The efficacy of predatory nematodes depends upon many factors. The correct species of nemas have to be selected for the pest; the timing is important; a pest population has to be present; application rates and methods need to be followed according to the instructions.

My mother had an empty part of the rose garden due to bad nematodes.
I used nematodes to kill the nematodes and now have roses growing there again.

I also interplant my roses with French marigolds to serve as pest traps for the nematodes.