Thursday, May 14, 2015

What Could Cause Early Season Corn to Turn Purple

The purpling of corn can be attributed to sugar accumulation. This sugar accumulation can arise from a phosphorus deficiency, since phosphorus is needed for sugar transport. 


(NUTRIENT) Purpling of corn leaves can be typical of a phosphorus deficiency, but often the problem is observed with younger plants when it’s very wet or cool. It is rare for an entire field to show purpling symptoms due to a phosphorus deficiency.  This would mean the field is either very deficient in phosphorus, or something is terribly wrong with the root system, which is not allowing plants to take up phosphorus.  If the problem is related to the roots, other nutrients would show deficiencies too, making for very sorry-looking plants.  I have seen phosphorus deficiency issues show up in areas of the field that have an abnormally high pH. Take soil samples or examine soil sampling reports.

(ROOTS) Most of the time, in young corn plants, purpling usually results from inability of the root system to grow out into the soil around the base of the plant. Sugars accumulate when roots can’t grow, and the anthocyanin pigment then forms. The inability of roots to grow may be because:
-dry surface soil or where soil has dried out before nodal roots could penetrate. 
-sidewall compaction may form at planting in heavier soils and dry to form a barrier, also hindering root growth.  
- In some cases, the seminal roots will have grown more than normal, but at some point they just can't support plant anymore.
- Anhydrous burn of corn roots. 
 In all of these cases, the purpling would only be visible in problem areas of the field.  Rain may help for symptoms to disappear and good growing conditions will encourage root growth.  If rain does not help, explore different possibilities for the purple symptoms of corn.

(GENETIC) If the entire field is showing signs of purpling, it sometimes can be linked to hybrid or genetics.  Dig up plants and examine roots to rule out other issues or keep an eye on the field over the course of several weeks. 

(INSECT) Some insect feeding (e.g. grape colaspis and/or white grubs) that prune root hairs on seedling corn plants can lead to purple discoloration on plants. The mechanism -- poorer absorption of nutrients (especially phosphorus) by the root systems. The pattern of purpling plants due to insects would be in a "clumped" distribution within the field.

(HERBICIDE) Some herbicides can cause corn to turn purple. The entire field or a specific pattern within the field may show symptoms. However, it is very, unlikely for an entire field to show purple symptoms for very, long. For example, glyphosate may cause corn leaves to become purple, but eventually the corn plants will die if they they don't consist of the glyphosate resistant gene.


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