in Lethbridge, she oversaw spore sampling in Alberta, while project colleagues did the same in Manitoba and Ontario.

“In a hot, dry year like 2018, white mould incidence was fairly low,” Chatterton said. “Even so, our work showed spores are continuously being released into the environment.”

Correlating spore counts to prevailing weather conditions to white mould incidence, Chatterton would ultimately like to develop a way to give growers advance warning of an outbreak. A PhD student at the University of British Columbia is examining how machine learning, a field related to artificial intelligence, could make this prediction faster and more precise.

“A prediction model would take into account some of those different weather variables,” Chatterton said. “We need three years of data to create a really robust data set for modelling and 2020 will be our third growing season doing the spore sampling.”

One observation to date is that fine-tuning irrigation could help keep white mould in check. When more irrigation is applied to dry beans, the canopy becomes denser and more likely to trap spores. A more open canopy, associated with less irrigation, traps fewer spores.

Seed source is one key to bacterial blight

With bacterial blight being a seed-borne disease, Chatterton started her inquiry with the seed itself. While most southern Alberta dry bean producers plant certified seed grown in Idaho, farm-saved seed is also available. Chatterton screened both kinds of seed for bacterial pathogens.

“There was definitely a big difference,” she said. “The seed lots coming from Alberta seed had very high levels of most bacterial pathogens. The Idaho seed was pretty much clean.”

One piece of a bacterial blight defense could be planting dry bean varieties known to be less susceptible to the disease. It hasn’t been clear, however, which varieties qualify.

“In 2019, we set up field trials with five different market classes, with two different cultivars each from two different seed sources,” Chatterton said.

To track disease development through the growing season, a technician visits these extensive trials to assign a disease rating on as many as 240 plots per site. This is complex research that, combined with the white mould work, will help growers stay ahead of disease and keep dry beans productive and profitable.

“The white mould spore sampling and the bacterial blight trials have both showed good progress,” Chatterton said. “We’ll be continuing this work in the 2020 growing season.”

After two years of study, the outline of a pea leaf weevil defence strategy is taking shape for field peas.

Pea leaf weevil is a challenging pest to handle, and could be more so in the future. Active in both field pea and faba beans, its populations can fluctuate significantly from year to year, meaning an insecticide seed treatment could be a help or an unnecessary expense. The available seed treatment is also a neonic, with an uncertain lifespan ahead of it. Research has shown that insecticides applied to the foliage are not very effective.

“Pea leaf weevil management is complicated, and insecticides are not always as effective as expected, so there is a need for alternatives,” said Dr. Meghan Vankosky, Field Crop Entomologist with Agriculture and Agri-Food Canada in Saskatoon.

Since the establishment of pea leaf weevil on the Prairies, Vankosky and colleagues have been working to build the foundations of an Integrated Pest Management approach to pea leaf weevil.

Now, with funding from the Canadian Agricultural Partnership AgriScience Program, Vankosky is building on existing knowledge to add new approaches to the pea leaf weevil management toolbox. Here’s a summary.

Beneficial insects. A class of ground beetles are potential predators of pea leaf weevil. “Of those beetles, we wanted to choose the ones that are most common and work on some bioassays in the lab to determine whether they actually eat pea leaf weevil or not,” Vankosky said. “In the last two years we’ve sampled extensively in Alberta and Saskatchewan for the ground beetles present in those two primary host crops of pea leaf weevil.” Bioassays are scheduled for Summer 2020.

Trap crops. Currently, pea leaf weevil populations are low in most of Alberta and Saskatchewan. About the only place with a consistent population is the Lacombe area, where more of Vankosky’s work has been taking place.

“In 2019, we planted plots of peas and faba beans next to each other and looked to see if weevils were more attracted to one crop than the other during their spring migration,” Vankosky said. “We did the same later in the season in late-July to observe food preferences of new- generation adult weevils.”

It appears that weevils prefer faba beans over field peas, suggesting that a strip of faba beans planted around a pea crop could collect weevils.

“What we’re finding is really positive,” said Vankosky. “We can attract weevils to a crop in the spring and in the fall.” These aggregated weevils could then be controlled by one or more methods: by ground beetles, by insecticides or by a third approach Vankosky is studying.

