SS
BLACELINE AND ROOTROTS OF PERSIAN WALNUT IN OREGON
by
P. W. Miller, J. H. Painter, & C. 0. Rawlings
Miscellaneous Paper 55
March 1958
Agriculture Experiment Station
Oregon_ptate College
Corvallis, Oregon
BLACKLINE AND ROOTROTS OF PERSIAN WALNUT IN OREGON*
Table of Contents
Introduction • **** • ******
••• ••■ •• ••• • •
• •• a** • •
History and Symptoms of Blackline, ••• ••
History . •
,
.
Symptoms. . • . • •• •
Survey Procedure
•
Page
1
• •••
ei • • Y• • • 0 •
a• •
1
1
••••
•• • • • •
3
Relation of Occurrence of Blackline to Various Factors • ■ • ••• • •
Kind of rootstock . . • •• • . • 6 • • •
• ••
•••
•
a a
Scion variety . . . . • •
**
• • • • ••
a a a • •
Tree trunk diameter • • • •••• •••• •
****
• • • •
Soil series . . . . . . • •• • *
a • •
•
*** ••• •
Height of graft union . . . . . *
• ** • • a • •
Interaction of tree trunk diameter, soil series
and incidence of blackline . . • ********** • • • •
5
5
6
6
7
7
Comparison of O ccurrence of Blackline in 1950 and 1956 .
8
• ***** • •0 A • • a • •
Time Required for Affected Trees to Become Unproductive. .
Types of Rootrots on Persian Walnut
Mushroom rootrot. .
• a a
Crown rot •
Phytophthora rootrot. • • •
• .
*** •
•
.
. • •
• • •• 9
• • • • • • • • •
•••
. . . •
• • •
7
**
Relation of Occurrence of Rootrots to Various Factors
• ••
Kind of rootstock * • ••• • • •• • •
• O 1a • •• •
••
Trunk diameter. •
.
. a • I . • . • . O f
•• • a ••• •
Soil series . • • • • •• • 414 a • ••
• • a • • • • ••• •
10
10
11
12
13
13
15
15
Discussion
•• • • • •
• • •
* I* • •• •
16
••
Decline and death of Persian walnut trees in
relation to blackline ***** . . • • •
• • • V • • • • a 16
Blackline causal theories • •• • • • •••••• • • • ••• • 18
Methods used to save trees affected with blackline. . ....
. . 23
Decline and death of Persian walnut trees in
relation to rootrots • . . . . • • •••
27
Summary. . o • . .•
• • • ■• *****
a• • . 6 • a
Literature Cited • • • • • • • • ******** • • •
*
•
• •
• • •
a • a • • •
28
• . 30
Acknowledgements:
To walnut growers who cooperated in these studies by making
their orchards available for survey.
To Dr, H. E. Hammar for making chemical analyses of walnut
bark samples.
BLACKLINE AND RooTRas OF PERSIAN WALNUT IN OREGON
By
P. W. Miller J. H. Painter and C. 0. Rawlings
Introduction
In a considerable number of ualnut orchards in Oregon, many
trees are declining and dying. Symptoms of decline range from the
dying of small shoots and branches to the death of whole trees. A
preliminary survey in 1948-49 indicated that a disorder popularly
known as blackline and rootrots of various types were primarily
responsible for this decline. To determine the extent of these
disorders and the conditions under which each occurs, a tree-bytree survey of a number of widely separated orchards on the most
prevalent soil series in western Oregon was begun in 1950 and has
been carried on yearly through 1956. Results of the survey and a
general discussion of blackline and rootrot diseases follow.
History and Symptoms of Blackline
History. The first report of blackline in Oregon was made by
Trunk (2L.) in 1932 at a meeting of Oregon walnut growers. As early
as 1926--when the trees were about 16 years of age--he observed
suckers coming from Hinds black walnut (juplans hindsii (Jeps.) Jeps.
rootstocks on which scions of the Persian walnut variety Franquette
Plant Pathologist, Horticulturist and Extension Horticulturist
respectively.
had been grafted. Investigation showed a narrow band of brown or black
tissues at the graft union resulting in a girdle. In 1933, Schuster
and Miller (17) described this disorder in more detail and reported
unsuccessful attempts to isolate a causal organism. Blackline has
since been discussed by a number of walnut growers and investigators
at meetings of Oregon walnut growers (10 11,12).
Blackline also occurs in California, where it was reported first
in 1932 by Trunk (24). In 1541, Smith (22) stated that blackline
occurs in walnut orchards in only certain districts in California and
only on Persian walnut varieties grafted on black walnut rootstocks.
He stated that it occurred mostly on trees 20 years of age or older
and was not confined to any one variety. In 1946, Davey (3) reported
that blackline was in a number of orchards in an area near San Francisco
Bay (Contra Costa, Santa Clara and Sonoma Counties).
In 1955, R. J. Cotelli stated that blackline is most prevalent
in the central coast area of California (Santa Clara, Contra Costa, and
Napa Counties) and that it rarely occurs in southern California.
Symptoms. The first symptoms of blackline are weak growth, sparse
foliage, and yellowing and premature dropping of leaves from certain
branches; death of the affected branches follows (Figure 1). Later, as
the disorder progresses, additional branches on the same side of the
tree die and finally the entire tree top dies. Failure of the newly
formed wood (xylem) of the Persian walnut top to unite with the wood of
the black walnut rootstock at the graft union causes girdling and
From correspondence dated April 6, 1955.
subsequent death of the branches (Figure 2). A dark-brown or black layer
of corky tissue forms between the xylems of the rootstock and scion
(Figure 3,A). At first, this layer is very narrow, but later it may become as much as * inch wide. t the beginning, only a sector of the trunk
at the union may be involved but in subsequent years, the blackline
gradually girdles the tree. As long as both the rootstock and top of
the tree remain alive, annual layers of bark and wood continue to form
from the cambium above and below the graft union. The original point of
the beginning of the girdle may be hidden by these newly formed layers of
bark and wood which meet but do not form a functional union. Trees
affected with blackline generally have an apparently perfect union between
the rootstock and scion for many years prior to the onset of the trouble.
Then girdling occurs in the new wood; the wood formed previously is not
affected (Figure 3,B).
