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 Title Page
 Table of Contents
 General appearance of the...
 Thrips on citrus
 Thrips on tomatoes
 Thrips on strawberries
 Thrips on deciduous fruits
 Thrips on other plants
 Characteristics and history of...
 Other flower-frequenting thrip...
 Acknowledgement














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 162
Title: Flower thrips
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Permanent Link: http://ufdc.ufl.edu/UF00027686/00001
 Material Information
Title: Flower thrips
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 162
Physical Description: Book
Language: English
Creator: Watson, J. R.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1922
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Bibliographic ID: UF00027686
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Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 25
    Table of Contents
        Page 26
    General appearance of the insect
        Page 27
        Page 28
    Thrips on citrus
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
    Thrips on tomatoes
        Page 38
    Thrips on strawberries
        Page 39
    Thrips on deciduous fruits
        Page 40
        Page 41
    Thrips on other plants
        Page 42
    Characteristics and history of the insect
        Page 43
        Page 44
        Page 45
        Page 46
    Other flower-frequenting thrips
        Page 47
        Page 48
    Acknowledgement
        Page 49
        Page 50
        Page 51
Full Text

Bulletin 162


UNIVERSITY OF FLORIDA

Agricultural Experiment Station






THE FLOWER THRIPS
By
J. R. WATSON


Fig. 7.-Florida flower thrips (highly magnified)


Bulletins will be sent free upon application to Experiment Station,
GAINESVILLE, FLORIDA


June, 1922


















CONTENTS


INTRODUCTION


GENERAL APPEARANCE OF THE INSECT................-----------

THRIPS ON CITRUS.......... --...................

THRIPS ON TOMATOES.............................. .-.

THRIPS ON STRAWBERRIES-.................-..........

THRIPS ON DECIDUOUS FRUITS.............................

THRIPS ON OTHER PLANTS..................... ...... .

On Dewberries and Blackberries...--.............-....

On Mulberries .--..........-------

On Peanuts........... .....................

On Roses ..................--- -

CHARACTERISTICS AND HISTORY OF THE INSECT....................

OTHER FLOWER-FREQUENTING THRIPS......................-....

Mason's Thrips ..................-----

The Cuban Citrus Thrips........................ ....

The Tobacco Thrips--.............. -- -

The Composite Thrips....... --......-- ...... ..

The Onion Thrips ........-........ ..... ..

The Black Garden Thrips............ ............-.

The M agnolia Thrips ............. .. ........................

The Buckeye Thrips.........-...........----

ACKNOWLEDGMENTS .....------.......... -


.......... ---.. .......-- 27

---------------- 29

-......- -..--. --- -....- 38

-... .....--......---.. 39

............--...-- .... 40

.-. -----...---. 42

........................... 42

-..-...............-... 42

-.. .................- 42

..... ......... 43

...-. ...- ..... ....... 43

....... ........... 47

...-...-............ 47

--..-.... .............. 47

......... ............. 47

.........-.... ...... 48

....... .... ............. 48

--... ..-.......... 48

.... ....... ............ 48

................... 48


. .......... ..... 49








THE FLOWER THRIPS
By J. R. WATSON

Thrips are minute insects which attack mostly succulent veg-
etation, altho one species lives on dried leaves and several are
predacious. They suck the sap from the plants they attack. Over
eighty species have been recorded from Florida,1 but most
damage to crops is due to a half dozen, all others either feeding
upon wild plants or being uncommon and unimportant.
Two or three species are injurious to oats, rye and most other
grasses, but those most likely to attract the attention of the
farmer and orchardist chiefly attack flowers and young tender
fruits. These are the flower thrips.
By far the most common of these insects is the Florida
flower thrips (Frankliniella bispinosa Morgan)" (fig. 7). This
is the species most commonly seen in flowers in all but the ex-
treme southern part of the state. It takes the place held in most
other sections of the the United States by the so-called grain
thrips (F. tritici) which is seen in Florida but rarely.
In the extreme southern part of the state the Florida flower
thrips is replaced largely by a closely related form (Frankliniella
cephalica var. masoni Watson).3 This insect is a trifle smaller
and yellower in color than our common flower thrips; that is,
it has less of the orange pigment. It is also somewhat quicker in
its motions. Under the microscope the front part of the head is
seen to be of quite a different shape from that of the Florida
flower thrips.

GENERAL APPEARANCE OF THE INSECT
The Florida flower thrips (fig. 7) is about one-twenty-fifth of
an inch in length. It is yellow in color with a marked tinge of
orange, especially about the middle of the thorax. When dis-
turbed it curves its abdomen up over its back as if threatening
to sting. This motion is preparatory to taking flight, and is for
the purpose of spreading out the wings and their fringe of
hairs. The hind legs are often used to aid in spreading the
wings. The wings, four in number, are thin membranes fringed
with long delicate hairs. When not in use, the wings are folded
1"Thysanoptera of Florida," Fla. Buggist, Vol. II, No. 1, 1918.
'Morgan, A. C., in "New Genera and Species of Thysanoptera," Pro. U.
S. Nat. Mus., Vol. 46, 1913.
"'New Thysanoptera from Florida," Fla. Buggist, Vol. III, No. 1, 1920.





Florida Agricultural Experiment Station


back over the abdomen. Under a lens the insect is seen to have
brownish-red eyes and a pair of eight-jointed antennae (feelers).
Near the end of the abdomen of the female the ovipositor (egg-
laying organ) may be seen. This is a curved, sword-like or saw-
like, hard structure which can be pushed out of an opening on
the under side and near the end of the abdomen. It is used to
cut a shallow incision in the tissue of the plants in which the
eggs are laid.
The male is considerably smaller than the female and is lighter
in color, the orange pigment being less in evidence. The ab-
domen is more rounded at the up-turned end and bears a num-
ber of curved processes known as the clasping organs and, of
course, possesses no ovipositor.
Altho it may be found occasionally on any green succulent
vegetation, this insect primarily inhabits blossoms, especially
open and dry ones. Long tubular blossoms with abundant nectar,
like trumpet flowers, are avoided usually. The blossoms of
plants having hairy, dry tubes, as those of wistaria and petunias,
often are highly infested.
Of all the common host plants, roses are perhaps the first
choice of the Florida flower thrips and the white varieties of
roses are preferred. Most plants of the rose family (Rosaceae),
especially plums, pears, peaches, strawberries, haws, etc., are
usually infested. Indeed, most flowers of a more or less open
structure, where the stamens and pistils are easily accessible,
are favorites. Flowers in which the stamens make a tube about
the pistil, as is true of the nightshade family-which includes
tomatoes, peppers, eggplants, etc.-are favorites of this
thrips. On the other hand, most of the Compositae, which in-
cludes sunflowers and their relatives, are infested but slightly
by the Florida flower thrips. It is probable that the smallness
of the individual flowers and the compact heads do not afford
good hiding and feeding places for this species. However, those
Compositae with rather large flowers loosely set in the head,
such as the white-blossomed "Spanish needles" (Bidens), are
infested heavily with the flower thrips. Blossoms with minute,
dry, scale-like envelopes are often attacked but seldom heavily
infested. The catkins of such trees as the chinquapin and oak,
come in this class, as do the blossoms of grains and other
grasses.
Thrips are provided with sucking mouth parts, but these are
too short to penetrate as deeply into plant tissue as most bugs





