How to control the pear thrips (Euthrips pyri Daniel)

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Title:
How to control the pear thrips (Euthrips pyri Daniel)
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Book
Creator:
Foster, Shirley Watson
Jones, P. R ( Paul Robert ) ( joint author )
United States -- Dept. of Agriculture
United States -- Bureau of Entomology
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Government Printing Office ( Washington )
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.
i'.


LIBRARy
SIrATE P'AN T OARD
PAre -r BOARD


Issued January 9, 1911.


U. S. DEPARTMENT


OF AGRICULTURE,


BUREAU OF ENTOMOLOGY-CIRCULAR No. 131.
L. 0. HOWARD. Entomologist and Chiet of Bureau.


HOW TO CONTROL THE PEAR THRIPS.


BY
S. W. FOSTER A)ND P. I. JONES,


Agents and ExptrlA.


WASHINGTON : GOVERNMENT PRINTING OFFiCE : 1911
67859J--Cir. 131-11--1


f!\33


1S
























B UREA U OF ENTOMOLOGY.


L. 0. HOWARD, Entomiologist and Chief of Bureau.
C. L. MARLATT, Assistant Entomologist and Acting Chief in Absence of Chief.
R. S. ('LIFTON, Eitcutire Assistant.
WV. F. TASTET, Chief Clerk.

F. HIt. ('HITTENDEN, in charge of truck crop and stored product insect investigations.
A. D. HOPKINS, in charge offorest insect investigations.
\W. D. HUNTER, in charge of southern field crop insect investigations.
F. M. WEBSTER, in charge of cereal and forage insect investigations.
A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.
E. F. PHILLIPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work.
ROLLA P. CURRIE, in charge of editorial work.
MABEL COLCORD, librarian.

DECIDUOUS FRUIT INSECT INVESTIGATIONS.
A. L. QUAINTANCE, in charge.
FRED. JOHNSON, S. W..FOSTER, E. L. JENNE, P. R. JONES, A. G. IIAMMAR,
C. \V. HOOKER, J. R. HORTON, WV. POSTIFF, J. B. GILL, agents and experts.
E. W. SCOTT, J. F. ZIMMER, entomological assistants.
[Cir. 131J
(II)






CIRCULAR No. 131. Issued January 9, 1911.
United States Department of Agriculture,
BUREAU OF ENTOMOLOGY.
L. 0. HOWARD, Entomologist and Chief of Bureau.
*a
HOW TO CONTROL THE PEAR THRIPS.a
(Euthrips pyri Daniel.)
By S. W. FOSTER and P. RIt. JONES,
Agents and E., jrts.
@
DISTRIBUTION.
The pear thrips (Euthrips pyri Daniel) (fig. 2) is at present coiliiled
to California and is very destructive throughout Santa Clara, Contra
-Costa, Solano, and Sacramento counties, with
SSISPI" MOOOc considerable areas infested in Alameda, Yolo,
--T- Napa, and Sonoma counties. (Fig. 1.) Re-
i '*A SS, ports of the presence of thllis species in other sec-
_L tions of California and in Oregon have been re-
PLUMAS ceived, but each case was closely investigated
SRA and the insect in quest ion found to be some ot lher
E\^ species. Bagnalb reports this insect in
SEngland; otherwise it is not known
,UOW outside the State of California.

ECONOMIC IMPORTANCE.
41k.. 0 1 k The pear thrips is at preseilt tne
A TV/ A most important in-
_^^__< sect pest wit li which
',4.0 the growers of de-
i \ ...... ciduous fruits in tlhe
SSANTA 2'- -- SA" BERNABQINO ,.,. i
BARBARA N count ies mentioned
have to contend.
On account of the
S- minute size of the
SAW DIGo 1 insect, the rapidity
FIG. L.-Map showing area infested by pear thrips in California. of its spread over
(Original.) large areas, and the
suddenness of attack in great numbers-completely blasting in a few
a The present paper is an abstract of a more comprehensive report on the life history
and control of the pear thrips to be published later. The recommendations given are
based on the results of experiments carried out in the principal centers of infestation
since the fall of 1908 to and including the summer of 1910.
b Journal of Economic Biology, vol. 4, No. 2, 1909,
1






HOW TO CONTROL THE PEAR THRIPS.


days all prospects for a crop of fruit-the control of this pest is a
matter of considerable difficulty.
As the insect is each year extending its range of food plants, its
capabilities for dissemination are correspondingly increased. There
is no reason to believe that the insect will disappear in a few yeais,
but it should be regarded as a permanent pest and at once realized
that only the most careful attention each year to necessary control
measures will make it possible to continue the profitable culture of
deciduous fruit in infested orchards.
Conservative estimates place the damage caused by the pear
tlhrips, in the Santa Clara Valley alone, during the years from 1904
to 1910 at nearly $2,000,000, while the loss for the entire State during
this period probably exceeds $3,500,000. It is safe to say that the
tllrips in the absence of treatment would cause an average yearly
loss to the State of over $1,000,000. Also each additional year an
increase of several hundred thousand dollars is to be expected, due
to the increase of area infested and the greater losses in the areas
previously infested.
CHARACTER OF INJURY.

Injury to the various fruit trees by this species is caused by the
feeding of the adults on thlie developing buds and early blossoms; by
the deposition of eggs into thlie fruit stems, leaf stems, and newly
formed fruit, and by the feeding of the larvm in the blossoms and
on the young fruits and foliage. On pears the greater injury is pro-
duced by the adults, which often prevent the trees from blooming,
wliile on prunes and cherries the larva frequently prevent a crop of
fruit from setting after the trees have come into full bloom. Also,
the deposition of eggs into the fruit stems of prunes and cherries so
weakens thle stems that much of thle young fruit falls. The feeding
injury is not produced by a biting or chewing process. By rasping the
tender surfaces in the developing fruit buds and the young fruits with
their hardened or chitinous mouthliparts, the thrips rupture the skin,
,causing an exudation of sap which is often followed by more or less
ferientati ion, especially before blooming. Tile feeding by larvae
,n prunes after blooming causes the well-known thlirips "scab,"
wlIile most. of the scarred aiid misshapen pears are caused by tlhe work
of tlhe adults.
LIFE HISTORY.
Alitlts.-Thie adults (fig. 2) or winged form of tile tlirips first
aIlp('arl on tlhe trees about tli(e iiiiddle of February and emergence








HOW TO CONTROL THE PEAR THRIPS. 3


from the ground continues till early April, maximum emergence,

however, occurring in late February and early March. Examina-


*o ' o
* ,',' ,*' A '


,,I.,,/~


h I~ /


.C,


FIG. 2.-Thti pear thrips ( EKildhrilp., ii): Adult, gr

tion of tlhe tables of emergence records (Tables I to V) will show the

dates of emergence for 1909-10:


TABLE I.-Total daily 'mergene of (hrips from nil c i.y,. at l(dbiratory, San Jo.C, Cal.,
19,19 fild 1910.


