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Grapevine trunk diseases: a larger problem than ever posed by phylloxera?

"Trunk Disease, a New Global Vineyard Threat" was the theme of my spring 2012 column. The PWV editor inserted a box called "California Input" written by Paul Verdegaal, University of California farm advisor. This comment on my column contains some familiar sentiments made by people around the world explaining poor performance of newly planted vineyards.

The "young vineyard decline" of some new vineyards in California was blamed on issues such as "improper planting, replanted vineyards, pushing vines to produce early, deficit irrigation" and extraordinarily "spur pruning" (hardly a new practice in California!), as perhaps contributing to the problem. These assertions may be true, but I for one am very skeptical and far from being convinced.

The question remains: Would these stresses be important if the young vines planted were healthy and not affected by trunk disease? Diseased plants usually are more susceptible to stress, trunk disease included.

I understand there remains a reluctance of some California nursery operators (and others worldwide) to admit that some of the vines they are selling can be infected with trunk disease, which can jeopardize the establishment and growth of young vineyards. Infected vines may not be fit for planting purposes!

My column followed up a text written by Dr. Doug Gubler and others from the University of California in the January/ February 2005 PWV, where they discussed grapevine trunk diseases in California. Most of the Gubler et al. content was about the then well-recognized Eutypa disease, but the end of the report included some new research about "Bot canker," caused by a group of Botryos-phaeriaceae fungi. A lot has occurred in the eight years since this report was published in PWV

Present situation in California

Gubler's Ph.D. student (by then co-author, Jose Urbez-Torres from Spain) and others published in 2006 an extensive survey of California vineyards aiming to identify the species of Botryosphaeriaceae associated with canker symptoms in California vineyards). (1) In the past, grapevine canker and consequent dieback symptoms had always been associated with Eutypa.

The 2006 survey was extensive, including 1,735 samples from 166 vineyards located in 21 counties. Botryosphaeriaceae species were found to be surprisingly widespread, being present in 148 of the 166 vineyards sampled, around 90%. In fact they were more abundant than the Eutypa dieback causal fungus Eutypa lata in the grapevine cankers tested. There were also seven Botryosphaeriaceae species discovered. The authors concluded that Botryosphaeriaceae may be a more important cause of grapevine dieback than was previously recognized.

Urbez-Torres and Gubler published a 2009 study of the pathogenicity of the nine Botryosphaeria species in California. (2) They showed that all nine species were able to infect both young and old vines, causing cankers, discoloration and streaking of the wood. However, there was a difference in virulence between the species from very virulent to weakly virulent, which indicates that the species of Botryosphaeria present in a vineyard may be a very important consideration. The most virulent species are Botryosphaeria rhodina (aka Lasiodiplodia theobromae) and Botryosphaeria lutea (aka Neoficsicoccum luteum).

A 2011 study by Orbez-Torres looked at susceptibility of grapevine pruning wounds to two of the more virulent strains of Bo tryosphaeria. (3) Experiments were done in the field using Chardonnay and Cabernet Sauvignon in the Napa Valley. Vines were pruned at different times and the pruning wounds inoculated or not, up to 84 days after pruning.

Results showed that pruning wound susceptibility was highest in November and lowest in March. Infection was highest immediately after pruning and declined with the age of the wound, but less so than for Eutypa. Based on this research and similar studies in California about Eutypa dieback, ideally growers should avoid wet weather when pruning to reduce risk of infection, but this is not always possible.

Other studies have confirmed that the trunk disease situation in California may be more serious than was previously understood. For example P.E. Rolshausen and others published a 2010 study of pruning wound susceptibility to grapevine trunk diseases. (4) The Botryosphaeria species tested had the highest infection rates of recent pruning wounds around 80%, and greater than Eutypa at around 30%.

These results highlight the potential threat of these pathogens if they become established in production vineyards. Very importantly, the authors also encourage the protection of pruning wounds for mother-vine source blocks used for plant material production in nurseries. These have been found worldwide to be the major source of contamination of young plants produced by nurseries. (12)

Investigations continue about the role of protective sprays for pruning wounds. The practice of "double pruning" developed at the Gubler laboratory enables growers with large acreage to reduce infection by Botryospluieria and Eutypa by a follow-up pruning in the spring with less rainfall.

