Soybean Growth Staging Timeline – Fungicide Timing/Recommendation
August 30, 2021
I hope everyone has had a good weekend. In response to this weekend’s Soybean Rust Update from Jonathan Croft, Joe Varn, and Dr. Mueller about confirming soybean rust on soybean in Bamberg, South Carolina, I wanted to provide a few recommendations as we begin applying fungicides or considering doing so.
The crop progress report from SC reports that approximately 50% of our soybean crop across the state is setting pods and that most of the crop has finished blooming. The critical time to protect soybean from a disease like soybean rust is from R3 (Beginning of pod – 3/16″ long pod on one of top 4 nodes) through R6 (Full seed in a pod within the top 4 nodes). Much of our soybean crop across the state is at this important growth stage and has good yield potential if we continue to receive some rain to fill pods.
A few questions that you must consider before applying a fungicide to soybean:
What growth stage are my soybeans currently at?
What fungicide product will I spray (1, 2, or 3 modes of action)?
Can I obtain the fungicide that I wish to spray (some reports of fungicide shortages in the southeast)?
If I have not yet made it to R3 does the weather look favorable for a fungicide application in the near future?
Based on data generated at Edisto REC, as you increase the number of modes of action (1, 2, or 3 MOA) in a single fungicide product, you also increase the residual or length of protection from disease with that product. Like most things, as you increase the number of MOA in a product the price of the product also increases. You can expect to typically get 2 to 3 weeks of efficacy from a 2 MOA product and 3 to 4 weeks of efficacy from a 3 MOA product.
To estimate “If I spray a product 1 time will I be in the clear from soybean rust”, you must first know the soybean growth stage you are currently at and then know how many days it takes to transition through the reproductive growth stages. Below are an average number of days and estimated ranges it takes to progress through the reproductive growth stages. Please refer to the
Soybean Production Guide for more information on Growth Stage determination.
R1-R2 – (Avg = 3) (Range = 0-7 days)
R2-R3 – (Avg = 10) (Range = 5-15 days)
R3-R4 – (Avg = 9) (Range = 5-15 days)
R4-R5 – (Avg = 9) (Range = 4-26 days)
R5-R6 – (Avg = 15) (Range = 11-20 days)
R6-R7 – (Avg = 18) (Range = 9-30 days)
R7-R8 – (Avg = 9) (Range = 7-18 days)
Based on the data above, we can expect it will take 20 to 30+ days to progress from the beginning of R3 through the beginning of R6 growth stages in SC.
Overall, our recommendation is if no weather concerns are in the near future (rain or storm keeping you out of the field from spraying) and you can wait on later planted soybean until R3 to spray, do so. If you have soybean between R3 and the beginning of R6 at this time with good yield potential, then applying a fungicide to those soybeans would be recommended. As with anything, there may be a few exceptions in certain situations, please do not hesitate to contact your local Extension Agent if you have any questions.
