While studying grapevine decline in Portugal, Dr. Cecelia Rego et al tested 3,340 unplanted vines representing nine different rootstock genotypes.(2) They found that 30% were infected with Cylindrocarpon and 23% infected with Phaeomoniella. (The infection rates of Phaeomoniella are likely understated; see “false negative” under More confusion below.)

Rootstock mother vines are widely infected with some of the same fungi listed in Tables I and II. Specifically, Phaeomoniella, Phaeoacremonium, Cylindrocarpon, and Fusarium have been found in rootstock mother vines and their offspring in California, Europe, South Africa, and New Zealand. Dr. Ian Pascoe reported extensive Phaeomoniella infection of rootstock mother vines and stunting, decline and dieback of vines one to 24 years old in Australia.(1)

There may be no apparent foliar symptoms in rootstock mother vines — you must look inside to detect damage. But in vines grafted onto young rootstocks of American parentage, these fungi can be serious pathogens with a wide range of symptoms.

Infection of harvested canes can be both internal and external. That is, some canes have spores in their xylem vessels and pith which remain essentially dormant as long as the tissue is green. After propagation and one year in a nursery plot, the pith and first xylem ring are woody enough for the spores to germinate (personal communication from Dr. Laura Mugnai). More canes (likely many more) have abundant spores on the outside, which get in during propagation through a disbudding site or via one of the end cuts.

Note in Tables I and II that some of the fungi, specifically Cylindrocarpon, Fusarium, Pythium, and Botryodiplodia, are known to live in soil and would more easily be kept out of the vines if the canes were not allowed to drape onto the soil. To prevent this problem, rootstock mother vines should be trellised and shoot positioned, and harvested canes should never come in contact with the soil. In contrast, scientists have not found that Phaeomoniella infection can be transmitted through soil or that treating the soil is curative for esca or young vine decline.

At the nursery
The presence of abundant spores of the various pathogenic fungi should be of great concern to both nursery staff and growers. During the process of grapevine production, each rootstock is wounded at both ends when it is removed from the mother vine, disbudded at two sites, and injured during grafting.(2)

“It is important to note that Pch (Phaeomoniella) produces pycnidia on the surface of grape wood,” says Dr. Doug Gubler, UC Davis Department of Plant Pathology. “The conidia produced from these pycnidia infect rootstock through the cut end and wounds produced by disbudding.”(2)

Disinfection of the canes prior to cutting and propagating could prevent a great deal of disease. Unfortunately, only a few nurseries in California do this effectively.

“Some California nurseries wash the cuttings and often soak them in tanks with diluted chlorine (followed by clean water rinse) before cold storage,” reports Dr. Andrew Walker, UC Davis Department of Viticulture & Enology. “Cuttings are rehydrated before grafting and a disinfecting dip in chlorine, and occasionally Benlate, is used to control fungi.”

In an Italian experiment reported at a New Zealand seminar last year, Dr. Laura Mugnai compared “sterile” and conventional propagation of cuttings from rootstock mother vines that were known to be infected with Phaeomoniella. Sterile propagation consisted of soaking the canes in clean water and ENOVIT fungicide, (which is 70% tiophanate-methyl at a rate of 1% by weight) keeping all tools sterilized, and growing the vines in a greenhouse in sterile planting media. Of the conventionally propagated vines, 49% ended up infected, compared to only 15% of the sterile propagated vines. (These statistics likely understate infection rates, see “false negative” under More confusion below.)

This experiment may give a good indication of rates of internal versus external contamination. Dr. Mugnai also notes, “Isolation experiments carried out on more unplanted bench grafts of different scion/rootstock combinations from nurseries in both Italy and France, fully confirmed these results.(1) The same wood browning was present in almost all the samples and P. chlamydosporum [now called Phaeomoniella chlamydospora] was isolated from 22% of them.” (Very similar to Dr. Rego’s result.)

In 1994, Dr. Strauss Ferreira published results of experiments with Phaeomoniella (then called Phialopora parasitica), which showed that the fungus gives off toxins which strongly inhibit callus formation.(3) In Dr. Gubler’s trials, it was found that, in cuttings exposed to inoculum, callus formation was partially to completely inhibited. Infection not only affected callus formation, it also reduced plant height, number of internodes, number of roots, root length, and dry weight above ground.(2)

Poor callus formation, root growth, and top growth are all red flags for growers, indicating either infection or poor callusing conditions.

Regardless of cause, poor growth and callus formation are undesirable for planting.

In hot water
Much research has been done, especially in Australia, using hot water to improve viability and reduce pest and disease problems in dormant plant material.(1) It is highly unlikely that such treatment will eliminate all young-vine-decline pathogens; results to date are encouraging enough to merit continued study.

Regarding callus formation, hot water treatment of dormant rootstock cuttings prior to propagation is most encouraging, according to Helen Waite and Peter May, Institute of Land and Food Resources, University of Melbourne, Australia.(1) If the process also reduces or kills pathogens, so much the better.

