The Horsfall–Barratt scale[1][2][3][4] is a system used in plant pathology to assess plant diseases where each plant is assigned a numerical value according to the percentage of leaf area showing disease symptoms. The Horsfall–Barratt scale was designed by James G. Horsfall and R.W. Barratt to compensate for human error (and logarithmic laws of perception) in estimating the amount of disease present. The scale is as follows:

IndexPercent Affected
10
20 to 3
33 to 6
46 to 12
512 to 25
625 to 50
750 to 75
875 to 87
987 to 94
1094 to 97
1197 to 100
12100

The scale is often used in modified form with index values from 0–11 or with different numbers of index points.

References

  1. Horsfall, J. G.; Barratt, R. W. (1945), "An Improved Grading System for Measuring Plant Disease. (Abstract.)", Phytopathology, American Phytopathological Society, 35: 655
  2. "This Week's Citation Classic" (PDF). Current Contents. Institute for Scientific Information (15): 14. 14 April 1986.
  3. Horsfall, J G (1945). "Fungicides and their action". Chronica Botanica. Waltham, Massachusetts: 1–239. ISBN 9788172680022. (Fungicides and Their Action at Google Books)
  4. Horsfall, J G; Cowling, E B (1978). "Pathometry: the measurement of plant disease". In Horsfall, J G; Cowling, E B (eds.). Plant disease: an advanced treatise. Volume II: How disease develops in populations. New York City: Academic Press. pp. 119–36.

Further reading


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