Bulletin 162, The Flower Thrips


are able to do. In feeding, thrips frequently change their posi-
tion. The effect of their numerous but shallow punctures is to
give the injured tissue a shrunken appearance, so much so that
the damage has been described as a rasping of the tissue.
Feeding is always on the most tender parts of the plants.
The flower thrips never attack woody tissue nor thick bark.
They sometimes feed on fresh succulent twigs. The writer has
seen them seriously injure camphor twigs. In absence of other
food they frequently attack unfolding buds and leaves, such
as those of the pear (fig. 9) and peach. Generally, however,
their attacks are confined to the tenderest parts of blossoms, as
the pistils, and stamens, and petals when these are rather thick
and succulent, as those of citrus.
Eggs are not laid in those parts of the flower which soon wilt
and drop off, but always in the more permanent parts. At-
tacked parts usually turn brown or even black and fail to develop
properly, appearing dry and shriveled. Or, if the injury is con-
fined to only one side of the fruit, it may become distorted in
shape.

THRIPS ON CITRUS

Character of Damage.-The greatest damage chargeable to
the Florida flower thrips is that done to citrus. In citrus blooms
thrips feed chiefly on the thick fleshy petals and stamens. These
turn brownish-yellow and drop prematurely. The damage done
to these temporary organs is of no practical consequence. But
some feeding is done on the ovary, or young fruit, and on the
expanded tip of the stem which bears the fruit (the receptacle).
This damage is due largely to the young of the next generation.
The winged adults leave the trees shortly after the petals have
fallen. However, the females lay their eggs in the receptacle
before leaving. These hatch in three or four days and the wing-
less young feed on the receptacle and on the young fruit until
they become mature and acquire wings and in their turn fly away
to seek more succulent forage. About two weeks at the time of
year when citrus is in bloom are required for them to hatch and
reach maturity.
The damage to citrus is of a double nature. The feeding of
the insects may cause the fruit to drop. The numerous, shallow
punctures on the surface of the developing fruit may cause char-
acteristic markings which lower the grade of the fruit (fig. 8).





Florida Agricultural Experiment Station


Dropping of Bloom.-It has been questioned whether thrips
reduce the crop. Some growers have gone so far as to contend
that thrips are beneficial in that they carry pollen from one
tree to another. There are two reasons why this contention
cannot stand. First, thrips are not efficient carriers of pollen.
They do not move freely enough from one blossom to another to
be of importance as pollen carriers. When in search of food,
however, they may fly considerable distance, evidenced by the
fact that they often fly into the windows of our houses. But,
if food is available, they leave a blossom only when disturbed
or the food becomes exhausted. That thrips do not move about
restlessly is indicated not only by direct observation, but also
by the fact that a freshly opened blossom does not become
heavily infested for a day or two. Second, it has never been
proven that any citrus blossom needs cross pollination. Indeed,
in all investigated varieties it has been found that fertilization
is unnecessary.
It has been contended that since citrus trees normally put forth
much more bloom than the amount of fruit which matures and
since there must be heavy dropping of bloom, the thrips only
thin out the bloom which the tree itself would drop later, were
there no thrips present. There is undoubtedly much truth in
this contention. But the question arises, "May not the thrips
sometimes over-do the thinning, particularly when they are un-
usually abundant or when bloom is scanty?"
In order to answer this question as far as possible some ex-
periments have been undertaken. These were commenced in
1915' and have been carried on since as opportunity afforded.
During some seasons no spraying was done, as thrips were not
abundant or the bloom was too irregular to make spraying
practical. The detailed results of the early experiments have
been recorded in the 1915 and 1916 annual reports of this sta-
tion. It will be sufficient to summarize the results here.
On trees with an abundant bloom and a moderately heavy
infestation of thrips one spraying increased the amount of fruit
from 6 to 10 percent, averaging about 7 percent, over unsprayed
trees. These figures have been obtained by carefully counting
the oranges on a large number of trees and by counting the
boxes of fruit at picking time. This increase is not enough to
be noticeable in a casual inspection of a tree and, hence, it is
not surprising that many growers who have sprayed for thrips
'An. Rpt., Fla. Agri., Exp. Sta., 1915.





Bulletin 162, The Flower Thrips


report that they can see no increase of fruit as a result of
spraying. The increase, however, does repay the cost of spray-
ing.
It was thought that the amount of bloom on a tree might
be a factor in determining the returns from spraying. It was
thought that the work of the insects in reducing the amount
of fruit on trees overloaded with bloom, might be inconsequen-
tial, because of the natural over-abundance of bloom. On the
other hand, the same amount of injury on a tree with scanty
bloom might seriously lessen the crop. Accordingly, in several
experiments the trees were divided into three classes-those
with light bloom, those with fair bloom and those with heavy
bloom-and the fruit of each class counted separately. A num-
ber of sprayed trees with light bloom produced an average
of 252 oranges, while those in the check rows averaged 58.
This gave an increase of 334 percent in case of sprayed trees.
Altho these tests were not sufficiently extensive for definite
conclusions, they indicate that when the bloom is light thrips
are relatively more important than when the bloom is heavy.
Usually the first effect of spraying is a heavy dropping of
young fruit. This is no cause for alarm, as close investigation
will show that all falling fruit is yellow; not in spots, as would
result from spray injury, but uniformly yellow. It is only im-
perfect fruit and that which has been injured by thrips, all of
which would have fallen in a few days, that is brought down
prematurely by the spray.
Counts made a few weeks after spraying usually have shown
about a 50-percent increase in the number of young oranges to
the tree as compared with those on check rows. The reduction
of this increase to 7 percent indicates that spraying causes the
trees to retain, temporarily, more fruit than they can carry to
maturity.
Marked Fruit.-The feeding of the thrips, both adults and
nymphs, on the young fruit causes a blemish (fig. 8) which
lowers its grade at packing time. This blemish is a smooth,
shining area, very irregular in shape. The surface is slightly
sunken and is lighter in color than the remainder of the skin.
The longer diameter of the spot usually extends around the
fruit rather than lengthwise. The smooth surface and irregular
shape of thrips marks are very characteristic and serve to dis-
tinguish them readily from other marks on the fruit; such as,




Florida Agricultural Experiment Station


mechanical injury, wounds made by grasshoppers or katydids,
melanose, or scab. Among the causes of mechanical injury are
wounds made by the wind's rubbing the fruit against twigs,
thorns or other fruit. Such marks are, however, rough and
lack the peculiarly irregular shape of the marks of thrips. Of
course thrips marks are often complicated by the operation of
one or more of the above factors, especially those of melanose.


