Help With Nematodes

HI Gardeners! I hope that your week was filled with evey thing nice! I am happy that Spring is here and I have been celebrating by working in my garden all week planting flowers and tomatoes. A friend came over and we were talking about pest control for tomatoe plants. I told her that I plan to use Nematodes ... She told me that Nematodes would destroy the plant's root system! I was socked because I had place my order at the garden center.
I was wondering if any one in the savvygardener community have heard about Nematodes destroying plant's rooting systems?
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