25 
SOOTY MOLD.! 
Sooty mold of the orange, or smut,” as it is sometimes erroneously 
called, is a malady which frequently causes serious damage. The 
fungus producing it is of saprophytic habit, deriving its nourishment 
from the sweet fluids (honeydew) secreted by certain insects, the 
attacks of which it invariably follows. As the honeydew falls it 
strikes principally on the upper surfaces of the leaves and exposed 
branches and upper portions of the fruit (the stem end, as the fruits 
are pendulous), and it is on these portions that the sooty mold grows. 
It develops also to some extent on the lower surfaces of the leaves, but 
is not so abundant here. In Florida sooty mold follows principally the 
attacks of the mealy wing or white fly (Aleyrodes citri R. & H.), wax 
seale (Ceroplastes floridensis), mealy bug (Dactylopius citri), orange 
plant louse or aphis (Aphis gossypit Glover), etc., and spreads as these 
insect pests spread. It is only where it follows the mealy wing, how- 
ever, that it becomes serious. In this State it is estimated that the 
loss it causes is not far short of $50,000 annually. 
Besides occurring on all varieties of citrous fruits, sooty mold is fre- 
quently found on a number of wild plants in Florida. It is particularly 
abundant on the gall berry (Ilex glabra), red bay (Persea carolinensis), 
and magnolia. On the gall berry it follows attacks of the wax scale 
(Ceroplastes floridensis), which also infests the orange. _ 
Sooty mold is probably common in all orange countries of the world. 
In California it causes much damage and is considered a serious malady. 
There it follows chiefly the black scale (Lecanium olew) and the cottony 
cushion scale (Icerya purchast). In Louisiana it is very common on the 
orange, following chiefly, as in Florida, the mealy wing and wax scale. 
It is also quite common in Spain, Italy, and many other orange-growing 
countries. | 
Symptoms.—Sooty mold may be readily recognized by the dense 
sooty-black membrane which it forms over the fruit and upper sur- 
faces of the leaves (Pl. VII, fig. 1). This membrane is made up of 
the densely interwoven, branched mycelial filaments (threads) of the 
fungus, the individual filaments of which can in some cases be distin- 
guished with a hand lens. When isolated the filaments are seen to 
vary in color from olive green to dark brown. They are at first 
loosely interwoven, but gradually become very numerous and crowded. 
Finally they become cemented together, forming a dense, compact 
membrane. The fungus, as nearly as can be determined, is entirely 
1Sooty mold of the orange is probably produced by several different species of the 
genus Meliola. The forms known as Meliola penzigi and Meliola cameliw appear to 
be the most common in Florida. In publications in this country the fungus has 
usually been referred to Capnodium citri and Fumago salicina. The disease is known 
in Italy under the names fumaggine, morfea, nero, etc., and in Germany as Russthau. 
*Smut is the name very generally applied to diseases produced by the true smut 
fungi ( Ustilaginee). 
