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.
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
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.