There has been a great deal of information running around about the efficiency or lack of with compost tea and fungus. Does it kill it? Or not?
Researchers in Canada have tested compost teas made from various types of compost for anti-fungal properties.
Doug notes: This is a study from 2010 and I’ve rebuilt it from the old website research notes to share with you.
How The Compost Teas Were Made
The teas were prepared by adding compost (made with chicken manure, bovine manure, sheep manure, shrimp, or seaweed) to well water (in a 1:5 ratio, by volume), covering, and storing in a dark place at room temperature for two weeks, with weekly stirring.
These are not considered aerated compost teas but without an analysis of which microorganisms were present, it is impossible to tell what’s doing the damage described below. “Something” is but …
The First Lab Tests
In laboratory trials, every one of the teas inhibited mycelial growth of the plant-pathogenic fungi Alternaria solani, Botrytis cinerea, and Phytophthora infestans.
The Second Lab Tests
The teas were then sterilized and the resulting protection was non-existent.
Researchers concluded that “something” likely the microorganisms they killed were responsible for inhibiting the pathogens.
No phytotoxic effects of the teas were seen on seedlings (phytotoxic – burning or leaf damage from the spray)
Prior to application, the teas were strained through several layers of cheesecloth.
The most pronounced inhibition of A. solani and B. cinerea was due to teas made with sheep manure, bovine manure, and shrimp; all of the teas completely inhibited mycelial growth of P. infestans.
Sterilization of the teas by either autoclaving or microfiltration resulted in no significant inhibition of mycelial growth of the plant pathogenic fungi, indicating that inhibition requires the presence of certain microorganisms.
In greenhouse trials, tomato seedlings were inoculated with B. cinerea (gray mold) or Oidium neolycopersici (tomato powdery mildew) either three days before or three days after the first of weekly foliar sprays (to runoff) of (presumably undiluted) compost teas.
No phytotoxic effects due to the tea sprays were observed.
Using the teas as an innoculant (preventative) on seedlings proved to be an excellent way to reduce powdery mildew problems compared to control seedlings.
The Most Effective Compost Tea
Compost made from sheep manure seemed to be the most effective overall on the trials while teas made from seaweed were the least effective. The correlation of numbers of bacteria to compost type is also high – the more bacteria (sheep) controlled better than did teas with lower bacterial counts (seaweed).
Subsequent trials reducing the amounts of bacteria in sheep compost tea to levels of the seaweed tea showed no loss in effectiveness so researchers concluded that it was the specific bacteria in the tea that was creating the effect, not the source material.
This is one trial. So one shouldn’t bet the farm on a single test of anything.
Reference: Souleymane B. Kone(Centre de Recherche en Horticulture, Universite Laval, Quebec City, Quebec, CANADA G1V 0A6), Antoine Dionne, Russell J. Tweddell, Hani Antoun, and Tyler J. Avis, ‚Suppressive Effect of Non-Aerated Compost Teas on Foliar Fungal Pathogens of Tomato,‚ Biological Control 52(2), February 2010, 167-173. (Elsevier Science, 6277 Sea Harbor Dr., Orlando, FL 32887-4900.)