Has anyone "cleansed" soil of Verticillum fungi? (I am unsure how to search
archives for this information).
You will probably find a lot on this topic at Soil Foodweb, Inc. http://www.soilfoodweb.com/
They deal mostly with compost tea but will probably cover biocontrol of
verticillum
From: http://www.elmcare.com/disease/verticillium_wilt.htm
"Verticillium wilt is caused by a fungus that lives in the soil. The fungus penetrates the root system of susceptible
plants, eventually blocking the plant’s water-conducting system.
The fungus affects more than 300 types of plants throughout the world - from raspberries and tomatoes, to maples and
elms. Although the disease occurs in naturally forested areas, it is found mostly in landscape plantings."
Broccoli Residues Can Control Verticillium Wilt of Cauliflower http://aggie-horticulture.tamu.edu/extension/newsletters/vpmnews/feb01/art1feb.html
"Verticillium wilt, a damaging disease of cauliflower, was successfully managed in a multiple-year field study by
incorporating broccoli residues into infested soil. In a study conducted from 1993 to 1995 in the Salinas Valley of
California, cauliflower disease incidence and severity were consistently and significantly reduced in the broccoli
residue plots when compared with no broccoli. The commercial standard plots fumigated with methyl bromide plus
chloropicrin had the lowest disease incidence and severity. In both years of our tarping study, Verticillium wilt
severity was lowest in the metham sodium treatment. The cauliflower-Verticillium host-pathogen system, therefore, can
act as a model for controlling soil-borne diseases without the use of synthetic chemicals.
Disease Control Alternatives
Controlling Verticillium wilt of cauliflower, like Verticillium diseases on most other crops, is difficult. The fungus
produces survival structures (microsclerotia) that can persist in the soil for many years. The ability of this fungus to
survive for long periods, in combination with a very broad host range, makes crop rotation impractical. Resistant
cauliflower cultivars are not available, and soil fumigants such as methyl bromide and chloropicrin provide some control
but are too expensive to use for cauliflower production, and may not even be available in the future for agricultural
use. Therefore, there is an urgent need to discover alternative soil-borne pathogen controls that are effective,
affordable, and not harmful to the environment.
During our initial work on cauliflower Verticillium wilt, we noticed that although broccoli is closely related to
cauliflower, broccoli crops were never infected with V. dahliae, even when planted in the same highly infested fields.
When greenhouse-grown broccoli was inoculated with V. Dahliae isolated from cauliflower, the broccoli did not develop
Verticillium wilt, and microsclerotia were not observed on broccoli roots. In addition, researchers have been interested
in the possible fungicidal properties of chemical substances present in many cruciferous crops. Substances such as
glucosinolates and other toxic volatile compounds, released during crop residue breakdown, could possibly be exploited
to control soil-borne pathogens, or otherwise suppress soil-borne diseases.
The quality and amount of glucosinolates differ among various crucifer plants. Because of broccoli’s apparent status as
a non-host of V. dahliae and the known fungicidal properties of the particular glucosinolates in this plant, we
conducted a series of studies to investigate the usefulness of broccoli residues in suppressing Verticillium wilt of
cauliflower.
Over the two-year period, we observed a significant decline in the number of microsclerotia in soil treated with
broccoli residue. In contrast, soil not treated with the broccoli residue experienced a five-fold increase in the number
of microsclerotia. Irrigation methods (furrow vs. drip) had no consistent, significant effect on the microsclerotial
populations between the two treatments. Likewise, differing amounts of irrigation water (deficit, moderate, and
excessive volumes) generally did not significantly influence pathogen numbers in broccoli or non-broccoli plots.
When we assessed the percent of Verticillium wilt infection and severity during the two-year study, we generally did not
see significant differences between the furrow and subsurface drip irrigation plots. However, Verticillium wilt
incidence was usually higher in the excessive irrigation regime when compared to moderate- and deficit-watering
treatments. For both years of the study, disease incidence and severity were consistently and significantly reduced in
the broccoli residue plots when compared with no broccoli. Not surprisingly, the commercial standard plots fumigated
with methyl bromide plus chloropicrin (the control plots with no V. dahliae microsclerotia) had the lowest disease
incidence and severity under all irrigation regimes."