BY: Christopher Forsythe, Agronomist for the On-Farm Network, MPSG
Dry bean acres have been trending upwards in Manitoba recently, and last year we saw a 28 per cent increase in dry beans compared to 2023. Since more farmers may be looking to increase their dry bean production this year, including potential first-time growers, it’s timely to look at fungicide economics for dry beans.
Farmers ask the question, how often are foliar fungicide applications profitable? From small plot research, we have seen that fungicides can be effective at reducing disease and/or improving dry bean yield, especially in wet conditions. We also have field-scale research conducted in Manitoba to help shed some light on the answer and hopefully inform application decisions as well.
White mould is the main dry bean disease farmers aim to manage with fungicide since it has more potential to reduce yields than any other foliar disease. In wet years, and especially when July rainfall right before flowering is high, the risk of white mould increases significantly, and farmers generally spray fungicide accordingly. These conditions are where farmers expect to see a response since the impact of a fungicide application on yield is dependent on the extent of disease pressure in the field.
Fungicide applications vary year to year, and from 2021 to 2024, roughly a third of dry bean acres received a fungicide application. Fungicide use is higher in years with a wet, humid July.
Since 2016, Manitoba Pulse & Soybean Growers’ (MPSG) On-Farm Network has been looking at whether foliar fungicides in dry beans improved yield and provided an economic return. There have been 23 field-scale trials with replicated strips running the length of the field completed to date comparing a single fungicide application at flowering (early pin bean or R2 stage) to no fungicide applied at all. July rainfall was higher than normal at four of the 23 trials and the other trials were drier than normal. The products tested have been Lance, Acapela, Cotegra, Allegro, Proline Gold, Dyax and Zolera FX. There were 20 trials planted on 30-inch rows and three trials were planted on 15-inch rows or narrower.
White mould was found at eight trials. At all but one, white mould incidence (per cent of plants with white mould symptoms) was reduced at varying levels with the fungicide application. At two out of the 23 trials (10 per cent) where one fungicide application was applied compared to no fungicide at all, yield was increased enough to pay for the fungicide product (not including application cost). Profit margins are calculated using real yield data and average fungicide product cost.
At these two trials, yield increased by 165 to 175 pounds per acre. Assuming a dry bean price of 47 cents per pounds and an average fungicide product cost of $22.50 per acre, this resulted in a profit of $57 per acre at those two sites (49 pounds per acre is break-even yield). But at 90 per cent of trials, a single fungicide application didn’t significantly improve yield.
At two trials (conducted in 2021 and 2024), two fungicide applications were compared to one fungicide application but neither resulted in a significant yield difference.
Curiously, in 2024, when it was a wetter year and disease pressure was a concern at two out of four field-scale dry bean fungicide trials, there was no yield advantage to fungicide at any sites. As for a possible explanation? At one trial, the second of two applications was applied past the product’s recommended crop staging window (the product was applied at full-pod or R4, whereas a second application should be applied at mid-bloom or R3). At the other trial, where it was a single fungicide application compared to none, perhaps the damaging disease period came on later in July and a second application was needed for a response.
Based on this on-farm research, most of the time it doesn’t pay to spray. This doesn’t mean you shouldn’t spray, but make your decision by considering the conditions at flowering (rainfall, humidity and temperature) and always use MPSG’s Fungicide Decision Worksheet for Managing White Mould in Dry Beans. Remember, dry bean fungicide is purely preventative. For white mould control you need to apply the fungicide before symptoms appear.
At the end of the day, applying fungicide can pay off sometimes, but an application every year may not be necessary depending on conditions. Increase your chances of a fungicide application paying off by using a reliable product, spraying early before symptoms appear, but not too early (early flowering is best), and always consult the decision worksheet.