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Czrcular No. 747

July 1946 + Washington, D.C.

UNITED STATES DEPARTMENT OF AGRICULTURE

Distinguishing Characteristics of Some
Forage-Grass Diseases Prevalent in
the North Central States’

By J. Lewis Atuison, associate pathologist, Division of Forage Crops and Diseases,
Bureau of Plant Industry, Soils, and Agricultural Engineering, Agricultural
Research Administration, United States Department of Agriculture, and assistant
professor of plant pathology, University of Wisconsin, and DoNaLp W. CHAMBER-
LAIN,’ formerly research assistant, Department of Plant Pathology, University

of Wisconsin
CONTENTS

Page Page
Diseases of perennial grasses____ 2| Diseases of perennial grasses—
Kentucky bluegrass__________ 2 Continued.
Powdery mul dewssn eee aie De Other grasses—Continued.
ERE UT SG Se eee ee erste ere Ee 3 Netiblotch:- gaa. 2 ia
Stripe smiutes ss twas 4| Diseases of annual grasses______ 12
eaticpotest sess Teese 5 SUGdame oT ass = 1 ales ees hale 12
Smooth bromegrass__________ 6 Bacteriakspovs ssa == wees 12
Bacterial blight (chocolate Bacterial stripe___________ 12
eo y eafablioht»— 22 2 sewels aie 13
BROWMISPOU =e se =e 7
ie eric pot mn 11a) 7 Anthracnose= 25 seaee. oo 14
SI ee 8 Nonparasitic foliage dis-
et 22 =e 9 ORGENS 5.55 52 Nee eres 14
Other grasses] =. 19 | Control measures___________ S46 15
IBTLOMMZSUbI pes 23a eS MG) Later bb xeY Oneyole we NS 16

BPPPPBPPLBIPAPE LD A

ASTURE and forage grasses have become increasingly important
P in the grassland agriculture of the United States, but for years
little other than mycological attention has been given to the diseases
known to attack grasses. The advent of grass-improvement investi-
gations, however, brought recognition that grasses, like most economic

1 Cooperative investigations of the Division of Forage Crops and Diseases,
Bureau of Plant Industry, Soils, and Agricultural Engineering, Agricultural
Research Administration, U. 8. Department of Agriculture, and the Wisconsin
Agricultural Experiment Station.

2 Now assistant in forage-crop investigations, Kentucky Agricultural Experi-
ment Station, Lexington.

675159°—46

2, CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

crop plants, are hosts to many diseases, some of which are very

destructive.

This circular brings together the information available on the more
important diseases of pasture and forage grasses in the north-central
region of the United States. Emphasis is placed on the distinguishing
characteristics of each disease, and no attempt is made to include al]

span?

Re in Fon gh tlh bis

the hosts or all the diseases known to occur in the
region. No attempt is made to rank the diseases
in the order of their economic importance. Grass —
diseases occur to a greater or less degree each
year, with varying damage, depending upon
environmental conditions and the manner in
which the grasses are grown.

DISEASES OF PERENNIAL GRASSES

KENTUCKY BLUEGRASS
Powdery Mildew

Powdery mildew, a fungus disease caused by
Erysiphe graminis DC., attacks many grasses
and is very common on Kentucky bluegrass
(Poa pratensis L.). It is a conspicuous disease.
The white powdery growth visible on the surface
of leaves is the vegetative and sporulating por-
tion of the fungus (fig. 1). Later, dried blotched
areas develop at the points where the fungus has
penetrated into the leaves. Severely infected
plants become weakened and retarded in growth.
Mildew is omnipresent and is seasonal in its
development. It first appears late in spring,
diminishes during the dry, hot period of summer,
and builds up again during the fall months.
Physiologic races of this fungus occur in nature.

T'1icurE 1.—Powdery
mildew on Ken-
tucky bluegrass.

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES

Rusts

Leaf rust, a fungus disease caused by Puccinia
poae-sudeticae (West.) Jorstad, attacks blue-
grass. Initial symptoms first appear on the leaf
blades as small chlorotic spots. These soon
develop into typical rust pustules (fig. 2).
Orange-colored spores are produced in large
numbers in each pustule and are liberated when
the pustulesrupture. Leaf rust is prevalent each
year but, like mildew, it is seasonal in its de-
velopment. It first appears late in spring,
diminishes somewhat during the dry, hot period
of summer, and becomes very abundant early ~
in fall. Leaf-rust development is favored by
periods of warm, humid weather.