After blackline becomes well-established, a decay of the bark of
the black walnut rootstock immediately beneath that part of the graft
union affected by blackline frequently occurs.
Survey Procedure
Forty-five widely separated orchards including 13,121 trees were
observed and mapped in the survey. A variety of soil series, ranging
from lighter, deeper, valley-floor and river-bottom soils to heavier
and shallower upland soils were represented. Approximately three-fourths
of the trees examined were varieties of Persian walnut (Juglans regia L.)
grafted on Hinds black walnut (J. hindsii (Jeps.) Jeps.) rootstocks. The
remainder were engrafted Persian and black walnut seedlings and Persian
walnut varieties grafted on J. nira L., J.
real
and hybrid (mostly
Royal) rootstocks, respectively (Table 1). Nearly all grafted trees
belonged to the Franquette variety, but a small number of trees of the
Mayette and Parisienne varieties were present in a few orchards. All
orchards but one were cleanly cultivated through the summer months; one
was in irrigated grass sod. Some were fertilized with nitrogenous
fertilizer. Eleven of the 45 orchards were re-surveyed each year from
1950 to 1956; most were re-surveyed at least five times, but 3 were
surveyed only twice. Two of the orchards (Franquette on J. hindsii
rootstocks and totaling 420 trees) were examined for blackline only in
1956, but trees were not measured. Re-surveying was done in an attempt
to determine yearly increase in the incidence of blackline and length
of time required for the affected trees to become unproductive and die.
However, exact records were difficult to obtain as many growers removed
the affected trees even before they became unproductive and, in some
cases, planted new trees.
Individual trees were ma pped on graph paper with symbols representing
normal, declining, and dead trees, trunk circumference of trees and kind
of rootstock. If the tree was grafted, the height above the ground of
the graft union was plotted. The year decline was first noted, the
portion of the tree top affected, extent of decline, and cause, if
determined, were recorded on the map. l'Jhen the tree showed decline
As the actual age of many trees could not be determined, trunk diameter
was used as a criterion of relative size; the circumference of the tree
trunk 2 feet above the ground was measured at the time the orchard was
first mapped and the measurement converted to diameter by dividing by
3.1416.
symptoms, it was examined for blackline or rootrot. To determine the
presence of blackline, a small rectangular or triangular piece of bark
is removed with a cleft-grafting chisel to expose the wood at the graft
union on the declining side, If blac k line is present, a narrow layer
or line of dark-brown or black tissues, up to i inch wide, occurs in the
wood at the graft union at the interface of the xylem of the scion and
the rootstock (Figures 3A, and 3B). Tree decline from rootrot was
determined by removing the soil from the crown and large basal roots and
examining for the presence of dead areas and fungus mycelium between the
bark and wood. Small roots and rootlets were not examined for lesions
because to do so was too time consuming and costly to be practical. If
both blackline and rootrot were found on the same tree, the tree was
recorded as affected with blackline only; in most cases, however, root
or crown rot eventually develops following girdling from blackline
(Figure
Li ).
Trees without decline symptoms in the tops were not examined
for blackline or rootrot. Such a procedure might exclude early cases of
blackline as many trees do net show decline symptoms until several years
after the-disorder begins; were the early, undiscovered cases added, the
incidence of blackline would undoubtedly be even greater than reported.
Relation of Occurrence of Blackline to Various Factors
Kind of rootstock. Blackline has been found
only in Persian walnut
trees grafted on J. hindsii or J. nigra rootstocks or on their hybrids or
those of other black walnut species with these. Not a single case of
From 1952 to 1955, all blackline determinations were made by the same
individual. In other years, several other trained people assisted in
the survey.
-6-
blackline has been found in any of the mapped Persian walnut trees grafted
on Jo
regia rootstocks (Table 1). Limited data suggest Persian walnut
trees grafted on J.
nigra rootstocks are not quite as subject to blackline
as ones on J. hindsii rootstocks (Table 1); of 403 trees examined in 3
mapped orchards of the Franquette variety grafted on J. nigra seedling
rootstocks, on Willamette and Olympic soils, 18,8% were affected with
blackline as compared with 70.1% of 670 trees in 3 other orchards of the
same variety of approximately the same age and on the same soil series
but on J. *.•■••■■•■■■.•.e.
in
hdsii
rootstocks.
Scion variety. Blackline has been found in grafted trees of all
commercial varieties grown in Oregon. However, trees of the Mayette
variety do not seem to be as subject to blackline under Oregon conditions
as those of the Franquette variety (Tables 1 and 2); only 2.8% of the
trees examined in
5 mapped
orchards of the Mayette variety grafted on
J. hindsii rootstocks were affected with blackline as compared with
32.6% affected of trees of the Franquette variety in the same orchards,
on the same rootstock, of approximately the same age and on the same
soil series (Table 2). Limited data suggest also that trees of the
Parisienne variety are also not as subject to blackline as trees of the
Franquette variety (Table 2).
In California, the Payne and Concord varieties , are reported to be
most subject to blackline.
Tree trunk diameter, Blackline was found in trees ranging from
3.3 to 29.3 inches in trunk diameter, being most prevalent in trees
9 to 19 inches in diameter. The greatest incidence of blackline
(52.5%)
occurred in the 11.1 to 13-inch trunk-diameter group (Table 3). During
early life, the tree is in a highly vegetative condition. As fruiting
becomes "heavier," vegetative growth declines and the tree becomes in-
creasingly
fruitful. Blackline usually develops during this period.
After a walnut tree reaches 20 inches or more in diameter, it is less
likely to become affected as shown br the fact that of 524 trees in
19.1 to 29-inch groups, only 26.7% had blackline compared with 52.5%
in
the 11.1 to 13-inch groups.
Soil series. Blackline was
found in Persian walnut grafted
on
black walnut rootstocks on all soil series (Table Lb). However, the
incidence of blackline was definitely greatest on the Olympic soil series;
78.8% of the trees examined on this soil series were affected with blackline as compared with 36.1% of the tree., on Carlton and smaller percentages
on other soil series.
