Cabbage Integrated Pest Management : An Ecological Guide.

Major Agronomic Practices2) Specific suppression, on the other hand, is usually explained by one or a few organisms. They exerthyperparasitism on the pathogen or induce systemic resistance in the plant to specific pathogens,much like a vaccination. With specific suppression, the causal agent can be clearly transferred fromone soil to another. Pathogens such as Rhizoctonia solani and Sclerotium rolfsii are examples wherespecific suppression may work but general suppression does not work. This is because these organismshave large propagules (e.g. spores) that are less reliant on external energy and nutrients and thusless susceptible to microbial competition. Specific hyperparasites such as the fungi Trichoderma andGliocladium species will colonize the propagules and reduce disease potential (ref. www33).Other biocontrol agents (or antagonists : for more information see section 7.10 ) that colonize compostsinclude bacteria like Bacillus, Enterobacter, Flavobacterium balusstinum, and Pseudomonas;actinomycetes like Streptomyces.These antagonists may appear naturally in compost. In some cases, antagonistic fungi or bacteria areadded to the compost just after the hot phase, when the compost is cooling down. There are not manymicro-organisms present inside the compost at that moment. When antagonists are added at that time,they can quickly build up their populations and this will result in compost with good disease suppressingquality. See box below.Fortified compostsAn interesting option is the use of fortified compost. This is compost added with antagonistic organismssuch as Trichoderma species (especially T. hamatum and T. harzianum) whereby Trichoderma worksas a compost process enhancer. Such fortified composts provide both nutrients to the crop (throughthe composts) and they provide effective control of a range of plant pathogens (mainly through theantagonistic fungi). After the primary heating period of composting is complete, the Trichoderma isadded to the compost. The fungi increase to high levels in the compost and can effectively reducediseases caused by Rhizoctonia solani, and species of Pythium, Phytophthora and Fusarium. In theUSA, fortified composts must be officially registered.In order for compost to substitute for currently used fungicides, the disease suppressive charactermust be consistent and somewhat quantifiable to reduce risk for the farmers. There are specializedcompost companies that produce consistently suppressive composts, especially for the nurseryindustry.Compost quality plays a role in the degree of disease suppression and the length of suppressive activity.Some general observations:Composts that are allowed to mature are more suppressive than piles used straight after the hot phase.Compost piles that are in the open (so exposed to naturally occurring micro-organisms), and especiallythose located near trees, are more suppressive than compost piles sheltered by a roof.Professional nursery industries now use disease suppressing composts widely and routinely. Based onthe successes there, researchers are testing compost on a number of field crops for potential diseasesuppression. Results of several studies are very promising.For example, studies in California, U.S.A., showed that soils on organic farms (using lots of compost)were more suppressive to two tomato diseases than soils from conventionally managed farms, due todifferences in soil organic matter, population of micro-organism, and nitrate level.Other researchers report less disease incidence (even foliar disease such as early blight in tomato),dramatic reduction in rootknot nematode damage, and higher yields on composted plots compared toconventional treatment in several crops.Cabbage Ecological Guide - 200028