Stem rust, caused by Puccinia graminis
Pers., the destructive rust common on cereal
crops, attacks several grasses, including blue-
grass. On bluegrass it can be distinguished
from leaf rust only by microscopic examination
of the pustule and spores. Stem rust is not so
prevalent on bluegrass as leaf rust; 1t occurs in
abundance only late in summer and in fall.
Physiologic races of stem rust occur commonly
in nature.

FiaureE 2.—Leaf rust
on Kentucky blue-
grass.

I'icurg 38.—Stripe smut on Kentucky bluegrass,

CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

Stripe Smut

Stripe smut, a fungus
disease caused by Ustilago
striaeformis (West.) Niessl,
attacks many grasses and

is common on bluegrass. ©

Initial symptoms appear
as chlorotic stripes on the
blades. Later the stripes
become grayish-black (fig.
3). Masses of smut spores
are released when the
stripes mature and rup-
ture. Spores are brown,
spherical to oval, and are
covered with short spines.
Severely infected plants
are stunted and dwarfed.
Stripe smut develops sys-
temically within its host.
Thus it is not seasonal in
its development and can
be found to a greater or
less degree any time during
the growing season.

A second stripe smut,
caused by Urocystis agro-
pyri (Preuss) Schroet., at-
tacks several grasses, in-
cluding bluegrass, and can
be distinguished from the
first only by microscopic
examination of its spores,
which are formed in balls
with one to three fertile
spores surrounded by a
single layer of empty cells.
This smut is not so com-
mon on bluegrass as Usti-
lago striaeformis.

| CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES 5

Leaf Spot

The leaf spot disease caused by Helmintho-
sporium vagans Drechsl., occurs only on
bluegrass. Initial infections appear as chlor-
otic specks on the blades. These rapidly
develop into ovate, straw-colored lesions with
reddish margins (fig. 4). A single lesion may
cover the entire width of a blade, and severely
infected leaves wither and die. Conidia of
the fungus are borne on the lesions or on with-
ered leaf tips. Conidia are characteristically
dark olivaceous, cylindrical, or slightly tapered,
with five to eight septations. The disease
occurs from late in spring until fall and attains
its greatest severity during midsummer. Leat
spot development is favored by periods of
humid, hot weather.

Fiaure 4.—Leaf spot
on Kentucky blue-
grass.

6 CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

SMOOTH BROMEGRASS
Bacterial Blight (Chocolate Spot)

Bacterial blight, caused by Pseudomonas
coronafaciens (Elliot) Stapp var. atropurpurea
(Reddy and Godkin) Stapp, attacks several
erasses and is a serious disease of smooth brome-
erass (Bromus inermis (Leyss.)). Initial symp-
toms appear as circular to elliptical water-
soaked areas of uniform size on the leaf blades.
These soon turn purplish black, and it is from
this stage that the common name chocolate spot
originates. This is a misnomer, however, as
lesions more frequently coalesce to form typically
blighted areas involving the entire blade and
sheath (fig. 5). As blighted leaves wither and
die, the lesions fade to a rusty brown, and occa-
sionally a dry exudate is present. Bacterial
blight often attains epiphytotic proportions by
mid-June. Its development is favored by
periods of humid, hot weather. The causal
organism is readily cultured and produces a
ereen-fluorescent, pigmented type of colony on
artificial media.

:
F
j
;
\
j
3

Figure 5.—Bacterial
blight on smooth
bromegrass.

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES 7

Brown Spot

Brown spot, caused by Pyrenophora (Helmin-
thosporium) broma (Died.) Drechsl., is a fungus
disease that attacks smooth bromegrass. Initial
symptoms appear as small, dark spots on the
first blades formed early in spring. As lesions
enlarge, a yellow halo forms around each spot
(fig. 6). Severely infected leaves yellow and
wither. Conidia of the fungus develop either on
the lesions or on the withered blades. The co-
nidia are light yellowish, with 1 to 10 septations.
Ordinarily this stage 1s rarely found. At this time,
however, small black bodies can be discerned
embedded in the dry, diseased leaves. These
bodies are the initials of the perfect or perithecial
stage of the fungus and carry it through the rest
of the growing season and through the winter.
They do not mature and release the perfect spore
stage until very early in the spring of the follow-
ing year. Ascospores are hght brown, with com-
monly 3 transverse septations, which are further
divided by a longitudinal septation. Brown spot
develops during periods of wet, cool weather and
is most prevalent very early in spring.

