Biology Reference
In-Depth Information
Drechslera erythrospilum (formerly
Helminthosporium erythrospilum
).
Red Leaf
Spot
on redtop and bent grasses, widespread in
eastern and midwestern states. Under wet condi-
tions lesions have small, pale centers with russet
borders; in dry weather leaves wither as in
drought but with less evident spotting. Conidia
are typically cylindrical, rounded at both ends,
yellowish, and germinate from any or all cells
(see
Fig. 1
).
Drechslera giganteum (formerly
Helminthosporium giganteum
).
Zonate Leaf
Spot
,
Eye Spot
on bent grasses, Canada and
Kentucky bluegrass, and Bermuda grass. The
disease is present in turf and in nursery rows.
Spots are small, 1/16 to 1/8 inch, bleached-straw
color in centers. In presence of moisture (dew is
sufficient) the fungus grows periodically into new
areas, giving the zoned appearance. In continued
wet weather leaves are killed and grass turns
brown. Metropolitan and velvet bent grasses are
less susceptible. Most injury is in July and
August. The fungus overwinters as dormant
mycelium in old leaves.
Drechslera poae (formerly
Helminthosporium
vagans
).
Bluegrass Leaf Spot
,
Going-Out
,
Melting-out
,
Foot Rot
, general but most injuri-
ous in northeastern states, on bluegrass only.
Scattered circular to elongate leaf spots, 0.5 to 3
by 1 to 8 mm, have prominent reddish brown to
black borders; centers are brown changing to
straw-colored or white with age. The disease,
favored by cool rainy weather, usually appears
in early spring, sometimes in late fall, and is
most severe on close-clipped turf. Grass thins
out
Guignardia
Blotch Diseases
.
Guignardia bidwellii f. sp. parthenocissi
Leaf
Spot
on Boston ivy, pepper-vine, and Virginia
creeper. Spots are numerous, angular, reddish
brown, usually dark brown at margins, with
black dots in center, minute pycnidia of the
anamorph
Phyllosticta
state. Leaves are quite
unsightly and there may be defoliation. Bordeaux
mixture applied two or three times, starting as
leaves are expanding, gives some control, but
the “cure” looks about as bad as the disease.
This fungus is a form of the species causing
black rot of grapes.
▶
Helminthosporium
Blights
.
Bipolaris cynodontis (formerly
Helminthosporium cynodontis
).
Bermuda Grass
Leaf Blotch
, general in South. Olive brown indef-
inite lesions on dry leaves.
Bipolaris setariae (formerly
Helminthosporium
setariae
(
Drechslera setariae
)).
Leaf and Petal
or Greasy Spot
on geranium, areca palm, fish-
tail palm, rhapis palm,
Calathea
spp.
Maranta
spp., and
Chamaedorea
spp.
Bipolaris sorokiniana (formerly
Helminthosporium sativum
).
Melting-out
, preva-
lent on bent grass in warm weather.
Leaf Spot
on
Russian wildrye (
Elymus
);
Spot Blotch
on
switchgrass (
Panicum
).
Bipolaris sorokiniana (formerly
Helminthosporium sorokiniana
).
Leaf Spot
and
Stem Spot
of wild rice.
Leaf and Pod Spot
on
bean.
Drechslera catenaria (formerly
Helminthosporium catenarium
).
Leaf Spot
on
ribbon-grass.
Drechslera dictyoides (formerly
Helminthosporium dictyoides
).
Fescue
Netblotch
, general on fescue. Dark streaks across
green leaves with darker lengthwise streaks form
a net pattern. Leaves turn yellow and die back
from tips.
▶
in large areas;
roots rot; weeds invade
exposed soil.
Control
Merion bluegrass is quite resistant to
leaf spot and will stand close-clipping. For other
bluegrasses cut high and fertilize well to help turf
withstand the disease.
Drechslera siccans (formerly
Helminthosporium siccans
; Teleomorph,
Pyrenophora lolii
).
Brown Blight
on fescue, and
ryegrass. Leaves die back with numerous dark
chocolate-brown spots, oval to elongate and
often coalescing. The disease appears in early
spring in cool, moist weather.
