Savannah morning news., 1885-06-29
Rust OF Orange.

EAuhJ Ol orange.
"a 6stract Of a paper read before the Biological
Society OF WaShinGtOR, d. C.)
The nature of the rust has been careful.
ly studied by the author, aud also bv one
OF his assistants, Mr.. Il. G.. Hubbard. at
Crescent City, Fla. 1t has always been
known, and has always given concern. II
varies from more or less pronounced
stain beneath the cuticle, to rough. .deep
brown incrustation. When heavily coat
ed the surface is chapped like that of a
russet apple. II may be first noticed
when the fruit is small or one-third grown
(early summer). 1t rapidly increa.es in
August and September, when the fruit is
lull grown, and ls most noticed when the
irult begins to color, though there is no
increase, but rather decrease, after that
time
Rusts are mostly due to fungi, but
there is nothing of this kind about the
orange rust. The oil cells are depleted
and the epithelial cells cogged with
brownlsh resin. The surface is fssured
and the rlnd shrinks and toughens. and
loses essential oil.
Carefully examined, a rusty orange will
be found covered with cast mite skins
thlck IN summer or fall, less noticeable
IN winter. The mites themselves will be
found on the non-rusted fruit, and all over
Wv IiCC III pl duO buAlilleI. l ne Hlluo
Is so minute as 10 be scarcely noticeable
slugly, but collectively gives the green
leaf and fruit the appearance of being
sprlnEled with fine golden dust. Pine pol
len is often mistaken for them, and they
for the pollen.
The attacks of the mite are always fol
lowed by rust on the fruit, but on the
leaves tney produce only dull, tarnished
appearance, contrasting with the polish
OF the healthy leaf, and sure indication of
depredations, even after the mites have
left. The leaves look dry and dusty. with
slight loss Of color, as from drouth. When
the foliage of the tree is bright, the
oranges are bright. The living mites are
not found on rusty oranges; they quit
both fruit and leaf and wander to fresh
nelds, when the oil is depleted or the sur
face too hardened tor their beaks.
The mite (phgtOptgS oieiDOrUS-Ash-
mead) is elongate, honey-yellOw, Ii nm.
long, and with two pairs of 4-jOinted legs,
each terminating in curved spine, with
opposing brIstles.s The eggs are laid
singly, or in small clusters, GU the leaves.
Iney are spherical, transparent, with q
yellow tinge. They hatch in summer in
four days, and the cast mite skins adhere,
as stated, to the surface of Leaf or fruit.
Its food is the essential oil which abOuuds
IN the succulent parts of citrus plants. 1t
Is stationary when feeding, but moves ac-
lively, and wanders from one part Of the
plant to another, especially to new
growth. Thousands occur on assingle
leaf, $4,000 having been computed by Mr.
Hubbard in winter time on leaf averag-
ing 10 square inches. They are still more
numerous in summer.
Rust rings eucircle the fruit much as
the eclyptic does the earth. There is
penumbral band between brightest sun
and deepest shade, and indicating the
preference of the mite for such halfshade.
FrOsts Kill the mites but not the eggs.
Drouth causes both to dry up. Birds,
insects, and especially spiders, are the
chief agencies IN distributing the mites
from place to place. The effect OF the
mite on the fruit, aside from the rusty
appearance which lowers the market
value, is in no wise Injurious, as the
quality is, if anything, improved, and
the disposition to rust decreased. The
effect on the leaf is to slightly check
growth.
The mite is generally distributed in
Florida, not elsewhere. Like most mites
affecting growing plants, it is worse on
high, dry lands, than in low, moist lands.
No method of culture or OF manuring, in
fact no method that does not comprehend
the true cause, has proved Of avail to pre-
vent LDe rust " NlNuDreakS ana Isolation
act as preventives, but insecticides are
the only remedial agencies, but they must
kill mites and eggs, and molting mites.
VIII ale oil soap, one pound to five gallons
wa ter, in early spring, before the new
gro with begins-Weaker solutions at fire.
Qu Mt tinteryals-cause the mites to fall to
the ground. Flowers Of sulphur is deadly
to tn active mites, but not to the eggs.
Ker osene emulsions as used against scale
ms ects, with sulphur added, are the most
sa :. isfactOry.- Prot. c. Y. Rl5ey.