Can soil testing detect Verticillium wilt?

Plans for Verticillium wilt treatment very often start with a soil test. However, commercial laboratories are unable to detect low levels of microsclerotia. I have experienced scenarios when soil tested 'clean' of Verticillium wilt, but there were nearby infected trees. For your best chances of early detection, utilize laboratory reports in conjunction with your weekly symptom checks on susceptible plants such as tomatoes and maples, along with your maps like the one provided.

Collect soil samples in late spring when microsclerotia become active. Do not sample during drought conditions since the lower moisture will make the microsclerotia more difficult to detect. One client's negative soil test in August missed an infamous Helminthosporium outbreak detected the following May. Remember, labs need the sample to be viable; refrigerate the soil if sending the sample will take over 48 hours.

Even without any signs of disease, high-risk areas, such as former tomato beds, should still be having preventive testing done. I would recommend rotating testing areas on an annual basis - I take orchards and put them into grids and sample 20% each year. Pairing these tests with resistant cover crops (in between cash crops) such as sudangrass will allow for a natural means of suppression of fungal growth.

False negatives can impact financial, emotional, and environmental costs. A vineyard that had replanted after testing "clean" lost 40% of the new vines to the presence of residual microsclerotia of the pathogen. As such, I recommend bioassays to evaluate suspect soil. Susceptible greens can be planted and observed over 6 weeks for the development of symptoms related to the disease before making large-scale plantings.

Read the full article: Verticillium Wilt Treatment: Complete Management Guide