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of the mean plant quality rating (S) divided by the cube
of the maximum quality rating is suggested to mimic
observations from the field that the most infected
plants in a field yield the smallest amount of dry
matter, but not on a 1:1 relationship between percent
infection and reduced yield. Often, moderately infected
stems and pods yield as much plant dry matter as clean,
or nearly clean plants. The cubic-shaped curve would
remove proportionally more dry-matter accumulation at
higher percent disease than at lower percent disease.
The maximum percent dry-matter reduction (M)
attributable to pod and stem blight and anthracnose
would have to be determined experimentally. The purpose
of {M} is to place a limit on the amount of damage
attributable to these type of plant pathogens. It is
very possible that {M} may change from season to season,
dependent upon the environmental conditions. A
reasonable value for {M} would be <15%.
Similarly, seed quality (as opposed to quantity,
above) could be evaluated with equation 3.
Q= (S**2 / Smax**2) P (Eq. 3)
Q= reduction in seed quality
S= average of stem and pod rating (based
on percent infection) at harvest
P= maximum quality reduction by pod
and stem blight and anthracnose
Smax= maximum pod and stem rating possible