Late season Midwest corn disease outbreak
By Mike Toohill, AgVenture WSC
Bloomington, IL
In my recent I-States and Missouri travels, late season corn disease is very widespread with most fields impacted by multiple diseases. Unfortunately, premature death is becoming more common by the day. Below are the 3 things that will impact the corn crop the most:
The Anthracnose “complex”: Anthracnose is by far the most common Midwest corn disease. I call this one the HUMIDITY disease and we all know that the Midwest has plenty of humid days every summer. The random leaf yellowing (below left) is the blight part of the “complex” that is often followed by top die back (below right). There is also an associated stalk rot. Genetics vary significantly in their ability to fight off this disease but even the most tolerant genetics treated with the best fungicide can die prematurely (as is case again 2024). In the absence of corn leaf aphids, silk clippers or noticeable Tar Spot or Southern Rust, delaying your fungicide application to brown silk or beyond is the best way to limit this disease. If you want to keep your fields green until black layer, a double pass reproductive stage fungicide program is the answer... but current economics limit this practice.
Tar Spot: Infection varies widely in my recent travels. It is likely that this cloud and rain “loving” disease was able to have an extra “cycle” in areas that had significant June rains (like parts of southwest Illinois). Pressure is very high in some fields in those areas, also resulting in premature death and significant yield loss (like in the below left picture that also has Anthracnose and Rusts on the leaves). Hybrids vary in their ability to fight off this disease but none are immune. Heavy Tar Spot pressure with early infection also might merit a double fungicide application. We are learning as much as we can on the genetic and fungicide components of Tar Spot “control” as the growing season winds down.
Southern Rust: This disease (below right picture that also has some Tar Spot, Anthracnose and Common Rust on the leaves) that sometimes arrives in the Midwest with southern winds/systems was able to infect numerous fields this summer. The remnants of Beryl was the likely source of most of the infection. The best approach seems to be a reproductive stage 3 MOA fungicide that limits spore eruption. Scouting should continue as the “residual” starts to fade. This disease is favored by humid, dewy weather (like we are encountering this week).
How will this week’s heat impact the disease situation? Unfortunately, the heat stress (especially if multiple nights with lows in the mid-70s or higher occur) will allow diseases to flourish as the plant’s defenses weaken. Premature death rates in diseased situations also increase with the temperature. Low N environments also magnify disease impact.
Yield loss when corn plants die prematurely:
40% at early dent.
12% at 50% milk/starch line.
When corn dies prematurely from disease… Stalk quality is often compromised and the plants are more vulnerable to stalk rots and wind. Monitor stalk quality and harvest accordingly.
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