(1) Unit of certification.

The unit of certification shall be a field, but a portion of the field may be approved for certification, provided the remainder is designated specifically, harvested separately and the seed is eliminated from certification.

(2) Isolation requirement.

A specific commercial hybrid to be inspected for certification must be so located that the ear parent is not less than 40 rods from other corn, provided; however, that the distance may be modified, depending on the acreage of the specific cross by the planting of border rows of pollen parent and except also as shown in subdivision (b), (1) and (2) below. The following table applies to all sides of the specific cross exposed to contamination from other corn, whether located directly opposite or diagonally, and indicates the minimum number of border rows required for fields of various sizes when located at different distances from the contaminating corn:

(1) For corn where the contaminating field is sweet corn or of types other than that being grown for certification.

(2) When differential maturity dates prevail and providing there are no receptive silks in the ear parent at the time pollen is being shed in the contaminating corn.

(3) Where natural barriers such as (i) woods intervene which are three rods or more in width and have sufficiently dense foliage to prevent cross pollination and (ii) where a thick hedge row 20 feet or more in height intervenes plus 10 rows of pollen parent.

(1) A commercial hybrid will be disqualified for certification if more than one per cent of the ear parent stalks have shed pollen on any one inspection or if the total for three inspections on different dates exceeds two per cent.

(2) Sucker tassels, portions of tassels, or tassels on main plants will be counted as shedding pollen when two inches or more of the central stem, the side branches or a combination of the two have the anthers extended from the glumes.