Someone mentioned nematodes, so I thought I would talk about them. I
once had to spend a few days cutting the rear ends off nematodes and
staring at them, and never once has nematode anal wrinkles come up at
a cocktail party I've attended. I have to use this information
*somehow*.

Nematodes are roundworms, not related to earthworms. There are
millions of them in each handfull of soil. Most are scavengers. A
very few genera are plant pathogens. They are divided into 4 main
categories: root knot nematodes, cyst nematodes, sting nematodes and
foliar nematodes. Root knot nematodes make nodules on roots, and
they disrupt water transport in the root system, as well as stunting
roots. Cyst nematodes and sting nematodes feed on roots, causing
stunting and "unthriftiness", but are often a problem by transmitting
viruses, or, by creating wounds, allowing access to root rot fungi.
Foliar nematodes are not well-studied, but they live in leaf tissue,
and can injure plants if they are present in significant numbers.

Nematodes are difficult to eradicate, and nematicides are usually
very toxic. The best treatments are those that are safe, and which
keep nematode populations low enough to avoid major damage. Potato
growers plant marigolds, which exude compounds that nematodes don't
like. Crop rotation works with nematodes that are crop-specific. In
warm regions, like much of Israel, soil solarization can be used to
kill nematodes.

For bonsai, root knot nematodes are the biggest threat, since they
have a broad host range and repotting the plant won't fix the problem
(the female nematode is embedded in the gall). The best option is to
prune roots to remove as many galls as possible, and then repot in
clean media. There are parasitic fungi that kill nematodes, and use
of such biocontrol agents will reduce the number of juvenile
nematodes.
--
Nina Shishkoff

Riverhead, NY

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