Tag Archives: thermal compost

Pathogen-Reducing Compost

January 14, 2020
© 2020

Benefits of compost are widely known: 1) enhances water holding capacity, soil structure, organic matter, drainage, and nutrient holding capacity of soil, 2) provides a source of beneficial microbes, 3) decreases both inputs (to your garden) and outputs (from your garden), a plus for sustainability, and, 4) reduces fertilizer and pesticide use.

However, did you know that well-made compost has the ability to reduce pathogens and enhance plant growth?

An extensive research study of 120 bioassays, involving 18 composts and seven pathogens, found positive disease suppression in 54 percent of the treatment combinations, a disease stimulating effect only rarely (3%), and no effect in 43 percent of the treatment combinations (Termorshuizen et al., 2006).

Other studies have shown that “backyard” compost is superior to the commercial product, possibly due largely to richer and varied starting materials, plus a more relaxed thermophillic phase (wherein temperatures are sanitizing but lower than those recorded in commercial composts). Backyard composting presented higher counts of bacteria, actinomycetes, and fungi. It also shows higher percentages of isolates producing extracellular enzymes which allow the breakdown of tough substrates, including polyethylene!

Although the studies show the efficacy of compost, no one has come up with the perfect recipe or management strategy to combat a particular soil pathogen. This is because the soil microbial community is so dynamic and complex. Quality control tools are also lacking.

Still, we know from research that microbial organisms in compost are able to reduce pathogens my means of: direct antagonism (antibiotic production and direct parasitism), predation, competition for resources, enzyme production, and, induced resistance in plants – through signaling networks and hormones.

Sun, Jan 19, 2-4. work party
Sat, Feb 1, 10-12, Work Party
Sat, Feb 1, 1-3, PRUNING CLASS
Sun, Feb 16, 2-4, Work Party
Sat, Mar 7, 10-12, work party

Note, compost is more effective as a pathogen prevention method than when used as a management strategy for some existing soil or plant pathogen. Elaine Ingham, veteran soil scientist, points out that compost and soil should be colonized with a sizeable and diverse body of microbes. “There are only so many seats at the table. If the good guys are already there, the bad guys are turned away.”

Image Credit: Zosia Rostomian & Jill Banfield, Creative Services, Berkeley Lab

Who are these microbial actors who play such a beneficial role in a garden? It’s bacteria, fungi, protozoa, and nematodes, none of which can be seen with the naked eye. There are millions of microbes in a gram of compost and hundreds of thousands different species. In fact, it’s the diversity of players that makes good compost a pathogen suppressor.

Commercial composts can differ widely in their suppressive effects and can vary as to which pathogens are diminished. However, commercial composts can meet the objective of adding organic matter to the soil. In contrast, the special compost that you can produce with backyard composting, using correct temperature, moisture, aeration and curing processes, will yield a compost that you can use sparingly as an inoculum throughout your garden. It will jump-start good soil biology and maintain nutrient cycling, creating an environment fostering pathogen-suppressive soil.

Next up – A template on making a thermal compost.
Also, watch the FreewayEstates.org calendar for a hands-on thermal composting class, coming in early May, 2020

Ruth

References:

Hadar & Papadopoulou, 2012 – Suppressive Composts: Microbial Ecology Links Between Abiotic Environments and Healthy Plants DOI: 10.1146/annurev-phyto-081211-172914

Vaz Moreira et al., 2008 – Diversity of Bacterial Isolates from Commercial and Homemade Composts. DOI: 10.1007/s00248-007-9314-2

Welgarz et al., 2018 – Microbial diversity and nitrogen-metabolizing gene abundance in backyard food waste composting systems DOI: 10.1111/jam.13945

Fayolle , L., 2006 –  Eradication of Plasmodiophora brassicae during composting of wastes
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/

Cangelos, G, 2014, Dead or Alive: Molecular Assessment of Microbial Viability
https://aem.asm.org/content/80/19/5884 DOI: 10.1128/AEM.01763-14

Plant Pathogens – Pasteurize? Sterilize? Sanitize? Boil Everything!

March 26, 2019

Recently, I was watching someone rinse a plastic polyethylene plant-potting container in a Brown Rotbleach solution for reuse. I was pretty sure that pot needed to be thoroughly rinsed of organic matter prior to the bleach rinse.

The observation made me think of several reasons why a gardener needs to know how kill plant pathogenic microbes, e.g., effectiveness of our thermal composting process, best product to spray on our pruning shears or, preparation of a previously purposed plastic pot for propagation.

