10/11/2025
The hot topic of the week is Southern Rust and “Cell Necrosis”.
Southern Rust is a fungal disease that infects corn. It appears as small circular orange to Light brown pustules, and forms primarily on the upper side of the leaf. In all my years studying plant diseases, this one has taken a back burner because it is rare in our geography. The organism requires living tissue to survive, and our winters in Western Wisconsin are generally too harsh for it to survive. The only way for the organism to be a concern for our corn crop is for the spores to overwinter in a warmer climate, and get blown up here on southern winds. Since the spores would need to travel in excess of 1000 miles, we haven’t worried about Southern Rust,,,,,until this year.
So, why is this a concern and why should I care?
Once Southern Rust infects the corn plant, it enters into its vascular system and causes “Cell Necrosis”. Necrosis is a form of cell injury which results in the premature death of cells in living tissue. In August while monitoring customers fields for silage harvest, I discovered fields infected with Southern Rust were drying down quickly, however the kernel “milk line” was not moving in correlation with the plant maturing.
The milk line is an indicator of starch content. As the plant matures, it deposits starch into the kernel, and it’s distinguished by a visible line on the kernel that slowly moves towards the tip as it fills and increases the energy content of the grain.
So why wasn’t the milk line moving ? I discovered that when Southern Rust infects the plant, it causes cell necrosis. Cell Necrosis reduces the corn’s ability to produce sugars as it goes through photosynthesis. If it cannot produce sugars, it isn’t depositing starch into the kernel and the result is a lower quality grain
How do we prevent it? Luckily many acres in the area were treated with a foliar fungicide which helps protect the plant and keeps it healthy. The early results I’ve seen so far have been significant in yield as well as quality and provided a positive economic return on investment.
Today while studying data off the log of our grain dryer, I discovered something interesting.
Lately we’ve been harvesting relatively dry grain, however the rate at which the grain dryer has been rolling through the grain has been significantly different day after day with the same outside humidity and temperature.
After looking at which fields the grain was pulled from, the harvest moisture and the log off the dryer showing the roll speed of the dryer, it hit me.
The fields that we applied a foliar fungicide were healthier, did not suffer from Southern Rust, also did not undergo cell necrosis which meant they were able to pack more starch into the kernel and have heavier test weight. The non treated fields have slightly less starch in the kernel which results in a lower test weight.
why is this important??? When corn is dried , 90% of the moisture is forced out through the tip of the kernel. The more starch in the kernel, the heavier the test weight. The additional starch is quite dense and it takes more heat and time to drive the moisture out of the grain which results in additional propane and electricity.
I’ve discovered that if that corn is as little as one pound heavier in test weight, the dryer rolls speed is reduced by 11-15%. However the additional yield is still an economic advantage
Now to throw another wrinkle to the equation.
From everything I’ve read, Southern Rust is specific to corn, and does not affect trees. HOWEVER, have you noticed that the maple trees started to turn color a month ago, then stopped? If southern rust limits sugar production, sugar is crucial to producing the beautiful brilliant fall colors in maple trees,,….is it possible that given our abnormally wet / humid summer that a similar disease has infected our maple trees?
Something to think about.
I realize I became a bit long winded, I’m hoping you were able to follow where my brain was going. You can agree or disagree with what I’m seeing, and I’m definitely open to any opinions on what I’m seeing.
Thank you
Kurt and Autumn.