In the 4 orchards in the Olympic series having the highest incidence
of blackline, 93.1% of the trees were affected, In the other 4
orchards
on this series, 30.4% were affected. In the 3 orchards on Chehalis soil
having the highest incidence of blackline, 27.9% of the trees were
affected. In the other orchards on this series, 12.2% were affected with
blackline.
Height of graft union. Blackline was found in trees grafted at all
levels from below the ground up to and into the limbs.
Interaction of tree trunk diameter, soil series and incidence of
blackline. Trees grown on Aiken soil developed blackline at a smaller
trunk diameter than those on other series; 16.6% of the trees on Aiken
soil developed blackline when trunk diameters were between 7.1 and 9 inches,
in comparison to 3.2% or less of the trees on other soil series at this
stage (Table 5). In the Olympic soil series, 30.7% of the trees developed
blackline when they were between 9 to 11 inches in trunk diameter. Trees
on the Umpqua soil series were the largest before they developed blackline;
very fe9 trees on this boil developed blackline until they reached 19 to
21 inches in trunk diameter,
The total number of trees in a trunk-diameter group was relatively
small in some cases, for example, there were only
55
trees or Jess in the
7.1 to 9-inch trunk-diameter group on Olympic Willamette, Umpqua and
Carlton soil series, but on Newberg Chehalis, Aiken and Melbourne series
there were 141,
167, 414
trunk-diameter groups (23
and 466 trees, respectively. In the larger
4-
inches), there were also relatively small
numbers of trees in the various groups in most cases. However, while the
data appear to indicate that older trees are less likely to become affected,
it should not be deduced that old trees are not subject to the disorder,
as blackline has been found in trees up to 29.3 inches in diameter.
Blackline in 1950 and 1956
In some orchards surveyed, a relatively rapid increase in the
incidence of blackl 4 ne occurred from 1950 to 1956; one orchard of the
Franquette variety grafted on the Hinds black walnut roots on Olympic
soil had a 81.8% net increase in the incidence of blackline as compared
with 19.1% in two orchards on Melbourne soil (Table 6). Except for the
orchard on Olympic soil, which was one of the most severely affected, no
outstanding difference in the percentage increase of blackline on different
soil series was found.
Average net increases in indicence of blackline in 11 orchards under
continuous survey for the 6-year period was
34.4%
of the total number at
the beginning of the survey. In most orchards, the rate of increase
fluctuated considerably from year to year. In the above 11 orchards, the
-9-
average annual percentage increases in new cases of blackline recorded
were 5.0, 2 2, 4.0 16.2, L.8 and L.2% in 1951, 1952, 1953, 1954, 1955
and 1956, respectively. Blackline initiation undoubtedly occurred prior
to the year of recording it in most cases.
Time Required for Affected Trees to Become Un roductive
Accurate data on how long affected trees live are difficult to obtain
because most growers remove the affected trees when they are no longer
productive.
Percentages of a number of blackline-affected trees that became unproductive each year from 1950 to 1955 were determined in an attempt to
obtain information on this subject. A study was made of 730 trees which
had i or less of the tops affected when first examined; 61% were still in
production five years after blackline was found (Table 7). The data also
indicate affected trees go out of production in a shorter period of time
when located on the heavier and shallower upland soils such as Aiken,
Melbourne and Olympic than when grown on lighter and deeper valley soils
such as the Newberg, Chehalis and Willamette series.
-10-
:T;
m10
es of i
2 .traL9 on j)211s1.aaw
Alnut s.
M ajor root diseases of walnuts caused by parasitic organisms in
the United States are mushroom rootrot, crown rot, and Phytophthora rootrot. Some non-parasitic rootrots are caused by poor drainage, lack of
adequate aeration and other adverse environmental conditions.
Mushroom rootrot, due to Armillaria mellea Vahl ex. Fr. (8 9), is
the most prevalent parasitic rootrot in Oregon. Fruiting bodies of the
causal fungus are honey-colored or light brown "toadstools" or mushrooms,
which generally ap pear in clusters about the base of infected trees;
development of fruiting bodies depends on weather and extent of root decay.
Roots, root, crown and basal part of the tree trunk are attacked by
the fungus. Poor growth of shoots attended by premature yellowing and
dropping of leaves is usually the first signs of infection. Only part
of a tree Corresponding to the side of the root system attacked by the
fungus may be affected at first, but later the whole root system is
invaded. A number of years may elapse before the tree finally dies. If
soil from the crown or main roots of an infected tree is removed, darkbrown or black root-like structures can generally be found clinging tightly
to the surface or just under the bark (Figure 5,A). These structures,
known as rhizomorphs, are one sign of the disease. They resemble roots
somewhat, but differ in that they do not have a central core or woody
cylinder; rhizomorphs may be absent, however, if conditions are unfavorable
for their development. If bark of the root of an infected tree is cut
away, white or tan strands of fungus growth will be found scattered through
the tissues. Frequently, a concentration of the fungus mycelium occurs
in the cambial region between the wood and bark, where it appears as a white
or tan, fan-shaped, flat fungus growth (Figure 5,B). White, fungus
mycelium is usually buried within the tissues and is seldom found on the
surface of the root. The fungus extends into the wood, causing it to
decay and become soft and spongy. The infected tissues have a mushroomlike smell. When the root crown, or collar, of the tree is completely
invaded, the tree dies. J.
nim is reported to be very resistant to
mushroom rootrot (14). J. hindsii is also believed to be resistant, but
the disease has recently been found on this species in California and
Oregon (408,11).
Crown rot is caused by the fungus Phytophthora cactorum (Leb. & Cohn)
Schroet. (21,22)--a "water mold" that thrives best in wet soil. This
fungus attacks the crown or large basal roots below ground and produces
dark-brown or black, irregular, watersoaked cankers or decayed areas in
the bark. The infected areas are soft or spongy and are usually confined
to the bark. The wood is not usually attacked, though the disease may
discolor it inward a short way. A black fluid often accumulates in the
cambial region and eventually finds its way to the surface. In the more
advanced stages, the disease extends outward on the large basal roots.
The first indication of infection is usually a general stunted
appearance in the tree tops accompanied by sparse, yellowish-green , foliage
and short shoot growth. In more advanced stages, the trees appear droughtstricken in midsummer, the leaves turn yellow and drop prematurely and
the shots and smaller branches die back; the tree usually succumbs the
following year.