Fig. 8.-Thrips marks on grapefruit


The injury is to the skin only; the pulp is unharmed and the
fruit retains its natural shape in contrast to the tomato when
attacked by thrips. Sometimes, however, these smooth spots
on citrus fruit afford points of attack for other parasites, es-
pecially scab and plant bugs.
The extent of this injury will vary greatly in different groves
and from season to season. Sometimes nearly 100 percent of
the fruit shows more or less marking. Taking the average of





Bulletin 162, The Flower Thrips


the state thru a series of years, probably 25 percent of the fruit
shows some marking, tho considerably less than a third of this
is serious. If the scar or mark is of sufficient size, it will lower
the grade of the fruit, reduce it from bright to golden, from
golden to russet, or even cause it to be classed as a cull.
Oranges are more apt to be scarred by thrips than are grape-
fruit. In some groves of mixed oranges and grapefruit in which
control experiments were carried on in 1921, about 75 percent
of the oranges and only 25 percent of the grapefruit were seri-
ously marked. Perhaps the comparatively less serious damage
to grapefruit is to be explained by reason of its thicker skin.

CONTROL MEASURES
Spraying experiments, looking toward the lessening of thrips
marks on fruit, have given more definite results than those look-
ing toward checking the dropping of the fruit. This is because
results are less likely to be obscured by other factors, such as
dropping due to drought, wind or excessive bloom.
To summarize the results of six years of spraying experi-
ments, it can be said that one opportune spraying generally has
reduced the amount of seriously marked fruit by 50 percent.
By seriously marked fruit is meant that which, in the hands of
a careful grader, has its grade lowered. This reduction is as
great as could be expected from commercial spraying. Not all
thrips are killed by a single application of spray. Those inside
the column of stamens are so well protected that many escape,
particularly if the blossoms have just opened; and then some
blossoms are certain to be passed over and left unsprayed. If
from 75 to 90 percent of the thrips in a grove are killed, the
spraying may be considered successful. But the greatest ob-
stacle to successful spraying comes from the irregularity of the
blooming period. Many trees will have passed the best time
for spraying while others are not yet in bloom. Late blossoms,
when they open, are infested by thrips which escaped the spray
or came into the grove afterward.
When to Spray.-As thrips are not present until the blossoms
open and usually are not abundant until several hours later, it
is useless to spray before many blossoms are open. This point
is not understood by many growers. They argue that, if they
spray just before the bloom opens, they will kill all the adult
thrips in the grove, leaving none to breed another generation.





Florida Agricultural Experiment Station


But the thrips found in blossoms fly there after they open. They
are not found on buds or foliage.
A question more worthy of consideration is, "Shall we spray
when there is maximum bloom, or a little later when we can
kill the young of the next generation?" As practically all adults
leave the blossoms as soon as the petals fall, and as most eggs
hatch within three days, it may seem reasonable to many that
spraying four days after the petals have fallen will kill all
thrips present and, therefore, prevent reinfestation. On the
other hand, it may seem best to spray when the maximum num-
ber of blossoms are open and the maximum number of thrips
present, and thus prevent the laying of eggs as much as possible.
To get light on this question was one of the chief aims of a
series of experiments carried out in 1921. Seven groves in
widely separated parts of the state were plotted and the stage
of bloom of each tree at spraying time recorded. Early in Oc-
tober the percentage of scarred fruit on these trees was ac-
curately determined. In every case the best control was obtained
on those trees which were in full bloom at the time of spraying.
It was found preferable, however, to spray a day or two after
the maximum bloom, rather than a day or two before.
A few experiments were carried out to determine the effect
of a second spray a week after the first. This was for the pur-
pose of killing the young thrips which hatched from eggs laid
before the first spraying. This is the procedure recommended in
California for the California citrus thrips, an insect related to
the Florida flower thrips but placed in a distinct genus.
In checking up the results of this experiment, it was found
that two sprayings gave slightly better results than one did,
about 60 against 50 percent. It is doubtful, however, if double
spraying will pay except in special cases; such as, when the
infestation is unusually heavy, when spraying with a combina-
tion spray for two troubles (as for scab and thrips), or when
the blooming is irregular.
Another question to consider is, "How abundant should thrips
be to make spraying profitable?" It is not probable that spray-
ing will pay every year. The insects vary greatly from year
to year and from place to place, and are often comparatively
scarce at blooming time. They may average anywhere from
one or two to as high as two hundred to a blossom, being most
abundant during periods of drought.





