PPDL Picture of the Week
October 19, 2020
Wonderful World of Crop Forensics
Bill Johnson, Professor of Weed Science, Botany and Plant Pathology, Purdue University
is the driving force for hybrid and cultivar performance and selection. This is the behind the scene thoughts when
one considers using a particular cultivar or hybrid. An example of this is the selection of a
disease resistant cultivar. A resistant
cultivar is selected with the idea that yield will be optimized if that
specific disease is expected to be an issue.
So, it is no surprise that when something goes wrong with yield at the
time of harvest the questions start flying.
of yield loss at harvest can be a tricky thing to pin down in most
situations. Many things can result in
crop performance issues and yield loss.
Any stress that corn or soybean may experience over the growing season
could potentially result in reduced yield.
These stresses can be environmental, induced by pesticide chemical
injury, disease, insects, nematodes, or competition with weeds. In most cases it is often combinations of
these things that result in stress to our row crops. We are dealing with living organisms that
respond in many ways to many variables in a growing season.
yield problems that result from herbicide injury can be difficult to identify
at harvest. In addition herbicide injury
symptom diagnosis is particularly difficult at harvest. The world of crop forensics leaves a little
bit to be desired. In many cases even
high priced analytical procedures are not effective. By the time of harvest many of the herbicides
are no longer detectable in tissues.
Very few symptoms may be present at the time of harvest. Comparisons of yield with neighbors or even
between two fields as can be a precarious situation. All variables, soil type, timing,
hybrid/cultivar, seed lot, etc would have to be held constant. Only the herbicide treatment could be
different to identify it as the problem.
In a field research setting, researchers go through a lot of effort
trying to hold variables the same between two plots just so that they can say,
“this herbicide performed different than that one.” Try as we might variability can still creep
into a study.
herbicide injury is predominantly done by observing foliar symptoms such as
chlorosis, speckling, and other visual observations can be made. Some symptoms seen at harvest, like those
seen from growth regulator injury (fused brace roots, lodging, and callus
growth) or ALS injury (bottle shaped ears) are accompanied with foliar symptoms
at the time or shortly after application.
In some cases the injury or yield loss seen at harvest can also be
caused by other factors or stresses as well as possible herbicide injury making
time to diagnose herbicide injury is during the growing season when visual
symptoms are present and tissue samples can still be analyzed. Document symptoms and collecting images of
unusual growth or appearance of plants will help coming to conclusions. Keeping accurate records is always essential
in identifying problems that may have occurred during the growing season.