Compost to control plant diseases (revised)

Black shank:field tom.: updt 9:5:'08 FL Dept. of Ag and Consumer Serv. plant disease

Field tomatoes stricken with P. nicotianae Breda de Haan
USDA Forestry image fr. Division of Plant Industry Archive
Florida Dept. of Ag. and Consumer Services

So a day or two ago I was innocently researching away about compost and just for fun, hit the Google ‘scholar’ option to see what came up under the wide-open search term “compost.” (Toe surgery confines me for the moment to whatever I can find on the Internet; even the University library six blocks away is too far).

Lo and behold, I found myself looking at a number of articles dating back to the eighties and continuing right up to the present day about managing diseases with compost. Slap my ass and call me Judy, but I never heard of such a thing. Like a good metaphor, however, it makes sense as soon as I hear it: so many plant diseases are soil-borne that changing the soil balance would reasonably affect disease contraction, severity, and so on.

A recent study conducted in Greece found that freshly cured compost (stuff that had finished decomposing, but hadn’t sat around long afterwards) helped suppress Phytophthora nicotianae Breda de Haan, a.k.a. “black shank”—a surprisingly vivid descriptor and quite apt, since this is what a stem looks like after it hits:

U Georgia, black shank

tobacco plant stem showing P. nicotianae Breda de Haan
USDA Forestry image fr. U. of Georgia Plant Pathology Archives

In this study, nine different composts were tested, all derived from local agri-businesses such as olive-oil and wine. Though aged composts were far less effective, all of the just-cured composts "demonstrated high levels of suppressiveness against Phytophthora nicotianae Breda de Haan in tomato." They didn't  improve things "a little," or "somewhat;" they had what the study abstract calls a "“general suppression phenomenon," decreasing disease incidence by 81 to 100%. Wow.

P. nicotianae is truly an equal opportunity disease, discriminating neither by plant, plant part, or world region. Though primarily considered a root and "collar" disease, it also affects stems, fruit, and leaves, as these photos show. Google it, and you’ll see reports about its impact on tomatoes, tobacco, eucalyptus, basil, and thyme, amongst others.

Best of all, this come-one, come-all charmer seems to be making a world tour: it first appeared in tomatoes in Australia in 1986, showed up in South African eucalyptus in 1999, has been making inroads in Chilean tomato fields for five years or so, and who knows, may be appearing in a field near you soon.

So anything that helps control it is hugely important and helpful.

Now, I call that interesting.

Let’s hear it for organic disease-control!

10 Responses to Compost to control plant diseases (revised)

  1. Great information… anything organic that will keep away something likely to attack our tomatoes is aces in our book. Thanks for sharing!

  2. Hear, hear!
    Organic + Free + Consumers being able to it themselves =
    A very unhappy Monsanto and friends!

  3. Great information. Yes, it does make sense that compost would help with disease control. I’d always heard about it from the angle that it makes plants stronger and therefore less susceptible to disease, but this is an interesting new perspective.
    Hope you toe heals up quickly! I’m heading for my ACL reconstruction on Dec.17. Merry Christmas to me, ha!

  4. Shibaguyz, there were some other studies specific to other tomato problems. I didn’t want to make this post too long, so I didn’t include them, but for your sake, I’ll try to put together another.
    Laurel–Oh, if I could make Monsanto unhappy–!
    Amy This was a new one on me, too, and I just love it.
    Good luck with your surgery. Me, I’d be pissed pink if I had to do two on one knee in a year, but rage at one’s surgeon may not be a good way to go. Here’s hoping someone else in your household knows how to cook a good holiday dinner.
    Blog on, people!

  5. Compost fighting disease is a great idea which I hope spreads. The flip side, of course, is that improperly composted diseased plant material can help spread it too. That said, I’d still rather spread compost in my yard than something chemical any day.

  6. Wow, that’s really interesting. It really does make sense though when we stop to think about it. Just think of all of that money people spend on chemicals when they could be more earth friendly (and probably easier on the pocketbook too!).

  7. Interesting. (And handy length.) Compost builds a plant’s strength so it can better fight off disease but using it more as a medicine is new to me.

  8. Yay for compost then! Plus, it smells and looks good, and bugs are more likely to like it, which feeds the chickens, etc., etc.– all of which is the more reason to spread it rather than stinky old chemicals…;-)

  9. I keep thinking abou8t this (I have composting on the brain right now). Why do you suppose the aged doesn’t work as well? Must be that some compound has leached out? Juglone, maybe?

  10. Krys–Yes, compost can spread disease, but if you get the temp up to about 55° C. (131°F), most plant and human pathogens will be killed.
    Me too, Lucy. Uh-oh–I’ve just lengthened this. Gulp.
    Susan–Yup–all of the above and more. And if I find out why the aged version isn’t as effective, I’ll let you know. My guess for the moment is that some of the active micro-organisms die off while it’s stored, making it less effective in certain arenas. It would still retain all of its physical attributes, but the chemical and biological ones would be reduced.

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