Bulletin 162, The Flower Thrips


In one grapefruit grove under observation in 1921 there was
an average of only ten thrips to the blossom. The owner was
spraying with lime-sulphur to control scab and, at our sugges-
tion, added nicotine sulphate to part of the spray solution. There
was noticeably less marked fruit on the sprayed portion. It was
estimated that the improvement in the fruit was worth more
than twice the cost of the nicotine sulphate. If, however, the
labor cost had been added to the cost of the insecticide, the
operation would have resulted in a loss. If it had been an orange
grove the increased amount of fruit would have come nearer
meeting the expenses of this combination spray. But it is doubt-
ful if spraying for thrips alone will ever pay when there are as
few as ten thrips to the blossom and when the bloom is ample.
In groves where there has been an average of 25 thrips to
the blossom, spraying has proven a profitable investment.
The Best Insecticides.-Of all the insecticides we have tried,
the tobacco extracts are most satisfactory. Any one of these
extracts is perfectly safe to use on the bloom and, if strong
enough, will kill any thrips with which it comes in contact. It is
better and more economical, however, to put something else in
the spray to act as a spreader for the tobacco. By so doing one
can use a lower concentration of tobacco and thus reduce the ex-
pense. One or two pounds of soap to 50 gallons of water is a
satisfactory spreader, but usually the use of lime-sulphur (at
rust-mite strength, 1 to 70) is recommended. The advantage of
lime-sulphur over soap is that there are apt to be a few rust mites
or red spiders in the trees at the time of blossoming and the
lime-sulphur is more effective against them.
In California lime-sulphur alone is recommended for spraying
thrips." But for our Florida flower thrips lime-sulphur is not
an efficient killing solution, even when used in the proportion
of 1 to 30. Many thrips, especially young ones will be killed; but
a high percentage, mostly adults, will revive, altho motionless
and apparently dead soon after being hit.
Any of the oil emulsions commonly used for whitefly and
purple scale will kill thrips but are not safe to use on blossoms
and young fruit.
As to strength, in order to get the best killing effects, it is
necessary to use a full pint (13 oz.) of nicotine sulphate (Black
leaf 40) to 100 gallons of lime-sulphur, in the proportion of 1
'Jones and Horton (Cal.) in "Orange Thrips," Bul. 99, p. 1, Bu. Ent.,
U. S. D. A.





Florida Agricultural Experiment Station


to 70. Formerly it was recommended that only 10 ounces of
the nicotine sulphate to 100 gallons of water be used, but careful
comparisons during 1921 clearly prove that the higher concen-
tration, 1 pint (13 ozs.) to 100 gallons, is preferable.
Black leaf 40 is the most commonly used tobacco extract.
However, it is expensive and when refuse tobacco can be ob-
tained readily and economically, one can make his own extract
and effect a considerable saving. To do this soak the tobacco
refuse over night in enough water to cover it well. (This will
require about 2 gallons of water to 1 pound of tobacco.) This
should give a stock solution about the color of strong tea. To
make up the spray solution, take 10 gallons of the stock solution,
88 gallons of water and 11/2 gallons of commercial lime-sulphur.
Strain, of course, before using. Before spraying the entire
grove, test out the material on a small scale. If all the thrips
hit by the spray are not killed, use more of the tobacco solution.
Any thrips hit by an efficient solution will die inside of 15
minutes.
Combination Sprays.-Many grapefruit groves need to be
sprayed for scab at blooming time with lime-sulphur. (See spray
No. 3, p. 50.) In such a case, in order to kill thrips also, the
only extra expense is that of the tobacco and, as has been shown
above, it has paid to use the tobacco when the infestation was as
low as ten thrips to the blossom. As the amount of lime-sulphur
is much greater than in our regular sprays for thrips,' the amount
of tobacco can be reduced to 9 or 10 ounces to 100 gallons of
lime-sulphur. It may pay also to add the tobacco to spray No. 4
when that is used. (See p. 50.)
Methods of Application.-It is essential that good pressure be
maintained when spraying for thrips, in order to reach those
protected behind the column of stamens. The spray should be
directed squarely into the bloom. Some persons in spraying are
inclined to direct the spray against the side of a bloom cluster.
When this is done the spray is apt not to reach the thrips
hidden away among the stamens. In spraying for thrips alone,
it is not necessary to spray the foliage as practically no
thrips are there. Trees and parts of trees not in bloom may be
skipped. The same is true of the blossoms in the interior of the
crown where the shade is dense. Fruit growing in such a situ-
ation seldom is marked seriously by thrips. Altho these insects
6Lime-sulphur, 1 to 40, is recommended for this spray but growers have
sometimes used it as strong as 1 to 30.





Bulletin 162, The Flower Thrips


avoid prolonged exposure to the direct rays of the sun, they like
best the sunny or well-lighted side of a tree and few are found
in blossoms in the interior of the tree. For this reason also
they are more numerous on the south side of a tree.
It has been our experience that, in the hands of most spray
crews, better killing results are obtained from the use of a
spray gun than from a rod with a nozzle. The driving force of
the discharge from a spray gun is more apt to force the liquid
behind the column of stamens into the interior of the blossoms
where the insects are most numerous.
Dusting.-In cooperation with W. W. Others, of the Bureau
of Entomology, United States Department of Agriculture, some
experiments have been started to test the practicability of con-
trolling thrips by the use of dusts of lime and nicotine sulphate.
Three different strengths, containing respectively 2.2, 5, and 10
percent of nicotine sulphate were tried. Wherever this ma-
terial was driven into the blooms with sufficient force to pen-
etrate behind the column of stamens the thrips were killed. The
killing was fully as high as in spraying and as high with the
2.2-percent material as with the 10-percent. In blossoms ex-
posed to only the drifting cloud of dust, however, the penetra-
tion was not as thoro as desired and a large number of thrips
escaped. It was estimated that between 50 and 60 percent of
the thrips in the grove were killed as compared with 85 or 90
percent in the case of satisfactory spraying. It is as yet too
early to form any reliable conclusions as to the practicability
of controlling thrips with dust.
Destroy Weeds About the Grove.-As a preventive measure
against an infestation of thrips, it is important that weeds,
whose blossoms are breeding grounds for these insects, be kept
down in and about the citrus grove during winter. Most grow-
ers practice clean culture thruout winter. Some low-hammock
groves, however, are never cultivated, and in some groves on
drained land there are often waste places, especially along ditch
banks, which grow weeds. In other groves weeds often grow
under trees and in fence corners where the cultivator cannot
reach them. One of the most common weeds in such places is
the white-blossomed Spanish bayonet, Bidens leucantha (L)
Wild. A blossom head of this plant often harbors as many thrips
as a citrus blossom and, when allowed to bloom in a citrus grove,
is a source of continuous infestation of the citrus. Indeed, ex-
perience during 1921 demonstrates that it is useless to spray





