Your dry bean field has pods and almost no flowers left.
You know your risk rating for white mould was on the high side because:
- You have had crop rotation with susceptible hosts (canola , beans, sunflowers) and the previous broadleaf crop had severe white mould infection
- your canopy is thick and you seeded on narrow rows
- you used a higher rate of nitrogen
You have already applied one fungicide pass about 2 weeks ago. You’ve had 15-25°C and 1-2 inches of rain in the last few weeks and forecast is calling for more. (or more came)
You’ve heard “no mould, no gold”, and you see some white mould in certain areas of your field so you suspect that you have a decent yield coming but you are concerned that white mould can impact yield and quality of dry beans.
Will there be benefit from a second application of fungicide now?
According to Provincial Pulse specialist Dennis Lange, “Fungicide will help if flowers are still present. It would be preventative for further infection. It is very important to only apply if you are within the pre harvest interval (PHI) timing. As of today, we may be 30- 35 days from harvesting depending on weather and the dry bean type.”
Several fungicide products for white mould in dry beans have a PHI of 30 days, for some it is 21 days and some are 14 days. Oxidate FC has a PHI of zero days but is not labelled for white mould control, only for bacterial blight.
The infection process of white mould in dry beans begins when sclerotia germinate to produce small, mushroom-like structures called apothecia.
Once mature, each apothecia can release millions of spores. Those spores use the flower petals as a food source.
Once a blossom is infected, the mycelium remains viable for more than a month. This is why the timing of fungicide applications is crucial for prevention of white mould spreading. Ensuring proper coverage of flower blossoms with fungicide helps prevent the flower from being food and thus the disease from developing further and infecting healthy plant tissue.
If warm, humid conditions persist throughout flowering and pod development, consider a second fungicide application 7 to 14 days after the first, if flowers are still present.
In addition to the late timing, with a thicker crop canopy fungicide may not be able to penetrate down into the lower canopy.
Once the crop starts to visibly ripen fungicide will likely not make a difference.
The MPSG On Farm Network has studied the effectiveness of a second fungicide application in dry beans targeting white mould, but only in 2 fields from 2016 to 2024.
July rainfall is critical for white mould development and keep in mind, both of these trials experienced well below normal July rainfall.
The OFN results showed that in dry beans two foliar fungicide applications did not improve yields vs one foliar application.
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