The work I will talk about today draws from past work done by Doug Gubler and some of his former students, in addition to other trunk disease researchers around the world. My work on trunk diseases for the past 4 years has been funded by a grant from the USDA-NIFA Specialty Crop Research Initiative. Here is the list of my collaborators. They are plant scientists, social scientists, and extension specialists and farm advisors. We work not only on trunk diseases of grape. Some of the same or related pathogens attack almond and pistachio. 1
1 st for some background on the study system. We see four main trunk diseases: Eutypa, Esca, Phomopsis, Botryosphaeria. Every vineyard in California eventually becomes infected by either one predominant trunk disease or a combination. Many California vineyards are being replanted prematurely because yield losses are so severe that the vineyard is barely profitable. 2
I remember when I was a student and my professor Doug Gubler taught us in the vineyards how to hunt for Eutypa. We were always thrilled to find these perfect, V- shaped wood cankers. 3
..but sometimes, they were not V-shaped. We would say, This doesn t look like Eutypa, Dr. Gubler. What s up? 4
Sometimes there wasn t a canker at all, but some black spots. 5
20 years ago, we thought it was all one trunk disease in CA Eutypa dieback. Over the years, we ve come to realize there are other important trunk diseases. and the list of pathogens has grown! Is still growing! Doug Gubler built this important foundation of knowledge. The work I m talking about today would not be possible otherwise. 6
In reality, though, not all of the fungi that cause cankers are aggressive pathogens.a relatively small number (the list above) are common and aggressive. These pathogens are not related to each other, but they have the same disease cycle. 7
They all infect grapevines during the dormant season. Rain induces spore production and dispersal. Cold temperatures are thought to delay the natural wound-healing process. 8
The trunk pathogens all cause chronic infections of the wood; the wood is where the pathogens reside. The pathogens that cause Botryosphaeria, Eutypa, and Phomopsis diebacks have some wood-degrading abilities and thus utilize the wood as a food source; they cause wood cankers. The Esca pathogens cannot or just barely decompose the wood, but instead use the vascular system of the vine to spread through the wood; they cause black streaking in the wood (appears as black dots in x-section). 9
Some of the trunk diseases have diagnostic leaf symptoms. For example, Eutypa dieback causes stunted shoots. The leaves are yellowed and deformed. Spurs with shoots that look like this tend to die within a few years; the symptoms get worse and worse over time and eventually the spur dies. 10
There are differences in cultivar susceptibility to Eutypa dieback. These photos I took at a research station in the Barossa, in South Australia where Eutypa dieback is the predominant trunk disease. 11
Cab is really susceptible! 12
The other trunk disease with diagnostic leaf symptoms is Esca. It causes an interveinal necrosis, which appears typically in late June. Basal leaves start showing symptoms first, and then symptoms progress on to the younger leaves farther up the shoot. This is a red cultivar.merlot. Red cultivars tend to have a red outline around the necrotic stripes that form in between the veins of the leaf. This trunk disease has changed names many times over the years..its been known as Measles, Young Vine Decline, Petri Disease, and Black Goo. We call it Esca.for now. Although the name has changed, the pathogens remain the same. Esca is the most severe trunk disease in Europe. They have the other trunk diseases, but Esca gets the most attention. 13
The leaf symptoms of Esca first appear as a faint drying at the margin and in between the veins (left). Then the dried areas turn scorched and necrotic. 14
This is a white cultivar, Sauvignon blanc. In the white cultivars, you see a yellow outline surrounding the necrotic tissue (left). Also, you can see spots (measles) on the fruit (right). These spots, and the leaf symptoms, are thought to be due to toxins that the pathogens make inside the infected wood. Esca symptoms may appear one year and not the next. Its not like Eutypa dieback, which shows progressively worse symptoms over time. Even though Esca symptoms may not appear each year, however, the pathogens are still inside the wood. Typically they will show up, eventually, on the same spur. The fruit on shoots with Esca symptoms never ripens properly and should be dropped, whether it is has spots on it or not. Studies in Italy on the effects of Esca on fruit quality show that fruit on other shoots of the same vine, not showing symptoms, does ripen properly. The wood infection, the symptoms, and their effects on fruit quality are localized.no need to drop all fruit from the vine. 15
The dieback-type diseases kill spurs, which is one of the most apparent canopy symptoms of trunk diseases. Here you can see a dead spur position (at center) that did not grow the previous summer. 16
