The Rise Of Grapevine Trunk Disease

Ξ December 21st, 2011 | → 0 Comments | ∇ A Day at a Time, Herbicides, Wine News |

Greybeard writes…
 
Vine Diseases are not my specialist subject, in fact before last week I knew practically nothing about them, but for some reason a casual reading of a blog post from Jim Budd set me off on a major tangential internet sortie.
 
Jim’s post was entitled “Bourgueil and Saint Nicolas de Bourgueil: the fight against eutypiose, BDA and esca”, and it was Bourgueil that hooked me, since I spent 10 wonderful days in that quaint Loire town in 2006 on a family holiday (which explains my fondness for Cabernet Franc). The fact that most of the piece was a transcript of a French article almost dissuaded me from continuing (I am nowhere near fluent in the language) except for an intriguing picture of a dying vine and Jim’s reference to “Fatal Wood Diseases”. I therefore clicked on the link to Vitisphere.com.
 
The post begins describing the disturbing development of ESCA, BDA (Black Dead Arm) and Eutypiose since the ban on the use of the controlling chemical Sodium Arsenite a decade ago. The accompanying picture shows a necrosis (canker) caused by Eutypiose.
The local viticultural body, FAV37 (la Fédération des Associations Viticoles d’Indre-et-Loire et de la Sarthe) completed a study in 2010 showing that in Indre-et-Loire alone damage from these diseases came to €12-14 million ($16-18 million) and are increasing their activities to dispose of the dead and diseased wood to try and prevent the spread of the disease.
 
The piece finishes stating that 30-40,000 vines were collected by a Chinon based wood company to recycle as barbeque fuel, but that this was only a small part of all the vines that actually died this year – a sobering thought.
 
So that was the story, but all it did was raise more questions than it answered; what exactly are the three diseases mentioned?; what causes them?; how prevalent are they?; Apart from a brief mention of sodium arsenite what else is being done to combat the disease other than making barbecue fuel?
The more sites I visited in trying to answer these starting questions, the more secondary questions (plus some ambiguity & contradiction) appeared, which sent me into yet more searches which eventually spat me out after 2 days with a glimmer of understanding and enough words to put together this piece – even though I may never get firsthand exposure to the topic.
 
The Diseases:
Eutypiose (Eutypiosis) is the French term for Eutypa dieback, first identified in the 1970s and since confirmed worldwide (Californian losses to the disease are estimated in excess of $260 million a year). The disease is caused by infection with the fungus Eutypa lata which results in stunted development and internal V-shaped necroses and external cankers. Leaves may show chlorosis, deformations and tattered edges.
In the 1970s the disease Dead Arm, made famous to consumers by the d’Arenberg Dead Arm Shiraz, was identified as really being two diseases, with the combined symptoms of Eutypa dieback caused by Eutypa lata and those of Excoriosis (Phomopsis Cane & Leaf Spot) caused by the different fungi Phomopsis viticola.
 
Black Dead Arm (BDA) is caused by yet another fungi, or to be accurate several species of the Botryosphaeriaceae, first described in 1974 in Tokaji, Hungary – giving the diseases alternative name of Botryosphaeria (Bot) canker. Over 12 species have been isolated from diseased vines globally and, while early research believed they were opportunistic pathogens that only caused symptoms in stressed vines, the current data suggests that certain strains are strong primary pathogens.
Symptoms include V-shaped necroses similar to those caused by Eutypa lata, brown necrosis along the length of the affected tissues. Confusingly, occasional stunted growth, leaf discolouration and damage adds to the similarity with Eutypa dieback, meaning the two diseases are often difficult to accurately diagnose.
In France the disease was also known as d’apoplexie lente (slow apoplexy) prior to its classification as BDA in the Medoc in 1999.
 
Esca (La Yesca in Spain) is another complex disease with variable symptom expression. Although first classified in Italy in 1900 it seems to have been around much longer with similar symptoms described in medieval works such as the influential Arabic agricultural tome Kitab al-Felahah by Ibn al-Awam, a 12th Century Moor from Seville, and earlier Latin and Greek texts. The name is Latin for food or bait (used by several Italian restaurants around the world including New York) and may be a reference to the fruiting bodies of the fungi responsible resembling bait lures as they sprout from the wood. A Wine Spectator article from 2008 reported that 5% of the vineyard surface area in France was affected by Esca, although later reports suggest that by 2010 this was as much as 10%.
The fungal pathogens are Phaeomoniella chlamydospora and various species of Phaeoacremonium which cause chronic symptoms of stunted growth, shoot tip dieback and internal wood decay of the trunk and larger branches. Leaf necrosis results in a “tiger stripe” pattern while berries show dark spots or “measles”, leading to the disease’s alternative name of Black Measles.
 