Florida Agricultural Experiment Station


citrus groves for thrips where these weeds are allowed to
bloom. In one of the groves observed these weeds were present
in only a part of it. The difference in the appearance of the
fruit was striking. One could point out easily by inspecting the
fruit, whether or not it came from the portions of the grove
infested with these weeds. It is important that such weeds be
cut, not only in the grove but about the margins as well. This
should be done by January so that most of the thrips will die
before the citrus trees begin to bloom.
THRIPS ON TOMATOES
Next to citrus, thrips probably do most damage to tomatoes.
Often they are abundant in tomato blooms, particularly during
dry weather. The tomato crop of the lower East Coast was
materially decreased by thrips in the spring of 1912.'
The most serious damage to tomatoes is the dropping of
blooms, caused by the thrips puncturing the pistils and stamens
in sucking sap and in depositing their eggs. When a plant is
young and its blossoms comparatively few, the thrips may de-
stroy all the early blossoms and thus prevent the setting of any
fruit. As early fruit is most profitable, its loss is a serious mat-
ter. On tomatoes, thrips usually attack the stamens first. If
there are but one or two thrips to each blossom, there may be
sufficient food for them in the stamens and little or no harm
will be done. But, if thrips are numerous, a dozen or more to
each blossom, other parts of the flowers, especially the pistil,
are attacked. Damaged pistils turn black and shrivel up. Soon
afterward the whole blossom turns yellow and falls off. If the
pistil is injured but slightly and on only one side, there results
a deformed fruit which the growers call a "catface."
Control.-Remedial measures for the control of thrips on to-
matoes are similar to those employed on citrus. The grower
must bear in mind, however, that it takes fewer thrips to de-
stroy a tomato bloom than it does a citrus bloom. An average of
a dozen thrips to the bloom will destroy all of them. If the plants
already have set a good crop of fruit, no harm will result. But,
if the insects attack the first blossoms, the damage may be
great.
The same strength of tobacco extract as recommended for
citrus is advised for tomatoes. Unless the tomatoes are at-
tacked by "White mold" also (see Fla. Agri. Exp. Sta. Buls. 125
'Watson, J. R., in "Tomato Insects," Bul. 125, p. 64, Fla. Agri. Exp. Sta.





Bulletin 162, The Flower Thrips


and 151), it will be better to use soap than lime-sulphur as a
spreader. Since tomatoes generally are attacked by various cat-
erpillars and other biting insects it is advisable to add 1 pound
of powdered lead arsenate to 50 gallons of spray material.
As with citrus, it is important to use good pressure in order
to force the liquid into the bloom. Strong pressure is bene-
ficial also, in that it creates more disturbance among the plants.
Thrips are disturbed quite easily and, when a strong stream of
water hits the vines, most of the insects crawl out of the blos-
soms to where they are more liable to be hit by the spray.

THRIPS ON STRAWBERRIES

Strawberry blossoms are a preferred host plant of the Flor-
ida flower thrips. A. L. Quaintance' states that in certain sec-
tions of the state in 1897-98 they "caused a reduction of the usual
yield of strawberries quite one-third." Since the writer came
to Florida in 1911 there has been no such widespread infesta-
tion, but in 1916 and again in 1920 there was much damage
done by thrips about Waldo and Starke. In each case the thrips
were accompanied by red spiders, and some of the damage the
growers attributed to the thrips was really caused by the
spiders.
As described by Quaintance,' thrips attack first the stigmas
and adjacent parts of the flower, the styles and finally the
ovaries, receptacles and petals. The injured parts turn black
in less than twenty-four hours, and before the end of another
day the whole blossom blackens and shrivels up. If the injury
is but slight, the blossom may not drop but produce a deformed
fruit instead.
This type of injury is quite different from that caused by red
spiders.' In the latter case the berry turns brown, gets hard
and gritty and fails to ripen. Only in extreme cases does it
turn black and shrivel up.
Control in the case of strawberries is the same as with toma-
toes. It is usually preferable to use the tobacco with the lime-
sulphur solution rather than with that of soap, since at that
season there is apt to be more or less red spiders on the vines
and by combining tobacco and sulphur both can be controlled.
'Quaintance, A. L., in "The Strawberry Thrips and the Onion Thrips,"
Fla. Agri. Exp. Sta. Bul. 46.
"'Florida Truck and Garden Insects," Bul. 151, Fla. Agri. Exp. Sta.





Florida Agricultural Experiment Station


THRIPS ON DECIDUOUS FRUITS
On pears, peaches and plums there are two types of injury
by thrips. The insects may attack the unfolding buds and de-
form the leaves (fig. 9) or they may attack the blossoms or
young fruit.
In investigating this subject, thrips were collected and lib-
erated on inclosed buds or blossoms. Other buds were inclosed in
similar cages, but without thrips, and used as checks.
The most successful cage for this purpose was a lantern globe.
The escape of the insects from the larger end was prevented by












0i









Fig. 9.-A pear twig injured by thrips
first tying a piece of cheesecloth over the opening and then
stuffing it with cotton, working from the inside; or by using
two pieces of cheesecloth with cotton between. The cotton was
necessary to prevent the thrips from escaping. It also allowed
some evaporation and thus largely prevented the undesirable
condensation of moisture on the inside. From ten to fifty thrips,
caught on different flowers, were liberated under each cage. High
mortality among these insects was caused partly by faulty ven-
tilation and other unnatural conditions and partly by the old age





Bulletin 162, The Flower Thrips


of the thrips. However, many of the cages after two or three
weeks contained old and young thrips, showing that the insects
could breed in the cages. This was true also in the cages con-
taining leaf buds only. Hence, blossoms, altho preferred, are
not absolutely necessary for development. After the foliage was
killed the insects died. This species can not live on the green
bark of deciduous trees as can the camphor thrips on its host.
Appearance of Injured Parts.-The buds and blossoms on
which were liberated but ten thrips gave uniformly negative
results. On many of the leaf buds in the cage in which thirty or
forty thrips were liberated there were distinct signs of injury.
Characterizing this injury were dwarfed and deformed leaves
(fig. 9) which were caused by the puncturing of the tender
foliage of the developing bud. No injury occurred in any of the
check cages.
This injury is similar to that caused by the pear thrips,
Taeniothrips inconsequens (Euthrips pyri), in California and
other states. But little of this type of injury was seen on trees
in any orchard, which fact indicates that thrips must be abun-
dant to cause much damage. Doubtless unfolding buds are the
second choice of the thrips as feeding or breeding ground, and
will be used but little unless blossoms are scarce or thrips are
abnormally abundant.
Blossoms of the trees were inclosed in the same sort of cages
as described above and treated in the same manner. The in-
sects preferred the bases of the petals for feeding, but the few
eggs found were on the inside of the calyxes.
The results from the blossoms were similar to those from the
buds. If only ten or twenty thrips were introduced, little or no
harm resulted. If more were used, the blossoms usually fell off.
In the orchards there were not enough thrips to do noticeable
damage.
In summarizing the experiments and observations on these
deciduous fruit trees it can be said that, if sufficiently abundant,
the Florida flower thrips will cause the deformation or even the
destruction of leaves and fruit. The general character of the
injury is similar to that of the pear thrips. However, the dam-
age actually caused in the groves near Gainesville during the
last ten years has been negligible.
In a paper read before the Florida Horticultural Society,
April, 1914, Ira Soar, of Dade City, described the severe injury
to these fruits of that year. Similar observations by Quaintance