Figure 7.—Leaf spot on
smooth bromegrass.

FieguRr 6.—Brown
spot on smooth
bromegrass.

Leaf Spot

Leaf spot, a fungus disease caused by
Selenophoma bromigena (Sace.) Sprague and
A. G. Johnson, attacks smooth bromegrass.
Initital infections appear as small, brown
specks on the leaves early in spring. As
lesions enlarge they become irregular in shape
and size. Mature lesions are translucent in
appearance, and black fruiting bodies develop
at random in them (fig. 7). These are the
pyenidia of the fungus, and in them masses
of conidia are produced. The conidia are
small, hyaline, slightly sickle-shaped, and are
nonseptate. Mature pycnidia often drop out
of the lesions, leaving pinhole perforations.
The disease is favored by periods of moist,
cool weather and diminishes in severity as
the season progresses, all but disappearing
during the hot, dry period of midsummer.

8 CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

Scald

Scald, caused by Rhynchosporium
secalis (Oud.) J. J. Davis, is a fungus
disease common on smooth bromegrass.
Specialized races of the parasite attack
several grasses. Initial symptoms ap-
pear on the leaf blades as irregular
water-soaked areas, which within a few
days dry, and each lesion takes on a char-
acteristic scalded appearance (fig. 8).
Dried lesions are typically grayish green,
and conidia are borne on them in concen-
tric rings. Conidia are hyaline, short-
cylindric, with one septation, and have
a short oblique beak. Severely infected
leaves wither and die. Scald appears
late in spring and early in summer, and
its development is favored by periods of
humid, warm weather.

FicurRE 8.—Seald on smooth
bromegrass.

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES 9

Ergot

Ergot, a fungus disease
-caused by Claviceps pur-
purea (Fr.) Tul., attacks
many grasses and is com-
mon on smooth bromegrass.
It attacks only the flower
and seed parts of its host
and is of economic impor-
tance only when grasses are
erown for a seed crop or are
allowed to flower and set
seed prior to grazing or cut-
ting for hay. The initial
symptoms appear at flower-
ing time, when a sticky
exudate, called the honey-
dew stage, is noticeable.
This exudate, containing
the conidial stage of the
fungus, attracts flies and
other insects, and much
secondary infection results
from insect transmission.
As the disease progresses,
black horny bodies called
sclerotia develop in place of
seeds (fig. 9). When ma-
ture, the sclerotia fall te the
eround or are harvested
with the seed crop. In
either case, they carry the
fungus over winter. When
planted with the seed or
carried over on the ground
by natural means, they
develop the perfect spore
stage of the fungus the fol-
lowing summer, and the
spores released cause the
initial infection each year.
Ergot development is fa-
vored by periods of warm,

FicguRE 9.—Ergot on smooth bromegrass,
showing typical sclerotia.

10 CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE |

moist weather. Livestock injury may result if severely infected
grasses are grazed or fed for hay. Substances in the sclerotia cause.
abortion and if fed over long periods cause break-down of the

Ficure 10.—Brown stripe on orchard
grass.

capillaries, particularly in hoofs
and ears.

OTHER’ GRASSES

Among other perennial grasses
subject to disease are timothy
(Phleum pratense L.), redtop (Agros-
tis gigantea Roth), orchard grass
(Dactylis glomerata L.), meadow
fescue (Festuca elatior L.), and
Canada bluegrass (Poa compressa

1x.)

Brown Stripe

Brown stripe, caused by Scole-
cotrichum gramianis Fckl., is a
fungus disease that attacks many
grasses, including all those listed
above. Symptoms on all grasses
are much the same and start with
a browning of the leaf blades from
the tips downward until the leaves
wither and die. In the browned
areas, black structures, arranged
linearly between the leaf veins,
are clearly visible (fig. 10). Each
structure represents a dense cluster
of conidiophores and conidia. The
latter are borne on unbranched,
irregular conidiophores and are
elongated, shghtly tapered, and
typically uniseptate. They are
readily disseminated by wind and
rain. Brown stripe is omnipresent
and is not at all seasonal in devel-
opment. It appears early in
spring and is present to a greater
or less degree throughout the
entire growing season.

