permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

ingrid wrote:

> 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."

There may be more information on this in:
http://www.ibiblio.org/ecolandtech/orgfarm/

Here's one on fusarium (damping off) control with compost:
http://www.ibiblio.org/ecolandtech/orgfarm/composting/damping-off.fusarium.compost

And one on using a type of mustard as a fumigant:
http://www.ibiblio.org/ecolandtech/orgfarm/composting/alternative-fumigants.fumitoxic.green-manure

And possibly more here:
http://www.ibiblio.org/ecolandtech/orgfarm/biocontrol/
http://www.ibiblio.org/ecolandtech/orgfarm/composting/
http://www.ibiblio.org/ecolandtech/orgfarm/composting/fungi-mycorrhizae.faq

LL