Crown rot is most frequently found on trees located in poorly
drained or abnormally wet soils or where excessive flood irrigation is
practiced.
-12-
The Persian walnut is reported to be very resistant to crown rot
when growing on its own roots (21,22).
Crown rot has not been found in Oregon. Disease symptoms resembling
those of crown rot have been observed, but repeated attempts to isolate
the causal organism from affected tissues by use of special Phytophthoraisolation techniques have been unsuccessful.
Phytophthora rootrot, caused by Phyto phthora cinnamomi Rands (23),
is very similar to crown rot in symptomology. Like crown rot, it is
caused by a "water mold" that thrives best under wet conditions. This
fungus attacks the roots and root crown, producing dark-brown or black,
irregularly shaped cankers or decayed areas in the bark and wood. Both
the young and the older roots are attacked. The infected areas are
soft, watersoaked and spongy. The symptoms in the tree top are almost
identical with those in trees infected with crown rot.
Like croon rot, Phytophthora rootrot has not been found in walnut
orchards in Oregon. However, inoculations made on potted J. sala and
J. hindsii seedlings with pure cultures of P. cinnamomi resulted in the
development of large irregular, soft, spongy cankers on the primary and
secondary roots of J. regia and eventual decay of the root and death
of the trees (12). The fungus also produced lesions on the roo ts of
inoculated J. hindsii seedlings, but they were located predominately.
on the secondary roots.
-13Relation of Occurrence of Rootrots to Various Factors
Kind
of rootstocks. The incidence of rootrots in Oregon was
•••■••
found to be generally greater in Persian walnut trees grafted on
Hinds black walnut rootstocks than in those grafted on Persian rootstocks
(Table 1). One of the primary reasons why Persian seedlings have not
been used heretofore as rootstocks in Oregon is that it has been generally
believed that they are much more susceptible to mushroom rootrot infection
than Hinds black walnut rootstocks. Because of this prevalent belief,
authorities in California do not advise their use as rootstocks in that
state (5,16), but the data obtained by the authors indicate that Persian
walnut rootstocks are not seriously affected by rootrots in Oregon.
In addition to the data given in Table 1, further evidence of
the relative unimportance of mushroom rootrot in the decline and death
of walnut trees in Oregon was shown by the results of experiments on
the exposure of J. hindsii, J. reria and Ptsrocarya sten?pter
DC. to
A. mellea. In the spring of 1951, twelve 2-year-old seedlings of each
of the species named were planted at Corvallis, Oregon, in 3 cold frames
in a randomized plot design and pure agar cultures of A. mellea distributed
ON*
••••••■••■••■•■01
in each frame. Pieces of bark contaminated with A. mellea were subsequently
added to the soil every year since 1951 so that in 1957 the substrate
was heavily infested with the fungus. Despite this "heavy" inoculum
potential, most of the trees made excellent top growth necessitating
topping them at intervals to keep them in bounds. In October, 1957
Since the end result is the same irrespective of type or causal
organism, all rootrots are grouped and considered together in the
present study.
the trees were dug and their root systems examined for evidence of
rhizomorphs or bark infection; no rhizomorphs were found and none of
the trees showed any visible signs of mushroom rootrot infection.
The results of these experiments and observations made in Oregon
walnut orchards tend to support the view held by Day (L&), Boyce (1)
and others who believe that A. mellea is a facultative parasite. Thus,
afta•
Day (IL) reports that this fungus is parasitic only when the vigor of
the host has been reduced by unfavorable environmental conditions,
particularly poor soil, acting alone or in conjunction with other
injurious agents. Boyce (1) states "Owing to its widespread distribution
in the forests of this country, if the fungus were a virulent parasite
great damage should occur but there is apparently little relation between
the occurrence of the fungus and the prevalence of the disease." He
further states "usually the presence of shoestring root rot should be
interpreted as indicating a debilitated condition of the tree from some
prior cause."
It is, of course, possible that different strains or races of
this organism varying in pathogenicity exist. The studies of Childs and
Zeller (2) would tend to support this view. These researchers reported
that in Oregon a "fir-strain" of A. mellea is prevalent which is not
as pathogenic as the "oak-strain." As Douglas fir is the most prevalent
forest tree species in western Oregon, it is possible that the fir
strain of this fungus predominates in this area. From the results of
field observations and these studies, it is concluded that the strain of
A. mellea present in most walnut orchards in Oregon is apparently of
minor importance in the decline and death of Persian walnuts in this
state, and that the continued use of J. hindsii as a rootstock solely
to escape mushroom rootrot is not warranted under Oregon conditions.
Trunk diameter. Rootrots were found in trees ranging from 2.9 to
26.1 inches in trunk diameter. The data obtained in this survey indicate
that there is little if any relation between the size of trees as measured
by their trunk diameter and the incidence of rootrots. Thus, trees Ito 9 inches in trunk diameter were found to be as subject to rootrots
as those measuring 19- to 21 inches (Table 9).
Soil series. Data on the relation of soil series on which the
trees grew to the incidence of rootrot are given in Table 8. It would
appear from the data that the occurrence of rootrot is greatest in
trees on the Carlton soil series. However, only two orchards on this
series are included, and one of these is on poorly drained soil that
has a relatively high water table during the winter. It is believed
that this unfavorable soil condition has predisposed the trees to
rootrot and its inclusion resulted in higher incidence of rootrot than
normal for this particular soil series. If this soil series is excluded,
there seems to be little, if any, relation between the occurrence of
rootrots and the soil on which the trees grew.
-16-
DISCUSSION
Decline and death
of Persian walnut trees in relation to blackline.
From the data obtained in this survey, it is concluded that blackline is the most !_mportant single cause of decline and death of Persian
walnut trees grafted on black walnut rootstocks in Oregon; blackline
caused greater loss of grafted walnut trees than all other factors
combined; about 7 of every 8 dying walnut trees in Oregon were found
affected with blackline. In terms of percentage of the trees surveyed,
34.6 percent of all Persian walnut trees grafted on black walnut rootstocks examined (9267) were affected with blackline. The actual extent
of this disorder is undoubtedly even greater than the data show because
blackline is often present before external symptoms appear. In this
survey, the trees were not examined for blackline unless there were
symptoms of decline in the tops. While the incidence of the disorder
is serious, the results of studies on the relation of trunk diameter
to the occurrence of blackline afford some hope that the industry in
Oregon will not be completely wiped out by blackline. Some trees are
fairly productive for a number of years after they become affected.