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES

Net Blotch

Net blotch, a fungus disease caused by
Helminthosporium dictyoides Drechsl., at-
tacks only meadow fescue. Early symptoms
appear as irregular brownish areas on the
leaves (fig. 11). Lesions are marked with a
delicate netted pattern, and it is from this
characteristic marking that the disease gets
its common name. In the later stages of
infection leaves wither and die from the tip
toward the base. Conidia of the fungus are
borne on the lesions or on the withered leaf
tips. Conidia are subhyaline to yellow and
are typically straight, with three to five
septations. Net blotch occurs from late in
spring until fall, attaming its greatest severity
during midsummer. The disease is favored
by periods of humid, hot weather.

Figure 11.—Net blotch
on meadow fescue.

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Bacterial stripe, caused by Pseudomonas an-
droposont (EK. F. Sm.) Stapp, attacks several
grasses and is common on Sudan grass. Initial
infections appear on the leaves as long, narrow,
irregular stripes (fig. 13). These soon dry, be-
come pigmented, and are covered with an abun-
dance of dry exudate. Severely infected leaves
dry and wither.
midsummer and continues until plant maturity.
Disease development is favored by periods of
warm, moist weather.

CIRCULAR

Bacterial Stripe

747, U. S. DEPARTMENT OF AGRICULTURE

DISEASES OF ANNUAL GRASSES

SUDAN GRASS

Bacterial Spot

Bacterial spot, caused by Pseudomonas syringae
Van Hall (Bacterium holci Kendr.), attacks several
grasses and is common on Sudan grass (Sorghum
vulgare Pers., var. sudanensis Piper and Hitchce.).
Initial infections appear as circular to elliptical
water-soaked spots on the lower leaves. These
spots soon become dry and papery and are lght-
colored (fig. 12). The disease appears soon after

.seedlings emerge in spring and progresses with

plant development throughout the entire growing
period, gradually spreading from the lower leaves
over all the others. Disease development is favored
by periods of warm, moist weather.

Figure 12.— Bacterial
spot on Sudan
grass.

Stripe first appears about

FiGuRE 13.—Bacterial
stripe on Sudan
grass,

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES

Leaf Bight

Leaf blight, caused by Helminthos-
porium turcicum Pass., is a serious fungus
disease of corn and sorghum in some areas
of the United States and is destructive on
Sudan grass in the North Central region.
As its name implies, symptoms are a con-
spicuous blighted or scalded appearance of
the foliage (fig. 14). Within a period of a
few days an entire field of Sudan grass
may develop extreme blighting and appear
characteristically burned or frosted. Coni-
dia of the fungus are produced in abun-
dance on the lesions. Conidia are dark,
shghtly thickened, with one to eight
septations, and have a distinctly protrud-

ing hilum at the basal end. Blight first.

appears about midsummer and continues
until plant maturity. Disease develop-
ment is favored by periods of warm,
moist weather.

Fiaure 14.— Leaf blight on
Sudan grass.

13

14

CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

Anthracnose

Anthracnose, caused by Colletotrichum grami-

nicolum (Ces.) G. W. Wils., is a fungus disease -

that attacks several grasses and is common on
Sudan grass. Initial symptoms appear on the
basal leaves as small necrotic eye spots with
visible black bodies in the center of each (fig. 15).
These open structures are filled with large
numbers of conidia, which, being readily washed
and splashed about by rain and dew, account
for much secondary infection. Conidia are
hyaline, shehtly curved, tapered, and nonseptate.
As the disease progresses, all leaves often become
infected. Individual lesions frequently coalesce,
and entire leaves wither and die. Anthracnose
appears about midsummer and develops rapidly
from that time on until plant maturity. The
disease is favored by periods of humid, hot
weather.

Nonparasitic Foliage Disorders

Nonparasitic foliage disorders caused by hered-
itary factors occur on several grasses, especially
Sudan grass. The symptoms are commonly
confused with those caused by parasitic organ-
isms. Several such disorders on Sudan grass
are shown in figure 16.