Primary symptoms predispose the vines to wood (white) rot caused by higher fungi such as Fomitiporia punctata, Fomitiporia mediterranea and Stereum hirsutum.
 
Esca affected vines may show chronic symptoms one year and the next appear perfectly normal, but the disease will reappear, each time causing an overall decline.
Eventually an acute form of the disease called vine apoplexy occurs, typically in mid-summer when rainfall is followed by hot, dry weather, where rapid withering of apparently healthy leaves and the death of vine organs, including grape clusters, happens in only a few days – the vine usually dies in the same year.
 
The main feature in common with all these diseases is that they affect vines at least eight years old or that may have been subjected to stress. It is clear from reading the reports and research papers that there isn’t always a clear diagnosis because of the similarities in symptoms; V-shaped necroses; longitudinal brown streaking in the stems; leaf chlorosis and patchy discolouration; stunted shoot growth; external cankers. In the absence of one exclusive diagnostic indicator much of the disease reported in the vineyards is probably a combination of two or all of the above.
 
It is also worth mentioning Petri Syndrome, named for Italian Lionello Petri who first published the symptoms in 1912. Also known as Young Vine Decline (Young Esca) the primary infectors of Ecsa, Phaeomoniella chlamydospora, Phaeoacremonium inflatipes and Phaeoacremonium aleophilum come together to cause disease in younger vines of 2 or 3 years. The disease stunts growth and leads to tissue decay with leaf chlorosis and necrosis. Internally, black spots or streaks are seen in the xylem tissues and the sap of infected plants can turn dark brown or black, giving the alternate disease name Black Goo.
Although common around the world this disease has been heavily researched in California since the late 1990s due to the high economic impact and the realization that infected nursery stock was the main source of diseased vines – vines pulled up for whatever reason were being replanted with plants already inoculated with the causes of the disease.
 
It would be easy to continue veering off into new areas by including other diseases such as Syrah Decline, Phomopsis or Black Foot, however the causes and mechanisms of these diseases are different or, in the case of Syrah Decline, still not fully understood, so we’ll put them to one side, at least until the end.
 
The Causes:
The key pathogens described above are all species of Ascomycetes (sac) fungi which produce spores in sacs (asci) which develop until the pressure within the asci shoots the spores out. Direct spore dispersal is up to 30cm but they travel further due to rain splash and wind – Eutypa ascospores are known to be able to travel as far as 30 miles (50km).
The exceptions are the Basidiomycete (higher) fungi such as Fomitiporia punctata, Fomitiporia mediterranea and Stereum hirsutum involved in Ecsa white rot, arguably a secondary symptom of the chronic form of the disease.
 
With BDA, Ecsa and Eutypa dieback fungal spores colonise the vine through open wood vessels, the result of pruning, frost, mechanical or graft wounds – although an Australian study shows that soil-borne infection should not be ignored. The spores develop, invading the xylem vessels where fungal growth results in the interruption of sap-flow which may induce a host defense reaction, resulting in further blockage. Wood necrosis and rot impairs the flow of nutrients leading to vine decline and slow death, while fungal phytotoxins weaken the vine causing associated symptoms.
 
Petri disease is more likely due to nursery vines infected by the fungi prior to planting, as opposed to infection through wounds, but the effects are similar.
 
Disease Management:
There is no reliable means of eradicating a pathogenic fungus once it becomes established within a vine, so removal of diseased wood or the entire plant is necessary (remedial surgery with disposal or burning of the wood debris). The best control is to protect vines from infection in the first place, but this can be challenging since the fungi are common in nature and considering the number of wounds made on each grapevine in a year with the extended period of wound susceptibility (which, for E. lata, is up to 7 weeks from pruning and greatest in early winter).
By timing any pruning as late as possible in the winter/early spring (Feb/Mar in the Northern Hemisphere) sap is flowing more freely which helps with wound healing. Spore release from infected vines is closely correlated with rainfall so new pruning should be avoided until at least 36 hours afterwards. Prof. Doug Gruber of UC Davis has championed a double-pruning technique where initial mechanically pruning leaves long spurs in early winter followed by hand-pruning to short spurs in late winter.
Application of fungicidal wound protectants in spray, paint or paste form should prevent fungal access through pruning wounds. Although spray-on liquid formulations are easily washed off with rainfall they are more feasible in large vineyards since application of paint or paste is labour intensive and only economically viable for high-value vineyards. However, which chemicals to use is the subject of intense research and contentious debate.
 
