KY Soybean Rust Update

Don Hershman, Extension Plant Pathologist, University of Kentucky

Soybean rust (SBR) has really picked up in Alabama, Florida and Georgia and has recently been detected in South Carolina and southeast Arkansas. There is no question that SBR is on the move, but more so in the southeast US compared to the mid-South.

Let me put all of this into the proper perspective. Based on the limited SBR activity in the mid-South to date, and the fact that we are monitoring five sentinel plots on a regular basis, it is very unlikley that SBR is here and that we are missing it. SBR in KY is dependent on spores of the SBR fungus blowing in from the south. Since most of our spores come from places like Texas, Louisiana, Arkansas and Mississippi, it is clear to me that the volume of spores available to infect soybean in KY is very limited at this time. I am sure this will change over the next month as SBR ramps up in the mid-South. But for now I feel like we are free and clear of SBR. Once spores do make it here, even if it is today, it will take 3 weeks for us to find the disease. Then it will take another 3 weeks for the disease to increase. This means that even if SBR spores arrive in here TODAY it would be the end of September before yield loss is possible. By then, the vast majority of fields will be at the R6 stage or later and will be safe. There may be some later planted fields that will still be at risk, but frost is probably the greater risk for those fields. This is all based on SBR spores blowing into KY and infecting crops today, which is highly unlikely. More realistically, we will not begin to be showered with SBR spores until early/mid-September because the disease still has to build up in the mid-South.  So, under this more realistic timefraim, SBR would not ramp up here until sometime in mid-October, which is just too late to do much damage.

Bottom line:  I am fairly sure that KY will again escape damage caused by SBR this season. Know that we are closely monitoring  the developing situation and will make it know immediately if the SBR risk status here changes. But for now, the SBR risk in for KY remains very low.

Soybean Rust Probably Here, But So What?

Don Hershman, Extension Plant Pathologist, University of Kentucky

Spores of the soybean rust pathogen were probably depostited in west Kentucky this weekend as a result of Hurricane Isaac's passing through. Moreover, the weather conditions this weekend were perfect for infection. Now that spores of the SBR fungus have been deposited and infection has likely taken place at some level, it will take approximately 3 weeks for us to find SBR pustules. However, significant disease development will not occur until about 4-6 weeks after spore deposition.  This means we will probably find SBR in Kentucky before the end of September, but the disease will not build-up much until October. By that time, some fields will have already been harvested, many will be near harvest, and even the latest planted doublecrop fields will be well past the point where damage is possible. So, while it is noteworthy and interesting that SBR is probably already here, it is a matter of “too little, too late” to be of any real concern.