Happy New Year!
The Garden Professor’s collective resolution is to have at least one new blog post a week for 2018. So I’m kicking things off with a little fact checking on the claims made for a product that’s “a complete ecosystem in a bottle.” The company touts its strong connection to science (“our products revolve around biology”). There is a long list of ingredients and claims – way too much for one post. We’ll start with the first four this week.
Ingredient claim #1: “Chitin/chitin degrading Bacillus: Chitin is a natural polymer that is found in crustaceans, such as crabs, lobsters, shrimp and oysters as well as other organisms, such as insects, worms and fungi. When added to the soil ecosystem, chitin (also referred to as chitosan) promotes the growth of chitin-degrading bacteria. These bacteria, in turn, create a hostile environment for pathogenic fungi and parasitic nematodes. Chitin also acts directly on plants to promote tissue repair and disease resistance.”
Fact check #1: A couple of technical points: oysters don’t have chitin. And they’re not crustaceans. They are MOLLUSKS. They have shells with CALCIUM. And chitosan is not the same thing as chitin. It’s an industrially produced material that comes from chitin.
Chitin is indeed found in arthropods, which include crustaceans and insects. Now, most of us don’t have crabs, lobsters and shrimp roaming our landscape, but we do have insects. Lots of them. They produce a lot of chitin when they molt and when they die. Do you really think we need to add more chitin for Bacillus to consumer? I sure haven’t seen any science supporting that practice.
What about the Bacillus species that degrade chitin? Well, if you’ve got insects in your landscape, you can bet you’ve got microbes that break down chitin as well. Otherwise you’d be up to your garden boots in chitin carcasses. So why do we need to add more bacteria?
Finally, there’s no evidence that chitin applied to plants in the landscape has any effect whatsoever. You might get responses in the lab, and chitosan (not chitin) might have some direct application. But like many other elicitors, you have to get it inside the plant to have a cellular effect. And plants are particularly adept at keeping things like decomposing bug bits outside of their tissues.
Ingredient claim #2: “Compost tea: The disease suppressive characteristics of compost have long been known and therefore the liquid extracts from compost, known as compost teas are being use to battle plant disease while stimulating plant growth. Beneficial organisms including bacteria (primarily from the genera Bacillus, Pseudomonas, and Penicillium) along with some yeast and fungi form a physical barrier against disease causing agents and provide a competitive environment in which the pathogenic species lose out. In addition, compost teas stimulate plant growth, translating into a healthier plant, which is more resistant to attack from disease. Compost teas have shown effectiveness in the control of late blight, grey mold, downy and powdery mildew, fusarium wilt, and apple scab among many others.”
Fact check #2. Just because compost has disease suppressing characteristics doesn’t mean that water leaching through it will have the same. We’ve been hearing for years that compost tea suppresses disease. Where’s the definitive research? It’s a topic I’ve been following for nearly two decades and there’s still nothing that’s consistently effective. (Another technical point here: it’s illegal to make pesticidal claims of a product that’s not registered for that use. Company lawyers may want to review that.)
There are many species of bacteria, including the ones mentioned, that form protective and beneficial biofilms on plant tissues such as fine roots. You can find these bacteria in compost and other sources of organic material – that’s their food source. You won’t find many of them in compost tea.
I’d love to see evidence of anything stimulating plant growth other than plant growth regulators (or hormones as they’re sometimes called).
Aren’t marketers getting tired of compost teas yet? I’m getting tired of hearing about them. I reviewed the science about them 10 years ago and haven’t seen anything to warrant an update.
Ingredient claim #3: “Essential oils: or essences they are called, are highly concentrated substances extracted from various parts of aromatic plants and trees. Essential oils are combined with other carrier oils and teas for stabilization. Essential oils are used against plant pests and disease by interfering with their reproduction and feeding habits while protecting beneficial predatory organisms.”
Fact check #3: Essential oils have no documented benefit when applied outdoors. They can be effective in closed spaces, like homes and greenhouses, but they dissipate quickly outside. What I really want to see, however, is the mechanism by which oils can identify – and actually protect! – beneficial insects while killing pests. (Hey, lawyers…we’ve got another pesticidal claim here…)
Ingredient claim #4: “Streptomyces griseoviridis: Is a naturally occurring soil bacteria. The microbe deprives pathogenic fungi of living space and nourishment by colonizing roots in advance of fungi. In addition the microbe secretes various enzymes and metabolites which inhibit pathogenic growth. Streptomyces griseoviridis has been shown to promote the growth and yield of all plants. Streptomyces griseoviridis is used for the prevention of root and stem rot, Pythium, Rhizoctonia, Helminthosporium, Sclerotinia, among others.”
Fact check #4: While this is a naturally occurring soil bacterium, it’s not clear where it naturally occurs. EPA information states it was first isolated in Finland from peat bogs. Is this something we should be introducing to our own soils? Its effectiveness in disease control and plant performance is sporadic and confined primarily to greenhouse application on crop plants. The diseases listed are common in greenhouses, but not necessarily in gardens and landscapes (presumably because there are natural controls outdoors in healthy soils). There is certainly nothing to support its use in gardens and landscapes, especially considering that many native, beneficial bacterial species can colonize plant roots and act as a protective biofilm.
Stay tuned for next time!