Elsewhere in the world

More recent studies have shown the presence of significant trunk diseases in Arkansas and Missouri, due to 15 different fungi, by Urbez-Torres and others. (5) These were all new reports, and highlight that grapevine trunk diseases can affect grapevine health of inter-specific hybrids and vinifera.

In a 2009 study by Urbez-Torres and others,6 Botryosphaeriaceae fungi were the most common fungi isolated from grapevines affected with dieback in Texas. The highlight of this study was to show that Phomopsis was demonstrated as a trunk disease pathogen able to cause cankers. All fungal species tested were the first reported in Texas.

In the northeast U.S., studies published in 2013 have shown that two species of Phomopsis, and one of closely related Dia-porthe eres were responsible for wood cankers and pruning wound infestations. (8) Diaporthe eres has recently (2012) been shown as a grapevine trunk disease in Croatia. (9)

It is a similar picture in Mexico. Urbez-Torres and others in 2008 reported two Botryosphaeria fungi as the primary cause of grapevine dieback and canker formation, and confirmed their pathogenicity. (7)

An Australia study published in 2010 included a survey of 73 vineyards in two states and samples taken from 2,239 grapevines. (10) The most common species found was Botryosphaeriaceae, and species varied with region.

There is a survey by Orbez-Torres and others in British Columbia, (11) where growers and scientists have only recently (since 2007), become concerned about trunk diseases. They surveyed young and old vineyards in 2011, using 173 vineyards, and identified trunk disease as a previously unknown problem. All vineyards sampled showed trunk disease symptoms, including both young and old vineyards.

The situation regarding production of nursery vines is equally serious. The two Spaniards David Gramaje and Josep Armengol published an extensive 2011 review of trunk diseases in the propagation process. (12) They conclude that fungal trunk diseases are a major cause of young vine decline worldwide, which reduces productivity and longevity. These diseases may be called Black Foot or Petri ("Black Goo") disease, and a number of fungal species are involved. These are species of Cylindrocarpon, Ilyonectria, Pha-eoachremonium, Phaeomoniella, Cadophora and Botryosphaeriaceae.

Many investigations around the world have shown that the major problem is fungal infection of cuttings taken principally from diseased rootstock mother vines. Contamination spreads further during the propagation process, especially in water baths.

Such infections can be avoided by using hot water treatment (HWT), as is employed by a couple of Australian nurs-cries. Why is it not more widely used? Nurserymen around the world are frightened of the process, but new research has produced safer protocols. There is an urgent need for more international research on HWT, so that the process may be more widely adopted. HWT and replanting of rootstock mother vines and preventing their infection will largely overcome the problem of selling trunk disease-infected vines.

I lid What can we conclude from all this?

* There has been much research activity since 2005, in California and elsewhere, which demonstrates that trunk disease by Botryosphaeriaceae is a widespread, typically misdiagnosed and an unrecognized problem before recent studies listed above.

* Some diseases, especially Botryosphaeria, can be virulent pathogens. They spread by infecting pruning wounds, which they do more successfully than does Elitypa. Botryosphaeriaceae is presently very widespread in California, found in around 90% of vineyards tested. (1)

* Worldwide, there is a serious problem with infected grapevines produced by nurseries, which causes early and enduring mortality, uneven establishment and variable vineyards. Further, infectious diseases such as Botryosphaeria dieback can infect healthy vines and the economic viability of vineyards can be threatened.

My take on all of this

* I can find no reference to recent extension activities on trunk diseases. There seems much less research on trunk disease than 10 years ago. I reviewed the American Vineyard Foundation-funded projects for 2013-14, 2012, 2011 and 2010, totaling 95. Of these, 42 were related to grapevine pests and diseases including breeding, and of these only two were about grapevine trunk diseases.

* Of the NationalNational Grape and Wine Initiative research programs under way in 2013, one of the 10 is about trunk diseases. A multi-crop (grape, pistachio and almond) project was funded in 2012 to tackle trunk diseases, Dr. Themis Michailides (UC Davis-Kearney in Parlier) and Dr. Kendra Baumgartner (ARS) pulled together a trans-disciplinary team to develop diagnostic tools and, eventually, measures to reduce the impact of diseases including Eutypa and Botryosphaeria. The research will cover wine grapes from five different regions and table grapes from two regions.

