CITEUS MELANOSE AND ITS CONTROL 7 
Considering the importance of citrus melanose, very little work 
seems to have been done on the subject either in the laboratory or in 
the grove, and that which has been published has until recently had 
but little effect upon the practical control of the disease. Prior to 
1921 citrus melanose was generally considered to be one of the many 
diseases that could not be controlled economically with fungicides, be- 
cause the harmful effects in the form of excessive increase in scale 
insects outweighed all beneficial effects resulting from a reduction of 
melanose. This increase in scale insects is due to the effect of the 
fungicide upon entomogenous fungi that attack these insects, thereby 
upsetting the natural biological scale control. With the introduction 
of Bordeaux-oil emulsion this objectionable feature was largely over- 
come. Commercial pruning has usually failed to give satisfactory 
control. 
SPECIES AND VARIETIES ATTACKED 
Citrus melanose occurs on a wide range of plants of the family 
Rutaceae, to which citrus belongs, and it seems that all commercial 
varieties of citrus grown under Florida conditions are attacked by 
the disease. Among the citrus varieties grown commercially, the 
kumquats 4 (Fortunella spp.) are perhaps the most susceptible; 
they are extremely so. The lemons {Citrus limonia Osbeck), sour 
oranges (0. aurantium L.), limes (C. aurantifolia Swingle), and 
grapefruit (0. grandis Osbeck) are very susceptible, whereas the 
round (sweet) oranges (C. sinensis Osbeck) and the kid-glove 
oranges (C. nobilis Lour.), although distinctly less susceptible than 
the grapefruits, are attacked severely whenever conditions are espe- 
cially favorable for infection. Observations over a period of eight 
years and inoculations made during six years fail to reveal any ap- 
preciable difference in the degree of susceptibility possessed by the 
commercial varieties within the same species. Susceptibility seems 
to be possessed to about the same degree by the fruit, the leaves, and 
the twigs. 
In addition to the commercial varieties of citrus found throughout 
the citrus belt, studies by means of inoculation tests have been con- 
ducted on the susceptibility to melanose attack of a rather wide 
range of rutaceous plants, including a number of citrus hybrids. 
These include representatives of 21 genera and 34 species. In some 
instances only one or two plants of a given species have been avail- 
able ; hence the susceptibility of these is recorded tentatively. More 
complete data resulting from inoculation tests will be found in that 
portion of the bulletin which deals with inoculation experiments. 
Table 1 gives the approximate susceptibility to melanose of a wide 
range of rutaceous plants under Florida conditions as indicated by 
extensive inoculation experiments and general observations. 
4 In so far as possible, the botanical classification of citrus species used in this 
bulletin follows that of W. T. Swingle (22). 
