LEMON DISEASES 
District No. 17 
RECOMMENDED: Hureka; Lisbon; Sici- 
ly; Villafranca. 
LEMON DISEASES 
Blue and Green Mold 
Penicillium italicum and P. digitatum. 
see Orange 
Twig Blight 
Sclerotinia libertiana 
The twigs die back from the tip in 
moist weather, showing to some extent a 
white moldy fungus upon the surface in 
which may be imbedded small, hard, 
seed-like bodies or sclerotia, at first white 
but finally becoming black. A mass of 
gum exudes at this point. This fungus, 
which is the same as that causing the 
cottony mold, occasionally infects the 
tree itself, both with lemons and other 
citrus trees, with the effect just described. 
The infection comes from spores pro- 
duced by the growth of the fungus upon 
the green manure crop. Not serious. 
Brown Rot 
Pythiacystis citrophthora 
A very virulent form of decay, spread- 
ing rapidly through the boxes from fruit 
to fruit. Affected specimens show a 
brown, rather dry decay of the rind upon 
which a delicate, scanty white mold de- 
velops when considerable moisture is 
present. Fruit out in the open shows no 
mold on the surface. Affected fruit has 
a peculiar odor which is very character- 
istic. Mostly seen in lemons held in stor- 
age for curing. In wet weather this de- 
cay often appears on the fruit while still 
on the tree, but it is mostly confined to 
that within two feet of the ground. The 
disease affects all kinds of citrus fruit in 
this manner. 
The fungus which causes this trouble 
is primarily a soil inhabitant, living nat- 
urally in the ground beneath the trees 
where its spores are produced. 
Orchard infection is prevented by keep- 
ing the trees pruned up somewhat from 
the ground, cultivating the soil under the 
trees in summer and covering it in win- 
ter with straw or a green cover crop. 
Spraying the ground under the trees in 
1235 
winter with thick Bordeaux mixture is 
also helpful. The worst infection, that 
of lemons in storage, is contracted in the 
tank of the washing machine where the 
water becomes extremely infectious from 
the presence of spores brought in with 
the orchard soil and dust. This is easily 
controlled by disinfection of the wash 
water with copper sulphate. 
Literature 
Bulletins 190, 218, California Experi- 
ment Station. 
Cottony Mold—White Rot 
Sclerotinia lbertiana 
Causes decay of the fruit in the curing 
house with the production of an abund- 
ant white mold spreading over the lem- 
ons. In this mold are found irregularly- 
shaped, black, seed-like bodies called scle- 
rotia, from which another stage of the 
fungus develops. The same fungus also 
develops in the orchard soil during the 
rainy season and often becomes very 
abundant upon green-manure crops or 
other vegetation growing about the lem- 
on trees, particularly upon the vetch. The 
sclerotia develop upon green-manure 
crops or directly upon the soil, the latter 
during the rainy season, and out of them 
grow little funnel-shaped toadstool-like 
bodies which give off the spores of the 
fungus. 
Infection occurs in wounds in the pres- 
ence of moisture, generally from the 
washing water and usually at the stem 
end. 
Washing in bluestone solution of the 
same strength used for brown rot does 
not kill the spores. 
In regard to the control of this trouble, 
we may say that the cottony mold has 
had a very marked prevalence since the 
use of vetch as an orchard cover crop 
became so general. 
There is much ground for believing 
that these facts are related to one an- 
other, cottony mold having become more 
abundant on account of the opportunity 
given for its development in the orchard 
by the presence of the vetch plant, upon 
which it develops particularly well. 
