By Darren Hefty
Fungicides – is it possible to just go variable rate or spot spray in fields?
When it comes to disease control and prevention, does your whole field need the same rate of fungicide? Precision ag has shown us without a doubt that fields are not the same from one end to the other. The question is “How do you manage this variance?”
At right is an example of a disease severity variance.
The blue and red zones in this field suffered significant loss due to sclerotinia white mold in soybeans in 2017. The farmer will rotate to corn in 2018 but plans to be back growing soybeans here in 2019. In his next soybean crop, how should he handle the red zones in comparison to the rest of the field? There are really three choices at R1 (first flower) that have the potential to maximize profitability if the disease strikes again. We would suggest spraying again at R3 and R5 to get the best control and the highest yields if white mold strikes, but these 3 choices are the R1 options.
- Spray a full rate of the best fungicide (Endura at $40 per acre) to control white mold across the entire field.
- Spray a full rate of Endura only in the blue and red zones where white mold is historically the worst (approximately 23 acres). Utilize a cheaper alternative or a reduced rate of Endura in the rest of the field (roughly 60 acres). If your second best fungicide is $10 per acre and a half rate of Endura is $20 per acre, either way will save a bunch of money. Granted, if the white mold is insufficiently controlled in those areas, that savings is all for nothing due to increased yield loss, but this is an option.
- Spray a full rate of Endura on the 23 worst acres and leave the other 60 acres untreated. If you haven’t seen white mold creeping out of the blue and red zones, you could take a chance and gamble that the next time white mold strikes it stays true to its past pattern. You’d have $2400 in your pocket to pay for any losses that occur out of that zone.
Again, white mold is best controlled with 2 to 3 fungicide applications, but the point is in 2018 you may be considering varying more than just fertility and planting population. Talk to your agronomist about spot treating (like #3) or variable rate application (example #2) of your fungicides. If you have a predictable area that is more prone to disease issues, this may be something that could benefit your profitability.