The yellow witches' broom of subalpine fir in the intermountain region

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UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
INTERMOUNTAIN FOREST & RANGE EXPERIMENT STATION
OGDEN UAH
No. hi7 June 1957

THE YELLOW WITCHES' BROOM OF SUBALPINE FIR
IN THE INTERMOUNTAIN REGION

James L. Mielke
Division of Forest Disease Research

The yellow witches! broom disease of true firs is caused by the
rust fungus Melampsorella caryophyllacearum Schroet. This fungus is
native to North America (1) and also Europe and Asia (5). It has been
known in Europe for about 150 years and approximately half that long in
this country (1).

The pathogen is not particularly destructive in Europe (5, 3), and
there is no record in the literature of it causing serious damage and
losses in any of the true fir species in North America. The purpose of
the present paper is to report an epidemic of the rust in subalpine fir
(Abies lasiocarpa (Hook.) Nutt.) on several areas in the southern portion
of the Intermountain Region.

RANGE OF THE RUST

In North America, Melampsorella caryophyllacearum is known from
Labrador and Newfoundland west to Alaska; south through Canada to the
northern United States, and still farther south in the western United
States to California and Mexico (2). It has been reported on Abies spp.
in all of the western states except Arizona and Nevada (1).

HOSTS

The fungus is one of the heteroecious rusts, i.e., it evidently
requires an alternate host for the completion of its life cycle (3, 5,
9, 10). The alternate hosts are species of Cerastium and Stellaria (2),
commonly called chickweeds in this region. Some species within each |
genus are annual and the others perennial.

Aecial hosts of the parasite are the true or balsam firs. In the
Intermountain Region the rust is known on white fir (Abies concolor
(Gord. & Glend.) Lindl.), grand fir (A. grandis (Dougl.) Lindl.), and
subalpine fir. The latter is by far the most common host of the three.

LIFE HISTORY OF THE RUST

The fungus is systemic and perennial not only on firs, but also on
those alternate host plants that are perennial species (75 10.).

Spores (aeciospores) are produced during the summer and early fall
in small yellowish-orange sacs (aecia) on the needles that are borne on
the witches! brooms. The aeciospores are wind disseminated and infect
the leaves of chickweeds (3). Small orange-red pustules (uredia) soon
develop and release urediosSpores which serve only to infect other chick-
weeds, thus intensifying the fungus on that host. The uredial stage is
followed by the formation of teliospores. These spores form within the
leaf cells where they overwinter (10). Teliospore germination and infec-‘'
tion of firs occurs the following spring (3).

DESCRIPTION OF THE DISEASE ON FIRS

The outstanding characteristic of this disease is the witches! broom
caused by it. The brooms are particularly conspicuous from midsummer to
late fall, for it is then that their yellowish-orange color is at the peak
of intensity and stands out in striking contrast to the normal dark green
foliage. Aeciospore production, which is then in progress on the diseased
needles, contributes to this color. Witches' brooms are upright, typical-
ly compact with a dense growth of many small and shortened branches, and
rarely exceed a diameter of 3 feet. The diseased needles are greatly
shortened and thickened.

In winter the brooms appear to be dead because the infected needles
shrivel and become dark in color. Shortly prior to the advent of spring
these needles drop leaving the brooms bare until new growth starts. The
new needles are a yellowish-green color until midsummer.

Witches! brooms occur on trunks and branches, but are most common on
the latter. Swellings commonly develop on both branches and trunks in
association with the brooms.

Twenty years ago Garrett (l) reported that in Utah the yellow
witches! brooms are often mistaken for some kind of "mistletoe." Even
though no mistletoes have ever been reported on subalpine fir in Region
h, this mistaken identity as to the cause of these brooms still exists
to a large extent. Mistletoes are seed-producing plants; Melampsorella
caryophyllacearum is a fungus and therefore reproduces by means of
spores.

A similar appearing witches' broom is present in this region on
Engelmann spruce, but it is caused by another rust fungus, Peridermium
coloradense (Diet.) Arth. & Kern (6, 7, 8, 9, 10). It is not certain
yet that this rust has an alternate host (ae

DAMAGE

Heavily infected trees are noticeably reduced in growth rate, and
as the disease continues to intensify within them they are eventually
killed. Trees of all ages are susceptible to the parasite. The disease
is particularly destructive to seedlings and saplings and considerable
mortality has occurred on some areas.

No systematic survey has yet been made to appraise accurately the
prevalence of this disease and the damage caused by it. Based on obser-
vations, however, heavily diseased stands of subalpine fir are known to
be present on three of the national forests in Region ) and more lightly
infected stands have been noted on most of the other forests.

In heavily diseased stands trees containing 30 to 50 or more brooms
are common. Many large trees have hundreds of infections. In such cases
almost every branch has one or more brooms. Estimates made in some of the
more severely diseased stands ranged from 80 percent to 90 percent of the
trees infected.