* Why is there not much written about trunk diseases in California now, in magazines such as PWV, nor discussed at conferences, as occurs elsewhere in the world? I note that "red blotch" is to be discussed at the January 2014 Unified Symposium, but not trunk diseases.

However, the Lodi Wineg rape Commission held a 2011 conference about trunk diseases, and another is scheduled. An outstanding presentation by Gubler and others is available on their website, with wonderful photos of symptoms. Lodi links are: lodigrowers.com/ guide-to-managing-vineyard-trunk-disease-in-lodi/ and lodigrowers.com/eutypa-dieback-in-n orthern-ca liforni a-vineyards-part-ii-of-ii.

* Maybe trunk diseases are not an issue in young vineyards anymore. Has "young vineyard decline" declined, and disappeared? Has concern for "red blotch virus" and "mealybug spread of leafroll virus" dominated disease thinking? Both are obviously serious issues, and worthy of attention. I believe grapevine trunk diseases are certainly more widespread. Concern raised by consultant Lucie Morton about "Black Goo" (Petri) disease in California in the 1990s led to the eventual formation of the International Council of Grapevine Trunk Diseases (see icgtducr.edu), which held its eighth international meeting in Valencia in 2012.

* California growers do not think the trunk disease issue unimportant. A 2012 poll of AVF members found that trunk diseases were the third highest viticulture research topic, ahead of leafroll virus (fifth) and mealybugs (11th), from a total of 22 presented.

* I speak here of California, but the U.S. wine sector is more than California. What about other U.S. wine-producing states? I ask the same questions about health of young and old vineyards, and research and extension efforts.

* Somewhat like Jose Urbez-Torres, I find trunk disease, especially Botryosphaeria, wherever I travel. This was most recently in Japan, on both young and old vines, and both Botryosphaeria and Diaporthe eres were found, the latter two on the island of Hokkaido. Again, the diseases were not previously described, and the death/decline was put down to old age or winter damage.

Might I have trunk disease in my vineyards?

American grape growers may well ask this question.

Let me list typical symptoms in mature and young vineyards, another column with photos is obviously required.

For mature vineyards, common symptoms are:

* Dead arms or whole vines. Often they were winter-pruned but fail to grow in the spring. They are often in patches, contiguous in vine and tractor row. These patches gradually grow. New symptoms can occur on isolated vines down-wind, spread by spores

* Trunk cankers and internal staining/ dead tissue are common.

* Staining at the base of last year's spur may be seen.

* Sometimes early season shoot growth is inhibited, and in late season the vines may show mild chlorosis and apoplexy, the latter with wilting of shoots and fruit.

For newly planted vineyards, the symptoms are:

* Vine growth will be variable in the first year, and in general, some vines will fail to thrive. This variability will continue for the life of the vineyard, and the least vigorous vines will die first.

* Poorly performing vines, and even some healthy ones, may show internal staining. This may be black (indicating Phaeomoniella, Phaevachremonium or Cylindrocarpon) or light brown (Botryosphaeria). The staining may be seen at the rootstock base, or under the graft union, or above the graft union.

* Some vines may not grow, others may fail in the first year, and some fail to grow during spring in following years. Depending on the degree of initial infection, "clumps" of infected vines may appear in subsequent years.

Conclusion

My review of recent research presented here, my other reading and widespread vineyard observations suggest to me that the vine and wine world may be facing a new disease crisis, which can be compared to phylloxera in the late 19th century.

American readers may have a different perspective about phylloxera than vine growers elsewhere in the world. Why? Because phylloxera is native American, as are downy mildew and powdery mildew (Oidium). These two fungal diseases and the insect pest phylloxera almost brought European viticulture to its knees by the 1890s.

The situation for phylloxera was resolved eventually by grafting to native American vines, or their hybrids, as rootstocks. This is now a world-wide practice. The phylloxera problem was solved because a source of genetic resistance was found.

Now compare phylloxera and trunk diseases. Both are vine killers--in fact phylloxera the more quickly. Trunk diseases spread more slowly and are insidious; that is why they have escaped observation for so long.