Date.



I-'eh). 9
ID)
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Mar. 1
2
3
4
5
6
7


Nin tier
thrips
emrincriii
in 19\m.


0
0
0
0
0
0
18
0
52
192
192
169
75
119
135
552
459
444
414
7 1
781
535
1.299
714
508
3t2
4:3,


Nuim),lr
thrips

in 1911).


_.1
lx;
Is
1 C,

4


27
34
33
14
23
62
.-'H
129
375
272
297
455
574
.*J 4
1, ')7
1,,j75
3.592
3,011
4,217
1,402
1, .05
539


N i ini ll'r
Date. hlri.;'
vinli im0.,
| in 1110.i '.


Mar. s.
9
II0
II
12
13
14
15
1 i
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Apr. 1
2
3


219
77tp
4,17
411-S

3 13
2 4 X
279
259
152
1I-5 2



42
6 1
28
2
6
1 .
3
2
3
7
7
0
2
0
3
0
1


1 Nillfl])r
I lhril,<
qrtlIrri'llIlI
in I'-)l.

Nuni)w


144
]1)41
73
17!9
4-5
21)
7
4
20
7
2
2







L.. ... ... I


A\\,,
*- ', '







4 HOW TO CONTROL THE PEAR THRIPS.


EMERGENCE RECORD FOR CONTRA COSTA COUNTY.

TABLE II.-Emergence of thrips from cages placed in ground under trees in pear and
prune orchards, Walnut Creek, Cal.


1909.


Number
Date. ofthrips
emerging.


Fel 13
16
19
26
2 fi
Mar. 2
5
10
12
16t
20
27
27


1910.


Number
Date. of thrips
emerging.


Feb.21
23
25
27
Mar. 1
3
5
a
9
11
13
15
17
19
21
27


1
4
23
36
56
237
1,170
2,110
892
1,773
557
198
71
3
6
5


TA B I.E III.-Emergence of thripsfroin soil samples taken from orchard in Norember awl
December and kept in cages at laboratory, Walnut Creek, (Cal.


1909. 1910.
II i __ _ L
Number Numher
Date. of thrirs Date. of I hrips
o011T. out.


Feb. 12
15
16
17
18
20
23
25
27
Mar. 1
4
7
10
14
19
22


Feb. 18
20
22
24
26
28
Mar. 2
4
6
8
10
12
14
1(.


11
I)
0
12
30
75.
377
91.
937
11)5
114
47
0
4


EMI{(;ENC(E RI-J(-RI) FOR SOLANO COUNTY, 1910.

TA Il I I V. 1i1irg ncr, of Ihrips from cages placed in ground un('dr trees in orchards,
Suisun. Cal.


I Nubiner i
D;I1 v. .of lhirij, i' D)atle.
(*ini rging.


I- 'I1. 17

21
-'l
:.' I


Feb.27
Mar. I
3
:4
II)
1i


Number
of thrips
1'1n1rTgi11g


20
47
121
I4l
4M






HOW TO CONTROL THE PEAR THRIPS.


0
TABLE V.-Emergence of thrips from samples taken from orchard-in No rem ber and Decem-
ber and kept in cages at laboratory, Suisun, Cal.

Number Number
Date. of thrips Date. of thrips
emerging, emerging.

Feb. 16 1 26 11
17 3 27 14
18 2 28 41
19 6 Mar. 1 105
20 1 2 247
21 1 3 243
22 4 7 612
23 2 12 357
24 5 16 82
25 11 19 8

By the time the fruit buds have swollen sufficiently to separate
the bud scales slightly at the tip the adults force their way within,
feeding upon the tenderest portions inside the buds. When the
thrips are present in sufficient numbers the
buds are completely d(lestroyed and the trees -
fail entirely to bloom. /
Eggs.-As soon as the first leaf surfaces
or fruit stems are exposed egg laying usually 4
begins, depending somewlhat on the variety
of fruit attacked. !
The first egg2s are
deposited the last,
deays of Februarys FIG. 3.-Thepearthrips: Eggs, high-
(lys of Fly magnified. (Original.)
and oviposition
i ^continues till near the middle of April, being
'^ Fat its maximum, however, from the 10th of
Jf f .Marcli to the 1st of April. Most of the eggs
jy^^ -(fig. 3) a re deposited just under the epidermis
,,^ xin the fruit stems, young fruit, and leaf
S_----u.-- stems. Tlhe eggs require from five to seven-
S i'.; teen days to liatclh, the average time being
r about eight days.
S Larr;t.-By the time the trees are break-
-ing into full bloom the adults have done
most of the damage caused by their feeding,
S" and oviposition is at its height. Many of
Stll('he earlier appearing adults are (lying off and
larvaie (fig. 4) are beginning to appear in
FIG. 4.-The pear thrips: Larva, numbers. The very first larvae can usually
greatly enlarged. (Original.) be found about March 20, and are in maxi-
mum numbers on the trees, feeding on the small fruit and young
foliage, from the first to middle of April. Reaching their full devel-
opment, the larvae drop from the trees, of their accord or with falling
calyces, or are blown by wind or knocked off by rain. After the





HOW TO CONTROL THE PEAR THRIPS.


middle of April the number on the trees diminishes rapidly, and by
the last of April all the larvae are off the trees and in the ground.
Here they work down into the first 3 or 4 inches of hard soil below
the loose surface mulch and construct a tiny cell, where they remain
until the following spring.
Pupxe.-The larvae mostly remain as such in these cells till Sep-
tember, when pupation begins, pupa (fig. 5) being most abundant
during October and November. Many adults can be found in the
ground in December, and by the 1st of January practically all the
thrips are in the adult stage and apparently ready to emerge and go
into the trees whenever conditions are right. Broadly speaking, the
thrips spend two months of the year in the adult, egg, and larval
condition on the trees and the other
ten months of the year as larvae,
pupae, and adults in the ground.
CONTROL MEASURES.
The pear thrips is in some respects
S/ "- k\ an unusual insect in that it remains
f in a dormant or semidormant condi-
SIAlthough on the trees for only two
,_ ... T \months out of the twelve, it is able
:_.___i __ n this short time, in the absence of
.... \treatment, to completely destroy all
S--.--.. |prospects of a crop of fruit, in many
ili l -cases within a very few days. The
y ... trees are attacked at the period of
ybud swelling and blossoming, when
they are most susceptible to injury.
These minute insects come literally
FIG. 5.-The pear thrips: Pupa, greatly in swarms, and may, if left alone,
enlarged. (Original.) completely destroy all of the fruit
buds of an orchard in four or five days. Many cases have been
known where a delay of four or five days in spraying resulted in
loss of the entire crop of fruit, and in some cases half of all the
buds were killed in three days after the thrips appeared on the trees
in great numbers. In view of this condition it is very evident that
any means of control must be very thorough and done in the most
exacting manner at the proper time.
EXPERIMENTS IN THRIPS CONTROL.
Many (experilmenilts with soil fumigants, fertilizers, and irrigation
were inadl with the hope of killing the thrips while in the ground,





