Armillaria root disease occurs in all major grapegrowing regions
of California. Armillaria mellea, the causal fungus, infects
woody grapevine roots and decomposes the underlying vascular tissue.
Armillaria root disease affects vineyards planted on sites that
were previously occupied by infected forest trees or orchard trees.
Despite its common name of oak root fungus, A. mellea
has a broad host range, infecting over 500 species of woody plants.5
Native hosts of A. mellea include oaks and other common forest trees
such as Douglas-fir, California bay laurel, and madrone.2
Armillaria mellea also infects many planted hosts in California,
including orchard trees (such as walnut) and woody landscape plants
(such as rose).
Attempts at eradication
Some of the most toxic fungicides are only partially effective at
delaying infection of grapevines by A. mellea. Pre-plant
soil fumigation with methyl bromide either kills A. mellea
mycelium in buried tree roots or weakens it, which predisposes the
pathogen to attack by antagonistic soilborne fungi.4
However, soil fumigants typically do not reach all infected tree
Efforts to eradicate A. mellea from infected grapevines through
fungicide/biocide application to the surrounding soil are unlikely
to affect the fungus, since it grows beneath root bark.
Results of previous studies demonstrated the potential of a cultural
approach called root collar excavation for control of
Armillaria root disease of grapevines.1 The technique
involves permanent removal of soil from the base of the vines
trunk, to the depth at which main roots originate (the root collar),
in an effort to protect this important part of the root system from
vascular tissue decay. Root collar excavation improves yields and
growth of infected grapevines, when applied before the fungus reaches
the root collar and girdles the vine.
Research on root collar excavation demonstrated that grapevines
can tolerate root disease and remain productive if the disease is
slowed down early in the infection process. Focusing control efforts
on infected grapevines that still produce normal clusters is a cost-effective
strategy, given that replants are not immediately productive and
are, unfortunately, likely to become infected by A. mellea.3
The goal of the research reported here was to evaluate the efficacy
of VESTA® (Biologically Integrated Organics, Inc., Sonoma, CA)
to improve yield and growth of vines with Armillaria root disease.
It was previously shown that vines with Armillaria root disease
have significantly fewer clusters, lower yields, and smaller clusters.1
In terms of growth, symptomatic vines also have fewer shoots, lower
pruning weights, and smaller shoots.1 Therefore, amelioration
of these impacts can be used as measures of the efficacy of VESTA.
VESTA is registered as an organic soil inoculant with the California
Department of Food & Agriculture. Laboratory assays show that
VESTA inhibits A. mellea growth in culture (BBC Laboratories,
Tempe, AZ). Viable bacteria isolated from VESTA Bacillus
and Pseudomonas species which were found to inhibit A.
mellea growth in culture may function as antagonists
of A. mellea in the field and/or as grapevine growth promoters.
VESTA results from a proprietary fermentation process of several
composts that vary in age and raw materials. The product of this
fermentation process is passed through a 100-micron filter in order
to allow application of the soil inoculant to crops via drip irrigation
systems. VESTA is extremely low in plant-available nutrients (0.001%
N, 0.001% phosphoric acid, 0.001% soluble potash), but is thought
to consist of complex C compounds that may help sustain the microorganisms
An experiment was designed that utilized VESTA as a therapeutic
treatment (a product applied to a diseased plant in an attempt to
prolong its life). The success of a therapeutic treatment depends
on how much vascular tissue in the root system has already been
destroyed, in addition to the ability of the treatment to decrease
further colonization of healthy tissue. Based on past research on
root collar excavation, we anticipated that timing applications
early in the infection process might be critical to the success
with the soil inoculant.
Observations were focused on vines that showed moderate symptoms
of Armillaria root disease (stunted shoots approximately half the
length of those of healthy vines, with some chlorotic leaves). Based
on past research, the appearance of moderate symptoms signifies
that the vines root collar is infected by a mycelial fan of
In years following the appearance of a mycelial fan at the root
collar, symptoms become more severe (shorter shoots with more chlorotic
leaves, premature defoliation, and berry dessication) as the fungus
eats through the underlying cambium and woody root tissue, thereby
girdling the base of the trunk. Moderately symptomatic vines are
more likely to benefit from a therapeutic treatment than severely
symptomatic vines because they still have some capacity for root
Research was conducted in two California North Coast vineyards,
both with Armillaria root disease, but with different mortality
rates. A Napa vineyard was planted in 1997 with dormant benchgrafts
of Cabernet Sauvignon (Clone 337) on 110-R rootstock with 6 x 8
foot spacing. A Sonoma vineyard was planted in 1991 with dormant
rootings of 3309C and field-grafted in 1992 with Pinot Noir, spaced
meter x meter.
Armillaria root disease was diagnosed in the Napa vineyard in 2001.
The Sonoma vineyard has a longer history of Armillaria root disease,
with the first symptomatic vines having been identified in 1996.
Before the start of this study, in 2001 and 2002, the disease severity
was calculated by mapping the change in status of every vine in
each vineyard. In the Sonoma vineyard, 10% of the vines died from
Armillaria root disease. In the Napa vineyard, the mortality rate
was only 2%.
Experimental treatments were replicated in each vineyard over two
years. Each vineyard was divided into sections and, within each
section, half of the rows were treated with VESTA (treated rows)
and the other half with water (non-treated rows) in 2003 and 2004.
