Laura Schmidt, MSc, PAg, Production Specialist – West, MPSG – Fall/Winter (December) Pulse Beat 2021
Faba beans are a small-acre crop in Manitoba, with roughly 7,500 acres grown annually. They are well adapted to cool, moist growing conditions and have the best nitrogen fixing ability of pulse crops, making them an attractive fit for agro-Manitoba. They are grown for human or animal consumption. Fabas destined for human consumption have traditionally been marketed to Egypt. More recently, local processing capacity in the province has expanded and faba flours, flakes, splits and whole beans are available to consumers. As capacity has increased there is a need to keep pace with both research priorities and agronomic understanding of this crop. So, here are some agronomy notes from 2021 to improve familiarity with this exciting pulse crop.
No need to worry with a cool start to the season. — Faba beans tolerate low temperatures well, and cool soils or late spring frosts are no reason for concern. Plant fabas once soils are passable in the spring and they’ll begin germinating once soil temperatures reach 3–5°C. The end of May in 2021 brought a hard frost to the northwest regions and down around the Riding Mountain National Park. This frost killed any above-ground soybeans at the time, of which thankfully there were few. Faba beans were around V2 (two unfurled bifoliate leaves) and showed signs of frost damage with dark splotches on leaf edges. In the rare instances where all of the above-ground tissue is damaged, fabas will regrow from the cotyledons below ground, much like peas.
A favourite snack of the pea leaf weevil (PWL). — While PLW has peas in the name, faba beans are their preferred food source. While scouting faba fields this August, leaf notching from PLW adults was easy to spot in western Manitoba. Catching weevils for proper identification is much easier in fabas than peas because you can easily sweep net through faba crops.
While the damage is already done by the larvae by late summer, scouting for PLW in the fall can help inform management decisions for next year. Seed treatments are one of the more effective tools and making note of PLW populations ahead of winter can be one way to determine if seed treatments will be economical. However, weevils will fly in the spring to reach new faba and pea crops, so they will readily disperse throughout a region.
Look-a-like foliar diseases and the question of fungicide use. — Leaf spotting from foliar diseases is common in faba beans from flowering to podding. Several pathogens can be to blame including chocolate spot (Botrytis spp.), Alternaria spp., Stemphylium spp. and Fusarium spp. Visually, these pathogens are tough to tell apart in the field and need to be plated in the lab for accurate diagnosis. However, since they are all fungal diseases, a fungicide should take care of it, right?
Researchers investigated foliar fungicides applied at 50% flowering over five years (2016–2020) at four locations in Alberta and Saskatchewan. Disease severity was lower with fungicide application, but there wasn’t much of a yield response. At $8–9/bu faba beans, the economics did not pencil out. In Manitoba, we have had one on-farm trial in 2020, where foliar fungicide yielded 15.7 bu/ac more than the untreated strips resulting in a return of around $100–125/ac. Here, I would suspect that timing is everything. Foliar diseases generally develop later in the growing season for fabas and it’s those cases of early infection with an environment conducive for disease development that a fungicide application will pay. This on-farm trial received 167% of normal rainfall in July and fungicide was applied at the optimal time to protect yield. An on-farm test would be one way to see if fungicide application is paying on your farm.
Lygus bugs can cause big quality damage. — Fabas are late maturing, resulting in movement of lygus bugs into fabas once alfalfa is cut or canola is swathed. Hot, dry weather like we had this year promotes lygus bug development and damage can be worse under these conditions.
Yield losses are not generally a concern, but quality can quickly be impacted. Lygus pierce pods to suck plant sap. Visible damage is found on the seeds due to enzymes in their saliva. Fabas need to have less than 4% perforated damage to be graded No. 3 Canada or better.
Fabas are susceptible to lygus damage until the pods and seeds become firm and most feeding occurs at the top of the plant. Monitor fields during pod development. A nominal threshold to prevent 15% damage is five lygus bugs per 10 sweeps. At research plots in Alberta in 2015 and 2016, a single lygus bug per ten sweeps resulted in 10–12% damage.
While control may be warranted, pollinator insects are important for seed set in fabas and should be taken into consideration when making spray decisions. Having pollinators in your fabas has been shown to increase yield by 17%, on average, so use practices or products that minimize the impact to pollinators.