HOW TO CONTROL THE PEAR THRIPS.


but all of them have proved to be absolutely of no avail, or at most
impractical and expensive. In most cases the general vigor and
health of the trees were improved by early fall irrigation and by the
application of fertilizers.
CULTIVATION.
Thorough plowing in the fall in prune orchards planted on gravelly
and sandy soils gave very helpful results. Success by deep plowing,
cross plowing, and harrowing in October and November was fairly gen-
eral in all experiments tried in Santa Clara County in the fall of 1908
and 1909. This manner of cultivation, when carried out to a depth
of from 7 to 9 inches, resulted in killing from 60 to SO per cent of the
thrips present in the soil, but was not a sufficient control, as enough
thrips escaped to cause great injury to the buds the following spring.
SPRAYING.
A long list of insecticides was tried out in spraying experiments,
both in the laboratory and by spraying the trees in the spring. All
poison sprays had to be abandoned because of the inability to poison
the thlrips, as both adults and larva do not feed in a way to be sub-
ject to poisoning. Sticky sprays were difficult to apply and proved
ineffective, as they do not retain this quality long and the thrips
seem capable of moving around on almost any kind of surface. Dust
sprays and preventive sprays h]ad to be abandoned because the d(lust
sprays failed to kill- and the rapid swNelling of buds and continued
appearance of new surface area gave the thrips plenty of feeding
ground and exposed places of entrance into the buds. Success with
contact sprays seemed more apparent; of these, various caustic
sprays, such as caustic-soda and carbolic-acid solutions, gave excel-
lent results in killing the thrips, but were, as a rule, uisafe because
of injury to the trees.
Solutions of tobacco extract were very promising, and when used
at sufficient strengths killed all the thrips actually reached, but they
lacked sufficient penetrating quality to enter the swelling buds, a con-
dition absolutely necessary, especially on pears, as most of the injury
is done inside the cluster buds. Mechanical mixtures of various
mineral oils and animal-oil soaps were tried and al)anloned because
of the difficulty of keeping them thoroughly mixed and the resulting
injury to the trees caused by free oil separating out. Fish-oil soap
emulsions with these various oils gave better results, the raw distil-
lates running from 30 to 40 Baum6 being decidedly preferable over
either the kerosenes or the heavy crude oils.
A distillate-oil emulsion made according to directions (see pages
8-10) gave better penetration into the swelling pear buds than any other
material which has been tried. There was one drawback, however;
when this emulsion was used in sufficient strengths to kill all the
67859-Cir. 131-11-2





HOW TO CONTROL THE PEAR THRIPS.


thrips present or even a large percentage of them, there was consid-
erable oil injury to the buds. It was found that the weaker emulsions
of from 3 to 6 per cent strengths had all the desired penetrating quali-
ties and with little or no injurious effect upon the trees. As the nico-
tine solutions killed all the thrips present and gave no spray injury
this led to a combination of the two in Contra Costa County in the
spring of 1909 with most satisfactory results.
A tobacco extract containing 23 per cent nicotine, diluted at the
rate of 1 to 60 in a 6 per cent distillate-oil emulsion, killed all the
thrips touched and penetrated well into the pear cluster buds. The
pubescent covering of the individual buds in the cluster, being resist-
ant to water, seemed to act on the dilution in distillate-oil emul-
sion in much the same manner as the wick upon oil in a lamp. Vari-
ous other combinations of nicotine solutions with "lime and sulphur
solutions" and "lysol solutions" and "soap solutions" were tried
extensively, but none proved to be as effective and at the same time
as practical as the combination of distillate-oil emulsion an(l the nico-
tine solutions.
DISTILLATE-OIL EMULSION.
Homnemade preparation.-Because of its cheapness and greater
efficiency as a penetrating spray, and therefore a more satisfactory
killing agent, growers are strongly advised to make their own emul-
sions and, preferably, the soap, although the latter can usually be
depended on if bought from reliable dealerss.
Directions for making.-To make soap use this formula or some
multiple of same:
W ater ...................................................... 6 gallons.
Lye (98 per cent)............................ ......----- .. 2 pounds.
Fish oil ................................................... 1 gallons.
Put the waterin a caldron or boiler and add(l( the lye. When the lye
is thoroughly dissolvedd an(l the water boiling, pour in the fish oil, stir-
ring in the meantime, and boil slowly for two hours. When the soap
has boiled sufficiently it should give a ropy effect when stirred and
brought up upon the ladle. This formula gives about 40 pounds of
moderately firm soap.
Growers are cautione(l to buy only genuine fish oil and not a fish-
oil compound or a mixture of fish oils and vegetable oils. Herein lies
part .of the secret of the penetrating efficiency of the dlistillate emul-
sions inlade by using animal-oil soap as tlie einulsifier. The cost of
the soap is $0.0165 per pound inade from fish oil at 35 cents a gallon.
'Thle dlistillate-oil stock emulsion should be made as follows:
Form u l'a a
Hot wat(r........................................ 12 gallons.
Fih-ofil or whalv-,il soap ............................ 30 pounds.
Ditillate oil (raw) 30 to 3:1 Ia m iim .................. 20 gallons.
a For a spray tank (of 200 gallons capacity, live tines this formula can be made at
one time.





HOW TO CONTROL THE PEAR THRIPS.


