ost everyone agrees that Indiana weather conditions during the past 14 days or so can only be described as 'crappy' for the growth and development of the state's corn crop. Daily high temperatures have been primarily in the 60's and low 70's. Daily low temperatures have been in the 50's and even 40's. About the only good news overheard down at the Chat 'n Chew Cafe is that surface soil moisture levels have been replenished in most areas of the state, although in some areas rainfall has been excessive.
We know that warm, sunny weather will eventually return to the Hoosier state. We also know that corn, being a temperature-dependent crop, will respond to that onset of warm, sunny weather by shifting to a faster rate of development. Therein lies the cause for issuing this fearmonger alert. When periods of slow corn growth (typically, cool growing conditions) are followed by a sharp transition to periods of rapid corn growth (typically, warm weather plus ample moisture), scattered plants throughout fields may begin exhibiting symptoms of unusual twisted growth. The whorls of the affected plants are tightly twisted, often bent over severely, and not unfurling on a timely basis.
Ones natural instincts would blame the twisted growth on herbicide injury, especially those characterized by the cell growth inhibitor mode of action. Where such herbicides are applied pre-plant or pre-emergence, shoot uptake of the herbicide by the emerging seedling can result in twisted growth. While, indeed, this season's conditions are conducive for this type of herbicide injury, twisted growth of corn may appear in fields where none of this herbicide chemistry has been applied.
Certain genetic backgrounds react to the change in growing conditions described above by basically going 'bonkers'. The upper whorls of the plants don't unfurl properly. Younger leaves deeper in the whorl continue to grow rapidly, but are unable to emerge from the unfurled upper leaves. The now tightly twisted whorl then bends and kinks from the pressure exerted from the younger leaves' continued growth. The growth stage where I've observed this phenomenon in past years was around four to six visible leaf collars (about knee-high). That growth stage accurately describes many of the state's corn fields right now.
At the peak of the problem, the appearance of these plants is indeed unsettling and one would think that the whorls would never unroll properly. Given another week, though, the majority of the affected plants does unroll and continue to grow normally.
If you didn't notice the twisted growth to begin with, you may notice the appearance of 'yellow tops' across the field after the whorls unroll. The younger leaves that had been trapped inside the twisted upper leaves emerge fairly yellow due to the fact that they had been shaded for quite some time. In addition to being fairly yellow, the leaves will exhibit a crinkly surface caused by their restricted expansion inside the twisted whorl. Another day or two will green these up and the problem will no longer be visible.
The Good News: Yield effects from periods of twisted growth due to weather-related causes are minimal, if any.