As you walk through Graham’s vineyards at Quinta dos Malvedos and Quinta do Tua you will pass roses planted at the head of each row of vines. But this splash of colour in the winter landscape is not only an eye-pleaser; it is also an ingenious and ornate part of our vineyard management: a natural method of disease diagnosis.
As is so often the case, this traditional viticultural practice provides a sustainable and minimum interventionist solution to a perennial concern. It is also a good example of how local knowledge, preserved by families who have worked the soil for generations, plays a major part in our vineyard management.
Since the mid-19th century Powdery Mildew, also known as Oidium, has been prevalent in European vineyards. It originated in the U.S.A and was the first fungal disease to be described by science.
Rose bushes are in fact more prone to contracting the Powdery Mildew fungus than the vines and they will therefore show signs of the disease before the latter. The rose bushes, therefore, act as a kind of ‘canary in the well shaft’: if they display signs of the disease then treatment can be applied immediately to the vines before they actually show visible signs of infection.
Powdery Mildew is a fungal mould that attacks vines and fruit-trees. It is a very visible disease, spreading a translucent, cobweb-like growth around the infected area, which later sprouts greyish spores. To the eye, the mould looks like a powdery white ash or soot: hence its name. This disease affects all green parts of the vine and will reduce fruit set and ripening of the grapes. No wine is made from vines that become infected by the Powdery Mildew.
As a prevention of this disease an organic copper sulphate mixture can be applied to the vines. The roses in the Douro tell us when it is necessary to treat the vines and when not, ensuring minimum intervention. We also have an ally in nature. The dry climate of the Douro Valley helps to moderate the risk of fungal infections to the vines. But the risk is still there. Planting roses at the head of each row and at strategic places throughout the vineyards is a traditional Douro method of pre-diagnosing the presence of Powdery Mildew in the vineyard.
This means that we only apply the absolute minimum amount of treatment against the disease and only in a localized way when it is needed. Nothing is ever done en masse in the Douro. Less intervention with the vines and with nature, in our view, produces better wines that are more intense and better express their natural varietal characteristics and the uniqueness of our terroir.