Corn
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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