29 
merely in external and visible manifestations, but even more in the im¬ 
paired vitality of the orauge trees. It may be added that some of the 
effects of frosts are not infrequently confounded with diseases of a very 
different nature. 
(4) The exceedingly dry season of the past year has also left its traces 
in the impaired vitality ot many trees, and the uncertainty of rain and 
the liability of drought are inducing many to introduce irrigation plants, 
which in the hands of careless cultivators are likely to become a source 
of harm as well as good. 
CLASSIFICATION OF DISEASES. 
The diseases affecting the orange may be arranged under four groups: 
(1) Those resulting from climatic conditions and environment, as frost, drought, 
natural defects of soil, natural excesses of soil constituents, and undue moisture. 
(2) Those produced by insect pests. Although this group is outside the limits of 
this paper, we may mention in passing that during the present season the long 
scale,* the red spider,! and the rust mitet are apparently the most troublesome pests 
of this nature, but the first is likely to be kept in check by the lady bugs ( Coccinell - 
idee), the second will succumb to spraying, and the third may be held in check by 
the character of the cultivation. 
(3) Those due to injurious cultivation and fertilization. 
(4) Those due to the agency of parasitic fungi and bacteria. 
Only the diseases of the last two groups will receive notice here. 
The diseases noticed during the early season of 1891 were as follows: 
> Probably ca used by improper cultivation or fertilization. 
I. Die-back. 
II. Foot-rot. ^ 
III. Blight. Possibly caused by bacteria. 
Leaf spot. \ Caused P arasi . tio 
VI. Sooty mold. Caused by a saprophytic fungus. 
VII. Leaf glaze. Caused by a leaf lichen. 
I.—DIE-BACK. 
(1) Nature of the disease .—This disease first makes its appearance in 
strong shoots of the season in the form of pustules or blisters on the 
stems near the point of attachment of the leaves. These when opened 
appear to contain a reddish, gummy substance. In later stages of the 
disease these pustules rupture and extend in cracks along the twig, the 
reddish gummy substance coming to the surface and spreading until 
the whole twig becomes diseased and finally dies back to the main stem. 
This peculiar and characteristic effect gives rise to the appropriate, if 
not elegant, popular name of the disease. In badly infected trees most 
or all of the fruit falls when young; that which matures is likely to be 
mis-shapen and discolored. There seems to be no evidence that the 
disease is contagious. 
Trees that have been affected with die-back and have recovered from 
its effects will reveal it years afterward in the sudden bends of the 
* Mytilasjpis gloverii, Pack, t Tetranychus telarius, L. 1 Tyjphlodromus oleivorus, Aslini. 
\ 
