Saturday, March 28, 2009

Beneficial nematodes

There are many different species of nematodes, but since a couple of blocks in my main vegetable garden have developed a root-knot nematode problem (primarily affecting susceptible tomatoes and peppers), I've been interested in ways to reduce their numbers.

Root-knot nematode damage on tomato (University of Missouri Extension)

Rotation management is the primary organic method, using non-susceptible crops and varieties to decrease numbers, prior to trying some susceptible sort of heirloom tomato, for example (actually, my heirlooms are going to go in containers this year). Using trap crops such as rape seed (canola) and French marigolds is another recommended strategy.

But, beneficial nematodes that are supposedly parasitic on root-knot nematodes, sting nematodes, and ring nematodes sounded particularly appealing. The notion of having good guys take care of the bad guys in an underground soil contest, hmmm -- sounds promising to me.

So I plopped down my credit card for a supply of 5 millon Steinernema feltiae (Sf) nematodes, supposedly enough for 100-150 square feet, about the size of my main garden area. The company suggests that this variety might achieve 100% control of root knot nematodes. We'll see.

They're shipped at exactly the right time for your area, and mine arrived yesterday. More seeds, my gardening companion asked? No, it's my beneficial nematodes, I said. Woo-hoo! We'll see if they're effective at all. I hope they're hungry. I haven't been able to find a great deal of credible research information about their effectiveness, but figure it's worth a try.

Fortunately, conditions were perfect this morning for application (use immediately (√), early morning is best (√), soil should be damp (√), over 55° (√), during a rain was ideal (√), and additional watering or rain expected next few days (√).

I'm still only going to plant resistant varieties in those blocks, so this isn't a great experimental test (I suppose I could try ONE non-resistant pepper, but that gives the bad guys food). Hmrph.


  1. I've been investigating beneficial nematodes too, but I've been looking mostly at the ones that supposedly aid against vine borers, Japanese beetles, fleas, etc (heterorhabditis). Unfortunately, one has to inject them into damaged stems to fight vine borers. Been there, done that (with Bt); too much work for limited success. I've read a couple of scientific journal articles on this and it seems to be a promising strategy for a lot of ailments but there's not enough research on home application out there yet to say for sure. And they aren't cheap and work for only a couple of months as I understand it. I have a very experienced gardening friend, however, who has been using the nematodes for a few years now and swears by them. Good luck!

  2. Thanks, CEN! I probably will need some good luck.

    Amazingly, the same species of nematode (the sf ones) are also predatory on all sorts of larvae and grubs, too. I was hoping they were totally specific! Oh well.

    We did use what must have been similar nematodes years ago for an outdoor flea problem caused by the previous owner's cats -- it seemed to work well to control the outdoor fleas, at least they disappeared, but who knows.

    I haven't figured out why the potential control would only work for several months - uh, do they 'starve'? They seem to have so many potential 'prey,' it wouldn't seem likely. But as you say, actual data in home garden settings (or even farm settings) is pretty sketchy, and the suppliers, hmmm. And they're definitely pricey!

    Glad to hear about your gardening friend's apparent success with them! I'm basically planning to use resistant varieties of tomatoes and peppers, in any case, practice better rotations, and use plenty of organic matter, not that I didn't already.

  3. From what I've gotten--and these critters can be pretty complicated--they go through several larval stages, the third being the "infective," and thus effective, stage. From that they move on to find new victims. (Well, one type actually moves on, the others apparently just wait in ambush for unsuspecting grubs or borers to come along.) But either way, not all of them make it to reproduce. For one thing, they are quite susceptible to dessication (our hot, drought-plagued summers). Most sources I've seen recommend bi-annual applications (but these seem mostly related to getting rid of fleas, lawn grubs, etc). And I can imagine that many folks just don't follow the directions as well as you will-- all the check-points you indicated about moisture, soil temp, etc. So they may lose many of their initial millions up front. Some sources also suggest more frequent applications may be necessary. Yep-- that's pricey.

    I just have to laugh at the sources that warn against application within two weeks of applying 2-4D. My guess is anybody using 2-4D is NOT using beneficial nematodes. But you never know....

    Btw, even though there's so little research on effectiveness, I read that the use of beneficial nematodes for pest management was recommended as far back at 1929! Then people got more interested in chemical "controls" and nematodes went to the back burner. Maybe they'll have their heyday yet.

    And yes, after all the confusing delineation of types of nematodes in the gardening catalogs, it does seem that most pretty much will take whatever comes along-- grub, borer, other nematodes, etc.

    At least, that's what I've "heard" on-line. I'm sure there's a specialist or two at Clemson who really know what they're talking about on this subject. Maybe I'll call the HGIC next week to see what they say.

  4. Hi, CEN-
    I'd be interested in the advice of our (Clemson University) Home and Garden Information Center horticultural experts, who are all excellent gardeners.
    The root-knot nematode fact sheet is excellent - and recently revised to include using marigolds as a trap crop, etc. but not a peep about beneficial nematodes.

    But we do have a nematology lab, although I don't know any of them. Perhaps I should send a sample from my infested beds to find out what I have, exactly!

  5. Beneficial nematodes work in Montana. I can't grow ANY root vegetables without using benefical nematodes. Without them, they are tunneled, marred, and half rotten. With them, they are pristine, big, and sweet.

  6. I'm just curious... I stumbled across this blog post because I'm considering using beneficial nematodes to combat root knot nematodes..... so did it work?

  7. This was quite a while ago, but actually they did work!

    1. Wow! I also just stumbled on this blog, and glad to see your update. I can't wait to try this here in S. Florida. At this time much of my garden (all three 4x8 beds) are under clear plastic solarizing to kill the nematodes. If this works for the strains of root knot nematodes here I may not have to solarize again.


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