Managing lygus bug in faba beans

Over a three-year period, AAFC scientist Hector Carcamo advanced knowledge around how to protect faba beans from this quality-reducing insect.

Many prairie farmers will associate the insect pest lygus bug with canola. In canola, long-established economic thresholds put growers in a solid position of knowing whether or not to spray.

The growth of faba bean acres in Alberta in recent years resulted in more lygus feeding on this valuable crop. Growers have asked for management strategies to help them fight back, and Agriculture and Agri-Food Canada’s Hector Carcamo took on the challenge.

“Lygus can be significant in some years,” said Carcamo, Lethbridge-based Research Scientist, Insect Pest Management. “Depending on the year, if conditions are right for them, you can have a large population that can be a concern.”

In faba beans, lygus damage tends to be more cosmetic than material. The crop may weigh the same in terms of yield, but lygus feeding produces a dark spot on the faba bean that causes quality and price downgrading in crop for export.

Between 2013 and 2016, with funding support from Alberta Pulse Growers and others, Carcamo conducted research designed to give growers some much-needed information around lygus bug in faba bean.

Survey quantifies lygus in faba

As Carcamo explains, this project attacked the lygus issue from a few directions. “The first thing to do is make sure the damage or the symptoms are caused by the organism you suspect,” he said. “So we dissected the pods and seeds and did a survey in the field.”

Canola growers are accustomed to dealing with one species of lygus. The ones feeding on faba beans could be from a different species and might, therefore, need somewhat different management approaches. A survey conducted by Scott Meers and Shelley Barkley of Alberta Agriculture and Forestry, however, found that the same species of lygus bug that feeds on canola also feeds on faba beans.

“We did a sweep for lygus at 10 spots in each field,” he said. “We found that lygus are most abundant at the pod through flowering stage. The best time to control them could be at early pod, just like with canola.”

This finding suggests that planting faba beans early could help avoid some lygus feeding that occurs later in the season.

Carcamo’s three-year study was intended to build up some basic information on lygus bug in faba beans. Before settling on a formal economic threshold for insecticide application, he believes that more research is needed. Regardless of when an application takes place, Carcamo stresses that growers should take care not to harm pollinators and the natural enemies of lygus. This is important for the ecosystem and for the health of the faba bean crop.

“We are making a preliminary recommendation that if you find fewer than two lygus per sweep, don’t worry,” Carcamo said. “But if you do spray insecticide, keep the bees in mind because their pollination is important for the yield of the faba beans.”

Research tackles key questions in faba bean agronomy

Robyne Bowness’s three-year project aims to bring data and clarity to issues like herbicide residue, desiccation, disease management and crop nutrition.

In 2015, when Alberta farmers grew 100,000 acres’ worth of faba beans, some wondered if this was just the start of even bigger things. By 2016, the market changed, prices dropped and faba bean acreage was cut in half.

To Robyne Bowness, Pulse Research Scientist with Alberta Agriculture and Forestry, this might have been a blessing in disguise. Before acres get too carried away, faba beans is a crop we need to know more about.

“The problem with faba beans,” Bowness said, “is that we haven’t done a lot of research on this crop over the past 20 years. There’s some basic research that we still need to do.”

In 2016, with funding from Alberta Pulse Growers, Bowness began a three-year project to address key issues around faba bean production. The work is taking place at locations in four different soil zones: Falher, Lacombe, Barrhead and Lethbridge.

The impact of herbicide residue. It’s long been suspected that faba beans can be damaged by the residue of herbicides used in the same field the previous year on wheat. In 2016, Bowness and her team grew wheat at the four locations, spraying each plot with various rates of herbicides sometimes linked to faba bean damage. Will the plots’ 2017 faba beans be affected? If so, which herbicides and rates might be the cause? Over the next two growing seasons, Bowness will put some hard numbers to this issue.

Fungicides for management of chocolate spot. Bowness is conducting three years’ worth of fungicide trials – of which 2016 was the first. “Research has shown in canola and cereals that fungicides work,” said Bowness. “How much of a problem is chocolate spot and how will these products help? We need to get the research to back us up on this.”

The right product and timing for desiccation. Reglone is considered the gold standard of desiccants, but growers might prefer to use Roundup and/or Heat, which cost less. Bowness will examine the effectiveness, and cost-effectiveness, of four different desiccant combinations.

The role of macro- and micro-nutrients. Anecdotal evidence abounds about the value of various macro-nutrients (such as phosphorous and potassium) and micro-nutrients (such as boron) in faba bean production. What’s lacking is hard data. Through three seasons of trials, Bowness aims to provide it. “Micro-nutrients may be of benefit, but right now it’s too early to say,” said Bowness. “We want to clear up the muddy waters.”

Bowness believes it could be a few years before we see another 100,000-acre faba bean crop in Alberta. Longer-term, she believes the crop’s high protein and market demand will move acres higher. When that times comes, Alberta growers will know far more about the crop than they do today.

“It might take a while to get going, but there’s a lot to like about faba bean,” said Bowness. “That drop in acreage from 2015 to 2016 might turn out to be a good thing after all.”

Study targets effective pea leaf weevil strategies

A large expansion of pea leaf weevil in 2015 made clear that pea and faba bean growers need better ways to deal with this insect.

It was the third week of April when Hector Carcamo saw his first pea leaf weevil of 2017, in his own garden.

For Carcamo, Lethbridge-based Research Scientist, Insect Pest Management, with Agriculture and Agri-Food Canada, the backyard appearance by this pest heralded the start of a busy research year.