I would guess that trunk disease is more widespread now than phylloxera. Remember that phylloxera is limited by quarantine in Australia, and most vineyards are own-rooted; Chilean vineyards are all own-rooted. So phylloxera is not everywhere, as in Washington state.

There is a cure for phylloxera which is cheap, environmentally friendly and sustainable: That is grafting to resistant rootstocks. There is no such cure for trunk diseases. There are no known sources of genetic resistance. We also have a situation where the majority of the world's nurseries are spreading trunk diseases; that is not the case for phylloxera.

These problems with trunk disease are not insurmountable. They can be overcome, as was phylloxera. The "cure" for trunk diseases will involve removal of infected vines, replanting with healthy material, and likely some pruning-wound treatment. Developing a cure will require increased recognition by growers and regulatory authorities and more research.

Final words about two paradoxical situations

One of my overseas clients is importing "high health" virus-free grafted vines from California. The photos (page 9) show trunk disease symptoms, but the California nurseryman assures my client there is "nothing to worry about."

Humbug!

The second paradox also involves imported vines. Growers in the UK, where I now live, import "virus-free" but trunk disease-infected grafted vines that typically grow very poorly. The UK growers could much more cheaply propagate own-rooted vines, as they do not have phylloxera in their vineyards! But they are told (by the nurseryman's agents!) that they need rootstocks. Humbug! I hope this column helps raise some awareness about trunk diseases. To solve the problem first requires recognition. I would be pleased to hear from others who might share my view, and may be concerned about the insidious spread of trunk diseases in North American vineyards.

Production practices have changed (including spur-pruning in various trellis systems), varieties have changed, chemical controls are different, according to Paul Verdegaal. "Arse-nite took care of a lot of problems. as did copper, lime sulfur, parathion, weed oil, etc. Propagation methods have gone more to centralized nurseries.

"During the last planting boom there was undoubtedly lots of poor quality (and/or infected) wood used for propagation to meet the demand. Nurseries are more careful now (maybe more care is needed?), and growers are more careful, but problems persist. Agricultural bankers like to see full production sooner rather than later. Legally or otherwise, plant material is moving faster and farther than ever before.

"We do have a relatively dry climate in California, compared to many other areas of the U.S., and other more traditional districts in the world, but also areas such as Missouri, Arkansas, Pennsylvania, Michigan, Kentucky, even New York, etc. are only beginning to see local commercial vinifera vineyards and wine-growing districts 'mature,' and with that more problems.

"We have limited chemical options right now with Rally, Topsin M, BrotoMax and VitiSeal. They cost money, require timely access; they and their application all come under regulatory scrutiny. Late pruning and/or cane pruning, with shoot thinning and reducing number and size of cuts if possible, along with protectants are standard suggestions. Variable weather patterns and the diverse array of pathogens make for a complex problem and don't make management easy or cheap."

Caption: Trunk disease symptoms in a one-year-old grafted vine exported by a California nursery.

"I agree that we do not have enough information as how to prevent Bot canker in existing vineyards--what matters most to growers," says Steve Thomas, vineyard manager at Kunde Family Estate in Kenwood, Calif. "We rely on the expensive painting of pruning cuts in 550 of our 600 vine acres in Sonoma Valley. We spend about $150 per acre painting cuts with paint plus a fungicide. We feel this is worth the expense to extend the life of the vineyard."

"In my experience, canker diseases are seldom misdiagnosed or unrecognized," says Paul Verdegaal, UC Extension farm advisor. "They are, however, sometimes ignored for one of two reasons: either the impacts of the disease are not fully appreciated or, more commonly, growers are uncertain as to how to best manage infected vineyards."

In writing this column, I acknowledge the excellent scientific work of Dr. Jose Urbez-Torres and his Spanish colleagues David Gramaje and Jos ep Armengol. Were it not for Dr. Doug Gubler of LIC Davis and his Ph.D. students, our knowledge- of grapevine trunk diseases in the U.S. and contiguous countries would not be nearly so complete. Congratulations to all of you! I would also like to acknowledge the helpful reviews made on drafts of this column by Don Neel, Steve Thomas, Paul Verdegaal, Lucie Morton and Jose Urbez-Torres. However, I take responsibility for the final text.

Bibliography

(1.) Urbez-Torres, J.R., G.M. Leavitt, T.M. Voegel, W.D. Gubler. 2006 "Identification and distribution of Botryosphaeria spp. associated with grapevine cankers in California." Plant Dis. 90: 1490-1503.