Have the water boiling hot when put into the spray tank and add
the soap immediately while the agitator is running at a good speed.
When the soap is all thoroughly dissolved, pour in the oil slowly,
keeping the mixture well agitated while the oil is going into the tank.
When all the oil is in and well mixed, pump out through the nozzles at
good pressure (not less than 175 pounds) into storage tanks.
No one should attempt to make this stock emulsion without a
power spraying machine, as thorough agitation and high pressure are
important requisites. Also, care should be usedl in having measure-
ments reasonably exact, the water boiling hot, and( soap thoroughly
dissolved, before any oil is put in. This stock emulsion contains
approximately 55 per cent oil, and to make a 3 per cent emulsion use
51 gallons of this stock in each 100-gallon tank. To dilute, first put
the stock emulsion in spray tank (have the agitator going), and then
add the water, keeping the agitator running all the time. This is
important with the commercial preparations as well as with the home-
madle emulsions. For the combination sprays of oil emulsions and
nicotine solutions, the nicotine should be added last, that is, after the
oil emulsion has been diluted to the desired strength. These solu-
tions should not be mixed together without first diluting one of them.
This concentrated emulsion will cost the grower about 5 cents per
gallon, as most of the various distillates used for spraying cost from
5 to 10 cents a gallon in drum lots.
In the spraying season of 1910 many growers of Contra Costa
County experienced great difficulty in making emulsions that would
remain emulsified when diluted. Part of this trouble was due to the
varying degrees of hardness in tlhe water, but more to the composition
of the oil, especially where the treated oils and in some cases ordinary
stove distillates were used. Even after these treated oils were emul-
sified by changing the amount of soap used and treating the water
to soften" it, the result was not satisfactory, as the diluted emulsion
from this lacked the essential penetrating quality and had a tendency
to collect in large drops rather than to spread out in a thin film.
Experiments conducted thus far indicate that success is more
uniformly obtained by using an untreated raw distillate 32 to 34
Baum6 with comparatively high flashing point. Some of the treated
oils have given good results, but as a whole the untreated raw, straight
distillates, comparatively free from naphtha and with a high flashing
point, have given far better and more general satisfaction.
Some of the oil companies, particularly in the Bakersfield and
Coalinga districts, put out raw short-cut d(listillates-that is, the first
distillate after the naphtha, gasolines, etc., have been removed.
This kind of oil when running 32 to 34 Baume should under all cir-
cumstances be given preference. The ordinary stove distillates
have not, as a rule, given as good satisfaction, possibly because they





HOW TO CONTROL THE PEAR THRIPS.


contain too much of the light gaseous oils, which lower the flashing
point.
There are several commercial preparations of oil emulsions and
miscible oils on the market, but these have not given as satisfactory
results against the adult thrips as the homemade preparation, espe-
cially on pears, on account of the noticeable lack of penetration into
the cluster buds. Besides, all of these commercial preparations are
far more expensive. Allowing 25 cents per hour for labor in making
the soap and thle concentrated homemade emulsion, the commercial
preparations cost the grower from 2 to 5 times more than the more
efficient homemade preparation.

COMMERCIAL RESULTS.

During the season of 1909-10 many large-scale experiments and
demonstrations were carried out in pear, prune, and cherry orchards
to determine more conclusively the effectiveness of this combined
spray and to put the treatment on a commercial basis; also, that
growers might see for themselves the results of the work and know
the monetary gain possible by such control measures as are recom-
mended. Tle commercial results from some of these experiments
are given below:
PRUNES, SANTA CLARA COUNTY.

The 16-acre prune orchard belonging to Mr. P. Landon, situated
in the Willo)ws district, near San Jose, Cal., consists of some of the
largest and finest prune trees in the valley. The trees, which are
about 25 years old, are planted 20 feet apart and thle branches now
overlap between tlhe rows. The orchard has very heavy sandy loam
and lhas been well cultivated and usually irrigated twice each year.
Tlhrips became injurious in the year 1906, increasing greatly in 1907,
and causing much injury over the entire orchard, so that instead of a
normal crop of a hundred or more tons of green undriedd) prunes the
entire 16 acres produced only 18 tons of green fruit. Injury by the
thrips was worse in 190S, the yield that year being only 10 tons of
green prunes.
DEMONSTRArTION F'OR 1909.

In tle fall of 190S, under direction of the Bureau of Entomology,
Mr. LaI) n plow4(,ed and cr.,'s plowed thllis orchard to a depth of 9
Inches, witli thorough ha'rrwing after each plowing. Tlirips were
verv 1 abilndant in the soil, there being sometimes as many as 3,000
t the square( foot.
T1w following lhle, giving tle emergence of adults in spring from
sILiiplels of soil taklen before a s( after plohwing, shliows that approxi-
niately 70 per (cent of tie thrill. were killed by cultivation:


10






HOW TO CONTROL THE PEAR THRIPS.


TABLE VI.-.Number of adult thrJrips emerging from cages conl.0 i ing samples of soil
taken before and after plotwing-Landon prunec orchard, 19)0S-9.

Plowed and cross plowefl. Before pluwing.

Cage I. Cage II. Cage III. 1'age IV. (Cage V. Cage VI.

475 :,9 "j,7 115 1,175 1 474

Average number of thrips per cage befirre plowing .........................------------------------- 1,364
Average number of thrips per cage after plowing and cross plowing........... 396
Percentage living in treated areas as against the number of thrips living inr un-
treated ground ................................................. per cent.. 30
Approximate percentage killed ...................................... do .... 70
In the spring of 1909, 5, acres of this 16-acre orchard were sprayed
three times; twice before blooming, for adults, the first application
March 8 and 9, just as cluster buds were spreading, and the second


FIG. 0.-Power sprayer at work in Lndoii prune orchard, 1'i09. (Original.)


application March 16 and 17, just as the white tips of the petals were
beginning to show. The third application or larval treatment was
put on April 11 and 12, after most of the petals had fallen. For all
sprayings a gasoline-power outfit, with tower platform and three
leads of hose, as shown in figure 6, was used, two men spraying from
the ground and one from the tower to cover the tops of the trees. The
material used was tihe recomme(lnded 3 per cent homemade distillate-






12 HOW TO CONTROL THE PEAR THRIPS.

oil emulsion with commercial tobacco extract No. 1 added at the
rate of 1-60, and the cost of the three applications was $157.38, the
labor required in spraying being three men at $2 per day and one
team at $2.50 per day, making a total of $8.50 per day, or a total of
$51 for the six days; gasoline for the engine cost $2.40; plowing and
cross plowing the previous fall, $26.65, making a total cost of $237.45
for the combined treatment of plowing and spraying the 51 acres, or
844.54 per acre, an average of $0.449 per tree.
Tlhe yield from this plat was 45 tons of green prunes, making an
average yield of 8.44 tons per acre, or 155.17 pounds per tree. The
prunes when dried averaged 54 to the pound, giving a commercial
value for the plat of $1,710, or a value of $320.82 per acre, or an
average of $2.948 per tree, as the prunes were sold on a 2'-cent basis
for dried prunes averaging 80 to a pound.
Plat !I.-The rest of the orchard, comprising 102 acres, and which
only had the plowing and cross plowing in the fall of 1908, at the cost