Apples and oranges
Although studies of esca and young vine decline currently overlap, the results in one area are not necessarily applicable to the other. For example, some studies relating to young vine decline have used Vitis vinifera instead of American rootstocks. Given that various genotypes of European and American vine species are unlikely to respond in the same way to various pathogens, it is very likely best that American rootstocks be used in research pertaining to young vine decline and Vitis vinifera be used when studying esca.

Dr. Larignon found internal infection of Phaeomoniella in Vitis vinifera canes only about 1% of the time while studying esca.(2) In Dr. Mugnai’s work with American rootstocks, the internal infection rate was much higher (see “Italian experiment” under At the nursery above). It is worth noting that a study of esca and eutypa published in 1992, Dr. Larignon et al found Phaeomoniella in 40% of samples taken from American rootstocks, Phaeoacremonium in 5%, and Sphaeropsis in less than 5% with a more diverse mixture of fungi from the graft union up (1).

A rose by any other name
Some confusion has arisen because of name changes. Here is the latest:

1) What Dr. Petri and Dr. Chiarappa called Cephalosporium and Dr. Ferriera called Phialophora is Phaeomoniella, and it causes “Petri’s vine decline” (also known as “slow dieback” and “black goo”).

2) What Dr. Petri called Acremonium is now Phaoeacremonium, which along with Phaeomoniella, Cylindrocarpon, and possibly a few other fungi, causes “young vine decline” (an umbrella term often used in California).

3) Two species of Phaeoacremonium, angustius (CBS 249.95) and inflatipes (CBS 222.95), both found in vines in California, are being recommended for reclassification as the much more common Phaeoacremonium aleophilum. What was commonly reported as inflatipes in California is aleophilum.

More confusion
Adding to the confusion, the type of culture testing currently practiced to detect the fungi responsible for young vine decline is subject to “false negative” results. That is, the fungi can be present yet not be detected. Estimates vary, but 60% detection and 40% false negative from 100% infected wood may be about right for Phaeomoniella, according to Glenn Friebertshauser, Agri-Analysis. That is, if a vine is infected, there is only a 60% chance of detecting the infection via culture.

This helps us to understand how vines that show the “long, dark brown striations, that can reach all the way to the roots” that Dr. Petri described can test negative. Or, as Dr. Pascoe says, “It appears that the ‘goo’ may be produced at some distance from the infected cells, and this suggests that a toxin may be involved and also explains why we’re sometimes unable to isolate P. chlamydosporum from perfectly typical symptoms.” Please review Tables I and II again with the understanding that a bit more than half of the actual infections of Phaeomoniella were likely detected.

If all of the vines that you send in for testing have internal and/or external symptoms associated with fungal infection and some test positive while others test negative, it is likely that all are infected. False negatives are a nagging problem not just in viticulture, but in human diseases as well. As they say, “Absence of evidence is not evidence of absence.” When in doubt, get more vines tested.

It is common for vines showing no foliar symptoms to have internal symptoms in the rootstock xylem and to test positive. Some have interpreted this to mean that the fungi involved are either weak pathogens or not pathogens at all. Please note that “apparently healthy” people are infected with HIV and hepatitis C — a slow pathogen is not necessarily a weak one.

On the North Coast, we are seeing the onset of decline in vines anywhere from one to 12 years old. Dr. Rego noted the same in vines up to 18 years old, and Dr. Pascoe in vines up to 24 years old. That is why Dr. Ferriera called it “slow die back.” It’s not so much that the dying is slow, but that the onset of symptoms can take many years.

One small bit of good news is that polymerase chain reaction (PCR) testing is coming of age for the Phaeos (but not Cylindrocarpon) and promises to be faster and more reliable than current tests.(2) The actual test takes only two days, though normal lab logistics and reporting require seven to 10 days, but that is far faster than the six to eight weeks required for culture testing. More important, PCR testing is nearly 100% accurate, compared to 60% for culture testing.

Why now?
How did these pathogens come in under the radar? As was the case at Pearl Harbor in World War II, the radar was switched off. Since Dr. Petri’s work in 1912, little was being done to check for fungal pathogens in rootstocks until quite recently.

What may be the biggest factor in widespread disease is the worldwide planting boom starting in the late 1980s, which continues today. When demand outpaces supply, quality standards tend to decline, and the product follows. Substandard vines that should be burned are instead planted and grow poorly, if at all. Again, it is up to growers to “motivate” nurseries to improve the quality of their planting material.

One researcher has suggested that the “new” rootstocks may be more susceptible to young vine decline than AXR-1 was, due perhaps to the partial-vinifera parentage of AXR-1. This is doubtful, as Dr. Petri noted dark gummosis in AXR-1 in Sicilian vines that were in decline without phylloxera.(1) In any case, rather than begging the question, research would need to be done to confirm this conjecture. However, it is a moot point as growers do not have the option to use AXR-1 due to its fatal flaw regarding phylloxera.

