SDS is in my good soybean field and fields across the midwest early this year. That makes sense since the year has been early since the heat hit in June and we saw unusally outrageous growth in corn and soybeans.
SDS is Sudden Death Sydrome which sounds really bad and it can be. It is the disease fusarium solari, a naturally occuring soil fungi that attacks high yielding soybean fields.
"Symptoms of SDS first appear as yellow, interveinal blotches. These blotches rapidly increase in size and interveinal tissues become necrotic. The leaf veins are the last to become necrotic. Petioles and stems of affected plants remain green until considerable leaf tissue has died. Most commonly, these symptoms occur in Indiana soybeans in late July and early August. As symptoms progress, leaf blades drop from the petioles, leaving erect, barren, somewhat green petioles attached to stems. Interveinal necrosis progresses faster on the upper than the lower leaves, the upper leaves are usually the first to defoliate. Leaf symptoms alone are not diagnostic for SDS, as similar leaf death may be experienced with brown stem rot. The root and lower stem tissues must be closely examined for diagnosis of SDS. "
In short, my take is that SDS doesn't attack low yielding soybeans. If you get your system to a higher level of yield you are going to see it. I saw it and Frogeye Leaf Spot in my high yielding soybeans in 2006. They still made a record yield for me, this field on this farm. To go the next level, I am going to have to control it and the linked article gives me some ideas.
My approach to soybeans is notill early following corn, a longer crop rotation with wheat or other cereal crop, high fertility, varietal resistance and seed quality, seed treatment and inoculated with the most competing strain of rhizobia and trichaderma I can apply to my seed. That has worked well for me. My double crop soybeans after wheat or other cereals adds to the disease stress but keeps me at an economically profitable level.
SDS can reduce that profit by robbing yield. How much can the farmer give up? The farmer is a master at production but costs to grow that crop can master him. I try to stay out of that situation but everyone is pushing every acre as much as they can with safe, environmentally friendly yet hopefully profitable growing conditions.
I have done all I can do and I hope for the best. The weather has the upper hand again today. An inch of rain would bring a few bushels more times thousands of acres times $10 soybeans or nearly $4 corn. That's a lot of money and we will spend every nickle of it, most of it right here where we live.
So, like SDS and everything else, aren't we all weather dependent?