Virginia Code Section 58.1-609.2(1) provides that the Virginia retail sales and use tax shall not apply to:

Commercial feeds, seeds, plants, fertilizers, liming materials, breeding and other livestock, semen, breeding fees, baby chicks, turkey poults, rabbits, quail, llamas, bees, agricultural chemicals, fuel for drying or curing crops, baler twine, containers for fruits and vegetables, farm machinery, tangible personal property, except for structural construction materials, necessary for use in agricultural production for market and sold to or purchased by a farmer to be affixed to real property owned or leased by a farmer; agricultural supplies provided the same are sold to and purchased by farmers for use in agricultural production, including beekeeping and fish, quail, rabbit, and worm farming for market.

Click on this link for a printable pdf file to provide to the seller.