NCSU Vermiculture Conference topic: Effects on Plant Growth and Pest and Disease Suppression Using Vermicompost Aqueous Extracts (Teas)
This work with vermicompost extracts was done at Ohio State University. Here are the key points I was able to take away from his talk:
To start: Differentiation was made between leachate (runoff from incompletely composted inputs) and teas. Caution was given about using leachate from manure based composts or leachate if there are slugs in the system since they can carry disease.
The way the tea was made for his studies — steep/dissolve vermicompost for 24 hours. One processes tested is to aerate the tea (bubble air through it).
Vermicompost tea (done in mesophilic conditions) is more valuable than a regular compost tea (made in thermophilic conditions) since beneficial microorganisms are killed by heat.
Characteristics of vermicompost water extracts:
Aerated teas have higher pH (up to 7.8 at 24 hours of brewing) but this will not affect the soil pH much. Aerating also increases electrical conductivity, nitrates, microbial activity and biomass. Note: if you add sugars to this mix, you’ll have a spike in microbial activity, but they’ll use up all the oxygen and then you’ll have a crash in population and possibly a toxic solution. Ideal temperature for brewing 25 degrees Celsius.
Effects of vermicompost extracts on plant growth:
In plant growth, using aerated vermicompost extracts improved growth (100 ml per plant per week).
Effects of vermicompost extracts for pest control:
Aphids: Fewest on plants fed at roots with aerated tea at 10% solution (100 ml per plant per week)
Spider mites: reduced spider mite damage at all concentrations of aerated worm compost teas
Nematodes were also suppressed by application of vermicompost tea.
Plant disease reduction:
Spraying vermicompost tea on leaf reduced plectosporium, verticillium, rhizoctonia (damping off). There are also studies showing that non-aerated teas can be just as effective.
Lots of microbial activity at 24 hours, lots less after 7 days for all strengths of tea at room temperature. If they are refrigerated microbial populations stay steady but then spike at 14 days.
Seed stimulation: germination rate was highest with 5% vermicompost tea.
Soaking the seeds in 5% vermicompost tea for over 1 hour had a very good increased germination compared to just soaking in water. If you are soaking for 24 hours, soaking in 5% tea is almost as good as soaking in water. At a high concentration (on the other end of the spectrum,) soaking seeds in a 20% tea at 24 hours, the concentration is deadly for the developing plant.
At an audience member’s request, to summarize results, vermicompost effective:
growth: up to 50%
suppress pathogens: 5-20%
germinate seeds: 1%
There was a discussion about difference between tea, extract, leachate, vermiwash (worm slime!) and “worm wine”. There is a Composting Council and a definition was read. Website: National Organic Standards Board (NOSB)and the NOP program. Extract is vermicompost steeped less than one hour. Tea is steeped more than one hour.
Rhonda Sherman finished the session by cautioning about pathogens from leachate, manure and foodwaste. She also advises against putting sugars in extracts or tea because of the danger of spiking growth of pathogens. We need to be aware of proper handling of potential pathogens and pesticides as an industry.
The reference text sold at the conference with articles by Norman Arancon, Rhonda Sherman and others, Vermiculture Technology: Earthworms, Organic Wastes, and Environmental Management is available on Amazon.com in hardcover and for Kindle.