Monday, September 21, 2009

Soybean Rust Update and Spray Advisory for Selected Fields

NOTE: This SBR update is directed to KENTUCKY SOYBEAN PRODUCERS. If you live in another state, read what I say, below, with the extreme sensitivity that what I am writing may not (and probably does not) apply to you. I encourage you to find out what is being said by the Extension Plant Pathologist your state by going to

On Friday of last week we found soybean rust in Ballard County in far west KY. The level of disease was as low as it could possibly be (one leaf out of 100 that had one lesion, with one pustule!). This was the third SBR find in KY, the other two finds being in Warren County and Henderson County.

I have been pretty open about my belief that the vast majority of soybeans in Kentucky are well beyond the point where they could possibly be damaged by soybean rust. However, I also know that some fields in the state were planted very late and that development in July may have been hindered by wet and cool conditions. The bottom line is that there may be the rare field that needs all of October to completely fill pods. When I say, rare field, I am talking about fields planted in July to a group 5 soybean. By way of comparison, our Grains Crop Specialist, Dr. Jim Herbek is conducting a planting date study here at the UKREC where he planted a mid-group 4 variety on July 7th. That field was at the beginning flowering stage (R1) on August 10 and currently is at the full seed (R6) stage. The fields I am referring too would probably be at the full pod (R4) stage or barely into beginning seed (R5) at the present time.

My guess is that we could have considerable soybean rust in west Kentucky by the middle of October. By then, most soybean fields in the state will be at the R6 stage or later, and some will have been harvested. But, I am aware of the possibility that a few soybean fields may still be filling pods during the second part of October (assuming we do not have a hard frost before then). So, while most of you will not be impacted, if you have a field that may still be filling pods by mid-October, it would be wise to consider the prospect of applying a triazole fungicide (like Folicur or a generic, all of which are fairly inexpensive) soon if a highly specific set of conditions exist.

If you believe you have fields that may still be filling pods the last two weeks of October, please contact your local county Extension office. I have given them a soybean rust "Yield Loss Calculator", developed by UK's Dr. Saratha Kumudini, that will help you decide if spraying is to your economic advantage or not.

This advisory applies to the area west of I-65. If you are east of I-65, I would say you are “good to go” for 2009.

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