I __ _'a.
- I -


F --Now-
a b c
FIGr. 7.-D)iagramrn showing yield in green prunes per acre upon the sprayed, plowed, and check blocks,
Landon prune orchard, 1909: a, Sprayed and plowed, 367.93 boxes, value $320.82 per acre; b, plowed
block, .5.it5 boxes, value S74.85 per acre; c, check block, 7 boxes, value $6.65 per acre. (Original.)

of S5 per acre, or $0.046 per tree, yielded 21 tons of green prunes, or
an average of 1.97 tons per acre, or 36.45 pounds per tree, giving a
(commercial value of the plat as $798, or a value of $74.85 per acre,
'averaging $0.692 per tree.
Plat III, chic,.-This plat, embracing 5 acres of the prune orchard
)belonging to Mr. F. Cottle, and immediately adjoining the Landon
or(.lard and of the same kind of soil and with similar trees in regard
to size and pr(viois care, received no treatment for thrips. The total
yield(l was 1,750 pounds of green prunes, or an average yield of 350
poundss per acre, or 3.24 pounds per tree, representing a commercial
value of $33.25 for the plat, or an average of $6.65 per acre or $0.06
per tree. The yield and value per acre upon the three plats is shown
(liagrammnlltically in figure 7.
The average gain lper acre upon Plat I was obtained after adding
the total (cost. off treatment per aceo to the value of tile crop per acre
firo(li the check pldat, nid suibtractinig that amount. from tlhe value of






HOW TO CONTROL THE PEAR THRIPS.


the yield per acre upon Plat I. This gave a net gain of $269.53 per
acre as returns upon an investment of $44.54, or a gain of about 600
per cent. The gain upon this plat due to the spraying alone was
$199.88 per acre, or $1.85 per tree.
Plat II, which received only the plowing and cross plowing, gave,
after adding the cost of the treatment to the yield per acre upon the
check plat and subtracting the total from the yield per acre upon
Plat II, a gain of $63.20 per acre for an investment of $5, or about
1,200 per cent on the investment.
Owing to the lateness of the third application on Plat I, the larve
caused considerable scabbing on the fruit, and the difference in
quality of the fruit from Plat I and Plat II was not as great as would
have been the case had the larval application been applied a few days
earlier.
RESULTS, 1910.
During the fall of 1909 part of the orchard was irrigated and the
entire 16 acres were plowed to a depth of 8 inches in November. One
small block was cross plowed. The entire orchard was harrowed
several times after the plowing.

PLowixv RESULT..

Soil samples were taken in similar cages as in the previous year and
yielded the following results:


(C :'' N11.


Tral in 'T1l.


Totl' P'er cent
IIII r leer killed.
I lri)d, kiled


II ......................................... Before hlowiL' ................... 2, xH 0
II-a .............................................I Plowed n ....................... 353 87
IV ............................................ Before plov. iir. .................... 3.379 0
IV-a ............................ ........ I'lowed once..................... 1,.'-, nI
I............................................... Before pliowini ... ............. 2,731 0
I-a............................................. 'lowing ail crun,-p I' i,;g ........ 27 98

The average percentage of thrips killed 1by one plowing was 71 per
cent and the average lnl)umber killed by plowing an(d cross plowing
98 per cent.
No spraying was d(lone in 1910, except a few trees for other experi-
ments.
SResults.-All of the trees on the 16 acres came into heavy bloom,
but only the 580 trees of Plat I and one block of about 80 trees which
was sprayed for larvme in 1909 set a heavy crop, as many thrips were
present in the rest of the orchard. The trees sprayed in 1909 were
stronger, and so many of the thrips had been killed by the treatment
that the accumulative results showed almost as great a difference in
the crop yield for 1910 as was the case in 1909, when the spraying was
actually done.

LIBRARY
____ Ab 'kww Tr "eA inn


13






HOW TO CONTROL THE PEAR THRIPS.


The primes averaged 57 to the pound, and computations made on
the basis of 5 cents for prunes running 80 to the pound. The different
yields and values were as follows:
Plat I-Demonstration block of 1909, consisting of 580 trees.-This
block yielded 35 tons 212 pounds of green prunes, worth $2,109.87
for 5SO trees, or $3.63 per tree or $392.04 an acre.
Plat II-Sprayed for larv?, in 1909, 80 trees.-This block yielded
2 tons 676 pounds of green prunes, worth $140.51 for 80 trees, or $1.99
per tree or S214.92 per acre. (This was part of Plat II in 1909.)
Plat III-Remainder of orchard, consisting of 10 acres, not sprayed
in 1909.-This block yielded 71 tons of green prunes worth $450.75
for 1,080 trees or 10 acres, making $0.417 a tree or $45.075 an acre.
An examination of the above statement of yields and values shows
that great headway can be made the first year in eliminating the
thrips injury from an orchard by thorough spraying and that a con-
sidleral)le benefit extends into the second year.
DEMONSTRATIONS FOR 1910.
The 6--acre prune orchard belonging to Mr. H. Curry was plowed
and cross-plowed in November, 1909, to a depth of 11 inches and har-
rowed after each plowing. The block was then sown to barley for
a cover crop which made a good growth and was at spraying time
nearly 3 feet. high.
Examination of two samples of soil 17 by 17 inches square, taken
before plowing, and two of the same size taken after plowing, showed
that approximately 61 per cent of the thrips were killed.
Plat A.-In addition to tlhe fall plowing, this block of 300 trees
received tllhree applications of commercial tobacco extract No. I com-
lbinedl at the rate of 1 to 66 with 3 per cent homemade distillate-oil
emiuilsion. The first spraying was applied March 7, just as the cluster
buds were spreading. The second for adult thrips was made March 17,
as the tips of tlle petals were showing. Thie third application which
was for tlhe larva, was nmade April 6, after most of the petals had
fallen. In all of the sp)rayillg an effort was made to direct the spray
intito the end of each bud and to drench the trees thoroughly.
Plat B.- This plat, consisting of 98 trees, received the cultivation,
but no spraying.
R..sults.-Tlie first application was made too late to obtain best
results, and a large number of buds was so far advanced that it was
dliffici lt to reach all of t-le thrips. A series of counts showed that all
of the exposed thrips were killed and about 30 per cent of those
within thlie buds. Tlhe second application killed practically all the
thrips left on tlie 1 trees (over 90 per cent), as the bud clusters were
spreading at this t in e. A fair mrl ion of tle blossoms set fruit on the


14





HOW TO CONTROL TILE PEAR THRIPS. 15

sprayed block and some on the plowed block, but the fruit on the
latter continued to drop until picking time. The yield upon the
various plats is shown diagrammaticallyin figure 8, and was as follows:
Plat A yielded 16,254 pounds of green prunes, or 8,127 pounds of
dried prunes, from the 300 trees. This made an average yield of
5,849.92 pounds of green prunes per acre, or 54.166 pounds per free.
Plat B yielded 1,032 pounds of green prunes or 516 pounds of dried
prunes from the 98 trees, or an average of 1,138.32 pounds per acre,
or 10.54 pounds of green prunes per tree.
Plat C, consisting of 10 acres, was left untreated to serve as a check
for comparison, and yielded 860 pounds of green prunes, or 430 pounds
of dried prunes, for the 1,080 trees. This gives an average yield of
86.4 pounds per acre, or 0.8 pound of green prunes per tree.