Florida Agricultural Experiment Station


at Lake City in 1898 are recorded in Bulletin 46 of this station.
The number of thrips varies greatly from year to year and
from month to month. This variation probably is due, in part,
to weather conditions. Dry weather favors the increase of the
thrips. Furthermore, many observations of the writer on citrus
and tomatoes during the last three years would indicate that
during winter and late spring, at least, these insects are usually
more numerous in South Florida than in Central Florida. This
may be due to a check on the growth and reproduction of the
plants, induced by cooler weather in the more northern districts.
THRIPS ON OTHER PLANTS
On Dewberries and Blackberries.-A type of injury similar
to that on pears is exhibited. In some cases, if the blossom is
not too severely injured, there
results a small berry with but
S few ovaries (kernels). An en-
tire crop of loganberries at
Gainesville was destroyed by
thrips in the spring of 1921.
Control of thrips on these trees
should be the same as on citrus.
On Mulberries. Generally
this insect confines its attacks
'to blossoms, less commonly to
young, tender, unfolding leaves.
But the mulberry affords an
exception. Not only are thrips
Common on blossoming catkins
but often they are exceedingly
1 abundant on green and ripe
fruit. No harm whatever will
result from eating the insects
with the fruit.
S On Peanuts.-Thrips some-
times attack the leaves of pea-
nut plants just after they break
m fthru the ground. The edges
%a fof attacked leaves turn pale and
dry up (fig. 10). The plant's
Fig. 10.-Peanuts showing the effects growth is checked and, in se-
of thrips growth is checked and, in se-





Bulletin 162, The Flower Thrips


vere cases, it may be dwarfed permanently. During the spring
of 1919 this trouble was widespread thruout Florida. It was
then that the cause of the mischief was recognized first, altho
the trouble itself had been noticed previously from time to time.
Usually it is not sufficiently prevalent in a field to necessitate
control measures, which, in this case, are the same as for to-
matoes or strawberries.
On Roses.-Of all cultivated plants the first choice of the
Florida flower thrips is undoubtedly roses. Thrips can be found
in roses at practically all seasons of the year and often when
they can be found nowhere else. They feed on the fleshy part
of the petals near the base and cause the petals to turn brown
and fall prematurely, indeed, often before they have fully opened.
This is a trouble often called "blight."
To control the insects use tobacco extract, as previously recom-
mended, or a strong solution of soap suds as a spray. Or the
following method may be used: Pour a little kerosene into a
bucket half full of water; go over the garden carefully and,
with a pair of scissors, cut off all roses; quickly drop each rose
into the bucket, taking particular pains that it is not jarred be-
fore being dropped. Disturb the blossoms and bushes as little
as possible while doing this, so as not to scare the insects away.
Pick off all the blossoms and buds that have begun to open.
Then look over the patch and pick off all buds that are nearly
full grown. These need not be destroyed but should be carried
out of the garden. In other words, thoroly pick the entire rose
crop, taking care not to disturb the thrips but to destroy them.
If this is repeated once every two weeks, the thrips may be kept
down indefinitely, unless weeds or bushes on which they breed
are allowed to grow near by. Spraying the rose bushes after the
roses are picked will help to clear up the infestation but should
by no means be considered as equivalent to picking and dropping
the blossoms into a kerosene-water solution.

CHARACTERISTICS AND HISTORY OF THE INSECT
The Florida flower thrips (Frankliniella bispinosa, Morgan) "
was described by Morgan as Euthrips tritici, var. bispinosa. The
insect had, of course, been known and studied in Florida long
before this. Quaintance worked out the main points of its life
"Morgan, A. C., in "New Genera and Species of Thysanoptera," Proc.
U. S. Nat. Mus., Vol. 46, 1913.





Florida Agricultural Experiment Station


history in 1897-98." But he confused it with the northern grain
thrips (Frankliniella tritici, Fitch), an insect found but once in
Florida. There is no doubt but that all references to F. tritici
in Florida literature have to do with F. bispinosa or possibly with
F. cephalica masoni. That this is true of Quaintance's writings
is proven by the pictures of the adults published in Bulletin 46.
The cuts, evidently reproductions of photographs, show the
second antennal segment plainly as that of bispinosa. The
insect is closely related to the grain thrips, so much so that it
was originally described as a variety only and given specific
rank by Hood. However, it is questionable whether it is not
related more closely to F. cephalica.
The most conspicuous and constant anatomical difference be-
tween the Florida flower thrips and tritici is in the second joint
of the antenna which, in the case of the Florida flower thrips, is
asymmetrical and very long. This insect seems to be a little
larger, and to bear more orange pigment than tritici.
The discovery that the Florida flower thrips is not identical
with the northern type, gives an opportunity for discarding the
old common name, "the grain thrips," which always has been
misleading, as the insect is not at all characteristic of grain. The
northern type received its name tritici because it was first found
on wheat. This was a mere accident. Indeed, unless in bloom,
grains and grasses are, of all vegetation except trees not in
bloom, the place where one is least apt to find this insect in
numbers. The grain thrips in Florida are Haplothrips graminis,
Frankliniella fuscus and Aeolothrips bicolor."
Distribution.-It seems that this species is confined almost to
Florida. Indeed, it has been found in no other state, but un-
doubtedly it occurs in Southern Georgia and Alabama. How-
ever, specimens sent to the writer from Atlanta, Georgia, and
Auburn, Alabama, were always typical tritici.
Life History.-Quaintance worked out the life history of this
insect which he found severely damaging strawberries at Lake
City in April, 1898. His results were published in Bulletin 46
of this station. He gives the time spent by the thrips in the
different stages as follows: Egg, 3 days; larva, 5 days; pupa, 4
days; total life history, 12 days. Quaintance's account leaves
several points to be cleared up. The data in Bulletin 46 seems
"Quaintance, A. L., in "The Strawberry Thrips and the Onion Thrips,"
Fla. Agri. Exp. Sta. Bul. 46, 1898.
1""Thysanoptera of Florida," Fla. Buggist, Vol. II, No. 1, 1918.