Then too, as previously pointed out, if a tree passes the most "susceptible"
size group without becoming affected with blackline, it is less likely
to become affected.
One of the most important facts disclosed by this survey is the
effect that the type of soil on which the trees are growing has on the
occurrence of blackline. In general, blackline is more prevalent in
soils of the Olympic series than on any of the others included in this
-1 7-
survey. It is noteworthy that the trees on. Olympic and Aiken soils had
smaller trunk diameters when they began to become affected with blackline
than those growing on any other soil series included in this study. Moreover, it appears that affected trees on Aiken, Olympic and Melbourne
become unproductive sooner than do trees in orchards on the Chehalis,
Newberg and Willamette series.
Inasmuch as soil series appears to be of considerable importance in
the relation to the occurrence of blackline, a general discussion of the
more important soil types in western Oregon -with respect to their origin
and physical characteristics is indicated. With respect to origin, the
soils may be grouped into two general categories: (a) those derived from
igneous or sedimentary rocks through weathering and (b) those derived
from material accumulated by deposition from water (6). From igneous rocks
are derived the Aiken and Olympic soils. From sedimentary rocks and shales
are derived the Carlton and Melbourne soils, all found in the uplands.
In the second group are included the Willamette, Newberg, Chehalis and
Umpqua soil series. They lie on the valley floor and along the flood
plains of streams and are derived from shale and sandstone or mixed
materials.
The Olympic and Aiken soil series on which the highest incidence of
blackline was found and on which the disorder developed in relatively
small trees are thus derived from igneous rocks, whereas all other soils
included are derived from shales and sandstones. Moreover, these soils
also differ in some respects in their mechanical analyses (Table 10). The
top soil of the Olympic clay, loam contains about twice as much clay as the
Chehalis
clay loam. Just what relation there is between differences in
origin and mechanical structure and the prevalence of blackline is not
known.
-18It is also noteworthy that the Franquette on J. hindsii rootstocks
is apparently more subject to blackline than the Mayette on the same
rootstock. Consequently, other commercial varieties less subject to
blackline must be found to replace it or else it must be grafted on
Persian rootstocks.
While the cause of blackline is not known, the disorder does not
appear to be due to a parasitic fungus or bacterium as numerous attempts
by Schuster and Miller (17) and by California researchers (3,22) to isolate a parasitic micro-organism from affected tissues have been negative*
Blackline causal theories. A number of theories have been suggested
by different investigators to account for the development of blackline.
Davey (3) lists most of the theories that have been suggested and gives
some facts and observations about each. To his list, we have added some
other suggested possible causes and our own observations, as follows:
Suggested Causal Theories
1. Certain species of walnut or
Pertinent Facts and Observations
1. Blackline occurs only on
species hybrids used as root-
Persian walnut trees grafted
stocks are not fully compatible
on black walnut (J. hindsii
with the Persian walnut.
or J nigra) rootstocks or on
hybrids between these two or
with other
species. In Oregon,
blackline was found to be most
prevalent in trees of the Franvette
variety grafted on Royal
hyrid (a species hybrid) rootstocks (Table 1). However, there
are hundreds of old Persian
-19-
walnut trees grafted on J. hindsii
and some of its hybrids that have
not developed blackline in 50 years
or more after being grafted.
2. Trees of certain varieties
Blackline is more prevalent on tre(
are not completely compatible
of certain varieties than on those
with the rootstock used.
of others; for example, in Oregon,
trees of the Franquette variety
have a higher incidence of blackline than do those of the Mayotte
variety (Tables 1 and 2). However,
numerous grafted Franquette trees
50 years of age and older are not
affected, In California, blackline is most prevalent in grafted
trees of the Payne and Concord
varieties. However, the disorder
i3 Wt. limited to these varieties
but has been observed on practically all varieties in that state
in some trees in certain orchards
but not in others. In Oregon,
numerous old trees of these same
varieties are not affected.
Blackline is traceable to
Numerous cases of blackline have
a bad union in the original
occurred where an apparently per-
graft.
feet union persisted for many
years (see Figure 3-B).
-20-
Blackline results from some
Many affected and non-affected
particular type of grafting
trees and limb-grafts were grafted
or budding.
by the same man, by the same
method and at the same time.
Blackline is caused by
Numerous cases of blackline have
grafting a relatively late-
occurred where early-leafing
leafing rootstock such as
persian varieties have been
the Franquette, on an early-,
grafted on early-leafing black
leafing rootstock such as
walnut rootstocks. Also, early-
J. hindsii.
leafing Persian seedlings and
•■••■
•■•*11.008I/a•■•■■••■•.
"sleeper" Persian seedlings,
leafing out as late as July, have
been grafted to the Franquette
variety, but blackline does not
always develop.
Blackline is caused by a
In Oregon, blackline is most
deficiency of moisture or
prevalent on trees on the Olympic
of one or more mineral nu.
soil series; these are relatively
trients'in.the soil.
uheavyn , shallow, upland soils and
are apt to become deficient in
available moisture in late summer
and early fall. However, there
are other soils that are often
lacking in moisture in late summer
and yet blackline is not
except,
tionally prevalent in trees growing
on them. As for the theory that
the disorder results from a
-2 1deficiency of mineral nutrients,
blackline is known to occur in
orchards where there is no known
nutritional deficiency.
7. Blackline is caused by
There is no correlation between
freezing of the tender
the occurrence of extremely cold
tissues at the union.
weather and the incidence of blackline. Many grafted trees in Oregon
have been badly injured by cold and
yet no blackline has developed.
Moreover, blackline occurs in below
ground-grafted trees where the
tissues at the union are not subject
to freezing.