There were three replicated sections in the Napa vineyard and two
replicated sections in the Sonoma vineyard. Within treated and non-treated
rows, 10 healthy and 10 symptomatic grapevines were randomly chosen
for data collection, to give a total of four experimental treatments:
- healthy non-treated,
- healthy treated,
- symptomatic non-treated,
- symptomatic treated.
Symptomatic grapevines were characterized
by having shoots approximately 50% the length of those of healthy
grapevines. All symptomatic grapevines were diagnosed with Armillaria
root disease by examination of their root collars for mycelial fans
of A. mellea.
To avoid sampling symptomless grapevines that were infected on deeper
parts of their root systems, grapevines immediately adjacent to
a dead grapevine or a severely symptomatic grapevine were excluded.
No mycelial fans were found at the root collars of healthy grapevines
selected for data collection.
The soil inoculant was injected into the irrigation system of treated
rows at the following phenological times and rates:
- budbreak (5 gal/acre),
- full bloom (5 gal/acre),
- 15% veraison (2 gal/acre),
- 85% veraison (2 gal/acre).
Petiole samples and soil samples were collected at full bloom in
2003 and 2004. Soil samples were collected using a hand auger to
a depth of 15 cm. Samples were submitted to DANR Analytical Laboratories,
Davis, CA, for nutrient composition analyses (for soil: total C,
total N, NO3-N, P, K, Zn, pH, CEC; for petioles: total N, P, K,
In 2003 and 2004, on the day of harvest, clusters were counted,
harvested, and weighed. During the dormant seasons, prunings from
the same grapevines from which yields were collected were weighed.
An analysis of variance (ANOVA) was used to determine the effects
of vine status (healthy or symptomatic), VESTA (treated or nontreated),
year (2003 or 2004), and their interactions on grapevine yield and
growth parameters, and petiole and soil nutrients.
Based on analyses of yield and growth parameters, VESTA had positive
effects on yield and cluster weights of symptomatic grapevines in
the Napa vineyard. Symptomatic treated grapevines had higher yields
than symptomatic nontreated grapevines, but these differences were
not statistically significant. (Figure I-A).
However, the yield increase observed with VESTA treatment of symptomatic
grapevines from 1.56 kg/vine to 2.01 kg/vine, a 22% increase, would
likely be considered economically significant, with material costs
offset by increased yields.
Symptomatic treated grapevines had higher cluster weights than symptomatic
non-treated grapevines, and these differences were statistically
significant (Figure I-B). In fact, cluster weights of symptomatic
treated grapevines were, statistically, as high as that of healthy
In the Napa vineyard, pruning weight increases were not statistically
significant (Figure II), but the same relative differences among
treatment groups in both study years were observed.
In the Napa vineyard, treated grapevines had significantly higher
soil C than non-treated vines (34.45 mg/g dry wt. versus 28.80 mg/g
dry wt.). Effects of VESTA on the other soil nutrition parameters
(total N, NO3N, P, K, Zn, pH, CEC) were not significant, nor
were effects on petiole nutrients (total N, P, K, B, Zn).
There were no significant effects of the soil inoculant on yield,
growth, or nutrition parameters in the Sonoma vineyard. It is possible
that symptomatic grapevines in this vineyard are more heavily infected
with A. mellea than those of the Napa vineyard, given the
longer history of Armillaria root disease. A higher application
rate of VESTA may be required for vineyards that have suffered losses
for more than five years.
It is also possible that the low yields on all vines in the Sonoma
vineyard made it difficult to detect statistically significant changes.
Given the extremely low yields among even the healthy grapevines
(mean yield for both study years, 0.94 kg/vine), it is difficult
to recognize significant yield increases, especially among the symptomatic
vines (0.68 kg/vine).
The mechanism by which VESTA affects Armillaria root disease is
not known. Bacteria present in VESTA may directly parasitize A.
mellea mycelium and/or secrete fungistatic compounds. Increased
soil C among treated grapevines suggests that higher microbial populations
were encouraged by VESTA, but it is not known whether these microbes
were the same species that have been identified from VESTA.
It is important to remember that the symptomatic grapevines in this
study have undergone substantial root system destruction over the
course of several years prior to VESTA applications. Their capacity
has been steadily deteriorating since they were first infected by
In summary, VESTA had no effect on yields of healthy vines, but
it did help symptomatic vines in the Napa vineyard with less Armillaria
root disease. It increased yields (economically speaking) and cluster
weights (statistically speaking) of symptomatic vines.
VESTA appears to be a promising approach for control of Armillaria
root disease, as long as vineyards are treated soon after the disease
is diagnosed. It is unrealistic to expect VESTA or any therapeutic
treatment to fully restore yield and growth to infected vines in
only two growing seasons.
Therapeutic treatments are more likely to be successful when used
early in the infection process, once symptoms appear in the vineyard.
- Baumgartner, K. 2004. Root collar excavation
for post-infection control of Armillaria root disease of grapevine.
Plant Disease 88:12351240.
- Baumgartner, K., D.M. Rizzo. 2001. Ecology
of Armillaria species in mixed-hardwood forests of California.
Plant Disease 85:947951.
- Baumgartner, K., D.M. Rizzo. 2002. Spread
of Armillaria Root Disease in a California vineyard. Amer.
Jour. of Enology & Viticulture 53:197203.
- Munnecke, D.E., M.J. Kolbezen, W.D. Wilbur,
H.D. Ohr. 1981. Interactions involved in controlling Armillaria
mellea. Plant Disease 65:384389.
- Raabe, R.D. 1962. Host list of the root
rot fungus Armillaria mellea. Hilgardia 33: 2588.