The cotton red spider (Tetranychus gloveri Bks.)

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CIRCULAR NO. 65.

United States Department of Agriculture,
BUREAU. OF ENTOMOLOGY, |

L. O. HOWARD, Entomologist.

THE COTTON RED SPIDER.
(Tetranychus glovert Bks.)
By E. 8. G. Titus, Special Field Agent.

Injury to cotton by the red spider, or rust-mite as it is also called,
has been quite prevalent in some sections of the cotton-growing area of
this country during the past two years. The cause of the injury is a
_ minute yellowish-red mite which feeds on the cotton plant, principally
on the under sides of the leaves, but at times attacking all parts of the
plant. The mites usually appear early in
the season, but do little appreciable dam-
age until midsummer or later. The in-
juries rarely become serious unless accom-
panied by long-continued dry weather; in
such an event the multiplication of the
mites is very rapid, and the consequent
injuries are often sufficient to kill the
plants.

The early attacks of this mite are quite
characteristic; the leaves presenting on
the upper side near the base a scarlet ap-
pearance, which, occurring at first between
the larger ribs, gradually spreads over the
leaf as the mites multiply, then dies out
and is replaced by a dirty yellow, the leaf
finally shriveling and falling to the ground. )
Larger and older leaves show the effect Fic. 1.—Tetranychus gloveri: Adult—
of the attack before younger leaves. ee a oka

The mites feed on the under side of the leaves, protected by a loose,
irregular web stretching at first from vein to vein, but later attached at
any point and in cases of severe injury sometimes covering both sides
of the leaf.

Rarely have the red spiders been found feeding on the upper side of
the leaves, and then only when they are protected or shaded by the
leaves above, or when a leaf has begun to curl from their injuries.

When present in considerable numbers almost all parts of the plant
may be attacked—flowers, squares, bolls, and stems. Severely injured
plants lose most of their leaves, flowers, and younger forms; quite often
only the young unfolding leaves at the tips of the branches are left green.

9

This species was first described by Mr. Nathan Banks, of the Bureau
of Entomology, in 1900,' from specimens collected on cotton by Prof.
H. A. Morgan, of Baton Rouge, La. In 1893-94 it had caused consid-
erable damage at Baton Rouge.” The pest is very probably distributed
throughout the entire cotton-growing area of the South, although during
late years its occurrence in injurious numbers had not been reported
until the summer of 1905, when it caused considerable damage to cot-
ton in South Carolina and Georgia. In 1904 red spider was found on
several plantations near Batesburg and at other points in South Caro-
lina. During the summer of 1905 many reports of its occurrence were
received from points in North: Carolina, South Carolina, Georgia, and
Alabama, and the writer found it in injurious numbers at several locali-
ties in these States.

The first published records of the species appear to be those by
Townend Glover, in an article on Cotton Insects published in 1855,° in
which he gives a description of the mite and its injuries to cotton under
the name of “The Red Spider. Acarus?’’ and in 1878,‘ in his Cotton
Insects under the name of “cotton rust,’ again referring the injury to
an “‘acarus.’?’ He recommends powdered sulphur or sulphur mixed
with slaking lime as remedies.

LIFE HISTORY.

When first deposited the eggs appear as minute translucent pearl-like
objects, found only by careful observance on the threads of the web, on
the plant hairs beneath it, and more rarely on the epidermis of the leaf
itself. As they mature they grow darker, becoming quite opaque, with
more or less of a red or greenish tinge.

The eggs hatch in from three to five days during hot, dry weather, and
the young mites commence feeding almost immediately. At this early
stage they have but six legs and but few red markings. They reach
maturity in from ten to fourteen days after hatching. At maturity the
mites vary from specimens with very small red spots to those that are
all red on the dorsum and have the legs lightly marked with red dots.
The mature mites are eight-legged. According to Mr. Banks, the adults
of this species are distinguished by the following characteristics: Bristles
of body not arising from tubercles; tarsus with but one claw, which is
strongly bent near its middle and four-cieft beyond; three fingers on
the tip of the thumb, which is not as long as the claw, the middle finger
largest from side view; mandibular plate broad, sides concave near tip
and apex truncate or slightly broadly emarginate (fig. 2).

ee oe See — ————————————————

11900: Banks, Tech. Series 8, Bur. Ent., Dept. Agric., pp. 76-7
21897: Morgan, Bul, 48, La. Agric. Exp. Sta., pp. 180-135.
31855: Glover, U. S. Patent Office Rept., p. 79, Pl. VI, fig. 7.
11878: Glover, Cotton Insects, plate 3.

3

Where and in what stage the mites hibernate is not known, but it is
probable that the early spring generations live upon some other than
the cotton plant, probably upon various weeds and in some sections on
water-oak.

MEANS OF DISTRIBUTION.

The distribution of mites over a field may be accomplished in several
ways. The minute mites cling to almost any substance that brushes
so forcibly against them as to remove them from the plant; and when
brought in contact with plants farther along the row, or elsewhere, they
will be brushed off and cling to them. The mites have been taken
from several insects, such as grasshoppers and small Hemiptera, found
visiting the cotton plants. Probably the most common means of dis-
tribution occurs during the cultivation of the crop. The hoe gangs and
the cultivators rapidly and thoroughly scatter the mites over the field,
Hoe gangs will spread them broadcast—down the rows during their
daily labor, and across the field when they leave it, since they usually
go by the shortest route. The effect of
distribution along the rows can be most ny on
easily traced in terraced cotton. |

The writer in 1904 and 1905 made short |
trips to South Carolina to study this pest. ; /

In several instances it was noticed that yp

from a point on the margin of afield where —

there were growing large poke-berry plants

(Phytolacca decandra) the infestation by Fre. 2.—retranychus gloveri: Palpus and
red spider had spread over a fan-shaped eae Plate culare ed anom
area of the adjoining cotton. Other places

were seen where this same weed occurred on terraces, and here also the
mites were present in considerable numbers on adjoining cotton. At
that time of the year (July and August) these weeds, as well as the
cocklebur (Xanthiwm spp.), showed the effect of red spider work. The
mites were too scarce, however, for positive identification. Specimens
occurring on corn, cowpeas, and beans were identified by Mr. Banks as
the cotton red spider. These plants all showed appreciable injury by
the pest. Especially was this true of one field of corn that was planted
in a cotton field, the rows alternating.

