“Can worm tea be sprayed as a fungicide and are there any trials?” ~ Maurice Franklin
There is definitely some evidence to indicate that worm casting tea (aka ‘worm juice’), and compost tea in general, can help to reduce the incidence of plant pathogens on various crops and ornamentals.
In fact, as I was very pleased to learn recently, even world-renowned vermicomposting researchers at Ohio State University have conducted trials with castings teas and achieved positive results.
Studies led by Drs Clive Edwards and Norman Arancon at OSU in recent years have repeatedly demonstrated the incredible plant-growth-boosting and disease fighting properties of solid vermicomposts, but the testing of compost teas hasn’t appeared to be a high-priority until quite recently.
Interestingly enough, in an interview with Peter Bogdanov of ‘Casting Call’ (Volume 4,#2, 1999), Dr. Edwards expressed some cynicism regarding the value of compost teas, primarily based on the lack of positive scientific evidence at the time.
The recent research (mentioned above) has been documented in an article in BioCycle (“The Effects of Vermicompost Teas on Plant Growth and Disease”; May 2006, p.28). As the name implies, the study examined both the growth-boosting and disease suppression abilities of worm tea. Compost tea was produced by standing 1 litre of vermicompost in 4 litres of aerated water for 24 hours.
Various dilutions of tea were were then prepared (0-10%) and tested. According to the article, all dilutions (even as low as 0.5%) significantly increased both the germination and growth of tomato plants in comparison with controls.
Given the fact that plants were provided with all the nutrients they needed via inorganic fertilization (as is typically the case with OSU worm compost studies), it can be safely assumed that all additional plant growth can be linked to mechanisms other than nutrient uptake.
The authors speculate that plant growth hormones (which have been found associated with humic acids) are responsible.
For the plant pathogen trial, vermicompost tea dilutions (0, 5, 10, 20, 40% tea) were prepared and applied to tomato plants already infected with Verticillium wilt. All dilutions (other than control) resulted in significant suppression of the disease.
One other interesting tidbit from the article – the researchers point out that compost teas produced with aeration are “much more stable and effective” than non-aerated teas. This supports what composting tea expert, Dr. Elaine Ingham (Soil Foodweb Inc.), has been saying for years. Speaking of Dr. Ingham, I would highly recommend you check out her website…
…to learn more about compost teas and their potential for plant pathogen suppression (check out the “SFI Approach” page for some great info).