8. Blackline results from the
8. Blackline occurs in orchards where
accumulation of boron or some
there is no indication of a toxic
other element or chemical sub-
accumulation of an element as evi-
stance which causes chronic
denced by freedom from visible
injury to the meristematic
symptoms of foliage injury. Also,
tissues at the graft union.
boron injury has occurred in the
foliage of many grafted trees that
have not developed blackline. Moreover, chemical analyses disclose_
that there is no meaningful
difference in the boron and other
mineral contents of the tissues
just above and below the graft union
and in the blackline area itself
(Table 11).
-229. Blacklins is the result of
The heartwoods of a number of
chronic injury to the meri-
affected trees were examined, and
stematic tissues at the graft
no evidence of wood decay was found
union brought about by some
(see Figure 3-B). It is true that
type of toxic emanations from
wound gums are generally present
within the stem such as might
in tissues adjacent to the blackline
originate from certain types
area, but these are probably an
of wood decay in the heartwood.
effect rather than a cause,
10. Blackline is due to a parasitic
organism.
10. Numerous attempts made in Oregon (17)
and by various researchers in California (22) to isolate a causal
parasitic organism were all negative.
12. Blackline is caused by a
virus.
11. A limited number of attempts made
by the authors and by Serr (18) to
transmit this disorder by grafting
were negative. However, a number of
known facts suggest the cause may be
a virus. For example, in many instances the affected trees are
grouped in certain areas in the
orchard. Davey (3) reported similar
observations in California. Blackline is most prevalent in the coastal
areas near San Francisco and has not
been found south of Merced, Calif.
The grouping of affected trees and
the limitation of blackline to cer-
suggestive of a transmissible agent
like a virus. A somewhat similar
rootstock disorder recently reported in Eureka lemon trees
grafted on Troyer citrage rootstock is believed to be due to a
virus (25). In the buckskin
disease of cherry and peaches (a
virus disease) Schneider (15) reported that there is wound-gum
accumulation in the sieve tubes of
blackline in walnuts is a virus
disease are now in progress.
Whatever the causal theory, it must take into account the following
facts: (a) blackline occurs only on Persian walnut trees grafted on black
walnut (J. hindsii or J. nigra) rootstocks, on their hybrids or on those of
other species with these; (b) the disorder starts in grafted trees where
Previously an apparently Perfect union existed; and (c) it is generally most
prevalent in grafted trees growing on the Olympic soil series in Oregon.
Methods used to save trees affected with blackline. In the past, attempts
have been made by certain growers and investigators to save trees affected
with blackline by one or mare of the following measures:
(a) The discolored areas have been cut out with .a chisel and growth
regulators applied to the cuts in an attempt to encourage
reunion. Vertical cuts with saws or chisels, spaced 3 to 6
inches apart, have also been extensively made across the union
of affected trees to encourage new callus formation; neither
these measures have been successful.
(b) Efforts have also been made to establish new unions across
the blackline area by (a) inarching suckers from the black
walnut rootstock into the trunk above and (b) bridging across
the girdle with short sections of scion wood. marching the
black walnut sprouts from the rootstocks, if successfully
accomplished, would only re-establish the scion top on the
same rootstock which, in turn, allows for re-development of
blackline. A similar situation prevails in bridging over the
union with sections of scion wood unless some species can be
found that does not develop blackline at the unions.
In bridging across the graft union one is confronted
with the difficulty of getting the scions to live. It is
p ossible that new or improved techniques could increase the
percentage of living scions. Serr (20) found an increased
percentage of living scions to result when the basal end of a
straight scion was inserted the first year and the top end
the following year. If a scion species that did not develop
blackline could be found, bridge-grafting could be practical.
(c) Some growers and investigators have attempted to save trees
affected with blackline by planting Persian seedlings around
them and later inarching the seedlings into the trunks above
the graft union. If it were possible to get the grafts to
"take," the trees would develop a Persian root system instead
of a black walnut root system and thus would not be subject to the
disorder. However, inarching attempts made so far have been
attended with but limited success, Probably one reason for failure
is that the affected trees have, in most cases, deteriorated too
far for the grafts to otake H . Once a tree shows evidence of decline
in the top, it is generally too late to use this remedial measure,
for by the time the young seedlings get established and are ready
to be inarched the grafts will not "take n because of lack of tree
vigor. Since some trees are lost from blackline before they are
20 years of age, this would mean grafting the trees when they are
still young and actively growing. Other reasons for failures in
marching seedlings are inherent in the basic difficulties of
grafting walnuts and of growing a large enough root system on the
seedlings soon enough to support the nearly mature walnut trees.
It is possible that new or improved techniques could make marching
more practical. One walnut grower, near Springfield, Oregon, had
a measure of success in marching Persian seedlings by allowing
several inches of the upper end of the scion to extend beyond the
point of union for a year or two years before being cut off, There
is a possibility also that the use of fast-growing Persian seedlings,
such as Manregian, for inarching might increase the practicability
of inarching.
(d) In the case of limb-grafted trees, multiple-grafts (10 to 15 grafts
per tree) are being used to some extent in California to increase
longevity of affected trees (19). When a limb becomes affected,
it is cut off below the girdle and regrafted. While this method
will not prevent blackline if the rootstock is in a black walnut
-26it has prolonged productivity since all grafts generally do not
develop blackline simultaneously.
(e) After a tree has been girdled by blackline, it is sometimes possible
to grow a new tree for a time by sawing off the tree top below the
union and grafting Persian scions on two or three of the most vigorous
suckers arising from below the union. All remaining suckers are cut
out and later all but one of the grafted suckers are removed and a
new top is grown from the one remaining. This is definitely not a
control measure, however, since there is a high percentage of blackline reoccurrence on grafts made on sprouts arising below the original
graft union.
(f) In California, Serr (19) tried injecting growth regulators and nutrients of various kinds into or near the graft union in an effort to
increase cambial activity and slow down progress of the disorder,
but so far without success.
(g) With trees grafted at or near the ground line, attempts have been made
by the authors to stimulate the production of roots from the Persian
scion by wounding the tissues just above the union and treating them
with root-stimulating growth regulators; these experiments are now in
progress. In this connection it is noteworthy that in one 20-year-old
grafted Franquette orchard, near Corvallis, Oregon, roots have been
produced naturally from Persian walnut tree tops following trunk injury; scion roots are present on 22 percent of the trees in this
orchard. Many of the trees with scion roots are vigorous despite
being affected with blackline indicating that the scion roots are
functioning in maintaining the vigor of the tree tops. If scion roots
could be produced when desired, it would aid materially in limiting
losses from this disorder as the trees would be on their own roots.
