Disease biology / life history
Michael White
Are most of these fungal diseases endophytes?
Most of the canker causing fungi (Eutypa, Botryosphaeria, Phomopsis) are what we can consider true pathogens. There are several Botryosphaeriaceae species that can also act as endophytes or latent pathogens. The latest research we have done testing nursery material indicates that in many occasions, species of Phaeoacremonium, Phaeomoniella and even Cylindrocarpon can be isolated from asymptomatic material so they could be considered endophytes or I like better the term latent pathogens.
Mark Hart
Are many of the fungi associated with trunk dieback secondary invaders?
Yes, most of the basidiomycetes fungi involved in the esca complex are secondary invaders
And if so, comment on differentiating between infection between primary infection mortality and secondary infection in a vine weakened by other necrosis in xylem tissues. Assigning mortality &impairment to a primary cause is important to vineyard management. Incidence surveys don’t address this.
The problem with this diseases is that won’t cause direct mortality just after infection. When spores infect pruning wounds it can take several years to actually see symptoms (cankers) and consequent dieback and mortality. During that time, other secondary fungi can colonize. We do not really know if the action of secondary fungi will enhance infection and mortality. What we know is that and infected plant will eventually die but because of the complexity of the disease and the many different fungi involved we cannot know exactly when that will happen. So when I said that from our surveys in BC we estimated over 10% of planted vines are infected, those will eventually die. Not sure if I completely understood your question but please feel free to contact me again for any clarification needed.
Piero Spada
How often is GTD multifaceted with multiple pathogens responsible for vine collapse vs. a single predominant pathogen?
Really good question. Usually we isolated more fungi involved in the decline the older the vines are, which makes sense since more organisms have had the chance to infect. Also, canker symptoms usually yield one or two main fungi, while xylem necrosis usually harbors a widest variety of fungi. However, very interestingly, we have observed throughout the research and field surveys that this is also region dependent. If you go to South Australia regions of the Barosa and Mclaren valleys the majority of infected vines only present Eutypa dieback caused by Eutypa lata. If you move to the Hunter Valley region in New South Wales, you will find most of the vines with cankers will have mix infections of Bot and Eutypa. Similarly in California. Here in BC we try to find more than one fungi associated with symptoms.
I would say it is a mix of sometimes single pathogens and in many occasions several fungi associated with the symptoms,which will depend on region, age of the vine, and symptoms observed.
Richard Smart
What is the role in recent spread of infected planting material from the nurseries? Many studies suggest that bench grafting leads to infection, which became popular since 1980.
We know and it has been well-demonstrated (as I documented in the webinar) that many of these fungi can be found in the nursery planting material. However, and this is entirely my opinion, in the case of planting material, the detection of the pathogen does not mean that plant is sentenced to death. Based on research conducted, when we see that over 90% of planting material has Cylindrocarpon species (caused of black foot) or over 80% of the plants will host Phaeomoniella chlamydospora, if having those pathogens means the plant will die, we won’t have viticulture anymore. We found these pathogens in asymptomatic tissue as well so I am of the opinion that there is an abiotic cause that can trigger these fungi to become really virulent. Of course we have seen very bad nursery material but there is also better and worse material regarding viruses as well.
With regard the bench grafting, I have not seen any scientific data that conclude that (we can suggest or hypothesize many things). What it is true is that bench grafting creates a wound, which is a potential point of entry for these pathogens.
Fritz Westover
Hi Jose. Do we know anything new about conditions needed and timing of spore release of these pathogens in Eastern or cool/cold climates? We seem to all be using information from CA with relation to when to apply protective fungicide sprays.
As I showed in the webinar, the only data available in regions like NY or MI goes back to early 1980s. The latest data we have is the one we have produced in BC (if you consider BC a cold/cool region),sorry but I have some troubles understanding what a region needs to have to be considered a cool/cold region. If you talk to most people in BC they do not think BC is a cool region but a short-season growing region. Anyway, some information from New Zealand but that is all. Research needs to be done in these areas to better understand as we cannot always refer of what it has been done in temperate regions such as California.
