Hello! Hello! I've been out of the province the past two weeks taking some time off to explore a different corner of the world (the Lofoten Islands in northern Norway to be specific). After some time well spent hiking and camping I returned to Ontario Sunday afternoon. Wow! What a change two weeks brings- a few combines have already started rolling getting beans off and I suspect that we will see a lot more harvest activity over the next 10 days. The other things that was noticeable on my drive back from the airport was the amount of top dieback in corn fields. With that- we have this weeks topic!
WHAT IS TOP DIEBACK?
As a corn crop reached maturity leaves begin to senesce and die off as they lose their photosynthetic capacity. The rate at which a crop senesces through the grain fill period is driven by environmental and genetic factors. We commonly think of this as a process that starts with the oldest leaves at the bottom of the plant and gradually moves upward. However, in some situations we can see senescence starting at the top of the plant with the youngest leaves. This is called “top dieback”.
Photo: Purdue University (2011)
WHAT CAUSES TOP DIEBACK?
There are two primary culprits that cause top dieback in corn- drought stress and anthracnose stalk rot.
Drought Stress- Excessive heat and moisture stress can result in early senescence of the leaves. Under severe conditions plants are unable to maintain leaf health and stressed corn leaves may take on a wilted look prior to complete necrosis. Essentially, the plant is remobilizing carbohydrates and nutrients stored in the stalks and leaves to provide starch for grain fill. Top dieback due to drought conditions will likely be seen across the majority of a field with varying severity depending on soil type, sandy knolls being the most severely impacted. Considering the 2022 summer weather patterns the majority of the top dieback symptomology that we are seeing in the area is likely due to extended periods of drought stress during the growing season.
Photo: Purdue University (2011)
Anthracnose- Anthracnose is a leaf and stalk disease caused by fungus Colletotichum gramincola. Anthracnose will cause black streaks and splotches to form on the stalk. The stalk should be closely examined, look for a rotted or discolored pith in the upper internodes. As the stalk rot progresses, water translocation to the top leaves is reduced, resulting in early senescence of the top leaves and top dieback symptoms. Top dieback due to anthracnose may appear as early as 1 to 3 weeks after tasseling. Anthracnose dieback usually occurs in a more random pattern across a field rather than affecting all plants within an area of a field.
Photos: Bayer CropScience Internal (2021)
IS THERE ANYTHING TO DO ABOUT IT?
At this point in the growing season there are no management options available, you may start to see positive differences in fields that were treated with a fungicide earlier. Now would be a good time to scout your fields and make notes on which ones are showing the most top dieback. Stalk strength is sacrificed as the crop pulls from the stalk and leaves to fill the grain- fields showing more stress will be more susceptible to lodging closer to harvest and may need to be prioritized if possible.
WILL IT HURT MY YIELD?
Regardless of the cause, the overall effect on grain yield will be determined by how early in the grain-filling process the dieback occurs. Yield loss from top dieback may result due to reduced photosynthesis in the top leaves. Yield losses are greater the earlier symptoms appear.
Thanks for tuning in again! As always- I enjoyed writing this and I'm glad to be back as we get geared up for harvest.
Lauren
Market Development Agronomist Bayer Crop Science
lauren.benoit@bayer.com
(226)-385-9068
P.S.I'll be at Canada's Outdoor Farm Show this week with the Bayer team! Stop by to say “Hello” and get your free ice cream. I look forward to seeing you! 🍦
