Why are roses planted at the end of vineyard rows?

Roses along Vittorio's Vineyard

Why are roses planted at the end of vineyard rows?  Do they allude to the winemaker’s fastidiousness or flair?  Do they aid in pollination or do they simply add color to a drab, green vineyard?

All of the above is possible; however, the most important mission for a vineyard rose is that of being “a canary in a coal mine”.  Roses are very susceptible to aphid and, worse, mildew.  Once detected on the roses, the vintner has a two or three day window to spray and protect the grapes from the same plight.

Particularly in the spring while the ground is drying from winter rains, vintners follow rigorous spraying regimes with either sulfur or organic compounds to eradicate mildew spores before grape clusters begin closing and tightening.

The vintner deals with some issue in the vineyards every year and no two years are ever the same.