Vine in sickness and health. Is subject to so many ailments and pests that sometimes one wonders how it manages to survive at all. One Oregon vineyard lists its particular local enemies thus: ‘Crown gall, weevils, thrips, birds, bears, other critters.’ Another vineyard, this time in California, knows when the grapes are ripe because whole tribes of raccoons come and eat them. In Germany wild boar can be a problem; in Australia it’s kangaroos; in South Africa, baboons. Deer, rabbits and birds are universal predators on defenceless grapes. That is, of course, assuming that the grapes succeed in surviving downy mildew (which likes warm, wet weather), powdery mildew (which prefers dry weather), early bunch stem necrosis and grey rot, and that the vine manages to avoid black goo, Pierce’s disease, fan leaf virus, leaf roll virus and eutypa or ‘dead arm’ (after which d’Arenberg’s Dead Arm Shiraz is named), to name only a few.
Vine in sickness and health
Vine diseases can be bacterial, fungal, viral or phytoplasma; some are controllable, some preventable, some deadly. Some of the fungal diseases, including downy mildew, powdery mildew, anthracnose and grey rot, can be controlled with the use of fungicide sprays, of which Bordeaux mixture, a solution of lime, copper sulphate and water, is the oldest.
Virus diseases like fan leaf and leaf roll are spread either by cuttings or by nematodes in the soil. Even vines that are virus-free when planted tend to become infected – though they certainly stay healthier longer than young vines that have no pretensions to being virus-free. (As one Burgundian puts it, ‘You’ll stay in better shape if you go to Africa healthy than if you go there unhealthy.’) But then even the term virus-free is only relative: of about 20 identified viruses only six are really dangerous, and it is those of which virus-free vines are free. When it comes to the others, vines must take their chance.
Pierce’s disease, on the other hand, is a bacterial disease which kills vines fast. It is one of the main targets of national quarantine regulations, and is spread by an insect called a sharpshooter which has sadly little respect for national boundaries; the disease is so far confined to certain parts of the USA – including Napa, although it seems to be under control – and Central and South America, but while the blue-green sharpshooter is relatively manageable and home-loving and seldom strays more than 15m (50ft) from streams, the larger and more mobile glassy-winged sharpshooter, which originates in the Southern states of the USA, is beginning to encroach into Oregon, Napa and Sonoma, and is capable of spreading Pierce’s disease very fast and very efficiently. Sharpshooters are found in Europe as well. European growers are not looking forward to an encounter with Pierce’s disease.
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Other insects, this time leaf hoppers, spread flavescence dorée, one of a group of phytoplasma diseases known as grapevine yellows. This will kill young vines and weaken old ones, and is potentially even more destructive than phylloxera, partly because of the speed with which it spreads, and partly because there is no treatment. Northern Italy has suffered greatly from it; it is found in France, Germany, Switzerland, Australia, New York State and elsewhere.
The only route open to growers is to control the leaf hopper population; this can be done by spraying insecticide. But here one comes up against one of the main tenets of modern viticulture: that biodiversity is a good thing, that sprays of all kinds should be reduced as much as possible, and that it is desirable, where possible, to move in the direction of organic viticulture. Try telling that to the authorities in Burgundy who took a very quality-conscious biodynamic grower to court for refusing to spray against leaf hoppers because it would wreck his biodynamic status. Neighbouring non-biodynamic growers would be a lot more concerned about his pristine vines being a haven for the leaf-hopper, and thus a source of grapevine yellows infection. A cause célèbre that will recur.
It should also be noted that the role of all insects may not be fully understood. For example, we now know that yeasts are spread by wasps, which harbour Saccharomyces cerevisiae in their gut, passing it to the grapes when they bite into them. Birds and other insects can also spread yeasts; wasps also carry other microorganisms which they transfer to the grapes, and which can add flavours to the wine. And then there are ladybirds. Lovely things, ladybirds: they eat aphids and mealybugs, and may be encouraged by growers because of this.
Trouble is, if they get into the grapes at harvest, and into the presses, they produce IPMP (2-isopropyl-3-methoxypyrazine) which taints the wine with a bitter, herbaceous flavour detectable at about one part per thousand, and which is ineradicable. Ontario, in Canada, lost a lot of wine to ladybird taint in the early part of the century. Potassium metabisulphite seems to be an effective deter rent to the insects; otherwise it’s back to insecticides, which rather defeats the object.