I used to worm every 6 wks, march through December here in Ohio, alternating between Safeguard crumbles and Vblazen (sp?) liquid poured over feed.
I've recently learned that too much worming can be bad,actually mutating the worms to be resistant to the wormer. A vet recommended checking for worms before worming,a very cheap fecal test, and then worming accordingly.
Hope this helps.