Tornadoes aren't the only twists popping up in the Midwest this time of year. Today, we're talking about all of the twisted leaves that are showing up in corn fields across the Midwest (or probably will be soon). What's going on? Why is this happening? Should we be concerned?
Let's talk "Twisted Whorl" Syndrome!
As you can see in these pictures, and maybe even in your own fields, plants exhibiting these symptoms become REALLY obvious as they grow. The picture on the right is a plant showing some likely Rapid Growth Syndrome symptoms already at V3. The picture on the right is a V5 plant showing the after-effects of one of the hail storms that have frequented Kansas in the last month.
First question: What's going on?
To understand what's happening, we need to step back and remember how that corn plant is growing. I like to think of a corn plant as a telescope. (The old-fashioned kind you'd see in Pirates of the Caribbean) A weird comparison, but stay with me - it's good, I promise.
I like the analogy because prior to V5, all of the major parts of the corn plant (leaves, stem, tillers, ears, tassel) are being developed underground in a very compressed space. After all of the necessary pieces are developed, the "telescope" starts to open up - the segments are elongated, and the corn grows taller.
In the case of a corn plant, those "segments" are the internodes of the stalk, and the connection points where the telescope locks are the nodes. Initially, the nodes are all stacked together in the crown region below ground, but then move quickly above ground when the internodes elongate. Corn usually has around 20 leaves, which means it has 20 nodes (4-5 of which will remain underground), so this equates to a telescope with around 15 segments.
The plain telescope is a great analogy for the stalk of a corn plant, but we also have to add the very important leaves to this scenario.
In addition to the elongating action of the telescope, imagine that we have to unscrew each section as we open the telescope - so now we have a circular motion included as the telescope extends. NOW imagine there is a leaf attached to each connection point where the telescope locks (nodes). All of these leaves are curled up together around our "telescope" (stalk), and they have to open at the same time as the telescope is extending, with one leaf opened as the next section starts to unscrew and elongate.
But this process doesn't always work perfectly or at the right speed - enter TWISTED WHORLS.
Second Question: Why is this happening?
Stepping away from the telescope to another example, if you're like me and have ever put up electric fence, you know that wire reels can be a great tool, but also a really big pain. (A similar example if you don't have experience with fence is a fishing reel) You have to be careful how fast you roll/unroll that wire/line and make sure you are coordinating the process well, because if you're going too fast or too slow, you'll end up with a twisted mangled mess on your hands.
Similarly, in corn plants experiencing twisted whorls, the internodes are elongating faster than the leaves are able to unroll. The whorl (curled center of the corn plant that contains developing leaves) gets really tight as developing leaves are pushed up before the older leaves can uncurl fully.
Symptoms we see from this process include plants that look twisted or bent and really long, skinny whorls that look like whips (hence the alternative name "buggy-whipping"). Shown in the picture to the right is an example of a very young (~V2) corn plant exhibiting typical buggy-whipping symptoms after a cold snap.
Several different things can cause twisted whorls,. "Rapid Growth Syndrome" is common. This specific problem is caused by a discrepancy in plant internode elongation and leaf unfurling - most likely the result of a sudden change in temperature. Corn growth is driven by Growing Degree Days, and higher temperatures mean the plants grow faster. (More on GDD in this blog post) It's believed that this change in growth rate creates a temporary development speed imbalance that results in the twisted whorls. Some herbicides, particularly those with shoot growth inhibitor (Group 15) or growth regulator (Group 4) modes of action, cause similar symptoms and are commonly blamed as the culprit for these symptoms. Early season damage to plants, particularly from hail or wind and even freezing temperatures can also cause some ugly, twisted-looking plants, which I expect to see a lot of in the next few weeks in our plots across Kansas.
Third (and most important) Question: Should we be concerned?
The answer can depend on what caused your twisty symptoms in the first place and how severely twisted your plants are. With Rapid Growth Syndrome, when talking to agronomists and crop specialists, the resounding answer is thankfully NO. These symptoms will generally show up early in the corn plant's lifetime - around V5 but as late as V12 sometimes, and although seeing a field of bent, buggy-whipped corn plants is concerning, the symptoms are generally temporary! The plants will resume a more normal appearance after they move past their "growing pains" and the leaves catch up to the growth of the stem.
In the case of twisted whorls caused by early hail/wind or freezing damage, plants should be able to escape the twisted whorls resulting from dead leaves as well. This is particularly true if the plants are smaller. What to do about the twists if your plants are more advanced? Some might think to cut off the damaged part of the plant, but a study done in corn that experienced a late (V9-V12) freeze in Wisconsin in 1992 (Carter, 1995) found that cutting back twisted whorls did NOT help yields. To tie in my research here, they also found that some fields with tillers on damaged plants were able to salvage yields that would have been completely lost.
When leaves finally do unfurl, the previously trapped leaves will likely be yellowish or even white, because they have not been able to photosynthesize inside the shade of the whorl. However, these leaves will green up as they are exposed to sunlight and able to function properly. In addition, because the leaves were not able to develop normally inside the cramped whorl, some may have a crinkled or rough appearance, similar to the plant shown on the left. By the time corn reaches late vegetative stages, these wrinkles (stretch marks, if you will) are the only indication that things were ever off kilter.
Happy scouting!
Stay tuned for more updates from the field and information on my corn tiller project progress!
Licht, M. (2018). Twisted whorls, buggy whipping, yellow leaves. Iowa State University.
Nielsen, R. L. (2019). Yellow tops and twisted whorls in corn. Purdue University.
Carter, P. R. (1995). Late Spring Frost and Postfrost Clipping Effect on Corn Growth and Yield.
Journal of Production Agriculture, 8(2), 203–209. https://doi.org/10.2134/jpa1995.0203