1. (1) A seed field shall be considered the unit for certification. A strip at least five feet in width and which is mowed, uncropped or planted to some crop other than the kind in question shall constitute a field boundary.

2. (2) Isolation requirements. All fields used for the production of foundation, registered, or certified seed must be isolated from other strains not meeting purity requirements for certified seed of the same species in accordance with the distances listed below:

   Class	Fields of less than 5 acres	Fields of 5 acres or more
   Foundation	80 rods	80 rods
   Registered	40 rods	40 rods
   Certified	20 rods	10 rods
   Different generation of same variety	10 rods	10 rods

3. (3) Volunteer plants shall be cause for rejection or reclassification of a seed field.

4. (4) Seed fields outside the region of adaptation. Certification of seed fields outside the region of adaptation of a variety shall be limited to stands not exceeding six years of age.

   (b) Specific requirements.

   Maximum permitted in each class
   Factor	Foundation	Registered	Certified
   Other varieties 1	0.10%	0.25%	0.50%
   Sweet clover	none	none	80 per acre
   Objectionable weeds whose seeds are inseparable 2	none	none	none

   1

   Other varieties shall be considered to include offtype plants and plants that can be differentiated from the variety that is being inspected.

   2

   Objectionable weeds whose seeds are inseparable are dodder (Cuscuta spp.) and bedstraw (Galium aparine), (Galium mollugo) and (Galium verum).

(a) General.