Trap and kill using pheromone-baited pitfall traps. Research led by Dr. Maya Evenden, an Entomologist at the University of Alberta, has demonstrated that pheromone-baited pitfall traps can be used to monitor pea leaf weevil. Vankosky and Evenden are now working to determine if these traps can be used to reduce weevil populations in field pea crops. Pitfall traps are dug into the soil, with the opening of the trap level with the soil surface. As weevils fall into the traps due to their attraction to the pheromone, they can be controlled by a reservoir of soapy water, antifreeze or some other agent. Placing these devices in a trap crop could give growers an additional option for killing adult weevils.

“The idea is to trap and kill adults in the late-summer and fall,” Vankosky said. “In 2019, we put pitfall traps into our pea and faba bean plots at Lacombe, and we’re now assessing how well they catch pea leaf weevils and differences between the two host crops. Some of these ideas for managing pea leaf weevil look promising, but there’s more work needed to validate them at field scale.”

By planting varieties with some degree of resistance, growers can stay a step ahead. Agronomic tactics could also play a role. Here’s a look at ongoing root rot work.

It’s too early to say that science has Aphanomyces on the run, but research continues to build a vital knowledge base and a toolkit for growers.

Dr. Syama Chatterton explained that growers and scientists first came face to face with this causal agent of pea root rot in 2012-13. Plant damage was different and more extensive than the accustomed causal agent, Fusarium.

“We spent the first five years doing surveys on the distribution of Aphanomyces across the prairie provinces,” said Chatterton, Plant Pathologist with Agriculture and Agri-Food Canada in Lethbridge. “Since 2018, we’re focusing more on management and breeding.”

Management: intercropping, pulse substitutions. Chatterton’s heard a lot of buzz about intercropping as a means of managing pulse disease. The idea is that glucosinolates from the roots of a Brassica crop (canola, mustard) could act as a biofumigant to keep disease down in the roots of its companion pulse crop. Chatterton has put this idea to the test, planting intercropped peas/canola and peas/brown mustard.

“Our last two years haven’t been very encouraging,” she said. “Where sites already have high root rot – and that’s all of our sites – intercropping isn’t making a difference on the root rot level of the peas.”

If you like peas in the rotation but are concerned about root rot, could a resistant pulse take the place of peas for a turn or two? With funding from the Canadian Agricultural Partnership AgriScience Program, Chatterton is continuing to study whether and how chickpeas, soybeans and faba beans reduce the level of root rot inoculum in the soil. She’ll build a case over the next few years.

Breeding: cross-province effort lays the foundation. Chatterton and Saskatchewan colleagues have divided up field research into two root rot causal agents. Chatterton is covering Fusarium and the Saskatchewan team is handling Aphanomyces. The goal is to identify registered pea germplasm lines with some resistance to Fusarium, Aphanomyces or ideally both, and move that resistance into Canadian-adapted lines. It’s a complex effort, one that will continue in 2020 and beyond.

“We spent most of 2019 looking at different methodologies for screening lines,” Chatterton said. “The traditional screening method is to soak the seeds in inoculum, but we find that most lines just die that way. We’ve looked at other methods where we can grow the plants out, so they’re a little bit older, then add inoculum so you get the right amount of disease without killing the plant.”

For Chatterton, this is part of her broader effort to ensure that pulses are a steady or expanding part of Alberta crop rotations.

“I love working on pulse crops because I think they’re so important to our sustainable agriculture system,” she said. “One of the challenges is that they’re susceptible to a fair amount of disease, yet there hasn’t been as much disease research as in other crops. I feel this research is essential for growers to continue to want pulses in their rotations.”

Four years of fieldwork have yielded insight on issues from herbicide residue to micronutrients to disease management.

When the price of faba beans shot up in 2015, many Alberta farmers decided to grow this pulse crop for the first time. Robyne Bowness Davidson’s phone started ringing soon after.

As Pulse Research Scientist with Alberta Agriculture and Forestry, she fielded a wide range of agronomy questions about faba beans. For some topics, Alberta-specific faba bean research didn’t exist or hadn’t been updated in decades.

Beginning in 2016, with support from Alberta Pulse Growers and others, Bowness Davidson set about answering some key questions. Fieldwork at Falher, St. Albert, Lacombe and Lethbridge provided new, Alberta-specific data to back agronomist recommendations and growers’ production practices. Here’s a quick summary.

Question: I’ve heard that pre-seed herbicides can damage faba beans. Do they?

In 2017 and 2018, Bowness Davidson assessed numerous pre-seed herbicides for their impact on faba beans. In Lethbridge, some applications made according to label guidelines caused damage. At other times, enhanced rates and off-label timing did not. For this reason, growers might be best to stick with what worked in Lacombe.

