The Helpful Gardener
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Ch. 8 Nematodes

Nematodes.

The word can strike fear into the hearts of gardeners. Like Quint's fingernails on chalk board in Jaws, I picture myself giving the speech...

"Y'all know me...y'know what I do... I'll get yer nematodes, but it'll cost ya..."

Even Spongbob had a run in with nematodes (not very accurately).

But as far as biomass goes, this is the biggest population on earth. The pile of nematodes weighs more than the pile of elephants, or blue whales, even (for the moment) more than the pile of people. There are more species here than you can shake a stick at; Jeff says nematologists have ID'd 20000 species, but expect there are a million! :shock: And like fungi or bacteria, only a few are pathogenic, the majority are benignly helpful, or actually beneficial. Predatory nematodes are known to most of us for grub control, but as Jeff points out, the mineralization that bacterial and fungal feeders do (with a whopping 100:1 C:N ratio, these guys move some nitrogen!) is really important.

But as Jeff also notes, this is one of the first orders to go in compacted soils. Can't move, can't eat. And compaction is a big problem in plowed land, chemically fertilized soils, or lawns where you drive in circles on a heavy tractor every week. Just sayin....

HG
Last edited by The Helpful Gardener on Sat Apr 03, 2010 9:05 pm, edited 1 time in total.
Scott Reil

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to me nematodes are the best poster boy candidates for an action packed and terrifying account of soil life.

Many of them look like monsters, with rasping and drilling machines for mouths. They have no eyes to humanize them, just ruthless appetite. Others look friendly, almost cuddly.

Makes you wonder if storytellers of old (and new, like the guy who wrote dune) didn't have microscopes to inspire them, since they described so many monsters.
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The Helpful Gardener
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The ones with complex setae (mouth parts) are the most sinister looking ones, but those are always bacterial feeders and the best of the lot from mineralization standpoint...

The nasties hide a switchblade type straw in a bulb in their pharyngea (throat) that they stick into plant roots to suck out the juices. Some of the switchblade crowd are actually fungal feeders though, and can actually help mitigate fungal population, and there are even a pretty common bunch that will feed on fungus until it is gone, but then switch to roots!

So if we damage the fungal colonies, and the fungal switchers shift to plant feeding, who's fault is that?

HG
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Scott Reil

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Frank Herbert wrote dune. just sayin'...
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just stay away from the series his kid wrote. unless you like mindless schlock you can't put down.

spice agony does sound cooler than drinking extract of nematode poo.
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Remember Frank was a biologist first and an author second; there is every reason to believe he might have been thinking "It needs a big nematode. A REALLY big nematode...". They do look alike (except for the BIG part...)

Toil, sounds like you are expecting to survive spice agony? Got a messiah complex? :lol:

OK, back to miniature roundworms. We can start the Dune thread on the Hoo Ha Forum... (best science fiction ever written, and that's from a Heinlein guy...STOP IT! :wink: )

HG
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I passing thought, but it seemed appropriate to ask here:

Companion planting guides often recommend planting marigolds, French marigolds, or Pyrethrum plant to REPEL nematodes.

But don't we want to keep the BENEFICIAL nematodes?

Am I correct in understanding that beneficial nematodes are the larger predatory nematodes?

Are gardeners sabotaging their gardens by planting marigolds, etc.?

Next, I was going to ask what ATTRACTS beneficial nematodes, but then I realized I already know the answer... or at least I think I do -- the lesser microbes! The bacteria, fungi, the ciliates, and so on up/across the foodweb. So back to brewing some AACT. 8)

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Heya Apple,

I've never seen any actual science when it comes to companion planting guides. If people have noticed that polyculture tends to result in less infestation, I'm not going to argue with them.
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"Another possible solution may be the solid planting of marigolds for 3 months in areas heavily contaminated with nematodes. The marigold, when grown on soil infested with nematodes, suppresses the population of these nematodes and reduces the numbers found in the roots of susceptible host plants. Three compounds of an a-terthienyl type, toxic to nematodes, have been identified in root exudates from these plants. Terthienyls are released from growing roots, even without their decay, but benefits require three to four months to become clear. There is some evidence that a-terthienyl is inhibitory to some plant-pathogenic fungi too. Marigolds also function as a trap crop since larvae which penetrate the roots do not develop beyond the second larval stage and do not lay eggs."

https://aggie-horticulture.tamu.edu/archives/parsons/fallgarden/nematode.html

not all the companion planting lore is old wives tales!

But I don't know the answer to AS's question, do they repel all nematodes including beneficial ones. I would speculate that if you are having damage from nematodes, that would mean you have a preponderance of non-beneficial ones, so might want to work on reducing the population.
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A natural nematicidal effect would likely drive away ALL nematodes, bennies and baddies alike. Does that leave you open to white grub? I dunno; needs a seperate experiment...

A preponderance of bad nematodes is an imbalance of the soil ecosystem. Take Jeff's nematode trapping fungus, or bacteria that attack nematodes, or viruses, or even the nematodes that eat nematodes; Nature presents LOTS of check and balances on these guys. It is usually OUR unbalancing of those restrictions that allows for these problems to arise in the first place...

HG
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So in other words, a marigold monoculture, if marigolds do as claimed, would pose its own problems.

On the other hand, much more simplistic thinking, a diversity fetish if you will, can yield potentially more stable and long lasting results, because nature tends to moderate.

On the other hand, when does the marigold exude nematode poison? Indiscriminately? Do we know?
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Toil wrote:So in other words, a marigold monoculture, if marigolds do as claimed, would pose its own problems.

On the other hand, when does the marigold exude nematode poison? Indiscriminately? Do we know?
I think part of our message is that ANY kind of monoculture would pose its own problems.

I don't know the when, except what I quoted above seems to imply that it takes a bunch of marigolds and some months for the effect to build up enough to make much difference. So when people put one marigold in a bed, they aren't doing much but decorating....
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It's interesting in that with nematodes, like with many other types of organisms, it's usually the bad ones that get all the press. Even though these seem to oftentimes make up a minority of the species, they are the only ones we think of when we think of that type of organism.

It is because of this that many gardeners are sadly wiping out large chunks of beneficial microbes by the use of fungicides and other -cides because they think that all fungi, bacteria, etc. are disease causing.

Ironically, not only does this mass microbial reduction reduce plant nutrition, but it actually encourages the resurgence of the detrimental organisms, since these are often the first to arrive in "deserted" soils. Furthermore, the absence of competitions helps these undesirable organisms to thrive.

Instead of reducing levels of these organisms, I'll bet it is actually more effective to increase levels of organisms. Since the majority of these are beneficial, simple odds are that they will out-compete the undesirable for resources, thus helping to keep the populations in check.

Also, as we saw with the protozoa, the nematodes consume bacteria, but are also helpful to them in aiding them with transportation. The closer you look, the more intricate this soil food web becomes.
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