Putting a Stop to Pythium: Humic Acid and Kelp Additives Boost ACT's Effectiveness against Damping Off

3/2/2017

Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum
Phytopathology
June 2004
Link Here

          The great state of Oregon has graced us with some insight into combatting damping-off caused by the fungal pathogen, Pythium. Researchers at Oregon State University wanted to know how to make the most effective (pythium suppressing) compost tea, so they tested several variables: aerated vs. non-aerated, compost type, tea additives, and dilution rates. The compost types were composted yard waste, vermicompost, and a commercial compost made from manure/agricultural waste. The additives were soluble kelp, humic acid, rock dusts, and molasses.
   The researchers grew cucumber seedlings planted in an inert growing medium that had been inoculated with Pythium. The seedlings were allowed to grow for nine days, at the end of which the number of healthy seedlings were counted and compared to the control group (seeds planted in non-Pythium inoculated soil). The various tea treatments were used to drench the soil medium upon the time of planting.
          Consistent disease reduction was only observed with the Aerated Compost Tea that had humic acid and soluble kelp as additives (the type of compost did not matter). Also notable, compost teas made with molasses had inconsistent suppressive effects, with a potential increase in disease. Dilution rates lowered effectiveness as well. The take home message: when making a compost tea, be sure you have sufficient aeration, cut back on the molasses, and use humic acid and kelp additives if you want to keep your seedlings happy and healthy.

5 Comments

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Tim Wilson

3/3/2017 04:36:06 pm

This study is over 10 years old. Be aware that a formula like this may be good for pathogen suppression but may not be so great for nutrient cycling. I need to read it again thoroughly but as I recall they used soil soup amendments, added some ingredients to a finished CT, filtered through a 0.2 micron filter (which is insane) and did not use direct microscopy with a compound microscope.

Luke Besmer

3/6/2017 07:50:48 am

Thanks for the comment! I think you are the first person to do so. The SoilSoup solution is treated as a molasses based additive, so that's why the conclude molasses to be less effective. I'd say it's a good start to make decisions from, but would like to see a follow up study that uses straight molasses. It reads that the ingredients were added to the beginning of the tea. Also, from the paper "The filter was immediately adhered to a glass slide with a 20-μl drop of sterile PPB and examined microscopically", so they just used the filter to collect microbes, and then looked at them under the scope. Again, I appreciate the comment, it made me look closer into the study and confirm what I thought was there. These papers are extremely tough to get through sometimes. Thanks again for commenting, please continue to do so!

3/6/2017 09:43:23 am

Luke;

The filtering of the specimen prior to examination is exactly what I was referencing. There are plenty of bacteria larger than this found in CT (e.g. 5 microns) One might conclude that a 0.2 micron filter might exclude a lot of organisms. They apparently only plate cultured fungi which some would call inaccurate.

I do find it unfortunate that they did not report a direct microscopy count of the microbial population.

As far as what I meant by adding ingredients to a finished CT, this is what I was referencing;

" Second, ACTs made with or without the fungal additive were amended with 0.1% (vol/vol) bacterial additive just prior to being used as a drench. Third, 0.01, 0.04, 0.125, and 0.3% molasses was added (vol/vol) to ACT made with
the fungal additive immediately before drenching. "

" Effect of residual nutrients on disease development.

When producing ACT, increasing the bacterial additive concentration from 0.5% to 1.0 or 1.5% (vol/vol) significantly (P < 0.05) decreased the number of healthy cucumber seedlings (Fig. 2), whereas mixing 0.1% (vol/vol) bacterial additive with suppressive ACT just before drenching negated disease suppression (Fig. 3).

Since molasses constituted one-third of the bacterial additive by
volume, the role of unused molasses in enhancing disease development was investigated. Mixing from 0.01 to 0.3% molasses with suppressive ACT just before drenching significantly (P <0.05) reduced suppression (Fig. 4). In the absence of P. ultimum, the healthy seedlings resulting from drenching with either bacterial additive (0.5%) or molasses (0.3%) in water or compost tea was not different from drenching with 100% water (data not shown). "

I may be misreading but it seems, as I thought/remembered. I've pointed out on numerous occasions that microbial profiles are changed by addition of feedstock.

This is an especially poorly written report. The study may have been great but the scientists are not good writers.

I noticed they referenced some studies about the use of molasses which were very poorly conducted studies. At least they pointed out their weaknesses. (e.g. inoculating with e-coli)

You should test this yourself. Mix up some samples of compost with water and separate containers of humic acid, soluble kelp, black strap molasses and plain water. Then look at specimens through the scope after 18 hours, 24-48 hours.

See for yourself. When we did this molasses was the champion and humic acid grew almost nothing at all. It actually seemed to suppress microbial growth. Maybe you will get different results.

Note: The evil bacteria do not create spores.

3/6/2017 11:22:52 pm

Hi Tim!
I think you might be reading it wrong in a couple places. I am pretty certain it is saying that the researchers looked at what was caught by the filter (page 3 end of first paragraph).
The take home message from this study is really about taking care of seedlings and identifying what works better with preventing pythium. This study is a good start, though as you have pointed out, it could be made to be more exact. Personally, I don't use much molasses, so will not have to change up the recipe too much. I do know that molasses is great stuff too though, it just looks likes its a matter of time and place though. Thanks again for the interest in the blog here, it's much appreciated.

3/7/2017 08:57:24 am

I think you are right about the filter but the added amendments I believe I read correctly.

I think you are making a mistake about black strap molasses, as the NOP compost tea council made previously.

I think the take away message you stated originally should be that this is a good botanical/mineral recipe for suppression of fungal pathogens causing damping off; that compost may or may not be necessary.

From what I've observed, adding humic acids to ACT wherein one wishes to grow out nutrient cycling microorganisms, the humic acids act as a microbial suppressant. Dr. Faust from Bioag has apparently concurred with this finding.

We need more people to test this finding with a variety of humic acids. I've not stated it as fact because I ran the test only with three brands and only on three occasions.

I encourage you to carry out the testing I suggested. I'd be interested to see your results. There is no alternative to learning for oneself.

Your comment will be posted after it is approved.

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Putting a Stop to Pythium: Humic Acid and Kelp Additives Boost ACT's Effectiveness against Damping Off

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