When should I apply beneficial nematodes?

[Kay Young]

I have seen different recommendations on the timing of applying beneficial nematodes. Some say now, some say wait until spring. The primary, but not only reason I am planning to use the nematodes is to avoid thrips on my roses. I don't know if that makes a difference in the timing, but it would seem they should be in the ground before bud break on the roses. Can someone enlighten me?

Thx,
K