- -


--- 7-
-. -
1


a o c
FIG. 8.-Diagramin showing yield per acre in gr''ii prunes, Curry orchard, 1910: a, Sp)rivt.,i and plowed,
136.08 boxes, value $19.08 per acre; b, plowed lHock, 26.46 boxes, value .*4.I-2 per acre; c, check block,
2 boxes, value $2.59 per acre. (Original.)

Scabbiness.-An exanmiuntion and count \ais ila(le of all the fruit
from 5 trees on the sprayed( block and from 5 tre.s in the unspnryed
block, giving thel, following results:

.I ,li Ne Per cent
Mal. number clean. scabby'. free from
prunes. scab.

Sprayed block................................................ Ill. I:;' 9.831 .1 91;
Unsprayedl block .............................. ................. 0 21f 0

It Will be seen from tle( above table that ttie sprayed fruit was prac-
tically free from scab (the 4 per cent that w as scalby being only very
slightly marked), whiile the iilnsp)rayed fruit wNs all baldly sca1bbe(d.
Size of fruit.-Comparisonls of the sprayed and(I unsprayed fruit
when dried showed the former to average 50 pl')unes to the pound and
the unsprayed 60 to the pound, making a diflerenc(e of $10 a ton,
which would pay nearly half the cost of the spraying.
Value of the crop.-As all of the values of the prune yields for 1910
have been figured on a 5-cent basis for prunes averaging 80 to the
pound dried, this basis is here employed, although the crop wvas sold
for more than the above quotation and lpremiumls were given for the
large size and quality of the fruit.





HOW TO CONTROL THE PEAR THRIPS.


Plat A, which produced 16,254 pounds of green prunes from 300
trees, gave a crop value of $528.255, or $1.7608 a tree, or $190.08 an
acre.
Plat B, which yielded 1,032 pounds of green prunes from 98 trees,
gave a crop value of $30.96, or $0.315 a tree, or $34.02 an acre.
Plat C, which yielded 860 pounds of green prunes from 1,080 trees,
gave a crop value of $25.80, or $0.024 a tree, or $2.592 an acre. .
Cost of spra!fing.-As 3,800 gallons of diluted spray material were
used for all three sprayings upon Plat A, the total cost at $0.01625
per diluted gallon would be $61.75. The labor and gasoline cost 2
cents a tree, each application, for the 300 trees, or a total of $18. The
total cost of the spraying was $79.75, or $0.265 a tree, or $28.78 an
acre for the three applications.
Gain duie to spraying.-The gain due to the spraying would be ob-
tained by adding the value of the crop per tree on Plat B to the cost
of the spraying and subtracting the l)roduct from the value of the
crop per tree of Plat A. This gives a gain due to the spraying of $1.18
per tree, or $127.44 an acre.

OTHER DEMONSTRATIONS.

In cooperation with or working under the advice of the Bureau of
Entomology, several fruit growers in Santa Clara, Contra Costa,
Solano, and Sacramento counties during 1910 gave thorough treat-
mnent to portions of their orchards and left similarly infested areas
untreated without any protection from thrips injury. Many of these
demonstrations were highly successful, but for lack of space only two
of these are recorded herein in some detail. These results show very
conclusively what can be done by the individual growers if the right
material is properly apl)lied in time to kill the thrips before the buds
have been destroyed, and that the treatment will increase the yield
and value of the crop, frequently paying several hlundlred per cent
on the investment.
PEARS, CONTRA COSTA COUNTY.
An orchard consisting of about 5 acres of Bartlett pears belonging
to Johnlm Swett & Sons, in tlie Alilmbra Valley, near Martinez, Cal.,
lhad been badly damaged by thrips for three years, causing almost
total failure of crop.
In tlhe spring of 1910 Mr. Frank T. Swett lhad 550 of tihe trees
sprayed twice for adults, and a portion of these received a third
a)pp)lication or larval treatment. All spraying consisted of tie rec-
oxminmIended material commerciall tobacco extract No. 1 diluted 1 part
to 66 in 3 per ceiit lolmemiade distillate-oil emuitlsion) put on tihe trees
with goo(l pressure, using gasoliLne-l)ower outfit with S-foot tower,
thus enabling one iman to cover thoroughly Ithe tops of tle trees and


16





HIOW TO CONTROL THE PEAR THRIPS.


drench all buds pointing upward which could not be properly sprayed
by the men on the ground.
Four trees in one side of this orchard, same variety, same age and
size, and(l all other conditions the same, were left unsprayed.
Results.-Without a single exception all of the 550 sprayed trees
came uniformly into full bloom, while the trees left unsprayed showed
only very few scattering blossoms and these badly injured. Figure 9


lFi,. 9. -S- \ i 1war orchard at time of 1( 'oluniin. SpraylI trees. (After .Sv.utt.)

slhows the condition of a sprayed tree at blossoming time. The 550
sprayed trees gave a yield of 1,700 boxes of No. 1 peairs and 150
boxes of No. 2 pears. The No. 1 pears, at an average net price of
80 cents per' box, gives $1,360, and thle 150 boxes of No. 2 pears, at
50 cents per box, gives S75, 111nikimg a total of Sl,435, the value of the
crop) from 550 sprayed trees, or practically $2.60 per tree.


17





HOW TO CONTROL L THE PEAR THRIPS.


Figure 10 shows an un-.p1)rayed tree at blossoming time. The
unsprayed trees gave a yield of less than one-fourth box per tree, all
of which was scarred, misshapen, and unmerchantable; but counting
them as No. 2 pears, at 5() cents per box, gives a return of about
12 cents per tree.
According to Mr. Swett, the spraying, including material, labor,
and all expenses connected with the operation, cost less than 25. cents


Fl'i;. Ii. -S evll pear orchard at time ofhiu iiinig 1 .iisrivri'vl trecs, sprLaycdL porliun of
orlihirili in 1i:i' kri- iindl (A.fter Swett.)

per t rec for t1* 5-") lr.,(-,. THlii,, i)lIs the valuei1 of iith crop (12" cents)
from thle chiec.k i r.-,givs 371, ceii t. Subtracting tIlis from I lie $2.60,
valiic of 11( crop per il''e' inll tlite sprayed block, leaves a li't gain of
2.1'5 )per tru'e, or )app)lro'ximately $225 per acne, or a return of over
900 per ce'lit Oil ill' illVeImeJlt('.


