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dimanche, 04 août 2013

VITICULTURE IN CALIFORNIA

VITCULURAL PROBLEMS IN CALIFORNIA: BAD LUCK OR LACK OF WISDOM ?


Claude Gilois

Decidedly, California is the victim of bad luck or lack rigor. In 1993,  viticulturists and  scientists, after 30 years of usage, came to the conclusion that  rootstocks used for 70% the viticulture in California, AxR1 ( ARG1), a cross between Vitis vinifera and Vitis rupestris were not resistant to phylloxera. The rootstocks were certainly well suited to Californian climatic and geological conditions but their resistance to phylloxera was insufficient and, in the nineties, the vast majority of the Californian vineyard had to be replanted.  However…. the University of Davis, which was advising viticulturists to use these rootstocks had been warned by some of the French scientists ( and also by South Africans)   that experiments conducted with these rootstocks in the 1930’s has shown that this  crossing was vulnerable to phylloxera.

Only an exceptional decade in terms of quality  (1990-1999) and a buoyant worldwide economy were able to prevent a disaster for the Californian wine industry which was able to absorb such a major reshaping without blinking an eyelid.

phylloxera.jpg

 Phylloxera

Then Pierce disease appeared on the scene. Caused by a bacteria (Xyella fastidiosa) transmitted by the  glassy  winged sharpshooter it results in  the formation of a gel that block the transmission of water throughout the vine and causes the death of this  one  without 1 to 3 years. This disease was first seen in the Temecula Valley, est of Los Angeles and destroyed approximately 335 hectares of vines ( one third of the vineyard) between 1998 and 2000, which forced the authorities to treat   the situation  as  an emergency . Measures taken since then have managed to contain the spread of the disease to an acceptable level. However…. this disease  was not new to California. In the 1880’s , the disease destroyed 16,000 hectares of vine in the suburbs of Los Angeles near Anaheim.

 

SHARPSHOOTER.gif

Glassy  winged sharpshooter

And now it is another disease, just as insidious, which is looming on the horizon. It is called leaf roll virus. This disease is not new and is present in a number of vineyards throughout the world but it is mostly under control except in South Africa which has, so far, the highest incidence of contamination and prevents the country to have its  place in the leading countries of the New World for the production of fine wines.  For Deborah Golino, a plant pathologist and the head of the Davis Foundation of ‘Plant Materials Service’, leaf roll virus is beginning to become a major problem for the Californian viticulture. 

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Wine mealybug

Leaf roll disease causes grapes to mature later as well as  losses of colour and reduced yields. This is a complex viral disease and, so far, 9 different virus have been identified and the scientists think that the list will get longer as time goes by. The symptoms of the diseases vary and are more visible on the red varieties than on the whites. The most spectacular results of the disease can be seen in the autumn when the vine leaves turned red with a significant number of then curling onto themselves, hence the name of the disease which more difficult to identify on the white varieties. It also has  different expressions on different rootstocks and clones which make the disease even more difficult to identify. Ironically, it is the replacement of the AxR1 ( and St. Georges) rootstocks which caused an increase in the incidence of the disease as these two rootstocks show a greater resistance to the disease. To understand the problem, one has to identify the vector of transmission. In  is case it is  the mealybug of which six different species have been so far identified. It is of course the vine mealybug which is the most dangerous.

Aditionnal research in the Carneros Valley  has shown that the mealybug is not the only vector of transmission for the disease and like any virus infection, mutations can easily take place making the treatment even more complicated.

 

It appears that problem was caused by vines……. introduced illegally from Israel in the Coachella Valley (in between  Los Angeles et San Diego) that  contains this new strain of mealybug that is the cause of the spread  of this disease. If the delay in maturation and the reduced yields are the main consequences of the disease, the consequences on  long-term basis are even more devastating as  the vines become so unproductive that they have to be uprooted every 15-20 years and the vineyard replanted.  It takes 4-5 years to get  production going to a satisfactory level and economic loss is considerable resulting in higher price of the wine at the end of the line. The second consequence is even far more devastating as self regulated old vines, which usually produce the best wines,  do not exist (as in most part of South African wine regions) making the production of fine wine that much  more difficult.

A threat that will need  the same speed of response and on the same magnitude that the one adopted for Pierce disease.

One would have, however, expected higher standards in California.

 

 

 

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