4 BULLETIN 1474, U. S. DEPARTMENT OF AGRICULTURE 
and gradually become dark colored,, sometimes almost black. They 
vary considerably in size, usually ranging from iy 2 to 4 millimeters 
in diameter. Generally the margin on the upper surface is regular 
in outline, but on the under surface it may be either regular or irreg- 
ular (pi. 7, C). The cause of this disorder has not been established. 
It does not seem to be infectious, as no fungus or other organism has 
been found associated consistently with the spots. 
Another spotting on leaves and fruit that is similar to melanose has 
been observed in Alabama and Texas on trees lacking vigor. It so 
closely resembles melanose that the two may easily be confused. In 
this type of injury the margin of the affected tissue is more regular, 
the excrescences much higher, and the color darker than in citrus 
melanose. 
RUST-MITE TEAR STAIN 
Kust-mite tear stain is frequently confused with melanose tear 
streak. Both occur on oranges and grapefruit and both are mahog- 
any brown in color. The melanose tear streak is rough to the touch 
and raised, while the rust-mite tear stain is smooth and flush with 
the surface of the unaffected parts. 
RUST-MITE RUSSET 
Kust-mite russet frequently occurs on oranges and grapefruit as a 
general discoloration or as distinct zones or bands that are usually 
quite smooth to the touch, but occasionally they may be slightly 
rough, faintly resembling " mud-cake " melanose. When the rust- 
mite russet is severe it is impossible to detect with accuracy a slight 
to moderate occurrence of melanose lesions in the same general area. 
HISTORICAL REVIEW 
The first published record of citrus melanose was made by Swingle 
and Webber (21) in 1896. They first observed it in November, 1892, 
near Citra, Fla. The hosts recorded in order of susceptibility were 
grapefruit, sweet orange, sour orange, lemon, mandarin, and Satsuma. 
The disease when first observed seemed to be of very recent origin 
or introduction, as evidenced by its limited distribution, but it spread 
rapidly during the next few years. They occasionally found micro- 
scopic evidence of fungal hyphse in the affected parts, but were un- 
able to obtain the fungus in culture. They considered the disease 
to be due to a " vegetable parasite." Spraying experiments conducted 
in 1894 at Stanton, Fla., showed that the disease was controlled by 
two applications of Bordeaux mixture or of ammoniacal solution of 
copper carbonate, the first made about two weeks after the flowers 
had fallen and the second about a month later. 
Floyd (10) concludes, after studying the disease from a physio- 
logical and histological standpoint, that it is caused by some unrecog- 
nized organism, and states "it is probable that the dead wood is a 
source of infection." He observed that fruit so located that water 
from deadwood drops upon it often has a tear-stain arrangement 
of the disease marking. He also noted that where melanose had 
been severe, pruning proved to be helpful in reducing the disease. 
