This is a problem that I'm having difficulty learning about. There's not much that shows up with a search. But I have them in my garden. I destroyed 3 12-yr-old plants this morning and I think it's time we talked about this problem.

Unlike HVX which can be controlled by knowing the symptoms, removing plants, not planting another hosta in the same place and using good garden hygiene, this problem is incidious, might be in the plant a long time before one takes notice and there's not much one can do about it.

A couple of years ago we have a late-season ice storm in late April. That summer, several of my largest hostas seemed stunted. But I hoped for the best. Last year, I noticed 'Salute' looked healthy but very small. And this year I included 'Alligator Shoes' in that category. Also, 'Cutting Edge'. Yesterday, I dug 'Salute' and found clear evidence of large galls on the roots caused by root-knot nematodes. Today I dug the other two which were in close proximity. More galls. I've got more hostas that don't look as healthy as they should, including 'Liberty' and 'Spilt Milk'. I don't know how many more I want to dig and destroy and later this week it will be hot - too hot to be digging up hostas to inspect the roots.

The big problem is that there are few things one can do and many kinds of plants that are affected. I can't just pop another perennial in the spot. I don't even know if I can find any marigolds at this point in the season - garden centres have almost nothing this year and I'm in a vulnerable age bracket and really limit going out.

Anyway, here are some pictures. If your hostas suddenly are smaller than they've been, this may be the problem. Note, on the advice of Bill Brashear, I washed 'Salute' so we could see the galls better. I didn't bother with the other two because there was the problem of disposing of the muddy water.

First three are 'Alligator Shoes'





Next four are 'Cutting Edge'





Last three are 'Salute'

Very informative and sorry about the loss of your plants.

Is this something that comes into toe gardens on a plant, or is it in the soil? Yay! Something else to watch for

http://ipm.ucanr.edu/PMG/PESTN...
Found this info, but I cannot find any hosta specific info:

Nematode-suppressive Plants
Certain marigolds, Tagetes species, suppress root knot and lesion nematodes. French marigolds (varieties include Nemagold, Petite Blanc, Queen Sophia, and Tangerine) are most effective. Avoid signet marigolds, T. signata or tenuifolia, because nematodes will feed and reproduce on these. Marigolds don't work well against the northern root knot nematode, Meloidogyne hapla, a species common in areas with cool winters. The effect of marigolds is greatest when you grow them as a solid planting for an entire season. When grown along with annual vegetables or beneath trees or vines (intercropping), nematode control usually isn't very good. To prevent marigold seed from getting in the soil, cut or mow the plants before the flowers open. As with other cultural control methods, nematode populations rapidly will increase as soon as you grow susceptible crops again.

Soil Amendments and Irrigation
You can add various organic amendments to the soil to reduce the effect of nematodes on crop plants. The amendments—which include peat, manure, and composts—are useful for increasing the water- and nutrient-holding capacity of the soil, especially sandy soils. Because nematodes more readily damage plants that are water-stressed, increasing the soil's capacity to hold water can lessen the effects of nematode injury. Likewise, more frequent irrigation can help reduce nematode damage. In either case, you will have just as many nematodes in the soil, but they will cause less damage.

Pesticides
Currently no chemical nematicides or soil fumigants are available to home gardeners for nematode control in backyard gardens and home landscapes.

Found this info, but I cannot find any hosta specific info:

Nematode-suppressive Plants
Certain marigolds, Tagetes species, suppress root knot and lesion nematodes. French marigolds (varieties include Nemagold, Petite Blanc, Queen Sophia, and Tangerine) are most effective. Avoid signet marigolds, T. signata or tenuifolia, because nematodes will feed and reproduce on these. Marigolds don't work well against the northern root knot nematode, Meloidogyne hapla, a species common in areas with cool winters. The effect of marigolds is greatest when you grow them as a solid planting for an entire season. When grown along with annual vegetables or beneath trees or vines (intercropping), nematode control usually isn't very good. To prevent marigold seed from getting in the soil, cut or mow the plants before the flowers open. As with other cultural control methods, nematode populations rapidly will increase as soon as you grow susceptible crops again.

Soil Amendments and Irrigation
You can add various organic amendments to the soil to reduce the effect of nematodes on crop plants. The amendments—which include peat, manure, and composts—are useful for increasing the water- and nutrient-holding capacity of the soil, especially sandy soils. Because nematodes more readily damage plants that are water-stressed, increasing the soil's capacity to hold water can lessen the effects of nematode injury. Likewise, more frequent irrigation can help reduce nematode damage. In either case, you will have just as many nematodes in the soil, but they will cause less damage.

Pesticides
Currently no chemical nematicides or soil fumigants are available to home gardeners for nematode control in backyard gardens and home landscapes.

Found some info on google scholar
[PDF] Nematicidal Dips for Control of Root-knot Nematodes on Astilbe, Hosta, and Iris
page 9

@ViolaAnn
I may be way out and off line here being from Texas, while you are in Canada. Two different climates and hostas do not grow here. But I do have root knot nematodes. I just am really not seeing them on your hostas. Not a religious joke...please do not take offense...the roots would almost look like rosary beads...with even more beads hanging around. Then the plant starts putting out an excess of thin, thready, stringy roots trying to get nutrients. Has a local agricultural expert confirmed them? Climate and plant are out of my comfort zone...just trying to help.

In the fight of root knot nematodes Chitin helps attract the right microbes...Chitin=Shrimp shell meal.
Root Knot Nematodes | Pat Welsh Organic and Southern California Gardening
https://www.patwelsh.com/pests...

May good health be yours!

Well, Christ Wilson from Hallson Gardens, now retired from the nursery business but still involved with the online discussion forums said much the same.

"I don't see signs of root knot in any of those pictures. The big crown pieces make it appear that the plants were much deeper at one time, but those are simply hostas crowns that were growing up and out over time. The roots sloughing off could be a sign of fusarium root rot, though, and that would explain the decline. Fusarium can be a problem in soils that have almost too much bark and too much air circulation present (dries out too quickly) and fusarium can a secondary problem with other soil nematodes like the lesion nematode which is a soil borne nematode only and not a root inhabiting nematode. I don't really see signs of lesion nematodes either but they don't show many obvious signs but can make fusarium get into the roots.

Since I would say fusarium is a greater possibility, and because fusarium can occur when lesion nematodes are present, I would consider a soil drench for fusarium and a soil drench for nematodes. Actinovate is a biological fungicide that can help slow down fusarium. Essentria is an organic essential oil insecticide that when used as a soil drench can greatly reduce all soil borne nematodes, including root knot if you actually had it. Ironically Essentria is rather similar to the stuff the AHS was pushing a while back for foliar nematodes. Though it doesn't actually work for nematodes in leaves it works well in the soil."

Now, if I can manage to get those products ...

Any chance it could be voles munching through the garden?

No. I've never seen a vole in my Ottawa garden.