Drinking a glass of wine, we seldom think about the trials and tribulations that the winemaker undergoes to get that finished product into a bottle. Like other farming ventures, viticulture can pose real challenges. As if the slings and arrows of Mother Nature weren’t bad enough, there’s a whole host of diseases to contend with. And they can come in all sort of forms; viral, bacterial, fungal, phytoplasmic. Today, we’re going to take a look at a few of the most common problems winemakers face in the vineyard.
These diseases are caused by fungi which can be disseminated in a number of ways but tend to spread the most when it’s wet, humid and warm. They can be controlled through applications of fungicides and there are some organic and natural options available on the market.
Powdery mildew hits the leaves, shoots and stems of infected vines. It appears as a whitish dusting of powder (hence the name) and it leads to major reduced yields. Caused by Uncinula necator, a fungus which is native to the northeastern part of the United States, powdery mildew is found worldwide. How does it spread? The answer, my friend, is blowing in the wind – literally. Spores are carried vine to vine, leaf to leaf as the wind blows.
Like powdery mildew, downy mildew is caused by a fungus, in this case, Plasmopara viticola, which rides on the back of the breeze to infect vines. It can also spread via water; splashes of rainwater can spatter neighboring vines and before you know it, the disease is everywhere. Downy mildew thrives in warm, humid conditions as well and is another American vine disease that now exists across the globe. Leaves develop yellow, oily spots and results in the death of new growth and fewer bunches at harvest.
Ah, Botrytis cinerea. In the right condition, Botrytis leads to noble rot and some of the world’s greatest dessert wines. But when it’s bad, it can lead to major losses in the vineyard; Botrytis bunch rot is responsible for reducing yields across the world.
Viruses are particularly nasty. It’s not just that they reduce yields or affect the quality of grapes at harvest. They can also outright kill off vines and are quite tricky to treat. They’re typically spread by insect vectors or various bugs that carry the viral pathogen and infect vines when they take a chomp out of root systems, trunks, or shoots. Viral diseases can also be transmitted by using contaminated tools or grafting infected vines to healthy rootstocks.
Leaf Roll Virus
While leaf roll won’t kill grapevines, it severely hampers the ability to produce healthy fruit. Common problems associated with leaf roll afflicted vines include uneven growth and maturation, which means that at harvest, sugar and acid levels, color and bunch sizes, can be all over the map. Early symptoms of the disease are the eponymous rolled leaves and associated discoloration. It’s spread by grafting and mealybugs.
This virus is new on the scene and has winemakers worried, particularly in California where it has been showing up across vineyards in recent decades. Red blotch is characterized by large red discolorations on leaves. Issues with ripening run rampant; the grapes remain fairly acidic while sugars fail to develop properly. As far as researchers can tell, red blotch is spread through infected cuttings and grafts. What was once thought to be isolated primarily to California and Oregon seems to have spread East; vineyards in New York have been afflicted by red blotch. So far it has yet to spread across the sea and as a disease that can take time to show symptoms, it’s well-worth testing for before planting new rootstocks into vineyards.
Xylella fastidiosa the bacterial agent behind Pierce’s Disease has become a real problem for California-based wineries. Spread by the glassy winged sharpshooter, a type of leafhopper which feeds on the plant sap, this deadly bacterial disease has no known cure. Infected vines are unable to draw water which causes first the leaves, then the shoots, and ultimately the vine to die. Although it’s always been around in some capacity, Pierce’s has become a massive problem in the Golden State since the 1990s and was discovered in France a few years ago.
These are just some of the many, many, diseases that can affect grapevines. There are plenty of pests like the notorious phylloxera louse. Depending on where you are in the world everything from birds to kangaroos can be a problem for vineyards. And there are dozens of other diseases that afflict the vine. Grapevine yellows and flavescence dorée which are caused by phytoplasmas, Eutypa dieback, a bacterial disease that cripple some vines but can still allow for fairly concentrated wines to be made. It’s a never-ending battle that plagues winemakers the world over and makes you appreciate all the hard work that goes into making fine wine.