PPDL Picture of the Week
August 3, 2020
Looking for signs in the field
Marcelo Zimmer, Weed Science
Program Specialist
Department of Botany and Plant
Pathology, Purdue University
Signs are cues that convey some
meaning of information. We use them every
day when wether it’s a stop sign telling us to stop at an intersection or a
burnt smell indicating that you left your popcorn in the microwave a little too
long. We can also use signs or patterns
in the field to help diagnose stresses to the crop. In instances of herbicide contamination in spray
equipment there are a couple signs or symptoms that can quickly help conclude
that the spray equipment contamination is too blame.
Sprayers make paths of straight
lines up and down the field and therefore when a problem occurs the signs of
the problem will also show up in these straight-line paths. Naturally occurring stresses such as nutrient
deficiencies, insect damage, and plant pathogens do not occur in these neat
straight lines. Being able to identify a
few of these signs or patterns in the field can go a long way to helping
identify the culprit. The two pictures
show examples of these unnatural or mechanical patterns in the field help to
diagnose sprayer contamination events.
In the first picture you can see
that the soybeans to the left of the black line appear to be stunted and
deformed as compared to soybeans to the right.
In this particular case the sprayer had made a single pass down the left
side of this field to reach another field behind and the operator decided he
might as well spray that strip while he was driving down it. A benign decision by the operator turned into
a key pattern that helped identify what had injured the soybean plants in the target
field that he was traveling to. The injured soybeans were in perfect straight
path that the sprayer had traveled, again a naturally occurring stress would
not occur in a straight line. In the
picture you can also see where the operator turned on the sprayer with
differences in soybean height above and below the horizontal black line. Using these patterns in the field as well as
symptoms on individual plants it became apparent that a herbicide had
contaminated the spray tank and was causing injury to the soybeans.
The second picture shows another
case where soybeans were injured by a herbicide contaminate in the
sprayer. Again signs in the field
indicated a mechanical pattern of injured soybeans. In this particular case the lines are not
perfectly straight, but the injury could be seen most prominently where the
sprayer entered the field with the pattern being the same width of the sprayer
boom. This time the injury did not
follow a straight-line path where the sprayer traveled, but rather tapered down
to a point in the center of the spray boom and lessened in severity as the
machine made the pass. This is a case of
the contamination actually being contained in the spray boom. The contaminate was at its highest
concentration at the beginning of the field and therefore the entire spray
swath of soybeans were injured. As the sprayer
traveled down the field or away from the camera the contaminate was flushed out
of the boom and eventually cleared leaving a tapering pattern of injury as
observed in the picture.
The symptoms on individual plants
go a long way towards indicating if a herbicide contaminate injured the plant,
but recognizing these mechanical patterns in the field greatly assist in
confirming a tank or boom contamination event.
If you notice these patterns in the field it is extremely helpful to
include pictures of those patterns or even field maps with sketches of the
patterns with plant samples when submitting them for diagnosis.