I bet that's it. Thanks for the ID!
This is a useful bit of information, from The American Phytopathological Society (
https://www.apsnet.org/edcente...)
"
Soil amendments, fertilization, biological agents and plant-produced chemicals. Soil can be treated with organic amendments, fertilizers, or biological agents to help control S rolfsii. The addition of organic amendments such as compost, oat or corn straw, or cotton gin trash to soil sometimes reduces southern blight incidence and development. This effect may be due to the increase of toxic ammonia and/or the increase of certain soil microorganisms in the soil. Furfuraldeyde, an organic (sugar derivative) amendment, has been shown to change the soil microflora, and this change has been related to a decrease of S. rolfsii in the soil in lab and greenhouse studies. Also, neem oil and pine bark extracts or pine bark powder have resulted in reduced growth of S. rolfsii. To date, these amendments have not been widely used for disease control, but future refinements may allow their use in the field. Fertilizer studies have shown that treatments with ammonium, calcium nitrate or calcium sulfate may help control southern blight. Increased nitrogen may inhibit sclerotia germination, alter host susceptibility, or alter the soil microorganisms. Biological control of S. rolfsii has been achieved to some degree with bacteria (Bacillus subtilis), actinomycetes, a mycorrhizal fungus, or certain Trichoderma species. There have been several studies to attempt to explain the mechanism for Trichoderma inhibition of S. rolfsii. Many studies have shown disease control by biological agents in laboratory and greenhouse tests, but disease control is less effective in the field. When control is seen in field studies, the required quantity of the biological product may be very high and not practical in most agronomic situations. In addition to the above, certain compounds in some aster roots and mustards are being studied for their inhibitory activity against this pathogen. ..."