When you cut into the dead spur, you can see the internal wood canker. A vine accumulates these wood cankers over time as different pruning wounds are infected by different trunk pathogens. Depending on how aggressive the trunk pathogen is and how susceptible the cultivar is, it can take one to several years for this symptom to appear. 17
Typically disease incidence increases as a vineyard matures, when you have conditions that are favorable for disease establishment and spread, such as a susceptible cultivar, high pathogen pressure, and lack of disease management. For example, in a susceptible cultivar such as Colombard (for which this data was gathered), by year 10, approximately 20% of the vines are symptomatic. By year 15, up to 75% of the vines may have canopy symptoms. This sharp increase in disease incidence is not due to a higher level of susceptibility in years 10 to 15, but rather that visible identification of canopy symptoms occurs years after wood infections are already well established. To lessen this sharp increase, preventative practices should be adopted when the vineyard is young and healthy in order to minimize infection of pruning wounds. Once disease incidence is high, however, management based on prevention is no longer optimum, and you should instead focus on post-infection practices. 18
Its important to protect as many pruning wounds as possible because each dead spur means fewer clusters per vine. Because the infections are chronic, they build over time as do the yield losses. 19
To describe the most relevant practices for the different levels of disease incidence encountered in the vineyard, I will outline a couple of scenarios. The first is Scenario 1, which applies to a young vineyard, 3 to 5-years-old. The vines are trained and undergo annual pruning. Symptoms are absent or at very low levels. Disease incidence can vary according to factors such as cultivar susceptibility and which trunk pathogens are present in the vineyard; symptoms can appear sooner with very susceptible cultivars and when vines are infected by very aggressive pathogens. Therefore, we provide a range of vineyard ages for scenario 1. However, we emphasize that disease incidence, and not vineyard age, should be the key criterion in developing a management plan. 20
Three practices have been shown to minimize infections of pruning wounds. This includes DELAYED PRUNING, DOUBLE PRUNING, and PRUNING-WOUND PROTECTANTS. We expect preventative practices to be most effective for scenario 1 because they minimize infections of pruning wounds, thus maintaining disease incidence at low levels. 21
Studies on pruning-wound susceptibility during the dormant season.just a hand-full of these studies..show that wounds become less susceptible as we approach budbreak. Rain triggers spore production. Because rain events are so frequent in December and early January, coupled with the long period of pruning-wound susceptibility, this is the worst time to prune. You should not considered getting into the vineyard until late February/early March for pruning. If your idea of delayed pruning is to prune in January, you are not decreasing the risk of trunk diseases because January is just as bad as December. The risk of infection is still high in February. If you must prune before late February/early March (and you care about trunk diseases), there are alternatives to delayed pruning. 22
This is a modification of delayed pruning for cordon-trained, spur-pruned vineyards and involves two passes: Pass 1 ( December & January, sometimes February) Often with a mechanicalpruning machine (left), canes are prepruned to approximately 10 to 12 inches above last year s spurs (right). No cuts are made down to the cordon. Pruning debris is pulled off the trellis wires by hand. Pass 2 (March ideally) Canes are pruned to 2-bud spurs by hand. This removes the section of the cane that may have been infected via pruning wounds after Pass 1. This is a relatively rapid pass when the labor-intensive step of pulling the pruning debris off the trellis wires is done during pass 1. 23
Here is a vineyard that has been pre-pruned. This is in Texas they have trunk diseases, too. 24
Because rain events are so frequent in December and January, it can be hard to get a mechanical pruner through wet soil. The 1 st pass can happen as soon as the ground is dry enough. For the 2 nd pass, late February/early March is best. 25
Fungicides that prevent infection of pruning wounds are labeled for dormant-season use in California: Topsin and Rally. In addition, there are other non-fungicidal materials that form a toxic or physical barrier to infection: Boric acid and VitiSeal. 26
If you prune in December or January, you may need two applications of Topsin and/or Rally. All pruning-wound protectants must remain continuously active for up to 4 weeks if vines are pruned in December or January, during the high risk period. Rain washes protectants off pruning wounds, so reapplication may be necessary. If you prune in February, when the wounds heal in 1-2 weeks, one application is likely enough. If you prune in March, the wounds heal so quickly that no applications are needed, unless rain is predicated immediately after you prune. 27
