Answer: Beneficial nematodes are naturally-occuring microorganisms; they feed on the larvae of many insect pests, including Japanese beetle grubs, root weevils, and cutworms. However, they will not harm earthworms or other beneficial creatures (including people!)--they are very specific to their lavae prey. Since they are microscopic, your wife won't even know they are there!
For more detailed reports on their effectiveness, I would contact BIRC, the Bio-Integral Resource Center, which is an organization that researches and educates on integrated pest management including biological controls like nematodes.
Congratulations on your decision to avoid strong chemical pesticides. By using beneficials like nematodes, you'll take care of the problems while promoting good soil health--and a healthy soil produces a healthy lawn.
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