-27This measure, if found successful, can obviously be Used only on trees
`grafted below the ground line. New orchards or replacements in Persian walnut orchards should consist only of trees grafted on vigorous
strains of Persian walnut seedlings, such as Nanregian, since, this .is
the only oertain: method known of escaping blackline at present.
Decline and death of Persian walnut
the data in Tables 1,
8,
and
9,
trees in relation to rootrots. From
it is evident that, in comparison with black-
line, rootrots are relatively unimportant in the decline and death of walnut
trees in Oregon except on Carlton soil series. This is shown by the fact
that of 13,121 trees examined on all kinds of rootstocks, only 3.4 percent
were found affected with rootrots while out of
9,267
Persian walnut trees
of largely the Franquette variety grafted on black walnut roots in these
same orchards,
313.6
percent of the trees were found affected with blackline,
Another surprising fact disclosed by this survey is that in Oregon the
incidence of rootrots is greater on Persian walnut trees grafted on Hinds
black walnut rootstocks than on those grafted on Persian rootstocks. One
of the chief reasons why Persian seedlings have not been used heretofore as
rootstocks in Oregon is that it is generally believed that they are much
more susceptible to mushroom rootrot than Hinds black walnut rootstocks, but
the results of this survey do not substantiate this belief. Just why A.
mellea is not as aggressively parasitic on the Persian walnut in Oregon as
it is in California is a matter of conjecture; it may be that there are
different strains of this organism which vary in pathogenicity. Also, soil
temperatures are higher in both winter and summer in California than in
Oregon; temperature may affect the parasitic activity of the fungus.
-28Summapy
Blackline was found to be the most important single cause of the decline
and death of Persian walnut trees grafted on black walnut rootstocks in Oregon.
This disorder was observed only on Persian walnut trees grafted on black walnut rootstocks (J. hindsii er J. nigra), on their hybrids or on those of
other species with these two. One case of graft union failure was noted in
a Franquette tree grafted on a Persian walnut hybrid of unknown parentage,
but not a single case of blackline was found in Persian walnut trees grafted
on J. regia rootstocks.
From limited data it would appear that Persian walnut trees grafted on
eastern black walnut (J. nigra) rootstocks are not quite as subject to blackline as those grafted on J. hindsii rootstocks. Under Oregon conditions, the
Mayotte variety is apparently not as "susceptible" to blackline as the Franquette variety.
Blackline was found in trees ranging from 3.3 to 29.3 inches in trunk
diameter; it was most prevalent in the 11- to 13-inch trunk-diameter group.
After a walnut tree attains a trunk diameter of at least 20 inches, it is
less
likely to become affected.
Blackline was observed on trees on soils of all series studied. However,
it was most prevalent in trees growing on the soils of the Olympic series,
which are generally relatively nheavyn , shallow, upland soils derived from
igneous rocks.
In the orchards studied, the majority of the affected trees growing on
Olympic and Aiken soils developed blackline at a smaller tree-trunk diameter
than those growing on soils of other series included in this survey. Also,
trees affected with blackline were found to go out of production ; sooner when
they were grown on Aiken, Melbourne, and Olympic soils than they did on the
-29deeper
valley floor soils such as Chehalis, Newberg, and lillametts.
Blackline was found in trees grafted at all levels from below the ground
up to and into the limbs.
In a study of 730 trees affected with blackline on 6 soils, 61 percent
were still in production
5 years
after
blackline was first found. Of the
trees going out of production, 4.9 percent were out after 1 year, 14.8 percent
after 2 years, 28.5 percent aft er 3 years, 37.1 percent after
39
percent after
4 years, and
5 years.
In comparison with blackline, mushroom rootrot and other kinds of rootrots were relatively unimportant in the decline and death of walnut trees in
Oregon. In general, the occurrence of rootrot was greater in Persian walnut
trees grafted on black walnut rootstocks than in those grafted on Persian
rootstocks.
Rootrots were found in trees ranging from 2.9 to 26.1 inches in trunk
diameter. Relatively small tree (7 to 9 inches in diameter) were found to
be as subject to rootrot as larger ones (19 to 21 inches in diameter).
Little, if any, relation was found between the incidence of rootrots and
soil series.
The conclusion from the data obtained in this survey is that J. hindsii
1•••■•••••■•01*
and J.
nigra, and their hybrids are not suitable as rootstocks for grafted
Persian walnut trees because of their susceptibility to blackline. For the
-presant, certain Persian walnut seedlings of the more vigorous types, .such
as Manregian, are considered to be the best choice as a rootstock for grafted
Persian walnut in Oregon,
-30Literature Cited
Boyce, J. S. 1948. Forest Pathology. 550 pp. McGraw-Hill Book Co.
Childs L., and S. M. Zeller. 1929. Observ ations on Armillaria Rootrot
of Orchard Trees. Phytopathology 191 . '869-873.
Davey, A. E. 1946. Walnut Gridle Disease (Blackline). Diamond Walnut
News 28 (4): 8-9.
Day, W. R. 1929. Environment and Disease. A Discussion of the Parasitism
of Armillaria Mellea (Vahl.) Fr. Forestry 3: 94-103.
Grasser, H. L. 1951, The Walnut Rootstock Problem. Western Fruit
Grower 5 (5): 23.
Kocher, A. E., E. J. Carpenter, C. V. Ruzek, and J. E. Cooter. Soil
Survey of Yamhill County, Oregon. U. S. Department of Agriculture.
66 p., illustrated. Series 1920.
Milbrath, D. G. 1929. Plant Pathology Notes, California State Dept.
of Agriculture Monthl y Bulletin 18 (12): 777.
Miller, P. W. 1951. Mushroom Rootrot of Walnuts in Oregon. Proceedings
of the Oregon State Horticulture Society (1950) 42: 142-144.
. 1953. Diseases of Filberts and Persian Walnuts.
