Cotton

Monitoring Procedures and Form for Weighted Nematode Ratings

The ratings and calculations will help to determine the weighted nematode rating (WNR), expressed as a percentage for your field.

Weighted root rating classes table
Weighted rating Percent of root system
with galls
0 0
1 1-25
3 26-50
5 51-75
7 76-100

How to sample:

  1. Divide the field into representative blocks
  2. Select 1 sample of 15 to 20 root systems in a random pattern from as broad of a representation of each block as possible. Remove as much of the root system as possible with a root lifter (for example, carrot or beet lifter) keeping side roots intact.
  3. Gently wash or shake the soil from the roots.
  4. To sort the root systems into weighted ratings (0, 1, 3, 5, 7) use the diagram above and silhouette the root system against the sky or a white board and evaluate for gall severity.
  5. Use the weighted root rating table below to record the number of roots in each weighted rating category and to calculate the WNR.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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