Corn in Mississippi
How does Roundup "purpling" differ from P deficiency?
Roundup/Touchdown
herbicide drift injury may also produce "purple" injury symptoms
which mimic phosphorus deficiency. These purple symptoms seem to be stimulated
by environment conditions which promote phosphorus deficiency. These
symptoms began appearing during the last week and a half of April, which
is also when phosphorus deficiency normally appears.
There are two primary differences which may allow you to diagnose whether
you are observing herbicide drift injury or phosphorus deficiency. This
photo shows a typical banding pattern which often results from slight
Roundup/Touchdown drift on a young corn plant's leaves. Lower leaves
show contact injury, either chlorosis (white/yellow tissue) or necrosis
(dead tissue) depending on severity, on more of the leaf surface, while
contact injury on subsequently higher leaves is closer to the leaf tip.
This pattern results from higher leaves being enclosed within the whorl
when the drift occurred. This banding pattern is more evident when injury
is relatively slight, so little herbicide translocation occurs within
a leaf or in new leaves. Herbicide injury also purples the midrib and
immediate leaf area. Chlorosis (whitening) often begins appearing on
leaves in the whorl several days after purple symptoms. This chlorosis
injury results from glyphosate translocation through the plant.
Guidelines for assessing Roundup drift injury.
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Phosphorus deficiency is more evident on lower leaves. Purpling begins at the leaf tip and progresses along leaf margins (edges), contrasting with Roundup injury which normally purples the midrib. New leaves emerging from the whorl do not show as much purpling. |
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