There is no option but to use American rootstocks.

Management and stress
Environmental stresses and/or mismanagement are often blamed for vines that perform very poorly. Growers are often brushed aside with vague “maybes,” such as, “Maybe you have a soil problem” or “Maybe you irrigated too much (or too little)” or “Maybe you have a nematode problem” or “Maybe the weather was too hot (or too cold) when you planted” (unlike Goldilocks, conditions are never “just right”) or — and this one is usually the clincher — “Maybe this is the wrong rootstock for this site.” This list of “maybes” is far from exhaustive.

What is clear is that growers can do their best to minimize stress, but their vines would not be so sensitive to stress if they were not diseased. Adverse weather and other stresses exacerbate the problems associated with these fungal diseases, but the fundamental problem is disease, not stress.

Regarding stress, Dr. Smart notes, “Such interactions are so obvious to the astute observer as to require little comment. Certainly any organism, be it plant or animal, weakened by a stress, be it environmental or pathological, is more predisposed to disease. However, sometimes the symptoms are confused, and the inexperienced might blame the unknown problem solely on the environmental stress, for which the symptoms are commonly better-known.”(3)

Some have noted that propagating rootstocks is extremely stressful. To this viticultural consultant, Lucie Morton responds, “There is no question that if vines are infected with black goo, they are much more vulnerable to any stress, including the process of grafting.

However, grafting is necessary … and healthy vines have many strategies for surviving stress. Diseased vines are greatly handicapped.(1)

“This argument about the practical importance of stress is eerily reminiscent of the 1970s-era academic conjecture that phylloxera-susceptible AXR-1 could be recommended as long as it was confined to “less stressful” sites with irrigation and deep fertile soils.

Lack of stress did not save AXR-1 from phylloxera, and lack of stress cannot be counted on to save vines from black goo, although it may delay the onset of decline for a number of years.

“Finally, great wines are most often associated with sites of low fertility and low water-holding capacity — that is sites with somewhat stressful conditions.”

In a recent report on California grapevine materials, Lynn Alley et al. (UC Davis) noted: “Virus and virus-like diseases have probably existed in California’s vineyards from the earliest years, but were poorly understood at the time and often went unrecognized or mis-diagnosed.

“Diseases caused by virus or bacteria-related problems were often attributed instead to unsound viticultural practices. In a 1931 book proposal, Frederic T. Bioletti, first head of the UC Department of Viticulture, addressed the issue of vine problems in a chapter entitled, ‘Vine Troubles Attributed to Climatic, Soil, and Cultural Conditions.’” The UC Davis report then noted that the diseases that Bioletti was dealing with were actually leaf roll virus, fanleaf virus, and Pierce’s disease.(4) Those who would attribute young vine decline to environmental stress and/or cultural practices should learn from Bioletti’s example.

Proponents of the stress hypothesis must also explain the very uneven distribution of failing vines compared to those showing normal to very vigorous growth (see Figure 1). What stress did the stunted vines experience that their healthier counterparts nearby did not?

Why are failing vines intermixed with productive vines? What stress results in a “shotgun” pattern of dying, stunted, weak, and thriving vines? Such patterns are more easily explained by having healthy vines mixed in with vines infected with various pathogens on planting day as illustrated in Tables I and II.

Michael Porter worked as a winemaking assistant and as a research assistant at Crocker Nuclear Lab, UC Davis while studying physics at Cal State University, Chico. He earned a master’s degree in earth sciences from Chico. He has taught geology, meteorology, oceanography, physics, and astronomy in junior colleges. Since 1984, he has provided soil fertility, vine nutrition, and water management consulting services.

• Wines & Vines, November 1995, p. 46, “Mystery Diseases Hit Young Vines,” Lucie Morton.
• Wines & Vines, January 1997, p. 62, “Update on Black Goo,” Lucie Morton.
• Practical Winery & Vineyard, May/June 1998, p. 32, “Young Grapevine Decline in California,” Heather Scheck et al.
• Practical Winery & Vineyard, November/December 1998, p. 5, “Another Disease Looming?” Richard Smart.
• Black Goo, Symptoms and Occurrence of Grape Declines, edited by Lucie Morton, 1999, International Ampelographic Society, Healdsburg, CA, and Santa Rosa Junior College libraries. If checked out, try the reserve desk.
  (To order a copy, cost is $29.95 plus $5 shipping/handling, contact IAS/ICGTD, fax: 540/933-6987, fortvin@shentel.net).
• Phytopathologica Mediterranea, Special Issue on Esca and Grapevine Declines, 2000, Mediterranean Phytopathological Union, Healdsburg, CA, and Santa Rosa Junior College libraries. If checked out, try the reserve desk.
  (To order a copy, cost is $67.25 plus $5 shipping/handling, contact IAS/ICGTD, fax: 540/933-6987, fortvin@shentel.net).