PRESS BULLETIN 141
Florida Agricullural Experimenl Sallon
STEM-END ROT OF CITRUS FRUITS-II
By H. S. Fawcett
In November, a serious rot of citrus fruits was described in Press Bulle-
tin 131, under the name of "Stem-End Rot." By "stem end" is meant the
place where the stem joins the fruit. Since that time investigations have
been carried on to learn the nature of the rot, in order that in the future
the disease may be successfully combated.
The fruit first begins to soften and sink a little round the stem end, with-
out the rind changing color. There is no blackening nor molding at first,
and the rind remains intact over the softened interior. The rot proceeds
inward along the fibers of the rag, and then outward into the pulp cells. At
first both the inside and outside of the fruit remain almost unchanged in
color; but, as the softening goes on, the rind turns dull brown. Finally the
rag and the pulp cells are disintegrated, and the entire fruit becomes soft "
and mushy. Early in the development of the rot, small white specks are
seen in the pulp. These are similar to those produced by freezing, or by the
This rot usually occurs on full-sized fruits after they have colored.
Though the softening may begin while the fruit is still hanging on the
tree, it usually develops after the fruit has dropped or after it has been
picked. In groves where the disease was most prevalent it was estimated
that from 10 to 50 per cent. of the fruit had dropped. Some of this dropping
wag due to withertip or other causes, but in many cases a large percentage
of the dropped fruit developed stem-end rot while lying on the ground. In
one instance 30 per cent. of the grapefruit were estimated to have dropped
from this cause. In other places the percentage was smaller, there being
only from 1 to 5 per cent. of the fruit affected.
But the dropping and rotting of the fruit in the grove is not the end of
the trouble. The rot may develop on fruit that to all appearances was per-
fectly sound when packed, and make itself apparent on arrival at the market.
Reports have been received of shipments of oranges having from one to
eighteen per cent. of the fruit affected by stem-end rot on arrival at New
February 5, 1910
The direct cause of the stem-end rot has been shown by laboratory ex-
periments to be the growth of a species of fungus which appears to belong
to the genus known as Achlya.' It is closely related to the water-molds, and
resembles in many respects the fungus causing the brown rot of lemons in
California. Our experiments indicate that this fungus infects the orange
only at the stem end. This was shown by placing pure cultures of this
fungus upon the stem ends of sound oranges. In almost every case the
oranges so treated developed the rot in two or three weeks, while in the
laboratory at about 65 degrees F. When cultures were placed on parts
of the oranges other than the stem ends, no infection resulted, except when
a cut or abrasion had been previously made.
How the Disease Spreads
1. That oranges already affected with the rot may spread the disease
to sound fruits has been shown by placing pieces of rotted fruits upon the
stem ends of sound oranges. The oranges so treated developed the rot in
the same manner as did those on which only the fungus had been placed.
Pieces of diseased oranges placed on parts of sound fruit other than the
stem ends caused no infection.
2. That the soil may be the means of infection was shown by placing
sound oranges, and a small portion of soil from under a severely infected
orange tree, together in water 'for 24 hours. They were then wrapped in
paper, and placed in a temperature of 85 degrees F. In one week 42 per
cent. of these fruits showed an infection with stem-end rot.
The following suggestions as to remedial measures are based on our
study and experiments to date: (1) All dropped fruits should be picked
up and destroyed, as they are liable to infect the soil and other fruits. (2)
All fruits on the trees showing softening at the stem end should be removed
and destroyed, as these too are liable to infect others. (3) As an additional
preventive the fruit on the trees should be sprayed with ammoniacal solution
of copper carbonate. The formula for this solution is; 5 ounces copper car-
bonate, and 3 pints of ammonia (26 degrees), to 50 gallons of water. Mix
the copper carbonate with enough water to make a paste, pour in the
ammonia, and dilute to the proper strength. Do not dissolve the copper
carbonate before you need it, as the solution will deteriorate on standing.
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