And is it safe to say no spray is needed if no rain is present or expected?
If you asked me this question 5 years ago I would say yes, no spray is needed if no rain, but then most data we had was from California. After finishing our 4 years study on spore trapping in BC we have observed that spores of both Eutypa and Bot are also in the environment during dry periods. This information agrees with recent studies conducted in Australia (not a cool/cold region). I think one of the main differences between these most current studies and those done 5 to 10 years ago are the detection methods. We mostly use DNA molecular detection tools, which are much more sensitive. We need to understand why these spores are also during times of dry (no rain) period. Australians are even looking at morning dew point.
Anne Kearney
Hi Jose, How do we best quarantine GTD infested materials – do you have recommendations for the best approach to quarantine or is the process similar to how we would quarantine for crown gall, etc?
What do you mean with quarantine? Not sure I understand this question. Do you mean quarantine at the import/export steps of material?, quarantine in the vineyard once we see a vine is infected?
Vanessa Tucker
If a mature infected vine is removed, can a young vine be planted in that place?
If the vine removed was infected with any of the canker pathogens, it is safe to say that a young vine can be planted as the canker causing fungi are air-borne and not soil borne. If the vine removed has been declining because of black-foot caused by Cylindrocarpon species, which are actually soilborne, we may have issues to get another young vine established if the inoculum in the soil is too high.
Bernard Prins
In the graph of the trunk diseases in British Columbia, many of the vineyards had more disease as they got older. However a few older vineyards showed low disease level. Do you have any idea why those few older vineyards had lower levels of disease?
No, we unfortunately have not had the time yet to follow up on that. Maybe variety difference (some cultivars are more susceptible than others), pruning time, lots to speculate but we are hoping to follow up on that.
Prevention
Sean MacDonald
Are there cultural practices such as undervine cultivation that could reduce populations of these diseases?
Answer: We have scientific data that pruning debris left in the vineyard (many times left over the undervine row) are a source of inoculum primarily for species in the Bortryosphaeriaceae, the ones causing Botryosphaeria dieback. If possible, pruning debris should be removed out of the vineyard as another sanitation practice. For more information on this, you can see the following research paper
https://link.springer.com/article/10.1007/s10658-015-0782-9.
Wendy McFadden-Smith
Can pathogens be spread with pruning tools?
Really good question and one we scientists we could not really answer until one of the research groups in Spain conducted finally the work. Please see:
https://apsjournals.apsnet.org/doi/10.1094/PDIS-12-14-1283-RE?mobileUi=0
The data of this study indicates that though spores of some grapevine trunk disease pathogens can be found in pruning shears, the amount of spores needed to have a successful infection will most-likely never happen under natural conditions. Even artificially inoculating the pruning shears with up to 106 spores/ml, the highest% of re-isolation from cut wounds was 28%. Using 104 spores/ml the average % of re-isolation significantly decreased and still 104 is way more than we could find under natural conditions.
Jesse COOPER
Any recommendations on equipment cleaning? Can spores be moved by vineyard tools?
See answer above on pruning shears.
My personal opinion is that we need to focus on spending time and money treating the pruning wounds to protect them from infection. The little research done on pruning shears and its ability to spread the pathogen shows it is not worth the time, effort and money to disinfect the pruning shear every time you finish pruning a vine. We need to protect the wounds.
Hans Walter-Peterson
How long is a pruning wound susceptible to infection?
The maximum we have seen in Californian studies is up to 12 weeks, very long time unfortunately. However, as I showed in the webinar the susceptibility of the wounds will depend significantly on the region and weather conditions related to the growing area.
Elsa Petit
Which hot water treatment would you recommend for dormant cuttings?
Lots of work done on this but primarily done for survival of the cuttings and no so much for trunk disease elimination though there are some papers about it. There are good summaries on hot water treatments in the manuscripts below
https://apsjournals.apsnet.org/doi/10.1094/PDIS-04-17-0512-FE
https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-01-11-0025
Jesse COOPER
Jesse COOPER
Should I also paint shoot tips on cane pruned vines?
