1. (1) Unit of certification. A field or portion of a field may be certified if the area to be certified is clearly defined. Portions of a field not meeting requirements for certification must not be allowed to reach the seed stage.

2. (2) A field producing certified seed must have the minimum isolation distance from fields of any other variety that do not meet varietal purity requirements for certification, as given in the following table:

   Red clover	Fields of less than 5 acres	Fields of 5 acres or more
   Certified	20 rods	10 rods
   Foundation	80 rods	80 rods

   (b) Specific requirements.

   Factor	Maximum permitted Certified
   Other varieties 1	0.50%

   1

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

(a) General.