A sod farmer in the Chicago area had a large acreage of Merion bluegrass to be sold as sod. The seed was contaminated with smooth bromegrass; hence the sod could not be certified. The owner asked for a mowing schedule which would destroy the brome but save the bluegrass.
A mixture of bluegrass and bromegrass was intended for sale as certified sod. Certification required elimination of the bromegrass. Both grass species are rhizomatous, so it seemed improbable that the grower could achieve certification. However, a mowing scheme could eliminate the bromegrass and salvage the bluegrass. The first step was to mow low when bromegrass commenced to produce an erect stem (jointing or transition stage).
The second step took place in April with ample fertility and moisture. The flowering stems of the bromegrass began elongation. By splitting a shoot longitudinally with a sharp blade, it was easy to locate the growing point. Mowing low again removed the growing points of the bromegrass. The bluegrass was not adversely affected because it produces many non-flowering shoots, whose growing points remain at the soil surface. Bromegrass recovered slowly from weakly developed shoot initials. These new shoots were allowed to develop for about 5 weeks before further mowing. During the resting phase, the shoots developed a jointed culm thereby raising the growing point to a vulnerable height once again.
Low mowing removed the growing point of many shoots. This killed the bromegrass because another cycle of basal (adventitious) buds had not produced new shoot initials. The bromegrass was eliminated and the sod was certified and sold.
This mowing scheme is quite similar to defoliation under rotational grazing. Livestock can act the mowers and graze the grasses for elimination or persistence if they are moved at appropriate times.
Livestock grazing grass-legume mixtures are in jeopardy when grasses in a stand dwindle in comparison to the legumes in the stand because of the associated risk of bloat. This risk can be diminished by monitoring the growth stage of grasses, taking precautions to avoid severe defoliation when desirable grasses are approaching the transition stage (early culm development).