EPIDEMIOLOGY

It is inconceivable that subalpine fir would be present as a species
on certain of the diseased areas today if the intensity of infection by
this native rust had always been as great in the past as it is at the
present time. If the fungus remains uncontrolled and continues at its
present destructive rate the end result will be either greatly reduced
stocking of the fir or probable elimination of the tree from some, areas.
The great abundance of young brooms, ranging from one to several years or
more of age, provides adequate evidence that intensification of the dis-
ease has been occurring at a rapid rate. Literally dozens of such brooms
may be observed in many trees.

Some factor, or factors, not yet determined has been responsible for
the increased intensification of the disease and infection of the firs to
a degree far surpassing that of any case hitherto reported in this country.
Moisture during the growing season is needed for infection of both the al-
ternate hosts and the firs. General observations indicate that the epi-
demic has been in progress for about 25 years, perhaps longer in some cases.
Very favorable climatic conditions (a series of moist summers) during this
period could account for the present behavior of the pathogen. However,
weather records do not support this possibility. Furthermore, weather

conditions alone do not provide the full answer because moist years or
periods, favorable for intensification and spread of the fungus, cer-
tainly must have occurred in the past.

Evidently the fungus cannot perpetuate itself without the presence
of the alternate host. Accordingly, the epidemic may be accounted for
by a marked increase, perhaps an invasion, of chickweeds on areas adja-
cent to and within the affected fir stands. At least two of our common
and well-known chickweeds, Stellaria media and Cerastium vulgatum, are
exotics that now occur over most of North America. These two plants are
present on many of our mountain range lands. Changes have occurred in
the composition of forage plants on such lands and it is entirely pos-
sible that chickweeds are now more common than they were in the past.

ECOLOGY OF CHICKWEEDS

No special studies have ever been conducted on the ecology of
chickweeds. The available information on these plants is based largely
on observation. According to the Range Plant Handbook (11), chickweeds
are common and are found on a wide variety of sites, but the majority
of the species occur in moist or wet places. They also often concentrate
in shaded or partially shaded places. Stellaria jamesiana is a native
perennial species ranging over most of the West (11). It is a common
plant in this region, occurring in the aspen and the fir-—spruce belts.
This species has tuberous rootstocks which enable it to propagate vege-
tatively as well as from seed. For the most part chickweeds are small,
sparse in stand, and relatively unimportant as range plants (11). Graz-—
ing animals, therefore, probably interfere little with the normal repro-
duction of these plants.

CONTROL

No attempt has been made to control the disease because it has
never been regarded as serious enough to warrant special attention.
Eradication of chickweed from the vicinity of the firs would ultimately
eliminate the disease, but chickweed is so abundant that this is consid-
ered as not feasible in either this country (3) or Europe (5). However,
the plants probably could be killed with some of the present-day herbi-
cides.

Tests are now under way with fungicides applied to the witches!
brooms. If these materials should prove effective it probably would be
feasible to apply them on high value areas such as summer homesites,
campgrounds, and around ranger stations. Cutting the brooms from
branches in young trees might provide some measure of control of the
disease locally. A test of this kind is under way.

Bae

10.

1S

12,

LITERATURE CITED

Arthur, J...
193. Manual of the rusts in the United States and Canada,
XV+438 pp. Lafayette: Purdue Research Foundation.

Boyce, J. Se
1943. Host relationship and distribution of conifer rusts in
the United States and Canada. Conn. Acad. Sci. Trans.

353 329-82.

1948. Forest pathology. Ed. 2. 550 pp. New York.

Garrett, A. 0.
1937. The Uredinales or rusts of Utah. Univ. Utah. Bul. 28(7):
1-81.

Neger, F. W.
192). Die Krankheiten unserer Waldb&ume und wichtigsten Garten-
gehtlze. Ed. 2, VII+296 pp. Stuttgart: F. Enke.

Padyg.o. Uh.
1940. Preliminary observations on the aecial hosts of Melamp-
sorella. Kansas Acad. Sci. Trans. 3: 17-153.

1941. Further notes on the witches! brooms and the substomatal
pycnia of Melampsorella. Kansas Acad. Sci. Trans. hh:
190-201.

1942. Distribution patterns in Melampsorella in the national
forests and parks of the western states. Mycologia 3):

606-627.

1945. Reports from recipients of grants from the research funds.
Amer. Phil. Soc. Yearbook, pp. 157-160.

1946. The development and germination of the intraepidermal
teliospores of Melampsorella cerastii. Mycologia 38:

77-99.

U. S. Department of Agriculture.
1937. Range plant handbook. Forest Service. Washington.

1953. Chickweed can be eliminated in alfalfa. In Report of the

Chief of the Bureau of Plant Industry, Soils, and Agri-
cultural Engineering, p. 28.

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