Biology Reference
In-Depth Information
Leaf Spots
Leaf spots are the most prevalent of plant dis-
eases, so common we seldom notice them, and
rightly so, for if we should attempt to control all
the miscellaneous leaf spots that appear in a small
suburban garden in a single season, we would
quickly go mad. A typical leaf spot is a rather
definitely delimited necrotic lesion, often with
a brown, sometimes white, center and a darker
margin. When the spots are so numerous they
grow together to form large dead areas, the dis-
ease becomes a blight, or perhaps a blotch, or
scorch. Certain types of lesions are called
anthracnose, spot anthracnose, blackspot. All of
these have been segregated out in their different
sections. What is left is a very large collection of
names.
The genus
Septoria
, for instance, has about
1000 species,
Mycosphaerella
500,
Cercospora
400, chiefly identified by the hosts on which they
appear.
Cercospora beticola
is so named because
it causes a leaf spot of beet,
C. apii
for its celery
host. Species recorded in this country as causing
a definite disease are listed under their respective
hosts. They are not repeated here unless the leaf
spot is of some importance or there is some useful
information that can be added to the name.
Most leaf spot diseases flourish in wet seasons.
A comparative few may be important enough to
call for control measures other than general san-
itation. Adequate protection usually means sev-
eral applications of fungicides, and the cost of
spraying trees and shrubs must be balanced
against the expected damage. Calling in a tree
expert with high-pressure apparatus is often an
expensive proposition. If the budget is limited,
it is more important to have an elm sprayed for
elm leaf beetles, which cause defoliation every
season, than for elm black spot, which may be
serious in only one year out of three or four.
When it comes to rose blackspot (no relation to
elm black spot), weekly protection with
a fungicide is necessary, but to save labor it can
be combined with insecticides.
Actinothyrium
Deuteromycetes, Coelomycetes
Pycnidia superficial, globose, with a more or less
fimbriate shield; spores filiform, hyaline.
Actinopelte dryina (see
Tubakia dryina
).
▶
On oak.
Actinothyrium
gloeosporioides (see
Tubakia dryina
). On oak.
Leaf Spot
on
sassafras.
Tubakia dryina (formerly
Actinopelte dryina
).
On oak. Very small dark spots between veins.
Conspicuous in midsummer but not serious.
Tubakia dryina (formerly
Actinothyrium
gloeosporioides
).
Leaf Spot
on sassafras.
▶
Alternaria
Blights
.
Alternaria
▶
alternata
Leaf
Spot
of
Calathea
spp.
