Last week we applied a bacterial vermicompost tea as a foliar spray on pear and apple trees infected with the Fire Blight bacterium. In the past few weeks we have drenched the soil around our tomato plants with slightly fungal vermicompost tea and we drenched our thermophilic compost windrows with highly fungal teas.

Studies by several groups including the Soil Ecology laboratory at Ohio State University, have demonstrated that vermicompost teas have dramatic effects on root rot plant pathogens  and foliar pathogens of tomatoes and cucumbers (references available on request). These studies are limited to rapidly growing plants in a horticultural setting in green houses. There are also other studies performed in the field on other plants including trees  showing dramatic effects with the use of vermicompost teas as drenches or foliar sprays. These studies are based on reports made by scientists (they are not necessarily peer-reviewed). We will discuss in the future how we link the peer-reviewed studies and the reports.

Very briefly, tomato and cucumber seeds were sown in pots. Teas were applied as drenches at various concentrations (5-20%) to the pots that were infected with 4 cucumber and tomato root pathogens. At weekly intervals, the plants were harvested and specific measurements were made especially root measurements.

The effects were dramatic: vermicompost teas at all concentrations had a measurable linear  effect both for tomatoes and cucumbers. A similar experiment was performed on plants infected with foliar pathogens with dramatic and quantifiable results. The root pathogens studied were: Fusarium oxysporum, Phytophtora capsici, Rhizoctonia solani and Pythium ultimum. One of the foliar pathogens of tomatoes (a very commom one) was Verticilium wilt.

Vermicompost teas used as foliar sprays or root drenchers are part of an ecologically based strategy at increasing the growth and diversity of soil and foliar dwelling organisms. These approaches are not silver bullets but a powerful tool when used with compost and an integrated fertility and pest management programme.

We do not know  what are the mechanisms of specific suppression by vermicompost teas. Several hypotheses have been proposed: destruction of the pathogen by a beneficial microbe, inhibition of growth, antibiotic production by beneficial microbes, competition for nutrients, competition for infection sites. One of the beneficial microbes that is present in vermicomposts and teas is Pseudomonas fluorescens. This organism has been shown to significantly suppress pathogens in tomato and in fruit trees (where it might impact Fire Blight bacteria). We hope to see if this microbe can help suppress Fire Blight in the future.

More interesting factoids. New DNA sequencing technology and advances in bioinformatics have shown that the rhizosphere (narrow zone of soil that is influenced by root secretions) contains several trillions of microbes (per gram root) and at least 30,000 species. This is considered the second genome of a plant and its interactions are important for the health of plants and the soil surrounding them. In humans, the effects of intestinal microbial communities on health are becoming increasingly apparent. Similar functions can be ascribed to microbial communities in the human gut and the plant rhizosphere. More on this in a future blog...