Biology Reference
In-Depth Information
Helminthosporium gigantea (
Drechslera
gigantea
).
Blight
or
Zonate Leaf Spot
on wild
rice and grasses.
Helminthosporium maydis (
Cochliobolus
heterostrophus
).
Southern Corn Leaf Blight
, eas-
ily confused with southern corn leaf spot due to
H. carbonum.
The leaf blight occurs throughout
the corn areas of the South and north to Illinois,
more important on field than on sweet corn. Gray-
ish tan to straw-colored spots with parallel sides
unite to blight most of the leaf tissue. The fields
appear burned by fire. Resistant varieties offer the
only control.
Helminthosporium turcicum (see
Setosphaeria turcica
).
Northern Corn Leaf Blight
on field and sweet corn and on grasses; found
from Wisconsin and Minnesota to Florida but
more severe in states with heavy dews, abundant
rainfall, and warm summers, losses running from
a trace to 50 %.
Setosphaeria turcica (formerly
Helminthosporium turcicum
).
Northern Corn
Leaf Blight
on field and sweet corn and on grasses;
found from Wisconsin and Minnesota to Florida
but more severe in states with heavy dews, abun-
dant rainfall, and warm summers, losses running
from a trace to 50 %. The disease starts on the
lower leaves and progresses upward. Small, ellip-
tical, dark grayish green, water-soaked spots turn
greenish tan and enlarge to spindle-shape, 1/2 to 2
inches wide, 2 to 6 inches long. Spores developing
on both leaf surfaces after rain or heavy dew give
a velvety dark green appearance to the center of
the lesions. Whole leaves may be killed; entire
fields turn dry. The fungus winters in corn residue
in the field and produces spores the next spring;
these are spread by wind.
Control
Use a 3-year or longer rotation.
Herpotrichia juniperi
Brown Felt Blight
of
conifers at high elevations; on fir, juniper, incense
cedar, spruce, pine, yew when under snow. When
the snow melts, lower branches are seen covered
with a dense felty growth of brown to nearly
black mycelium, which kills foliage by excluding
light and air as well as by invading hyphae.
Small, black perithecia are scattered over the
felt. This pathogen also found on dwarf mistletoe.
Heterosporium
Deuteromycetes, Hyphomycetes
Conidiophores dark, simple, bearing conidia suc-
cessively on new growing tips; conidia dark, with
three or more cells, cylindrical, with rough walls
(echinulate to verrucose); parasitic, causing leaf
spots, or saprophytic.
Heterosporium syringae
Lilac Leaf Blight
.
A velvety, olive green bloom of spores if formed
in blighted, gray-brown leaf areas, which may
crack and fall away. Infection is on mature leaves
and the fungus is often associated with
Cladosporium
. If necessary, spray after mid-
June with bordeaux mixture.
Higginisia
See
Coccomyces
under Leaf Spots.
Higginisia hiemalis
Cherry Leaf Blight
. See
▶
▶
Blumeriella
jaapi
and
Coccomyces
▶
biemalisi
, Cherry Leaf Spot.
Higginisia kerriae
Kerria Leaf
and
Twig Blight
.
See
Coccomyces
▶
▶
kerriae under Leaf Spots.
Hypoderma
Herpotrichia
Ascomycetes, Rhytismatales
Ascomycetes, Dothidiales
Ascospores formed in hysterothecia (elongated
perithecia or apothecia) extending along ever-
green needles; asci
Mycelium dark, perithecia superficial; spores
with several crosswalls, olivaceous when mature.
long-stalked; ascospores