METHODS OF CONTROL.

Enemies.—No parasites have yet been reported as living in this red
spider. However, there are several species of predaceous insects that
prey upon the mites and their eggs. Among these are larvee of Chrysopas
or lacewings, and lady-beetle larvee and adults. One species of Pentilia,
a minute black lady-beetle, is very destructive to the red spider; this
and other Coccinellids (lady-beetles) were noticed feeding on the mites
at several places visited in 1905.

4

Cultural methods. —These are: (1) Rotation of crops. (2) Destruc-
‘tion of cotton stalks, weeds, and grasses in the infested fields after
cotton picking is over in the fall, by pulling and burning where pos-
sible. (3) Deep fall or winter plowing, taking care to thoroughly turn
under all the vegetation. (4) Burning off or otherwise destroying the
weeds, grasses, and rubbish on the terrace edges, ditches, and borders
of the field. (5) Keeping down all weeds and grasses in the early
spring.

Remedial measures.—A careful outlook should be kept on the young
cotton in the early spring, and at the first indication of injury prompt
action should be taken. If, when first noticed, there are but few
infested plants, these may be pulled and burned, care being taken not
to distribute the mites to the surrounding cotton during the operation.
The cotton surrounding the infested place should then be thoroughly
sprayed with one of the mixtures described below, preferably one con-
taining sulphur. Spray the plants thoroughly, taking especial care to
cover the wnder sides of the leaves and the stems and branches.

If a large area is infested when first noticed, or if it should be found
desirable to spray whole fields, a barrel or tank outfit should be
used. The pump should have no copper about it, a brass cylinder
being preferable. With one man to pump and two lines of hose, very

rapid work can be done. Sufficient hose should be used to allow free

movement around the plants being sprayed. It will be well to have
an iron pipe attached to the hose with the outer end bent upward and
threaded for the attachment of the nozzle. The pipe should be long
enough for this elbow to reach the ground when the man doing the
spraying is standing upright. Use a nozzle distributing a fine spray.
By this means the under sides of the leaves can be easily sprayed by
simply moving the pipe up and down through the plant.

Among the many remedies that have been used against red spiders
on various occasions the sulphur nuxtures stand foremost. Water,
kerosene emulsion, and soap washes will also kill many of the mites and
some of the eggs. There will, however, be some eggs left to hatch, and
these sprays leave nothing on the leaf to kill the young freshly hatched
mites. No spray can be expected to reach all the mites or their eggs,
but the sulphur preparations, when properly prepared and applied,
adhere to the leaves, and there will be enough sulphur left on the leat
to destroy most of the young mites that appear later.

INSECTICIDE FORMULZ.

Sulphur.—Ordinary powdered sulphur can be used dry, blown from
one of the powder guns manufactured for dry sprays. It may also be
used mixed with flour, road dust, or plaster of paris.

Lime-sulphur.—Into slaking lime dissolve an equal amount of pow-
dered sulphur. If only a small quantity is to be made, the heat gener-

a a ee RR A i Bh es —

5)
ated by the slaking will be sufficient to cause the sulphur and lime to
unite. If considerable quantities are being prepared, it will be well to.
slake the lime in boiling water in an iron kettle (never in copper) and
keep the mixture boiling for a short time after the sulphur has become
well incorporated. The mixture should be constantly stirred until it is
smooth and even. Five pounds of sulphur and 5 pounds of lime will
make, after diluting, 100 gallons of spray mixture. This may be used
stronger, if desirable, but care must be taken not to injure the plants.

Lye-sulphur.—‘‘ Mix 20 pounds flowers of sulphur into a paste with
cold water, add 10 pounds of pulverized caustic soda (98 per cent).
The dissolving lye will liquefy the sulphur and boil. Water must be
added from time to time to prevent burning until a concentrated solu-
tion of 20 gallons has been obtained. Two gallons of this is sufficient
for 50 gallons of spray, giving a strength of 2 pounds of sulphur and 1
of lye to 50 gallons of water.’’?! This has been successfully used against
the orange red spider in California.

Kerosene emulsion.—Dissolve 1 pound hard or 1 quart soft soap in
1 gallon hot water, add 1 gallon coal oil, and emulsify. The most
thorough and feasible method is to pump the spray mixture back upon
itself until it is thoroughly emulsified. Dilute to 10 gallons and use
as soon as possible. With the recent advent of a certain naphtha soap
which will emulsify without heating, kerosene emulsion can be readily
made in the field with cold water.

Water.—This treatment is quite commonly used by greenhouse men
in fighting red spider in propagation houses, conservatories, and parks.
The water is driven onto the plants in a fine spray with considerable
force. j

11903: Marlatt, Farmers’ Bul. 172, U. S. Dept, Agr., p. 41.

Approved:
JAMES WILSON,
Secretary of Agriculture.

WASHINGTON, D. C., October 30, 1905.

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