As for humans the vine is a living being, sensitive to its environment thus exposed to external threats. Besides frost, hail and other climatic occurrences, caused by humans or not, vine is exposed to different diseases. This is what I am going to talk about this time, vine’s diseases that have always been there more or less and that are going to increase with the ongoing climat change.
Vine’s diseases can happen at different stages of the vine’s life cycle and on different spots. In this way symptoms can be seen too late to prevent the disease and save the plant. Careful care is mandatory in the way the vineyard is managed but also in the selection of new plantings.
We all have in mind the Phylloxera crisis that destroyed European vineyards in the late 19th but I am not going to talk about it. I prefer to focus on other diseases as harmful as it and even worse for some.
Most part of the time the disease is from a bacteria or a fungi. Being unable to travel by itself they use a carrier, a kind of vehicle as insects. They contribute in their way to spread these diseases without being conscious of it.
The flavescence dorée:
Cicadelle is a small insect developing in warm and moderate regions. Being from North America it is quite inoffensive for the plant by itself but it is a vector of a major disease from the beginning of the 20th century called the flavescence dorée. This disease is the consequence of a bacteria that lead to the yellowing of the vine’s leaves. Consequently, it disturbs the photosynthesis thus health of the vine leading to a loss of productivity, fruit quality and finally death. Once in place this bacteria can spread really fast thanks to the cicadelle.
To stop the spreading careful care is established by nurseries treating young plants with hot water. Other means exist as chemicals, faster, more effective in their way but being chemicals, they also have collateral damages.
One thing is certain, once the disease being declared there is less chance to save the plant. It is common to dig it out and to burn it to kill the bacteria and to prevent any spreading.
Flavescence dorée is more and more seen even in area that used to be protected. Global warming plays an important role in this.
Grey and acid rot:
These two kinds of rot occur after an insect or a damage (hail for example) affect the fruit directly. When the fruit is wounded it is more likely that any kind of disease or fungi is susceptible to develop from the wound.
Grey rot aka Botrytis cinerea can develop after a caterpillar, called Eudemis, penetrate the fruit leading to an open door to fungi. Affected berries weaken rapidly especially in humid conditions. The same thing occurs when the drosophila fly lays its larvas inside the berry.
Acid rot is a consequence of the attack of this fly. Larvas give an entry point to fungi but also to acetic bacteria consequently to the oxidation of the pulp being eaten by it.
These two rots have the same consequence: yields reduction and loss of quality. A way to stop the spreading of it is to manage the development of Eudemis and drosophila fly. Sexual confusion is promising for the caterpillar and predator introduction quite effective for the fly.
This disease is less spread than flavescence dorée but it is quite worrying being extreme. It is another specie of cicadelle that is a carrier of a bacteria leading to the Pierce disease. When they eat the sap, insects inoculate the bacteria. Its action is as fast as the plant dies within one to two years. It creates a kind of plug within the sap system. The vine is unable to feed nor hydrate itself leading to its death by dehydration.
This disease spreads in regions where seasonality is low and not high enough. Indeed, cold winters that allow a real vine dormancy seems effective enough to stop the disease. Unfortunately, once Pierce disease is declared there is no way to save the vine. The only way is to prevent its spreading by acting on the vector as for the flavescence dorée.
You can easily guess that this disease is passed on by an insect that is called cochenille. This one infects the vine in winter as a larva placing itself underneath the vine’s bark. In spring it travels to the youngest parts.
This disease is not lethal directly but it highly decreases vine productivity and health. Indeed, the principal symptom is the rolling of the leaves (leafroll) that disturbs the photosynthesis and consequently sugar content, size, yield and maturation of the fruit.
There is no cure for this disease but some things can be done to prevent its occurrence and its spreading: selection of healthy plants and predator introduction to kill the cochenille. The fact of removing out from the vineyard woods from the pruning can also help.
Oïdium and Mildew:
It is maybe the most known diseases in the vineyard. Both are fungi from North America. They don’t lead to the death of the vine but decrease highly its quality and yields.
Oïdium is more susceptible to humid conditions and when there is a high diurnal range, it covers the vine with a fine white layer. Depending on its development stage the impact can be more or less harmful. If it appears soon after grapes have started to emerge it stops their development not only on their size but also on their colour (véraison). Grapes aromas are not good and the hypothetic resulting wine may not be of good quality.
Mildew is more susceptible to humid and warm conditions. It affects vine leaves displaying yellow oily spots at the back of it. This is the first stage. Then when the disease go through other stages white downy filaments can appear. If nothing is done leaves fall stopping the photosynthesis leading to a dramatic loss of fruit development.
The famous « bouillie bordelaise » was created to fight the spreading of the mildew. However, it is made of copper sulfate, a heavy metal, and has limits if used too late. Moreover, if used in excess it contaminates soil.
A high training system, away from the soil, to prevent leaves from the humidity; a clear vegetation to promote air circulation are some good ways to prevent these cryptogamic diseases to happen.
This is the most widespread wood disease. Besides it is one of the oldest vine diseases. It is quite brutal and exists in two variations: a « slow » one and a « lethal » one that can kill the vine in few days!
This disease infects the vine by pruning wounds or damages caused by hail or whatever. Fungi develop in these wounds and spread within the wood causing the stop of any vital flux inside the vine. In a way the vine is asphyxiated from the inside. Warm and dry period of time can be responsible of this « lethal » variation.
To mitigate the contamination tools used to prune must be carefully cleaned between each vine, pruning can also be performed later in winter when temperatures are at the lowest. Fast destruction of infected woods must be also done.
As you can see vine is not spared by mother earth and you also see that is not all about climatic risks directly. What is sure is that global warming has a key role to play in the spreading of some carriers and diseases. Winegrowers face more than ever all these changes and have to adapt now.
Gauthier Bernardo DipWSET