A 2009 study showed that Topsin M, aka thiophanate-methyl, was the best overall product across the Ascomycetes – yet a mixture of active ingredients is more likely to handle the spectrum of different fungi found in the vineyard.
 
Different cocktails reported include;
MBC fungicide (Benomyl, Carbendazim, Topsin M) & chlorobutinol
Biopaste (boric acid), Garrison® (cyproconazole and iodocarb) and Topsin M
Carbendazim & prochloraz (-manganese)
ATCS® acrylic paint (alone or mixed with Bavistin® or boric acid)
 
The biggest likely problem is that many of these fungicidal chemicals are likely to be removed from the market due to environmental and human health concerns, as happened with Sodium Arsenite (the only product that kept all main disease symptoms in check). This carcinogen was banned in Europe in 1991 (with extensions for Spain, France and Portugal until 2003), a fact that French viticulturalists claim is the direct cause of the relentless increase in Grapevine Trunk Disease over the last decade and has some calling for its re-introduction.
 
In reality biological & ecological control methods may be the only long term options available to growers, something which is starting to become understood.
Biological control agents include the fungi Trichoderma and Fusarium lateritium and the bacteria Bacillus subtilis, which have been shown to control infection by E. lata in trials, although results were variable. Researchers are also looking at garlic extracts and lactoferrin as wound protectants.
Biological control agents available today are based on Trichoderma species: BioTricho®, Eco-77® (both based on single strains of Trichoderma harzianum) & Vinevax®™ which is based on a mixture of five strains of T. harzianum and T. atroviride. Another agent, Trichodex® (Trichoderma harzianum T39) is also used as a treatment to prevent Botrytis cinerea (grey rot).
 
Some strains of Trichoderma work better than others, and are more effective on some varieties, such as Chenin Blanc, compared to others, such as Cabernet Sauvignon & Sauvignon Blanc. This may be why the French report poor results with Trichoderma as both these grapes seem more susceptible to Esca, BDA and Eutypa dieback (with Merlot and Semillon less so) and may be why Esca is especially prolific in southwest France and the Loire.
 
For Petri Syndrome then treatment to account for possible nursery stock infection is advised. Hot Water Treatment (HWT) at 50°C (122°F) for 30 minutes & then cooling to 2-3°C (36-37°F) for rootstock and scion wood is effective in controlling Phaeomoniella. This is similar to the method oif controlling Black foot Disease.
 
Also I came across tales of more organic remedies that are worth recounting. The first was from a Loire grower who uses companion plants (wild leek, Allium ampeloprasum) to “re-mycorhize the under-soil” which he believes has been sterilised by over use of the weed killer Roundup. In the Wine Terroirs article “Experimental cure of Esca in the Loire” the grower, Didier Barrouillet, claims he has seen vines recovering from esca.
In the same vein the 7th International Workshop on Grapevine Trunk Diseases, held in Chile last year, reported some success using soil bio-fumigation with mustard (Brassica juncea). Although used here for Black Foot Disease research the idea of bio-fumigation, using companion crops or “green manure” from Brassica species looks to be bearing fruit (!).
 
Discussion:
Those last two topics brings home the message to me that viticulture at its simplest level is only agriculture, and growing anything in the soil requires a healthy respect for that soil and the complex eco-system it harbours – something that the ever increasing use of pesticides, fungicides and herbicides can only disrupt.
 
The pathogens and symptoms of Grapevine Trunk Diseases mirror this, it would be wrong to fixate on a single cause or cure when they are a complex interaction of numerous fungi acting on genetically distinct sets of vines. A vine can, and probably does, become infected by multiple pathogens many times and while susceptibility to the effects of BDA, Ecsa and Eutypa dieback varies between grape varieties there is no sub-species of Vitis vinifera that is immune.
 
I should also reiterate that during my time reading and re-reading the different papers and presentations I encountered repeated ambiguity & contradiction both on disease naming, symptoms and causes. I endeavoured to filter through the pages to ensure as much consistency as possible, but I have no doubt that the current view of these diseases is still incomplete with more interactions awaiting to be discovered. Syrah Decline is a case in point – but I’m not going to go down that tangent just yet!
 
Slainte!
 
Greybeard
 
Additional reading:
Grapevine Trunk Diseases in California and Control Strategies (UCD Presentation)
 
Emerging diseases of vine in the central part of Spain, Vicente González and María Luisa Tello, of the Madrid Institute for research and Rural Development, agriculture and food (Imidra)
 
Abstracts from the International Workshop on Grapevine Trunk Diseases (next in Valencia, Spain, 18-21 June 2012)
 

 

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