This is all that I could find:

It is extremely difficult to eradicate due to the long incubation period of the larvae and the hardiness of the eggs – it is virtually impossible to kill whipworm eggs laying dormant in the soil, so infestation is frequent. Prevention is therefore imperative.

-- http://www.soidogrescue.org/common-health-problems.html

I DID see, in several places, that the monthly heartworm preventative will also prevent whipworm.

I wonder if any of these could give some guidance:
- your vet
- your state veterinary board
- your state master gardener program