Stem Sampling for Verticillium Wilt

Brown streaks appear in the xylem of plants with Verticillium wilt.

If you have evidence of a Verticillium problem in your field or if you want to plant a new variety next season with unknown Verticillium tolerance, conduct a stem sampling (percent vascular discoloration) test. Stem sampling can take place any time from crop maturity through harvest.

How to do a stem sample (percent vascular discoloration) test:

  1. Cut and examine 25 plant stems from various parts of a field that has a history of Verticillium. Look for discoloration.
  2. If 20% or more of the stems are discolored, take action to address your situation. For instance, rotate the field out of cotton, solarize the soil, or plant Verticillium-tolerant varieties.
  3. When 80% or more of the cotton stems are discolored, expect major losses in lint production in subsequent cotton crops planted in that particular field.
Percentage of plants with
vascular discoloration
Verticillium wilt level
10 Low
50 High

If the percentage of discolored stems is high, or if you would like to determine the length of time for rotation out of cotton, consider sampling the Verticillium inoculum (microsclerotia) levels using soil sampling.

Important links

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