Its not that kind of quarantine. Its called a quarantine but its actually an agricultural law. States that are known to harbor various insects (in this case, burrowing nematode, root knot nematode, guava nematode) are forbidden from mailing plants that have terrestrial roots, whether growing in the ground or not, to other states that are known to NOT have those insects. And even to other states that DO already have them.
Since only licensed, inspected nurseries are supposed to be mailing plant material across state lines ANYWAY (but yes we all know this is just a pipe dream the USDA has), the theory is that they can prevent the spread of harmful plant pests from state to state by limiting the travel of infected plant material. And hopefully limiting backyard gardeners from mailing infected plants.
States that already have nematodes can only mail plant material that has been physically been tested (the tests are done by soil sampling) and inspected and proven free of nematodes or whatever the other insect it is that they are trying to stop.
EVERY STATE almost has at least ONE quarantine. In the North they tend to be pests that can decimate tree species and forests. In the South they tend to be pests that can decimate agriculture.
I used to have nematode certification but I let it slide. You have to pay for the testing, and even so, you have to choose what specific plants you want tested. Those plants go on your own personal 'able to mail' list. And those are the ONLY plants you can mail.
So even if I had a certification, it would just be for plant A, B or C. Not every plant I have.
This has become such a serious issue that many states have upped the criminal liability for getting caught sending uninspected plant material through the mail from a class two misdemeanor to a class three felony.
The main pests for down here in the lower Southern tier are nematodes and Imported Red Fireants.
Nematodes are a state by state 'opt in' quarantine.
The Fireant quarantine is FEDERAL and carries a higher price if you get caught