18






HOW TO CONTROL THE PEAR THRIPS. 19

In the letter giving the results upon which these itemized figures
are based, Mr. Swett continues:
The results from spraying on prune trees were very marked. Owing to cross limbs
we could not use the tower in spraying the prune orchard. The crop was protected
only up to the distance from the ground that could be reached by Ihe spray rods.
We wet the tops of the trees as best we could, but could not drive the spray into the
bud and flower clusters directly from the izzles. Anyone can tell where the rods
reached, for above the line there is no crop, and below that line the limbs mostly
have to be propped.
CHERRIES, SACRA M E NTO COUNTY.
A good demonstration showing the possibility of control and the
commercial ad(lvantage by spraying cherries was given by Mr. T. W.
Dean, near Courtland, Cal. Mr. Dean has about 1- acres or 180 trees
in bearing, wlhiclh were sprayed upon an average four times in the
spring of 1910.(some of the trees sprayed five times and the remiaind(ler
only three times). The cost of the spraying was approximately $90,
or 50 cents per tree. Mr. Dean slipped 1,362 boxes of cherries from
the 180 trees, or 7.56 boxes per tree, which, at a net value of $1.196 per
box, gives a return of $1,619.95, or .q8.99 per tree.
Sixty-five trees belonging. to Mr. I. G. Doty and immediately
adjoining tlhe above orchardl were not sprayed. Tihe 65 trees gave a
yield of 43 boxes, averaging practically two-thirds of a box per tree,
or a cash value of $0.798 per tree. Adding this to the cost of spray-
ing, 50 cents per tree, gives $1.30 as the amount, to be deducted
from the value of tihe crop per tree in thle sprayed orchard. The
difference is $7.49 per tree, or approximately $898.S.0 per acre,
the net gain due to sprayiiig, paving over 1,400 per cent on the
investment.
RECOMMENDATIONS.

Spraying is by far the most satisfactory means for controlling the
pear thrips on all classes of ((decid(his fruit trees in California.
However, to spray successfully involves an entirely different concep-
tion of the operation than as ordinarily practic('ed(l against other orchard
insects. Only the most eficint spray materials should be use(l,
namely, the combination of dist illate-oil emulsion and tobacco extract
or distillate-oil emulsion and nicotine solutions. The spraying must
be thoroughly done and put on tlhe trees when the thrips appear in
numbers, not waiting till many buds have been destroyed. It is
strongly advised( to use power machines, and growers are urged to
use them for all the spraying, and to have a tower platform elevated
over the tank so that one man can thoroughly (dren'lch the tops of the
trees. Figures 6 and 11 show two good types of power outfits at
work. It is absolutely necessary to use high pressure-from 150 to
200 pounds-and only angle nozzles should be employed, and these






HOW TO CONTROL THE PEAR THRIPS.


must be held close to the bud clusters to force the spray directly into
tie ends of thie buds. This is absolutely necessary to secure good
penetration and get satisfactory results. Plenty of material-3 to 5
gallons per tree for pears, depending on the size of the tree-should be
used(l; more liquid is required for large prune trees; large cherry trees
may require 7 to S gallons per tree for satisfactory results. Only two
rows should be sprayed at a time, using three men, one on the tower
to spray tlhe tops of the trees, thus reaching all buds pointing upward,
and two men on the ground (one to each row) to spray the lower
bu(Is and those pointing downward or laterallv.



k



















FHiG. I.-IP0%Ir outfit rn'vy for use in spraL ITIL' vxpvriiiiil in pear orChard., Contri Costa ('0o ly,
Cal., V.Ii. (Origi.:>.)

TIMING TlHE APPLICATIONS.
'le, spraiyillg must lbe done on time, and for best results all tlhe trees
slC oul(l be treated( within a few 41i\'s. Diirinllg thell seLason o(f 1910 more
of the faiilutre to gel satisfactory results was (Il1e to lateness of applica-
tion than to ill)- other one cause. Thrips were in the trees and in
gr'eIat, numbers before many of tle( growers 1)r.halsl tlir spraviying
slpp)lies, a d( il l y a.1sV ,s half the 1)bl(s were entirely dlestroye(l and
tilie ,otliers 6idly injuiedl 1b1efore e ti trees ha(ld 1en gie eel e tlIlie iirst
tppl Icica t i i T i i. gi rower should have evey t1i1g in reaId(Ihess, till
ilate.iills on lian1. oq,(celit ratd '(,1 ('lulsion Iiale p1), and(1 spray machin-
cry in pe(ifect woilkiiii ordlcr by tie first of March ald have atll other
orch ia rd work in si lie sI Iae' Hlin NIvl te h llie thri sj a)ppea hin Ilum hl)(ers


20






HOW TO CONTROL THE PEAR THRIPS.


the spraying may be done at once and before the buds have been
seriously injured by the feeding of the adults. The grower should
have enough spray machines to cover the orchard quickly. At least
one good power outfit is necessary for every 30 acres of orchard.

SCHEDULE OF APPLICATIONS.
In badly infested orchards three applications are necessary the
first year for controlling the pentr thrips. Two of these sprayings
should be directed against the adults and one against the larva, and
to obtain sat isfactory results must be timed properly.
First application.-The first spraying should come as soon as the
thrips can be found on the trees in numbers. This will usually be
the first two or three days of Mairch, just as the earliest buds are
separating slightly at the tips. In figures 12, 13, and 14 are shown
photographs of the more advanced buds of Bartlett pear, Imperial
and French prunes,
and Black Tartarian
cherry, which were
taken at time of first
application.
Second applica-
tion.-The second
spraying, whichis also
for adults, should
come from four to ,
ten days after the
first,dlependingsome-
what on variety of Yir. 12.--Barll f uit, stage of b time of first sprain against thrips. (Original.)
fruit, stage of bud
development, aind rapidity of emergence of thrips from the ground.
On pears this will usually be just as the earliest cluster buds are
spreading, and on prunes and cherries when the tips of the petals first
begin to show.
Both of these applications are important and necessary to insure
the production of a good crop of uninjured blossoms. The nozzles
should lbe held close to the bud clusters and the spray directed into
the ends of the buds. This m nkes it necessary that the spraying be
d(lone mostly from above.
Third applicatf;on.-The third spraying is for larvae and properly
comes just as most of the pet als are falling from the trees, depending
somewhat upon the variety of fruit. In any case the small, white,
active larva, can be easily seen, and when they first become abun-
(lant spraying should be done. In this larval spraying on cherries
and pirunes where there is a large amount of leaf surface exposed, the


1






HOW TO CONTROL THE PEAR THRIPS.


spray should be directed first against the underside of the leaves,
beginning with the lowest branches and spraying upward. Most of
the larva are feeding on the under surface of the leaves, and spraying
the upper surface first would serve to knock the larve from the trees
without their coning into contact with the spray. Angle nozzles of
the typ e shown in figure 15, giving coarse, penetrating spray, should
be used for all applications.