Since Topsin has been extensively studied, relative to other protectants, we use it here to illustrate an important point regarding the early adoption of preventative practices in young vineyards. This example uses figures for an acre of Cabernet Sauvignon vines in San Joaquin County, California (aka Lodi, Crush District 11). We show the cumulative net returns expected over the course of 25 years. The healthy vineyard featured in this graph is a best-case scenario, but it is atypical. In our experience, all vineyards become infected by trunk diseases; we do not expect to find a vineyard in California without some level of yield loss. Nonetheless, the simulated, healthy vineyard provides an optimum reference for our economic simulation. The infected vineyard is a worst-case scenario, in which neither Topsin applications nor other management practices are taken. In this simulated, infected vineyard, taking no action to manage trunk diseases results in losses of $39,662 per acre over 25 years. Thus taking no action in young vineyards is a poor investment decision, given that it can take up to 10 years to break even on the high vineyard establishment costs. If we assume a very modest level of disease control efficacy 50% the cumulative net returns from adopting Topsin applications are significantly higher than taking no action. Starting Topsin applications in years 3 or 5 can result in a positive return on investment ($12,784 and $5,787 per acre, respectively); whereas initiating Topsin applications in year 10 results in net losses (-$19,624 per acre), although is not as costly as taking no action (-$39,662). 28
The earlier in the vineyard s lifespan you start preventing trunk diseases, the less steep this increase will be as the vineyard matures. None of the practices are 100% effective each year. Because we do not know the climate conditions that favor spore germination or infection of pruning wounds, we have to make uniform assumptions about practice efficacy across pathogens, regions, cultivars, etc 29
When we surveyed growers on their usage of the three practices, we found that delayed pruning is most common in all regions. The CENTRAL COAST results are from survey done in I think April 2014, organized by Mark Battany in Templeton. 30
Delayed pruning is the most common practice in all regions. In the Central Coast, 62% of growers said they use delayed pruning often or always. Double pruning is the least common. Only 25% of growers here use double pruning often or always. Napa has the highest rates of adoption of these preventative practices. Lodi and Mendocino has the lowest. We don t use these surveys to give you grades.its not a test. Instead, this helps us as researchers understand which types of practices we need to study more, in terms of for example timing during the dormant season or mechanization to reduce labor costs. It also helps us identify what might be regions where more outreach is needed. 31
Scenario 2 is a mature vineyard, 10-years-old. There is a relatively low percentage of vines with symptoms of trunk diseases, approximately 20% of vines in the vineyard. Because disease incidence can vary according to factors other than vineyard age, disease incidence in this case, 20% is the most important factor to consider. We recommend you use post-infection practices on the symptomatic vines. Of the remaining 80% of the vineyard that shows no symptoms, many of these vines may not be infected. Therefore, it makes sense to use preventative practices on the entire vineyard. Furthermore, the infections are localized in the wood, and so a symptomatic vine with one dead spur likely has other healthy spurs that should be protected from infection. 32
Of these post infection practices, only vine surgery has been studied, and only with respect to Eutypa dieback. Sanitation involves cuttings out infected spurs and cordons, and removing them from the vineyard as they can be a source of spores to infect neighboring vines. Replanting is not a trunk-management practice per se, but rather a consequence of not managing trunk diseases. 33
There are two levels of vine surgery, depending on the percentage of symptomatic shoots and dead spurs on a vine. If canopy symptoms are restricted to one cordon, you can retrain a new cordon by laying down a healthy cane. The main drawback of having some old cordons and some new cordons is that the fruit ripens at different rates. If there is a canker at the head of the vine, however, the new cordon can be re-infected. This form of vine surgery is not as effective afterwards for as long a period of time as retraining from the base of the trunk. 34
If more than one cordon has canopy symptoms, the entire vine can be retrained from a sucker at the base of the trunk. Although it is costly, due mainly to labor costs for removal and retraining (approximately two years to complete), this approach allows a relatively rapid return to full production and quality, as it utilizes a well-established root system. Furthermore, this aggressive approach removes the pathogen. 35
You can do this on a row-by-row basis or for an entire block of vines. 36
