Download AGRICULTURPL EXPERINT STATION

AGRICULTURPL EXPERINT STATION
Oregon State Agricultural College
W. A. Schoenfeld, Director
Corvallis
January, l93
Circular of Information No. 133
CROUN GALL OF ROSES
by
F. P.McWhorter, Plant Pathologist, Oregon State Agricultural College and
Agent, Bureau of Plant Industry, United States Department of Agriculture
and Freeman Weiss, Pathologist Office of Horticultural Crops and Diseases,
United States Department of Agriculture
Crown gall, so named because infected plants frequently form large galL
within the "crown" region, is common on rose, apple, pear, and other nursery
stock.
Although not particularly destructive to roses, ft is of economic
importance on this host not only because of its effect on roses, but because
it will readily transfer from them to many kinds of greenhouse plants and ruL
the sale value of these. The disease therefore assumes a double importanc
the commercial grower of rose stocks and budded roses since crown-gall-disa3eJ
roses are unfit for further propagation and are a menace to herbaceous p1ant
in greenhouses where they may ultimately be planted.
c
The galls are produced by the stimulative action of a small bacterium.
They may occur on the roots at the ground end of the cane (a common position
in lined-out manetti), at the ground line, at the point of budding, or
Root galls
aerially, especially at positions where flowers have been cut.
should
not
be
confused
are large and usually present on large roots; these
with nematode galls which are small and prevalent on small lateral roots.
Aerial galls are especially common on Butterfly, Ophelia and Rapture. The
galls greatly reduce the vigor of the plants and their ability to produce
flowers.
There is a crown-gall-like condition on Odorata stocks which may be
confused with true crown gall. These galls or swellings occur only on the
larger roots, near the crown, but never above ground, thus differing from
true crown gall end also from nenmatode galls to which Odorata and other roses
are susceptible, but which are characteristically found on the smaller roots.
The nature of this intermediate type of gall is unknown, but it is not believed
These galls vary in size from
to be of either bacterial or nenmatode origin.
that of a mustard seed to that of a small pea; they are hard, roughly globular,
and appear to originate from the woody cylinder, breaking through the bark.
Extreme care therefore must be used in diagnosing gall-typo formations on
Odorata stocks.
The control of crown gall must be based on the following considerations:
The causal bacterium readily becomes established in soils where
diseased plants are growing.
1.
2.
It can be transferred by a.
b.
c.
3.
Planting susceptible plants in contaminated soil.
Pruning diseased plants, then pruning healthy.
Budding from diseased plants to healthy, or using
cuttings from diseased plants.
The causal bacterium can enter only through wounds.
Some greenhouse and nursery crops are practically immune to crown
gall; others are very susceptible.
4.
From these considerations practical points leading to control are:
Removal of diseased plants from nursery plantings as soon as observed. In the case of lined-out plants the diseased plant, neighboring
Diseased plants should
plants and the soil about them should be removed.
be burnt.
1.
In greenhouse plantings some growers prefer not only to remove the
diseased plant and soil but also to drench the neighboring soil with 1:1000
Caution should be exercised, however, in the
corrosive sublimate solution.
use of this chemical in rose houses, as the mercuric chloride solution is
changed in contact with soil, especially soil containing large amounts aC
manure or other organic matter, so that free mercury is produced. The vapor
of mercury is toxic to rose plants and has been known to cause stunting of
roses throughout a house where this treatment was applied, including even
roses having no contact with the treated soil.
Crop rotation should be practiced to reduce soil infestation.
2.
Some practically immune nursery plants are: coniferous evergreens, barberries,
boxwood, Cornus, Hydrangea, lilacs, maples, Osnianthus, privet, Viburnum.
11omaniaca
Some immune greenhouse plants are: most begonias (except l3egonia
families
including
and Vernon), all ferns, plants of the lily and related
narcissus, tulips, lilies, etc.
Since the causal organism enters only through a wound, all cuttings
3.
for "lining out" should be thoroughly callused before planting.
The budding process furnishes an ideal means for transfer. Extreme
care should be used in selecting bud wood, especially when taking bud wood
from susceptible varieties such as Ophelia and others mentioned above.
4.
Under greenhouse conditions flower cutting furnishes a means of
infection. The transfer is probably aided by sprinkling or spraying shortly
after or during the flower cutting. To prevent this means of infection it is
better to remove diseased individuals than to attempt to sterilize the cutting
5.
instrument bet'wen the cutting of diseased and healthy plants. Fortunately
the organism is easily killed with a strong (2 to 4%) solution of forinalin.
Wound dressings and germicidal paints have been tested on rose plants after
excision of the galls, but with only partial success, and in general are not
recommended as a means of preventing gall infection.
Under average gxeethouse conditions where steam sterilization is
6.
not available it is usually more satisfactory to change the soil or grow nonsusceptible plants than to rely on chemical means of soil sterilization.
There are some differences in the susceptibility of rose stocks
7.
and varieties to crown gall, but all of the common understock species are
susceptible. Little progress has been made in the development and selection
of stocks resistant to the disease.