The Hawaiian gazette., 1915-06-04
THEBLACkDL|GHTS
OR FUMAGlNES
Indirect Injury Due To Cloaking
the Cane Leaves From
Sunlight
Not Themselves Parasitic But a
Sure Sign Of HopperS
and Pests

The influence Of the fumagnc fungi
which grow on the surface OF leaves in
the excreted sugary juices from leaf
hoppers, pnnt-Iice and other sucking
insect pests of crops has been investi-
gated by G. Nicholas, a French bot
anist.
1t has been generally held that the
iumagine fungi are injurious because
I the thick black coating which they
! form on the leaves of coffee cane and
other plants are injurious chiefly be-
| cause they hinder assimilation and res
I piTation. This idea was not based on
| any precise observations. so Nieholas
/ undertook experiments to determine
the exact injury that does take place.
Scientific Results
| The experimental worked with or
ange, oleander, olive, guava, gardenia
and several ornamentas. Leaves COW
cred with fumagine were divided in
two, one half being freed from the
fungus. The two halves or symetrieal
portions of them, were placed in glass
tubes containing air of known analy'
sis, saturated with moisture and con-
tanning eight to ten per cent of car
bonic acid gas, from which all green
plants compound starch and sugar in
the presence of sunlight. Two analy-
ses of the amount of gas removed by
each half of each leaf were made.
NJ. Nicholas found marked retarda-
ton of the life process of the leaf in
all cases where the fumagine fungi
were present. The adverse influence
of the black cOaling was in direct
proportion to its thickness and density.
Black Blight Secondary 80. D..
The fumagines or "black blights, -
as they are called in Hawaii, are en-
tirely external to the leaves Of plants
In habit they are "saprophytes, OF
microscopic plants living on dead fooc
As distinguished from the PARASITES,
which get their food from living
sources. |.'a ... q.
Their presence indicates an epidemic
of some insect pest which lives By
sucking the juices from the leaves ant
stems of plants. In cane field thu
black blight or fumagine on leaf anS
cane is a pretty sure indication of !
new outbreak of leaf hopper. On eOf
fee the fumagine is telltale on tn
presence of plant-lice,. mealy bugs
scales, or the torpedo bug.
Insect pests of this class make N
use of the sugar in the plant juice
which they suck. They are after tn
albumen in the plant juices. Strain
ing tn" cane juice through its ,ligestis
apparatus the leaf-hopper uses the a
- luminous portion of the cane juice
fuild w its own body tissues and O.
crrtcs the sugar in almost pure for
Ms glucose. Bees, ants and other i
sertS feed on the glucoes excreted al
the fumagines grow rapidly In it,
n Tell Tales for Pests
The average observer places mo
IL blame on the fumagiDe than on the i
sect pest which is the first cause
the damage to his crops. The bota
nm lists have long known that the bla'
hhghtS are not parasitic bat are, on
an index Of the presence of dangG
out pest hut they do injure the plan
on which they grow because tn
ter screen the leaves from the sunlig
rirt and prevent healthy growth,
has Whenever there is an outbreak
pre-, fumRginc on any crop the plant
ma SHOULD call in an cntOmOlogist to liI
rity nose the trouble. The black billy
,ore woulI not grow on the leaves a
,tes cloak them from the sunshine If le
hOppers, aphis, torpedo bugs and otl
the pests had not paved the way and p
Law. vided coating OF glucose for 4
ted. fumagnes to grow in.