Really good question and no data I am aware off on this. Having cane pruned vines will take much longer the fungus to reach the spur and permanent framework of the vine as the cane is much longer than a normal two buds spur pruned vine. Not sure if when we prune those canes the following year we can say we have taken away the infection as the fungus is notable to colonize all the cane. Some species in the Botryosphaeriaceae have been shown to be able to colonize up to 1 cm a month of wood tissue so still maybe not enough to reach the spur.
Nelson
I enjoyed the webinar, very informative. My only question is why are all the trials, test, and pictures of cordon trained vines?
Good question, but I have also have cane pruned vines mostly from work done in New Zealand, some California table grapes and now in BC where cane prune is very common.
Would not cane pruning be a simple option of eliminating diseased wood resulting in less pruning wounds and less area for fungi to enter the vines. This would not eliminate the problem for sure but could it not be one way of mitigating the infection of these pathogens? We need all the help we can get and this seems a simple way to at least minimize the chance for infection. I was surprised that this never came up in the conversation?
Actually I have this question asked many times,primarily when I visit regions where cane pruning due to the varieties,conditions or just historical are more favorable for that. I have observed a very interesting case that can answer your question. For many years trunk diseases were not on the radar in Oregon and industry thought that because they historically cane prune vines. Well, in the past 5 years, Oregon is experiencing a tremendous mortality and sudden collapse of vines due to trunk diseases, to a point that many people in the industry now thinks is a crisis.Let me explain you why I think this happens. When we cane prune vines, most of the wounds (even though we have less compared to cordon-spur pruned) are done at the head of the vine. The pathogen infects those wounds and go directly into the trunk. It takes much longer for the pathogen to completely colonize the entire trunk as this is also growing with the age of the vine so we do not realize the vines are infected. Now that most vineyards in Oregon are reaching that 20-25 year-old age, vines are collapsing because the fungus has finally finished colonizing and girdling the whole trunk (see picture below). If a spur position gets infected, we see it within two years and we are still able to cut that cordon or spur before the infection reach the trunk. But when infections happen at the head of the trunk, it takes much more time to observe symptoms.So whether you spur prune or cane prune, the wounds need to be treated and protected.I hope my explanation is clear and make sense. Please do not hesitate to contact me or even phone me if you would like to discuss this further. Similar to the Oregon situation was observed in Marlborough New Zealand where all sauvignon blanc is cane prune. It took a while for them to realize they had a trunk disease issue because the symptoms took much longer to be observed. In the meantime, trunk diseases were well known in the area of Hawke’s Bay in the north island of New Zealand where most vines are spur prune just because symptoms were observed earlier in those spurs.
Jesse COOPER
Are there any studies on bacterial products to combat or cause destruction of released spores?
There are studies on several strains of Bacillusas pruning wound protectants with the idea that the Bacillus strain will entirely colonized the wound before the spore of the GTD fungi arrives. So far I have not seen any really good product based on Bacillus.
Management
Richard Smart
Should growers test “cordon/spurs”thought due to winter kill for GTD symptoms?
Yes, they should see if the mortality of the cordon or spur is really because of the winter or due to fungal infection. I would say the way these symptom is observed in the vineyard will significantly help to determine winter kill of fungus kill. Usually when we have winter kill we see a large area or specific areas of a vineyard affected and with GTD the spread would be more random across the vineyard not necessarily in a specific or limited area of the block.
Scott Riege
We had some vine loss during the winter of 2018- is it too late to have the trunks tested for some of these diseases?
If you have vines dead from a year ago it would be very difficult to relate the vine loss to trunk diseases. Are the entire vines dead and the tissue dry and dead as well? Are you able to see symptoms of trunk diseases in the wood even the vine is dead (i.e. cankers)?
Mark Delaney
Can fungus affect the roots, if so what then?
The Cylindrocarpon group of fungi causing black foot actually start infecting the roots causing a severe decline and loose vigor in young but also mature vines. Unfortunately we have no product to use against this type of infections. For the other pathogens causing cankers, the vine will most-likely die before the canker caused by the fungus (Eutypa, Botryosphaeria) reach the roots.
