Vineyard Most Wanted

The Top Issues Facing Grape Growers World Wide


There are a number of different pests and diseases that affect vineyards worldwide and each presents a different challenge depending on the climate and growing practices of that region. These viticultural criminals that affect grapevines come in several different forms including insects, bacteria, viruses, and fungi. To be considered a “most wanted” suspect they must have the potential to inflict severe economic impact on the industry in that particular region. The list below is by no means an exhaustive list however it does cover the top suspects.  
Phylloxera, a root louse, native to North America, is one of the major pests affecting vineyards world wide.  If left unchecked it will feed on the roots to cause severe nutrient deficiencies which will affect the photosynthetic ability of the plant leading to stunted growth, and slowed ripening eventually killing the vine.  Phylloxera currently affects Europe, North America, Most of South America, New Zealand and large parts of Australia.  
There are few treatments available to kill the root louse once it has been introduced and the best protection is to use a resistant rootstock that can withstand the damage caused by the louse’s feeding such as 3309 or SO4.  Fumigants such as Methyl Bromide were once used after the affected vines had been pulled out but now it is not always allowed by law and should not be taken lightly as it is extremely devastating to all soil life. The proven way to protect a vineyard, long term, from Phylloxera once it is found is by using rootstocks that are resistant to the pest when the vineyard is replanted.  
The European Grapevine Moth has been a common nuisance for European growers for centuries however for the new world it is a new threat that has just been discovered. The moth has three mating flights per season during which they will lay eggs in the clusters of grapevines. Symptoms of the infestation include webbing and orange headed larve present in the clusters. The third flight is typically the most damaging to vineyards as the larva will puncture the softening fruit to feed. This leaves the vine susceptible to secondary disease infections such as Botrytis which can cause color instability in the wine and Acetobacter which increases the level of volatile acidity in the fruit pre-fermentation. 
The European grapevine moth can be treated with several different methods.  Vineyards in Europe, use Pheromone capsules to disrupt the mating of the moths however both newly affected Chile and California have put in place aggressive plans to eradicate the moth completely.  California’s five year plan which began in 2010 included state-wide coordinated sprays with the pesticides Intrepid, Altecor, and Movento as well as Pheromone sprays.  According to Greg Clark of the Napa Valley Register, no moths were caught in 2014 and 2015 making this “one of the most successful eradication efforts of an agricultural pest in California history”.  This shows positive progress in the fight to eradicate the European Grapevine Moth from the New World.
Meanwhile Bordeaux is dealing with a crisis of its own in the Flavescence dorée.  Originally uncovered in the prestigious growing area of the Medoc, the Flavescence is a bacterial agent called Candidatus Phytoplasma vitis that has become problematic due to the importation of the Scaphoideus titanus leafhopper species from North America. The disease shows first symptoms through stunted growth, yellowing leaves, black pustules and inhibited lignification. The second season, the symptoms are more pronounced and can shrivel grape clusters after which the vine declines rapidly.  If not rapidly eliminated, this disease could be as devastating to Bordeaux as Phylloxera was due to its ability to kill a vine within 3 years of infection.  
The most effective method of controlling the Flavescence is through controlling the spread of the vector.  Currently Pheromone capsules can be used to disrupt the mating of the Leafhopper and rapidly removing any vines that seem to be showing infection helps reduce source plants.  For the Vitis grape species it is not curable once it is systemic in the vine and the best protection is to remove affected material quickly and prevent the importation of infected vines or the leafhopper from affected regions. The producers and growers of Bordeaux are working closely together to attack this issue immediately as this disease could be catastrophic.  
Another problematic disease currently affecting Europe is Esca.  This disease is the thought to be caused by a number of trunk diseases which causes stunted growth, discoloration of leaves and fruit, reduced yields, disrupted photosynthesis and in more severe cases total die off of the entire vine.  It is best known for a Tiger strip necrosis pattern on the leaves of affected vines.  Italy has had a particularly difficult time with the widespread infections.  Esca is not always catastrophic and the range of severity varies from region to region. Growers can find it difficult to maintain profitable yields when dealing with the disease.  
Once Esca has entered a vine it can not be cured so removal is the best treatment.  In the Piedmont wineries are combatting it through the removal of infected vines to reduce the spread of the infection. Esca can be controlled through the protection of pruning wounds and through hot water treatment of nursery stock to prevent spreading.  Esca can be very mild to deadly and it is important for vine growers to keep a vigilant eye for symptoms of the disease as early detection is critical.
There are several types of viruses that affect grapevines worldwide.  Leaf roll and Fan Leaf are the two most ubiquitous viruses and affect vineyards in Europe and across the new world.  Both cause deformation of the leaves of the vine and severely reduced yields although the viruses themselves rarely lead to vine death.  Leaf roll virus can be vectored by the grapevine mealybug or certain scale species and Fan Leaf virus is vectored by the dagger nematode, Xiphinema index.  Both viruses can be spread more widely by infected nursery stock.  Dr. Peter Cousins of the USDA works to breed nematode resistant rootstocks that will protect the vines from the spread of viruses as an infection can cause a major decrease in yields and profitability for farmers.  
The control of these diseases is closely linked with control of the vectors.  For Leaf roll viruses, controlling the population of grapevine mealybugs is very important.  Some vineyards in Napa Valley have taken to using dogs to sniff out the insects during the dormant period and treating affected vineyards with insecticides such as Movento or Applaud.  For Fan Leaf virus, it is important to make sure during the planting preparation that the manager has chosen a rootstock that is resistant to the dagger nematode species found in the individual country because resistance varies from rootstock to rootstock depending on the country.  For South African X. index, the rootstocks Freedom and Harmony were found to have the best resistance to the nematode.  For vines already infected with a virus, quick removal is the best option to minimize the spread.
More widespread perennial issues include fungal diseases such as Botrytis, Powdery Mildew, and Odium (Downy Mildew) which affect growers in most major vine growing regions.  These diseases can cause problems with fruit set, photosynthesis as well as fruit ripeness.  They can be mitigated by increasing airflow through the canopy, proper disposal of pruning material and reducing standing water as well as sprays of sulfur or fungicides such as Pristine or Kali-green.  Fungal diseases are particularly difficult in humid environments but they affect growers of almost every region.  The severity of the infection depends highly on the local climate.
Animals can also pose a threat to vineyards and should be monitored closely for damage that can impact the vineyard in negative ways.  Animals typically cause harm by eating the fruit. Problems can arise when they eat so much that yields begin to be significantly impacted or they cause widespread damage to the clusters which allow Botrytis or Acetobacter to move in.  Birds can be particularly damaging by pecking at the skin of the grapes.  Vineyards on the Central coast of California sometimes bring in full time Falconers to discourage birds through natural predators.  Animals must be managed so that the fruit can reach the winery safe and sound.
There are a variety of pests and diseases that affect vineyards worldwide including those outlined above and each comes with its own challenges for the vineyard manager. As viticulture is an agricultural based occupation, growers are at the mercy of nature and their environment however by remaining vigilant and reacting quickly to problems they will have a better chance of preserving the health of their vineyard.   

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