MATERIALS TO USE.

The combination of 3 per cent homemade distillate-oil emulsion,
made from raw distillate, 32 to 34 Baume, and the nicotine solutions,


a b
l-';. I.I. --it, Frenich prune buils; b, Imperial prune buds; showing stage of earliest
1,ils at time of first :iiplii lionn against thrips. ((Original.)

is giv,. en pIr'ffercii( over ill otilicr sprays used so far. To dilute,
,,ics 0i,1 out 5 gall,,Is of the stock emulsion for each 100-gallon
spray Itank, or 11 gallons for a 200-gallon tank; start the engine; pour
lle stoc('k eIlhulsion int1) tlhe s)pray'tank, and while the agitator is
rulnilig, ad(id t1h< water to fill up the tank, putting in the strong
1i,.,,ii .le soluItion last 1and 1 al't,(r tihe stock emulsion has been diluted.
For sprai'ying. in tliv interior c'mliities add to this dilute oil-emulsion


22






HOW TO CONTROL THE PEAR THRIPS.


commercial tobacco extract No. 1, which is a dark, almost viscoUs
liquid containing 2.75 per cent nicotine, at the rate of 1 to 75; or
tobacco extract No. 2, which is a li.ght-co)lorcd liquid containing 40
per cent of almost nonvolatile nicotine at the rate of 1 to 1,500, or a
fraction more than a pint to a 200-
gallontank. This form of the nicotine
has been highly efficient and will in ,
all probability be more satisfactory
than the former. By reason of its
greater concentration the handlingg,
and transportation charges will be
much less; also, the nicotine contain( d
in this prel)aration is much less vola-
tile, thus allowing the use of smaller
amount of actual nicotine in the dilu-
tion, as it remains an active killing
agent for a longer time on the trees.
In Santa Clara County greater
dilutions than these have been found
to be satisfactory, due most likely to
different climatic conditions, evap)o-
ration there being much less at this
time than in the interior counties ,.14.--Buds of Black Tartarian cherry at
where thle atmnosl)phere is (drier. Grow- time of first nplic:tioLn againstt thrips.
ers in te Santa Clara Valley ae About one-half natural size. (Ori'inil.)
ers in thie Santa. Clar'a V alley are
advised to use the 3 per cent di-tillat.-oil emulsion, with tobacco
extract No. 1 a(lded at the rate of 1 to 100 or tobacco extract No.
2 at the rate of 1 to 2.000. These recommendations hold for all
thrips- sprayings, for both adults and
i lrvi and on all varieties of deciduous
fruits attacked bythepearthrips. No or-
chards should be sprayed(, however, when
the trees are in full bloom. All spraying
for ilults should be done before the blos-
sonis appear and spraying for larvw after
a large prol)ortion of the pet als have
fallen.
In the 1prune orchtards of Santa Clara
FIG. 15.-Angle nozzle of the large cham- In the prune orchas of Santa Clara
her type used in spraying experiments. Valley deep fall plowig and cross-plow-
(Original.) ing las proved a valuable and profita-
ble aid in controlling the thrips. Those who can do so are strongly
advised to irrigate their orchards in September or October, and when
the soil is in p)rol)per condition plow with disk plows to a depth of 7 or


23






2HOW TO CONTROL THE PEAR THRIPS.


S inches and harrow, then cross plow 8 to 9 inches deep and harrow
again. All plowing should be (done during the months of October and
November. During this season the thrips are passing through the
tender pupal stage and are more easily killed by mechanical means
than at any other season of the year.
Plowinrg lias not proved satisfactory as even a partial means of
controlling tlhe thrips in the pear orchards of thle interior counties.
This i- due, perhaps, to several conditions, one of which is the differ-
elt ty ple of soil, and another, the fict that the area of soil infested
withi thrips around pear trees is very much less tlian around prune
trees, thle branches of which spread farther, covering a greater surface
of ground. Tlhe larva inl leaving the trees fall to tlie ground directly
from thle foliage and young fruit, rather tliau crawl down the trunks
of tlhe trees; hence in a prunle orchard they are more widely distrib-
uted throughout the soil between the trees and can be reached by the
pl)(w-s, while in a pear orchlard most of the larvae i the ground are
lose around the base of tlhe trees.
SUMMARY.
Tlhe pear thrips *can be controlled by thorough spraying on any
variety of thlie deciduous fruits grown in thie infested areas of Cali-
fornia.
The sprayings necessary to control the thrips are expensive, but the
outlay of money and labor gives large returns. Many experiments
in spraying have given net ret turns of from S100 to $600 per acre more
than was secured from adjoining untreated areas.
Thle thrips work rapidly and may destroy all p)rospects of a crop
in less than a week's time. Spraying, to be successful, must be done
thoroughlily and at the time to kill thle thliri)ps before thle fruit buds
have lbeel destroyed.
Those who 'can do( so s.uccessfhlly are advised to irri.rate and plow
in tlhe fall. Tllis is to be followed by tlhorougli spraying tlhe follow-
ing spring.
14. hen the tlirips begin to lIpptsir on thlie trees in numbers, spraying
should be done thoroughly, using loigl p.-,I re, l(,l(liIUZ. lozzleZs close
to buds. and dirc;ig tMe sprJi (directll hif, Mhe end.s of the buds, and
II,, ,ly hisf thl e ..;(7c.s'.
(irowers sliould not attellipt to spray too ), iany trees witli one
macline. More profitlable ret turIs will he gained by spraying lialf of
t le orchlard thoroughly and at the proj)ert ies tlan sp)Jrayi.g. all tlie
(orV]rd poorly on, ti Ile. Results of tlhe work il 1909) and 1910 showN
,('i ,lsively HI lut o ie application is ]lot sufl'ireiit when tlie thirips are
abulld'.a t.


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UNIVERSITY OF FLORIDA

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