“The response in Lacombe was exactly what we’d expect,” Bowness Davidson said. “If you double the rate, or you spray too close to emergence, or spray after planting, or don’t follow label, then you’ll have damage to the fabas. If you do everything you’re supposed to do, it should be fine.”

She also advises growers to carefully read the label on wheat herbicides used the year before planting faba beans, and will continue studying this usage in 2020.

Question: Someone’s trying to sell me micronutrients for faba beans. Good idea?

“At four locations over three years, sprayed individually or in different combinations, we didn’t see a response to the micronutrients,” Bowness Davidson said. “It’s not that micronutrients aren’t important, they are, but our soils generally seem to have enough. Spending that extra $2 or $3 per acre hoping to get some extra yield might not be a sound investment according to our research so far.”

Question: What’s the best fungicide for chocolate spot and ascochyta?

Most recent years haven’t been conducive to these key faba bean diseases, which makes them difficult to study.

“With 2016 being kind of a questionable year for harvest, and 2017 and 2018 being very dry in Alberta, we weren’t finding that we had really great data,” Bowness Davidson said. “With the cool, wet conditions in 2019, though, we got some excellent data and we’ll keep working on fungicide application in 2020.”

Since 2015, Bowness Davidson has assembled Alberta data to answer some of growers’ top faba bean questions. Today’s market price might not be as good as it was in 2015, but the case for growing faba beans in Alberta is strong.

“We have really good growing conditions and lots of moisture generally, we have rich soils, warm days and cool nights,” Bowness Davidson said. “I think in central Alberta especially, up in the Peace, and southern Alberta when there’s access to irrigation, I’d say faba beans are a very good fit for Alberta.”

With this insect’s range expanding, and few current tools working well, new research is considering cultural and biological control methods.

Let’s say you grew a high-yielding cereal crop one year. By planting time the following year, a soil test illustrates the field is relatively nitrogen poor. That’s okay, because you’re growing peas next.

However, if pea leaf weevils are present that spring, this low soil nitrogen could cause big headaches down the road. Field Crop Entomologist Meghan Vankosky explains that bacteria in a pulse crop’s root nodules fix nitrogen that can be used by the plant to produce yield and to improve soil nitrogen reserves. Since pea leaf weevil larvae feed on those nodules, they impair the plant’s ability to fix nitrogen.

“There’s real concern for potential yield loss due to pea leaf weevil if you’re planting peas into low nitrogen soil, which is what we like to do,” said Vankosky, Research Scientist with Agriculture and Agri-Food Canada.

Currently, only one foliar insecticide is registered for pea leaf weevil. Insecticide seed treatment can work but must be purchased long before there’s evidence of a pea leaf weevil infestation.

“For growers in areas with high pea leaf weevil pressure, the recommendation tends to be insecticide seed treatment,” said Vankosky. “Outside those areas, it’s a gamble for producers to treat seeds but if weevils show up in big numbers, the foliar spray isn’t very effective either.”

In 2018, Vankosky began a three-year research project to study Integrated Pest Management (IPM) for pea leaf weevil in pea and faba bean crops with funding from the Canadian Pulse Science Research Cluster. The project will examine three potential ways to manage pea leaf weevil with less environmental impact.

1. Beneficial insects. “We know there are potential natural enemies of this pest, but the current research barely scratches the surface,” said Vankosky. “We want to figure out the species here on the Canadian Prairies that might eat pea leaf weevil and the impact of that.”

2. Trap crops. Another strategy that will be tested is the planting of trap strips in July. When the new generation of pea leaf weevil feed on the trap crops in the fall, researchers will test alternative control methods to determine if it is feasible to control pest populations in the fall.

3. Pheromone traps. Using a pheromone-baited pitfall trap developed by University of Alberta Entomologist Maya Evenden, Vankosky is testing whether this system could be part of a trap-and-kill strategy to manage pea leaf weevil populations. An agent as mild as soapy water could be enough to kill trapped weevils.

With research showing a vigorous pea leaf weevil spread in Alberta over the last few years, Vankosky wants to give growers options beyond the current limited toolbox.

“The idea is to reduce the number of weevils overwintering or going into the fields in the spring,” Vankosky said. “We need to quantify the efficacy of these ideas. We’re not recommending anything to farmers without first testing those ideas ourselves.”