I tried and failed to make a helpful chart. It proved far too difficult, due to so many factors to consider:

varied expressions of quantities
different types of substrates and their porosity
amount of contact time needed
type of organism and state of organism
health hazards
the level of disinfectant desired
shelf life of product
humidity in relation to temperature
corrosiveness
cost of product
where the organism lies and whether you can even get at the bugger

Method

 

Botrytis cinerea (gray mold-fungal) Nectria galligena (apple canker) Weed seed

(sow thistle)

Verticillium dahliae (Verticillium wilt)

 

Pseudomonas syringae pv. tomato (Bacterial speck)
0°F yawn
165°F Dead 1 hr Dead 1 hr
5% sodium hypochlorite (bleach) sol. 2g/liter 20 hr LD90
4%v/v iso. alcohol effective
.3% iodine solution 93% dead 93% dead
Quaternary ammonium 4g/liter 20 hr LD90

Heat destroys microbes best and heat with humidity is even better. However, except during our thermal composting process, heating to 149F for two hours is not practical. As such, I tried to get some answers about products that are available and familiar.

Sat, Apr 6, 10-12, Work Party
Sun Apr 21, 2-4, Work Party
Sat May 4, 10-12, Work Party
Sun May 19, 2-4, Work Party

Let’s start with bleach. Sodium hypochlorite is very reactive, affected by surface contamination from organic matter and it’s irritating to use. It’s difficult to know what dose to use and, at the concentrations that many people use, it leaves a residue on the surface. (1000 ppm will destroy all microbial pathogens but for the tough resting spores. Using household bleach (5.25% sodium hypochlorite), the dilution would be 1:50 or 5T per gallon.)

Ethanol (think Everclear) can kill most organisms but it is highly flammable and evaporates quickly. It dries out the organism (which is why the similar product, isopropyl alcohol, is better as a disinfectant for the skin). Alcohols reportedly won’t kill some spores and they harden rubber and some plastics on tools.

I could not get a clear idea whether hydrogen peroxide is a good pathogen hunter. Articles refer to its effectiveness, especially on inanimate surfaces, but indicate that hydrogen dioxide is a superior disinfectant on plant production surfaces.

Quaternary ammonium chloride. Hmm. There is a lot of controversy about Quats and they are reported to be not always effective against the tough customer – the fungal resting spores.

This brings me to a possible unsung hero – iodine. Remember when you went camping where the water was bad. You mixed the two tablets in water and waited. That second tablet helps with the discoloring and the taste and also is a solubilizing agent. One potential downside is shelf life – about five years.

A flameless loop sterilizer might be the ultimate tool but not readily available and you would need a power source. (We will leave out solarization, which, for the time being anyway, might be challenging in Western Washington.)

This study is way more complex that I could have ever imagined. There is no one size fits all solution. Shown here is a popular chart from two State of Washington professors (who are also fine authors of plant pathology books).

Good reads:
Investigation on the fungitoxic effect of an iodine solution on three plant pathogens in vitro. Bengt Boysen.
Bachelor project in the Danish-Swedish Horticulture programme
2004-1 (ISSN 1652-1579)

Time and Temperature Requirements for Weed Seed Thermal Death
Ruth M. Dahlquist, Timothy S. Prather, and James J. Stapleton
Weed Science 2007 55:619–625

Soil Solarization and Thermal Death: A Logarithmic Relationship Between Time and Temperature for Four Soilborne Plant Pathogens.
G.S. Pullman, J.E. DeVay and R.H. Garber
American Phytopathological Society, Vol 71, No. 9, 1981 p 959

Temperatures Necessary to Kill Fungi in Wood
USDA Technical Note 259, Forest Products Lab Feb 1956

Safe Procurement and Production Manual A Systems Approach for the Production of Healthy Nursery Stock
Griesbach J., Parke, J.L., Oregon Association of Nurseries, January 2012
https://www.researchgate.net/publication/282649506

Dose Curves of Disinfectants Applied to Plant Production Surfaces to Control Botrytis cinerea
W.E. Copes, Plant Disease-American Phytopathological Society, May 2004

Chemical Disinfectants
https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html

Quaternary Ammonium Compounds
Quaternary ammonium compounds are the most commonly employed broad-spectrum hard surface disinfectants employed in animal research facilities.
From: Laboratory Animal Medicine (Third Edition), 2015
https://www.sciencedirect.com/topics/neuroscience/quaternary-ammonium-compounds

EPA Hard Surface Disinfectants
https://www.education.nh.gov/instruction/school_health/documents/disinfectants.pdf

Ruth