Moving Beyond Purpling Leaves to Necrosis

There are reports coming from the Northwest Region of Manitoba (Grandview, Dauphin, Ste. Rose) where flag leaves on some wheat plants are turning a purple color, then bronze, and then becomes necrotic. In severe cases, the flag leaf has dropped off entirely.  Tissue samples have been sent into various labs with the diagnosis being physiological.  The good news is all the remaining leaves under the flag are in perfect condition

In an earlier post on Crop Chatter – Seeing Purpling Leaves in Wheat? – we reviewed the basics of why we see purpling plants.  However, in previous years we have seen that in severe cases, the flag leaf has become necrotic and sometimes dropped off, much like what is being reported in the Northwest.  Unfortunately, since it is physiological in nature, there isn’t much to be done. 

Of course, the next question is what will be the impact to yield if the flag leaf has become necrotic and/or dropped off.  In previous years when this has occurred, we haven’t heard any news of a significant yield reduction, which is good news.  However, we don’t have any firm data to say either way.   Everyone knows the importance of the flag leaf in yield determination, so one would expect there would be some impact. 

If we use the following table illustrating yield loss due to impact of rust on the flag leaf, we can see that the greater impact to yield occurs at flowering and when majority of the flag leaf is impacted.  As the crop matures the importance of the flag leaf diminishes as yield has largely been determined (with the exception of some kernel weight added during the grain filling process). This table is only a guideline however as yield loss is only estimated and growing conditions the remainder of the growing season will shape final yield.  As previously mentioned, all the remaining leaves on the affected plants are in perfect condition which will help with grain filling for the rest of the season.

Special thanks to Kathy for reporting what is happening in the Northwest Region!

Submitted by:  Pam de Rocquigny, MAFRI Cereal Crops Specialist

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