I use a small clear glass or vase, cool, cold, or room temp water. Cut up a piece of leaf into the water, let sit overnight. With a bright light background, you'll see the wigglies with a strong magnifying glass if they're there.

I usually do 3 at a time, the third one being plain water, as a control.

Thanks Mary Ann!

And if you determine that you do have nematodes......I am going to share the instructions that Chris gave me on a different forum. Alexa, this might be good for the FAQ.

Cooking Nematodes, courtesy of Chris W (Hallsons)
Get a thermometer that will accurately measure around 120 to 130 degrees. After you find a decent one check it against either a glass of ice water or a pan of boiling water. In a glass of ice water (make sure it has both ice and water for a correct reading) it should read 32 degrees. In a pan of boiling water it should read 212. You will also want some kind of timer.

Next find out the temperature of your hot tap water. You want water around 120 to 125 degrees - no hotter than 130. Turn up your hot water heater if you need it hotter. Find a faucet as close to the hot water heater as you can find so you get some good hot water.

Now get some large tubs or buckets. You will need one for the hot water and a second full of cold water. Get your water, test the temp with your thermometer, then dig up a hosta (or two or three depending on the size of the bucket) and drop them in the hot water. If the temp is around 120 degrees let them soak for 10 minutes. If the temp is around 130 degrees let them soak for 5 minutes. Watch the thermometer as it might drop down too much, but don't worry if it cools a little - the cooking will still happen even if it gets down near 110, just leave them in a couple extra minutes if it gets that cold. After the time is up, immediately drop them in cold water to stop the cooking process. Let them soak for quite a while so they really get a chance to cool off.

Now get some really, really hot water and pour it in and around the old planting holes. For this use much hotter, near boiling water to REALLY make sure you've killed them in the soil around the infected plants. To be perfectly safe you will would want to leave that area vacant from any hostas (or other plants) for a season, but the hot water typically does a really good job of ridding that spot of any errant foliar nematodes.

If you have other hostas touching the infected ones you will want to heat treat those too. Plants within a few feet you might consider, but if these are new this season the nematodes most likely haven't traveled far. But keep an eye on others nearby and heat treat as needed.

After your soil has been treated you can replant them, or move them to another spot. The hosta leaves will disappear and the crowns will typically come back smaller next season, but the nematodes that were in the plant will be gone. I have not lost a single plant when using this method and I've never seen the nematodes return to any of the plants in the following 3 seasons after treating.

I have tried treating Athyrium (lady ferns) with this method and they did even better than the hostas. They did not shrink or loss any vigor after the hot water bath, even though all of the foliage was cooked.

Thanks grrl - I had read the article on Hallsons but needed the leaf/water/microscope test. The hosta has been in a pot for two years and I'm positive it has 'nodes because it has the classic signs. I just wanted to check it to see if I could find them for possible future use. This infected hosta will be tossed rather than treated. I purchased it and one other at WalMart three years ago right before HVX became a big thing - now I only shop from trusted vendors who know and care about infected plants.

Has anyone tried planting marigolds or calendula in the vicinity of a plant infected with nematodes? I found this advice on an internet site.

Do you think it works?

Never heard of the marigold thing... googled it and found it's supposed to help with root-knot nematodes....Hostas have foliar nematodes.....

One website stated: French marigolds 'Nemagold', 'Petite Blanc', 'Queen Sophia', and 'Tangerine' are effective. Signet marigolds (Tagetes signata or tennifolia) should be avoided.

Anyway, you learn something new every day..and lavendergirl, thanks for the detailed instructions... I'll save them.. Only time I tried the hot water thing, I cooked mine to oblivion, even though I was careful with the temperature and timing, based on the instructions I had at the time..

You were right I guess. I had lavender not hostas. Here is a link that I found very instructive in dealing with nematodes

http://www.oisat.org/downloads/nematode.pdf