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
