One group of nematodes that should be kept on your radar are root-knot nematodes (any member of the genus Meloidogyne), which are common plant parasites. Learn more, here.
Root-knot nematodes - Nursery Management
Fine Gardening – Issue 211 - FineGardening
Root-Knot Nematodes in the Vegetable Garden
It's a good time to check vegetables for root knot nematode - Vegetable Growers News
6 steps to sample soil for root-knot nematodes
Can My Plant Be Saved From Root Rot? - FineGardening
Pests and Disease - Page 2 of 33 - FineGardening
root knot nematode of watermelon
Can My Plant Be Saved From Root Rot? - FineGardening
Be on the Lookout for Root-Knot Nematodes - FineGardening
Beware of Root-Knot Nematodes in Your Garden
Dealing with root knot nematodes in a vegetable garden - Greg Alder's Yard Posts: Southern California food gardening