Viticultures might be experts at vine training and pruning, but equally important is how well they control and reduce major grapevine diseases such as Black rot, Downy Mildew, Powdery Mildew, Pierce’s Disease and Grey Mold.
This aspect of vine management is vital as some diseases can be devastating; they can wipe out an entire vineyard. To ensure a bountiful harvest, viticulturists worldwide must be able to identify grapevine diseases and disorders caused by fungi, bacteria and insects early in the harvest, the only way to ensure a bountiful harvest.
Guignardia bidwellii/ Blackrot
The fungus Guignardia bidwellii causes Blackrot damage to all the green aerial parts of the vine and also the fruit, it’s a disease that favors warm wet seasons and affects most wine growing regions of the world. Blackrot, a native of North America made its way into France at the end of the nineteenth century and has since spread to various regions in the country.
The first symptoms of the disease appear on the leaves which become brown then black and hard. These hardened mummies eventually shrivel up, die and fall on the ground. The mummified berries on the ground can pose a problem for the following year as spring rains release the spores which result in secondary contamination of the new leaves and grapes.
To efficiently protect vineyards, it is vital to remove all mummies and to prune adequately during the dormant season. Effective vine management would include using fungicides just before or just after bloom.
This vine disease caused by the fungus Plasmopara viticola; it is common, severe, and detrimental to vineyards. Downey Mildew occurs primarily in areas which are warm and wet during the vegetative period; in the spring and early summer.
It affects all the green parts of the vines the leaves become white and dense on the surface once the fungus attacks. The underside of the leaf develops downy fungal masses as the mold grows.
The infected grape berries start showing signs of infection from early bloom are grayish in color.
Effective vine management of downy disease calls for the use of fungicides which may be used before the infection period acting as a preventive measure.
Erysiphe Necator / Powdery Mildew
This fungal disease attacks the aerial part of the plant, firstly the upper surface of the leaves start showing yellow blotches then as the infection develops, and a whitish grey powdery coating becomes noticeable. Powdery Mildew is caused by Erysiphe necator a parasitic mushroom that favors moisture and shade.
This is how The French National Institute for Agricultural Research (INRA) France’s describes the infected fruit
“As the fruit develops the berries are covered with powdery mildew which gives them a gray-green hue, their growth is slowed down, and their film becomes thicker and corkier.”
Vine management of Powdery Mildew?
Adequate sun seems to be the answer. INRA says that in areas of production where powdery mildew is chronically severe, it is often very tough to control the development of this disease in the vineyards and estates. In fact, only preventive chemical protection makes it possible to control it effectively.
Xylella fastidiosa/ Pierce Disease
Californian vine growers are familiar with Xyella Fastidioasa, the disease that has devastated Californian vineyards over the years. Southern California, for example suffered losses of around 35,000 hectares.
The bacteria which leads to Pierce disease first discovered by Newton Pierce in 1892 on Californiangrapes, is caused by vicious winged insects known as sharpshooters.
The leaf hopper once installed gets its nutrients from xylem, the water conducting system of the plant then starts infecting the leaves:these become red or yellow and eventually die.
The University of California agriculture and Resources (UCPM) say that progress has been made over the years in vine management of the disease. The report says that “insecticide treatments aimed at controlling the vector in areas adjacent to the vineyard have reduced the incidence of Pierce's disease by reducing the numbers of sharpshooters immigrating into the vineyards in early spring.”
Botrytis Bunch Rot / Grey Mold
The fungus Botrytis gives rise to two different kinds of infections on grapes. The first is grey mold, the result of consistently wet or humid conditions which can seriously affect the grapes.It is caused by frequent spring rain before ripening leading to infection. The shoots wilt or break off, and the grapes become infected through the damaged epidermis.
The entire cluster then gets damaged with noticeable grayish brown growth of the fungus. The tighter the cluster of the cultivar the faster the disease will spread. This decay results in high crop lost devastating, for the vineyard and the owners.
UCPM says that the disease can be controlled “By employing cultural control methods, properly applying fungicides, and using resistant cultivars when practical”
These are major diseases which have to be managed on a yearly basis, a challenging task for viticulturists. Today they have a better understanding of pest behavior and how to manage their estates , but most important is being vigilant, recognizing and implementing a plan of action to keep diseases at bay.