Bulletin 162, The Flower Thrips


to have been gathered from limited material. The average time
taken for several thousand eggs to hatch in April was found to be
three days. A dozen or so hatched when only two days old and
a few hundred required four days. Quaintance's period of 12
days for the entire life history was found somewhat below the
average of the insects in our breeding work which was con-
ducted in test tubes in the laboratory during April and May.
Altho a number completed their development in 10 days, the
average length of time was 15 days. A number required 18
days, and one required 24 days.
Since the age at which adults begin to lay eggs must be con-
sidered in any estimate of the time taken to produce a genera-
tion, some breeding was arranged to determine this age. It
was found that while many begin to lay eggs when but three days
old and a few even earlier, most of them lay only a few eggs
before the fifth day. This indicates that about twenty days is
the average time required to produce a generation. At that rate
there would be 18 generations in a year. But the rate of repro-
duction is much slower in winter, often ceasing altogether. In-
deed, few young thrips are found out of doors between December
1 and March 1. Occasionally, however, a few young ones are
found out of doors in the latitude of Gainesville during periods
of warm weather, even in January. There are probably a dozen
generations in a year. Life-history studies have not been carried
out farther south.
The adult lives longer than would be expected of such a
small delicate insect which passes thru its early life stages so
rapidly. In breeding cages used in our experiments, where con-
ditions, especially those of moisture, were abnormal, many thrips
lived several weeks. One female caught out of doors lived 59
days during winter. She was probably several days old when
caught. Another female lived 20 days during March under a
lantern globe on a pear tree in an orchard. Here conditions
were more nearly normal, altho the moisture was excessive.
Under natural conditions it is probable that thrips may live
much longer, especially in winter. If they do not breed during
coldest weather, they must live thru the winter as adults. We
have no evidence that they spend any considerable time in the
egg stage. Moreover, the delicate and short-lived nature of the
tissues in which the eggs are laid would seem to preclude that
method of over-wintering.





Florida Agricultural Experiment Station


Even during the coldest days of winter thrips always were
found in rose blossoms, even on those badly frost bitten. They
were inactive on the coldest days, but would move if disturbed.
It has been proven by these studies that the Florida flower
thrips spends the winter as an adult in blossoms, but there
may be some breeding any month of the year, that is, on the
warmest days. There are no indications that they ever enter
the ground or seek shelter other than in the depths of flowers.
They are capable of living as adults for at least eight weeks
during winter. This length of time is sufficient to tide them
over the non-reproductive period, as breeding usually begins late
in February or in March and continues until some time in De-
cember. However, their numbers always are reduced greatly
during winter.
Heavy Rains Destructive of Thrips.-It has been noticed for
a long time that thrips are much more abundant during and
immediately following a period of drought, but that they dis-
appear as the rains begin. In 1916, close observations were
made to determine the reason for their disappearance. As many
insects in Florida are controlled during the hot, moist, rainy
season by entomogenous fungi, a search was made for any
fungus parasitizing thrips. Altho Microcera-like fungi occasion-
ally have been found growing on dead thrips, there is no evi-
dence that entomogenous fungi are an important factor in their
control. Nor was lack of food the factor, as often the number of
thrips is reduced greatly without a corresponding reduction in
the number of blossoms.
On the other hand, after hard, dashing rains, or even pro-
longed rains, not especially violent, there always was a great re-
duction in the numbers of thrips. For instance, thrips were
abundant on roses and other blossoms on the Experiment Station
grounds early in December, 1915; but, from December 17 to De-
cember 20, this section received 4.26 inches of rain. On 50 roses
examined December 22 no thrips were found. Similar observa-
tions, tho less striking in results, were made during the sum-
mers from 1915 to 1921. Results equally striking were gotten
with a garden hose. The flowers were drenched thoroly, washing
the insects to the ground and killing them. It is evident that
prolonged or dashing rains are very destructive to thrips and
form the chief natural factor in keeping them down.
Natural Enemies of Thrips.-Animal enemies seem no more
effective than fungi as agents in keeping thrips down. The





Bulletin 162, The Flower Thrips


most successful one is a small predacious bug (Tripheps insidu-
osus). This insect feeds readily on thrips and usually is com-
mon in flowers and other places frequented by thrips.

OTHER FLOWER-FREQUENTING THRIPS

Mason's Thrips.-As stated above, on the lower East Coast a
closely related insect is found in flowers along with the Florida
flower thrips. This insect was first collected by A. C. Mason
and described in 1918 by the writer as Frankliniella cephalica,
var. masoni.' Its nearest relative (F. cephalica)" occurs in
Mexico and Southern Texas. Perhaps it is significant that this
insect is confined largely to that portion of the state where
plants and animals are of tropical origin. In this state a few
specimens have been found as far north as Daytona.
It is smaller and yellower than the Florida flower thrips and
has decidedly less of the orange pigment. Anatomically, it may
be distinguished by the shape of the fore part of the head
which, instead of being full between the eyes, is hollowed out.
Detailed life history studies of this species have not been made
but it is not probable that its life history differs greatly from
that of its relative, the Florida flower thrips.
Control measures for the two are the same. It is possible
that the latter can be killed by smaller doses of tobacco than are
necessary for the Florida flower thrips, as it seems to be more
delicate.
The Cuban Citrus Thrips.-Another close relative of our Flor-
ida flower thrips is Frankliniella insularis,1 an insect said to
be very destructive to citrus in Cuba. It was found on Carica
at Miami by A. C. Mason in 1918." It is not common in Florida,
possibly having been introduced recently from Cuba. By its dark
brown color it is readily distinguished from others of the genus
Frankliniella.
The Tobatco Thrips.-Another close relative of the Florida
flower thrips is the tobacco thrips (Frankliniella fusca). This,
as its name indicates, is a brown insect. It is more of a foliage-
""New Thysanoptera from Florida," Fla. Buggist, Vol. III, No. 1, p. 27,
1920.
"Crawford, D. L., in "Some Thysanoptera of Mexico and the South,"
Pomona College, J1. Ent., Vol. I, No. 4, pp. 105-121, 1909.
"Franklin, H. J., in "On a Collection of Thysanopterous Insects from
Barbados and St. Vincent Island," Proc. U. S. Nat. Mus., Vol. XXXIII, p.
715, 1908.
""The Cuban Citrus Thrips in Florida," Fla. Buggist, Vol. II, No. 4,
1919.