(2.) Urbez-Torres, J.R., W.D. Gubler. 2009 "Pathogenicity of Botryosphaeriaceae species isolated from grapevine cankers in California." Plant Dis. 93: 584-592.

(3.) Urbez-Torres, J.R., W.D. Gubler. 2011 "Susceptibility of grapevine pruning wounds to infection by Lasiodiplodia theobromae and Neofusicoccum parvum." Plant Pathology 60: 261-270.

(4.) Rolfshausen, P.E., J.R. Urbez-Torres, S. Rooney-Latham, A. Eskalen, R.J. Smith, W.D. Gubler. 2010. "Evaluation of Pruning Wound Susceptibility and Protection Against Fungi Associated with Grapevine Trunk Diseases." Am. J. Enol. & Vitic. 61: 113-119.

(5.) Urbez-Torres, J.R., F. Peduto, R.K. Striegler, K.E. Urreo-Romero, J.C. Rupe, R.D. Cartwright, W.D. Gubler. 2012 "Characterization of fungal pathogens associated with grapevine trunk diseases in Arkansas and Missouri." Fungal Diversity 52: 169-189.

(6.) Urbez-Torres, J.R., P. Adams, J. Kamas and W.D.Gubler. 2009 "Identification, Incidence, and Pathogenicity of Fungal Species associated with Grapevine Dieback in Texas." Am. J. Enol. & Vitic. 60: 497-507.

(7.) Urbez-Torres, J.R., G.M. Leavitt, J.C. Guerrero, J. Guevera, W.D. Gubler. 2008 "Identification and Pathogenicity of Las iodiplodia theobromae and Diplodia seriata, the Causal Agents of Bot Canker Disease of Grapevines in Mexico." Plant Dis. 92: 519-529.

(8.) Baumgartner, K., P.T. Fujiyoshi, R. Trevadon, L.A. Castlebury, W.F. Wilcox, P.E. Rolshausen. 2013 "Characterization of Species of Diaporthe from Wood Cankers of Grape in Eastern North American Vineyards." Plant Disease 97: 912-920.

(9.) Kaliterna, J., T. Milicevic, B. Cvetkovic. 2012 "Grapevine Trunk Diseases

Associated with Fungi from the Diaporthaceae Family in Croatian Vineyards." Arh Hig Rada Toksikol. 63: 471-479.

(10.) Pitt, W.M., R. Huang, C.C. Steel, S. Savocchia. 2010 "Identification, Distribution and Current Taxonomy of Botryosphaeriaceae Species associated with Grapevine Decline in New South Wales and South Australia." Aust. J. Grape Wine Res.16: 258271.

(11.) Urbez-Torres, JR., P. Haag, P. Bowen, and D.T. O'Gorman. "Grapevine Trunk Diseases in British Columbia: Incidence and characterization of the fungal pathogens associated with black foot disease of grapevine." Plant Disease (In press) dx.doi. org/10.1094/PDIS-05-13-0524-RE.

(12.) Urbez-Torres, J.R., P. Haag, P. Bowen, and D.T. O'Gorman. "Grapevine Trunk Diseases in British Columbia: Incidence and characterization of the fungal pathogens associated with Esca and Petri diseases of grapevine." Plant Disease (In press).

(13.) Gramaje, D., J. Armengol. 2011 "Fungal Trunk Pathogens in the Grapevine Propagation Process: Potential Inoculum Sources, Detection, Identification, and Management Strategies." Plant Disease. 95: 1040-1055.

Dr. Richard Smart is rewriting and thoroughly revising "Sunlight into Wine." He is happy to receive statements from growers and win makers about their commercial success with various aspects of canopy management. Interested persons should contact Dr. Smart by email at richard@smartvit.-com.au. Dr. Smart visits the U.S. frequently, and consulting appointments also .can be made by email. See smartvit.com.au.
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Title Annotation:SMART VITICULTURE
Comment:Grapevine trunk diseases: a larger problem than ever posed by phylloxera?(SMART VITICULTURE)
Author:Smart, Richard
Publication:Wines & Vines
Geographic Code:1U9CA
Date:Jan 1, 2014
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