U. S. Dept. of Agriculture Yearbook 1953: 800-808.
Miller, P. IL I C. O. Rawlings, and J. H. Painter. 1952. Causes of the
Decline of Walnut Trees in Oregon: Second Report., Proceedings of the
Oregon State Horticulture Society (1951) 43: 183-185.
1954. A Survey of the Causes of the Decline in Vigor and Death of Some
Walnut Trees in Oregon: A Four-Year Report of Progress. Proceedings
of the Oregon State Horticulture Society (1953) 45: 202-207.
Miller, P. VT. and L. F. Roth. 1956. Relative Susceptibility of Potted
Seedlings of Juglans regia, J. Hindsii, and Pterocarya steno tera to
mo
isease
Phytophthora cinnamI7-151aFt
D Reporter 40: 53
.
Rawlings, C. O., J. H. Painter, and P. W. Miller. 1951. Importance
of Blackline in Certain Oregon Walnut Orchards. Proceedings of the
Oregon State Horticulture Society (1950) 42: 150-151.
Roy, H. 1936. Lepourridie sur les Moyers de l t Isere. Journal of
Agriculture prat., Paris, N. S., C 23, 467-470.
(15) Schneider, H. 1945. Anatomy of Buckskin -- Diseased Peach and Cherry.
Phytopatholo KT 34: 610-635.
-31-
(16) Schneider, H., E. AC Bodine, and H. E. Thomas. 1945. Armillaria Rootrot in the Santa Clara Valley of California, Plant Disease Reporter 29:
495-496.
(17) Schuster, C. E., and P. W. Miller. 1933. A Disorder of Persian (English)
Walnuts Grafted on Black-Walnut Stocks Resulting in Girdling. Phytopathology 23: 408-409.
(18) Serr, E. F. 1947. A Readers Digest of Cultural Problems: University
Reports Progress in Walnut Research. Diamond Walnut News 29 (1): 12-13.
(19)
(20)
. 1949.
Diamond Walnut News. 3r (6): 14.
Progress in Walnut Research.
. 1953• Grafting in Black Walnut Sprouts:
Another Method of Saving "Blackline" Trees. Diamond Walnut News 35: 12.
(21) Smith, C. 0., and J. m . Barrett. 1931. Crown Rot of Juglans in California. Journal of Avicultae Research 43: 885-904.
(22) Smith, R. E. 1941. Diseases of Fruits and Nuts. California Agriculture
College Extension Circular 120.
(23) Torgeson, D. C., R. A. Young, and J. A. Milbrath. 1954. Phytophthora
Rootrot- Diseases of Lawson Cyprus and other Ornamentals, Oregon
Agricultural Experiment Station Bulletin 537. 18 pp.
(24) Trunk, C. 1933. A Serious Trouble of Walnuts. Proceedings of the
Oregon State Horticulture Society (1932) 24: 163-168.
(25) Weathers, L. G., E. C. Calavan, J. M. Wallace and D. W. Christiansen.
1955. Lemon on Troyer Citrage Root. California Agriculture 9 (11):
11-12.
Figure 1. A Franquette walnut tree grafted on Hinds black
walnut rootstock affected with blackline in its initial
stages; note dead limbs on left side of tree.
Figure 2. Franquette walnut tree grafted on Hinds black
walnut rootstock affected with blackline in its advanced
stages; note dead limbs in tree tops and suckers coming
from root below the union.
a
A
B
Figure 3. Blackline of grafted Persian walnut trees: A, tangential section through the graft union showing blackline; B, radial section through
the graft union showing the separation of the phloem and xylem of the scion
from that of the rootstock: a, Persian walnut scion; b, black walnut root.
Figure 4. Side view of a radial section
of bark removed from across the graft
union of a Persian walnut affected with
blackline: a, Persian walnut bark, b,
black walnut bark. In addition to the
blackline, denoted by arrow, a rot is
shown in the black walnut bark mostly
below the union progressing from the
outside inwardly toward the cambium
layer. Many trees having blackline
show this rotted condition in the black
walnut bark just below the graft union.
A
B
Figure 5. Mushroom rootrot of Persian walnut caused by Armillaria
mellea: A, infected root with fungus rhizomorphs on surface; B, an
infected walnut tree showing fungus mycelium in the cambial region.
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Table 3
RELATION OF OCCURRENCE OF BLACKLINE ON PERSIAN WALNUT 1 TREES
GRAFTED ON BLACK WALNUT 2 ROOTSTOCKS TO TREE DIAMTER,
WESTERN OREGON, 1950-56
Trunk-diameter
group3
Total trees in group4
Trees in group
affected with
blackline
nc es
ber
Percent
1-3
26 3
0
.3.1-5
152
2.6
5.1-7
482
8.5
03
20.9
1752
42.1
1718
52.5
1509
41.9
712
43.3
17.1-19
432
40.3
19.1-21
263
27.4
21.1-23
171
31.0
23.1+
90
16.6
Total
8847
7.1-9
9.1-11
11.1-13
13.1-15
15.1-17
13
Neartrall Franquette variety; a few miscellaneous other varieties
included,
2 Antral' are J. hindsii; a small percentage are J. nigra and
miscellaneous _ hybrids.
Trunk diameter measured 2 feet above ground.
L. 420 trees not measured in one orchard on Umpqua soil series not
included.
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Table 9
RELATION OF THE
OCCURRENCE OF ROOTROTS ON PERSIAN WALNUT 1 TREES
IN 43 MAPPED ORCHARDS TO TRUNK DIAMETER, WESTERN OREGON, 1950-56
Trunk-diameter
group2
Inches
1
- 3
Trees in age groups 3
Number
Trees with
rootrots
Percent
673
0.1
349
0.9
5.1- 7
1049
2.3
7.1- 9
1842
4.5
9.1-11
2131
4.9
11.1-13
2165
3.0
13.1-15
2017
jTY
15.1-17
1091
4.3
17.1-19
650
5.5
19.1-21
347
4.6
21.1-23
191
23.1+
196
0.1
Total
12,701
3.5
3.1-
1
5
Nearly all are Franquette variety; a few miscellaneous varieties
included.
2 Trunk diameter measured 2 feet above ground.
3 420 trees on Umpqua soil series examined for the presence of
blackline only not included.
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