Soil Sampling for Verticillium Wilt
If percent stem discoloration is high, or if you would like to determine how long to rotate out of cotton, consider sampling the Verticillium inoculum (microsclerotia) levels using soil sampling. To monitor inoculum levels from one season to the next, sample soil at the same time each year.
Take samples in the summer to help you decide whether to plant an alternate crop or a resistant variety the following season.
To sample Verticillium inoculum levels:
Laboratories that analyze soil samples for Verticillium report results in number of sclerotia per gram of soil. Where a single (susceptible) cotton variety is planted without rotation:
Since microsclerotia are produced gradually as infected plant debris decays, the number found in the soil increases after plowdown and peaks in midsummer the following year. Therefore, take soil samples at the same time each year in order to monitor changes in inoculum level to determine if it is safe to plant Verticillium susceptible cotton.