If a trunk sucker forms, it can be advantageous to train the new vine with the existing vine in place, a practice similar to trunk renewal, which is used in cold climates to replace trunks lost to winter injury. In this way, there is still some fruit to harvest from the old vine as the new vine is trained; it is not a total loss of yields during the retraining process. In mature vineyards, however, trunk suckers may not naturally grow from the base of every vine, so cutting off the vine just above the graft union can sometimes activate basal buds. 37
Regardless of whether or not you train the new vine with the old vine in place, its important to cut down as close to the graft union as possible. The trunk can get infected, just as the cordons can; you want to make sure you cut away the entire infection. 38
This is a vine autopsy. You can see wood cankers not only in the cordons (at left), but also in the trunk (at right). Close to the graft union, the wood looks much healthier. That s a good place to cut. 39
Vine surgery creates large wounds. When retraining a cordon, the wound is located at the top of the trunk, infection of which can jeopardize both new and old cordons. When retraining the trunk, the wound is located at the base of the trunk, infection of which can jeopardize the only remaining section of the vine that exists above ground. To minimize the risk of infection, perform vine surgery in February or March and then apply a pruning-wound protectant (in this case, B-lock). 40
Sanitation When it rains, trunk pathogens produce spores from infected/dead wood. Therefore, removing or burning wood eliminates local sources of inoculum. To further reduce the spread of trunk diseases within an infected vineyard, prune away dead spurs or cordons with dead spurs/wood cankers, and then burn or remove this infected wood from the vineyard. 41
Sanitation creates large wounds. As such, perform this practice in February or later and afterwards apply a pruning-wound protectant to all cuts that are made. The efficacy of sanitation has not been evaluated experimentally. We assume that it can reduce spore populations in the vineyard. For many trunk pathogens (Eutypa lata is the exception), spores are spread by rain when it drops onto infected wood and then splashes over to a susceptible pruning wound. 42
One of the goals of our project is to create new extension tools. Monica Cooper noticed the need for a trunk disease pamphlet she developed a pamphlet for mealybugs and suggested we do the same. Our trunk disease pamphlet was coauthored by me, postdoc in my lab Renaud Travadon, and viticulture farm advisors Monica Cooper, Rhonda Smith, and Larry Bettiga. It has pictures and descriptions for disease diagnosis. It also outlines management practices for young, healthy vineyards vs. mature, diseased vineyards. 43
We developed a searchable DNA-sequence database (http://trunkdb.grapeipm.org) to address misidentification of trunk pathogens in the laboratory. This is meant to improve the accuracy of trunk-disease diagnosis at commercial diagnostic labs and within the research community. Its especially important in grape-growing regions across the US, where different climates, different cultivars, and different fungi contribute to differences in symptom expression and composition of the trunk-disease community. The DNA-sequence database is a valuable resource for diagnosticians because it pools results from many published papers not accessible outside an academic institution. 44
We developed a new set of management guidelines with the viticulture farm advisors..these are posted on our SCRI project website (link to this page specifically is http://treeandvinetrunkdiseases.org/trunk-disease-management-in-california-2) 45
We incorporated the results of our economic analyses into the management guidelines. Here you see the # of profitable years expected in a vineyard when preventative practices are adopted in young vineyards 3 and 5-yrs-old versus a mature vineyard of 10 yrs-old, where trunk diseases are already starting to become established. On this page you can find a link to our economic tool for comparing preventative practices. 46
You can select the region you are in and specific management practices to compare. (link to website is http://maxnorton.github.io/kaplan-model/) 47
The economic model incorporates regional differences, in terms of vineyard establishment costs, fruit pricing, and practice costs. Here you can see the figures we use for the Central Coast. If these figures do not apply to your vineyard, you can click on ADJUST PARAMETERS to change them. 48
You can see how adopting a practice in year 3 vs. year 10 affects vineyard longevity. This table shows the last profitable year for an acre of Cabernet Sauvignon in Lodi (sorry about that forgot to change the table!). If you adopt delayed pruning or Topsin applications or double pruning in year 3, you add 7 more years of profitability to the vineyard. This is what our model estimates, assuming that the practices are only 50% effective.they only protect half of the pruning wounds. 49
Our research is funded by grants from the Specialty Crop Research Initiative, AVF, and the CATGC. Visit our project website, to learn more about our research, which also includes similar projects for the same diseases on almonds and pistachios. 50