A rose is a rose is a rose....or is it, Gertrude Stein?
One of the questions that come up on almost every tour I do is "Why are roses planted at the end of the vine rows?". So, to answer this question once and for all (or until my next tour): drum roll please...
Roses were initially used to be a warning sign to growers: if the delicate rose was attacked by a fungus (such as mildew), then it would only be a matter of time before the more robust grape vines would be hit. Scientists have since discovered that the mildew strains that roses are susceptible to are not the same for grapevines, HOWEVER, if conditions are good for mildew on roses, they are also pretty darn good for other fungal diseases that can ruin a perfectly good grapevine.
Another reason why roses are planted at the end of vine rows is due to the fact that, as Brett Michaels from the glam metal band Poison knows too well, every rose has its thorn. Back when vineyard work was done with horses and oxen, the roses and their armor functioned as a natural electric fence, assuring that the animals would make a complete turn at the end of the row and not damage the last vine.
Nowadays, growers plant roses both as a nod to these traditions and simply because they add a splash of color and a little romance to the landscape. Nothing wrong with that.