With funding support from Alberta Pulse Growers, he’s now entering the second year of a three-year project to study the biology and management of pea leaf weevil in faba beans and field peas.

“In 2015, we saw a very large increase in the intensity and geographic expansion of pea leaf weevil,” Carcamo said. “There previously had been a mild winter, so they were able to overwinter. We counted pea leaf weevil in faba beans at both the pod and flowering stage.”

As Carcamo explains, this study’s first aim is to determine the impact of pea leaf weevil on nodulation and yield of faba bean. The project will also consider whether a foliar insecticide, insecticide seed treatment or both could be effective management strategies. Research plots in Lethbridge and Lacombe are the locations for this work.

“In order to develop a chemical management strategy, we have to look at the biology of the weevil,” Carcamo said, “and gather more information on its feeding and other practices.”

Peas or faba beans: which do weevils prefer?

Carcamo cites previous greenhouse research done elsewhere that showed pea leaf weevil appears to prefer faba beans to peas. If this could be confirmed, it could open up a viable management strategy. Growers could plant a strip of faba beans around a pea field; the insects might stay in the faba beans and steer clear of the peas. Based on his field observations from 2016, however, Carcamo’s now inclined to believe that weevils don’t favor one crop over the other. Work in 2017 and 2018 could change this view, however.

One year of field work has found it’s likely that seeding dates are highly relevant in weevil management. This could form the basis for agronomic recommendations for growers.

“We believe that seeding date can be a huge factor,” Carcamo said. “It’s very clear that peas or faba beans that are seeded earlier have more damage, so there may be an advantage to seeding them later.”

Whether the management strategies proposed by Carcamo involve cultural practices, insecticide application or other tactics, he maintains that growers need to deal with pea leaf weevil in an integrated manner. In the same spirit, this project involves scientists from multiple disciplines.

“Our number one objective in this project is to develop management strategies for pea leaf weevil in faba beans,” Carcamo said. “One should do this research in an integrated manner, making sure that what we do for one pest does not harm another component. We need to use the right tactic for the right pest.”

An early warning system for pea leaf weevil

Three years of producer-funded research enabled the development of a semiochemical-baited trap to monitor pea leaf weevil in the prairie provinces.

Pea leaf weevil is a tiny insect that punches far above its weight in terms of potential impact on crop yield. The size of a grain of rice, this non-native invasive insect has emerged in recent years as a threat to Alberta’s most-planted pulse crop.

Complicating growers’ pea leaf weevil defense is the fact that this insect appears intermittently. Some years it’s a significant problem, while in others it’s just a minor inconvenience.

What if pea growers had a way to determine whether next year’s pea leaf weevil activity was likely to be problematic?

University of Alberta entomologist Maya Evenden spent three years working on just such a solution. With support from Alberta Pulse Growers, via the Alberta Crop Industry Development Fund, Evenden has developed the tools for a pea leaf weevil monitoring system.

Two naturally occurring chemicals as bait

“There are two times in the life cycle of pea leaf weevil where you can monitor adult activity,” Evenden said. “You can do it in the spring when adult weevils come into the field and in the fall when the next generation of adults leave the field in search of overwintering locations. You can use traps in the fall to check them when they go to overwinter. That would tell you whether or not you needed to use an insecticide seed treatment the following spring.”

As Evenden explains, her pea leaf weevil monitoring traps required some type of bait to attract weevils. She used two different types of semiochemicals, or information-bearing chemicals: an aggregation pheromones and volatile chemicals emitted by pea plants.

Over three years of field studies, Evenden used a variety of trap configurations, and various combinations and doses of aggregation pheromone and/or volatile chemicals as bait. Many field trapping studies were conducted in commercial field pea crops during three field seasons to optimize the best bait and trap type to attract and retain weevils.

In addition, Evenden’s team conducted a painstaking mark-recapture experiment over two years that involved the collection of approximately 20,000 weevils from pea fields. Of these, 10,000 were marked with a spot of nail polish on the thorax. The marked weevils were released at eight different distances from the traps to test the traps’ effective radius. As very few marked weevils were trapped in this experiment, more work is needed to establish how many traps might be needed, given the size of a field, for monitoring of pea leaf weevil populations.

After three years of field work led by Evenden, there is now a practical tool for monitoring pea leaf weevil. Evenden’s work with this insect will continue. Building on knowledge gained in the monitoring project, she’s now working to determine the extent of pea leaf weevil in the province.

“We’ve learned a lot about the chemical ecology of weevils and are now tracking it all over Alberta to get a field-scale reading of where pea leaf weevil is,” Evenden said.

Root rot in field peas is a major constraint to production causing severe stand and yield loses. This research will take a concentrated look at the pathogens causing disease in peas, the effectiveness in various seed treatments as well as develop a risk assessment tool which will allow producers to determine their level of risk prior to planting. The outcomes of this four year study will be invaluable to providing information regarding the root rot disease complex and provide practical management options.

Western Canada must advance agronomic practices to increase yields and profitability. Next generation agronomy will include efficient and effective use of: in-crop nitrogen, foliar fungicides, and plant growth regulators (PGRs). Although some of these practices are currently used in Alberta, further research is required to examine their performance in management systems and in combination with other agronomic practices (inter-row seeding, seeding rates & nitrogen stabilizers).

This study will examine combinations of advanced agronomic practices on wheat, feed barley and field pea. Small plot field trials will test interactions of 48 wheat management practices, 52 barley management practices, and 15 pea management practices at Magrath (irrigated), High River (thin black soil), Killam (thin black soil), St Albert (black soil), and Falher (grey Luvisol) to maximize harvestability, yields, quality & profitability.