Florida Agricultural Experiment Station


frequenting insect and is found on many plants, including
strawberries, oats, turnips, dewberries, mustard and plantain.
It is, however, as a pest of tobacco that this insect is best known.
It may be controlled by the methods outlined above.
The Composite Thrips.-In the blossom heads of the plants
of the sunflower family commonly occurs another brownish
thrips (Thrips abdominalis). In addition to its color, which
never shows any orange tints, it may be distinguished from the
Florida flower thrips by its smaller size. It is of little economic
importance and is mentioned here merely that it may not be
confused with the Florida flower thrips.
The Onion Thrips."--Closely related to the above is the onion
thrips (Thrips tabaci). It is found occasionally in flowers, but
its usual habitat is onions, of which it is the most serious insect
pest. Like the last mentioned thrips, its color is brown without
orange tinge. It may be controlled by the same measures recom-
mended for tomatoes.
The Black Garden Thrips.-Found occasionally on flowers as
well as on leaves, is a large thrips which is shining, coal black
in color. This is Leptothrips mali. It is much more restless than
the others and usually is seen actively running about. It belongs
to an entirely different family from the flower thrips and at
once can be distinguished under a good lens by the abdomen
which, in both sexes, ends in a long tubular appendage instead
of a saw-like appendage, as in the case of the females of the
flower thrips. G. F. Mosnette has shown"1 that this insect is
predacious.
The Magnolia Thrips.-The blossoms of magnolia and swamp
bay are frequented by another species of thrips (Thrips spino-
sus) which is smaller and darker than the Florida flower thrips.
The Buckeye Thrips.-Another tube-bearing thrips (Hetero-
thrips aesculi), black like the garden thrips, occurs in the blos-
soms of the wild buckeye (Aesculus pavia) and also in the blos-
soms of the wild azalea (Azalea nudiflora), or "swamp honey-
suckle." It is of no economic importance, but should not be con-
fused with the Florida flower thrips.
"Quaintance, A. L., in "The Strawberry Thrips and the Onion Thrips,"
Fla. Agri. Exp. Sta. Bul. 46, 1898.
"Mosnette, G. F., in "Insects of the Avocado," Fla. Buggist, Vol. II,
No. 3, 1919.





Bulletin 162, The Flower Thrips


ACKNOWLEDGMENTS

In the experimental work which has furnished the material
for this bulletin the author has enjoyed the valuable cooperation
of the owners of groves in which the work has been carried on.
He also has enjoyed the cooperation of County Agents E. F.
DeBusk, H. E. Stevens and Alfred Warren and of former County
Agent K. E. Bragdon, all of whom have rendered much help
and made all the arrangements for the experiments in their
respective counties.
Figure 7 is a reproduction of a drawing by H. L. Dozier, a
former assistant in the Department of Entomology of the Flor-
ida Experiment Station. The photographic work in connection
with figures 8, 9, and 10, was done by either Mr. Dozier; A. C.
Mason, another former assistant in this department; or A. H.
Beyer, present assistant entomologist.
The spray schedule for citrus is copied, with a few changes,
from Bulletin 30, of the Agricultural Extension Division, Uni-
versity of Florida.









A SPRAY SCHEDULE FOR CITRUS
(From Bulletin 30, Agricultural Extension Division, College of Agriculture, University of Florida)


ENEMY


1 Grapefruit Scab



2 Grapefruit Scab
Rust mites
Red spiders


3 Grapefruit
and
Oranges


Scab, Thrips,
Rust mites,
Red spiders


4 Grapefruit Scab
and
Oranges Scab and
Melanose


5 Grapefruit
and
Oranges
6 Grapefruit


Scab, Scale-craw-
.ers, Rust mites
Scab and Melanose
Rust mites
Tearstain


No. FRUIT


MATERIALS TIME OF APPLICATION REMARKS

Bordeaux-oil mixture Just before the first Bordeaux mixture plus 1% of oil
(3-3-50) flush of growth in the form of an oil emulsion
stock solution. (See remarks un-
_der No. 7.)
Lime-sulphur solution Just before the petals To be applied, if scab infections
(32 Baume); 21/ gals. in open appear on the new growth, or if
100 gals. water iny weather favorable for scab
follows No. 1.
Lime-sulphur solution, 21/2 At height of bloom Add the nicotine, if 25 or more
gals., and 13 ozs. nicotine thrips to the bloom are present. If
sulphate to 100 gals. of thrips are abundant but no scab,
the spray solution; or bor- ise 1' gals. lime-sulphur and 13
ideaux-oil (% of oil) ozs. nicotine-sulphate to 100 gals.
Lime-sulphur solution, 2 7 to 14 days after Lime-sulphur will also kill rust
gals. in 100 gals. water No. 3 nites and red spiders, and for
Bordeaux-oil (12% of oil) 'hrins 13 ozs. nicotine-suluhate is
added. Bordeaux-oil is not as ef-
fective as lime-sulphur for above
insects.
Lime-sulphur solution, 22 9 to 14 days after To be given if rainy weather, fav-
gals. in 100 gals. water No. 4 orable for scab or melanose, fol-
Bordeaux-oil (1% of oil) lows No. 4.
Lime-sulphur solution, 1% April 5th to 15th If any two lime-sulphur sprays out
to 2 gals. in 100 gals. of Nos. 3, 4, and 5 have been given,
water his can be omitted; otherwise, this
is the critical spraying for rust
nites on grapefruit.











A SPRAY SCHEDULE FOR CITRUS-(Continued)

(From Bulletin 30, Agricultural Extension Division, College of Agriculture, University of Florida)


No. FRUIT

7 Grapefruit
and
Oranges


ENEMY


Whiteflies
Scale insects
Rust mites


8 Oranges Rust mites
Tearstain


9 Grapefruit
and
Oranges
10 Grapefruit
and
Oranges


Whitefly
Scale insects

Rust mites


MATERIALS


TIME OF APPLICATION


REMARKS


Oil emulsion, 1% plus 21/ In May when the The oil emulsion should be used so
lbs. dry soda-sulphur in fruit is at least 1 that the diluted spray material will
100 gals. water inch in diameter contain 1% oil; that is, if the
emulsion contains 66% oil, 1/2
gals. would be required for 100
gals. water. It may be necessary
to repeat this spray a month later,
if many applications of bordeaux-
oil are used.
Lime-sulphur solution, 11/ In June On oranges this is the critical rust
to 2 gals. in 100 gals. mite spray, if the fruit has not
water received any previous lime-sulphur
application.
Oil emulsion 1% Preferably in Sept. orTo be given, if scale insects or
Oct., but certainly be- whiteflies are noticeable.
fore Feb. 1st.
Lime-sulphur solution, 11/ November to To be given only if rust mites are
to 2 gals. in 100 gals. January noticeable.
water


i i




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