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Agronomy Update

Green Snap Presence in Iowa

Published on Thursday, July 21, 2016

Most parts of Iowa experienced conditions that were drier and warmer than usual throughout the month of June. Recently though, we received some much needed rain. Unfortunately, in some instances, these rains were accompanied by high winds and thunderstorms which occurred just prior to corn tasseling in many fields. High winds just prior to tassel can cause green snap (brittle snap) in corn.

There are two key times when corn is the most susceptible to green snap. The first is between the V5 to V8 growth stage and the second is two weeks prior to tassel up until the R1 growth stage. The fields that were most affected by the high winds throughout my geography were about one week from tasseling. In this same area, and even in the same fields where significant damage was observed, the earlier tasseling hybrids did not sustain as much damage from green snap.  

 

What Causes Green Snap?  
Green snap is caused by a number of factors including the growth stage of the crop, the time of day at which the wind occurred, the susceptibility of the hybrid, and the growing conditions just prior to a wind event to name a few. The timeframe between V5 to V8 and up until R1 is the period at which the plant is growing very rapidly, which can leave the stalks vulnerable to breakage. The stalks are more susceptible to breaking in the early morning hours when the plant cells rigid and less able to bend with high wind.  

How Does Green Snap Affect Yield?  
Green snap often occurs at a node on the stalk near the developing ear. If the node below the ear breaks, then that plant will not develop an ear at all. Even if the plant breaks right above the ear, the yield will still be greatly reduced. This is because the leaf area is greatly diminished and competition from neighboring plants will reduce light penetration to the broken off plant. Since the breakage often occurs near tassel time, there is not enough time for neighboring plants to compensate for the missing plants. Ultimately, the yield reduction is typically equal to the percent of plants that green snapped.     

It is important to scout fields after thunderstorms to determine if green snap has occurred. It is not always visible from the edge of fields, especially if there are different hybrids and growth stages within a field resulting in different effects from wind. 

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Pat Holloway
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