Figure 15.—Anthracnose
on Sudan grass.

a a

CHARACTERISTICS OF SOME FORAGE-GRASS DISEASES 15

Figure 16.—Nonparasitice foliage disorders on Sudan grass.

CONTROL MEASURES

The grass diseases reviewed in this circular are not effectively con-
trolled by the accepted regular control methods of sanitation, crop
rotation, or use of chemicals. Sanitation and crop rotation are both
impractical because most of the diseases attack more than one species,
many of which are noneconomic ones growing and harboring the
diseases in locations inaccessible for such control programs. Spraying
or dusting with fungicides, invaluable in the case of many crop diseases,
is obviously impractical with grasses. Seed treatment is of value
only for those diseases known to be seed- or soil-borne and can arrest
only that phase of a disease that attacks the plant in the seedling
stage of development.

16 CIRCULAR 747, U. S. DEPARTMENT OF AGRICULTURE

The development of disease-resistant strains of grasses offers the
only practical contro] measure. Resistance to many of the diseases
reviewed has been demonstrated (J, 2, 4, and 9). The presence of
physiological races in certain of the fungi discussed has been recog-
nized (2, 5, and 6).* Such knowledge will aid greatly in the develop-
ment of grass improvement programs. Improvement programs are
in progress with all the major grass species reviewed (J, 3, 7, and 8).

LITERATURE CITED

(1) AnueReEN, H. L., Smitu, D. C., and NieusEn, E. L.
1945. BEHAVIOR OF VARIOUS SELECTIONS OF KENTUCKY BLUEGRASS, POA
PRATENSIS L., WHEN GROWN AS SPACED PLANTS AND IN MASS SEED-
Inas. Amer. Soc. Agron. Jour. 37: 268-281.
(2) Auuison, J. L.
1945. SELENOPHOMA BROMIGENA LEAF SPOT ON BROMUS INERMIS. Phyto-
pathology 35: 233-240, illus.
(3) Burton, G. W.
1942. TIFT SUDAN, A UTOPIA GRASS FOR [THE] SOUTHEAST. South. Seeds_
mano CO) Seenol, Sos alluse
(4) CHAMBERLAIN, D. W., and Auuison, J. L.
1945. THE BROWN LEAF SPOT ON BROMUS INERMIS CAUSED BY PYRENOPHORA
BROMI. Phytopathology 35: 241—248, illus.
(5) Davis, W. H.
1930. TWO PHYSIOLOGIC FORMS OF USTILAGO STRIAEFORMIS (WESTD.)
NIESSL. Phytopathology 20: 65-74.
(6) Harpison, J. R.
1944. SPECIALIZATION OF PATHOGENICITY IN ERYSIPHE GRAMINIS ON WILD
AND CULTIVATED GRASSES. Phytopathology 34: 1-20.
(7) Hayss, H. K., and Scumip, A. R.
1943. SELECTION IN SELF-POLLINATED LINES OF BROMUS INERMIS LEYSS.,
FESTUCA ELATIOR L., AND DACTYLIS GLOMERATA L. Amer. Soe.
Agron. Jour. 35: 934-948.
(8) Kanpur, R. E.
1940. SWEET SORGHUM CROSS IMPROVES SUDAN GRASS. South. Seeds-
mand (12)278) 185 1195923:
(9) Tsrane, Y. S.
1944. VARIATION AND INHERITANCE OF CERTAIN CHARACTERS OF BROME
GRASS, BROMUS INERMIS LEyss. Amer. Soc. Agron. Jour. 36:
508--522.

3 Italic numbers in parentheses refer to Literature Cited.

4See also FiscoEer, G. W., and LEvinn, M. N. SUMMARY OF THE RECORDED
DATA ON THE REACTION OF WILD AND CULTIVATED GRASSES TO STEM RUST (PUCCINIA
GRAMINIS), LEAF RUST (P- RUBIGOVERA), STRIPE RUST (P. GLUMARUM), AND CROWN
RUST (P. CORONATA) IN THE UNITED STATES AND CANADA. U.S. Bur. Plant Indus.,
Plant Dis. Rptr. Sup. 130, 30 pp. 1941. [Processed.]

U.S. GOVERNMENT PRINTING OFFICE: 1946

For sale by the Superintendent of Documents, U. S. Government Printing Oftice
Washington 25, D. C. - Price 5 cents

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