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Issued January 9, 1911.

eS VEPAKT MENT OP VAGRICU L tiie.
BUREAU OF ENTOMOLOGY—CIRCULAR No. 181.

HOW TO CONTROL THE PEAR THRIPS.

S. W. FOSTER anp P. R. JONES,

Agents and Experts.

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1911
67859°—Cir. 131—11——1

d, BANEAS A

BUREAU OF ENTOMOLOGY.

L. O. Howarp, Entomologist and Chief of Bureau.
C. L. Maruart, Assistant Entomologist and Acting Chief in Absence of Chief.
R.S. Currron, Executive Assistant.
W. FP. Taster, Chief Clerk.

F. H. CuitrENpDEN, in charge of truck crop and stored product insect investigations.
A. D. Hopxins, in charge of forest 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. Puixurrs, in charge of bee culture.

D. M. RoGers, in charge of preventing spread of moths, field work.
Routia P. Currie, in charge of editorial work.

Mase. Cotcorp, librarian.

Decipuowus Fruit Insect INVESTIGATIONS.
A. L. QUAINTANCE, in charge.

Frep. Jonnson, S. W. Foster, E. L. JENNE, P. R. Jones, A. G. Hammar,
C. W. Hooxer, J. R. Horton, W. Postirr, J. B. GiLL, agents and experts.

E. W. Scort, J. F. Zimmer, entomological assistants.
(Cir. 131]
(11)

CIRCULAR No. 131. Issued January 9, 1911.
United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.

L. O. HOWARD, Entomologist and Chief of Bureau.

HOW TO CONTROL THE PEAR THRIPS.¢
(Euthrips pyri Daniel.)

By 8. W. Foster and P. R. Jonzs,
Agents and Experts.

DISTRIBUTION.

The pear thrips (Luthrips pyri Daniel) (fig. 2) is at present confined
to California and is very destructive throughout Santa Clara, Contra
Costa, Solano, and Sacramento counties, with
considerable areas infested in Alameda, Yolo,
Napa, and Sonoma counties. (Fig. 1.) Re-
ports of the presence of this species in other sec-
tions of California and in Oregon have been re-
ceived, but each case was closely investigated
and the insect in question found to be some other
species. Bagnal? reports this insect in
England; otherwise it is not known
outside the State of California.

ECONOMIC IMPORTANCE.

The pear thrips is at present tne
most important in-
sect pest with which
the growers of de-
ciduous fruits in the
counties mentioned
have to contend.
On account of the
minute size of the

\ \ prow jmee b insect, the rapidity

Fic. 1.—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

SAN BERNARDINO

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.

2 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 years,
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
thrips, 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
thrips 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 the developing buds and early blossoms; by
the deposition of eggs into the fruit stems, leaf stems, and newly
formed fruit, and by the feeding of the larvz 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,
while on prunes and cherries the larve 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 the stems that much of the 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 mouthparts, the thrips rupture the skin,
causing an exudation of sap which is often followed by more or less
fermentation, especially before blooming. The feeding by larve
on prunes after blooming causes the well-known thrips ‘‘scab,”
while most of the scarred and misshapen pears are caused by the work
of the adults.

LIFE HISTORY.

Adulis—The adults (fig. 2) or winged form of the thrips first
appear on the trees about the middle 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-

aie Le ge
ZB eee SS

: a.
SAAN ANNININ

Hf i ee
MMMM

Fig. 2.—The pear thrips (E£uthrips pyri): Adult, greatly enlarged. (Original.)

tion of the tables of emergence records (Tables I to V) will show the
dates of emergence for 1909-10:

TaBLeE I.—Total daily emergence of thrips from all cages at laboratory, San Jose, Cal.,
1909 and 1910.

Number | Number | Number | Number

: thrips thrips thrips thrips
Date. emerging | emerging | Date. emerging | emerging
in 1909. in 1910. in 1909. in 1910.
Feb. 9 0 25 Mar. 8 219 275
10 0 18 9 776 144
11 0 16 10 497 100
12 0 16 11 498 73
13 0 4 12 338 179
14 0 88 15 313 45
15 18 22 14 248 20
16 0 27 15 279 Ui
17 52 34 16 259 4
18 192 33 17 152 20
19 192 14 18 42 7
20 169 23 19 61 2
21 75 62 20 28 2
22 119 129 21 2s | |Szaneneone.
23 135 375 22 at ee See ee
24 552 272 23 115 Fi Wee Sah
25 459 297 24 Sees Meee
26 444 455 25 2) t\ (eee ce eee
27 414 574 26 Bb lease cee |
28 781 657 27 ha Eh Sea Se |
Mar. 1 781 1,975 28 eh | eee cek eee od
2 535 3, 592 29 UN eae ao ee
3 1, 299 3,011 30 Be) | rare caeve pee
4 714 4,217 31 Oils eee |
5 508 1, 402 Apr. 1 BS |e ae ae
6 362 1, 595 2 OM eee =,
7 438 539 3 Ll eee. eres 2 |

HOW TO CONTROL THE PEAR THRIPS.

EMERGENCE RECORD FOR CoNTRA Costa COUNTY.

TasLe I1.—Emergence of thrips from cages placed in ground under trees in pear and
prune orchards, Walnut Creek, Cal.

1909.
Number
| Date. of thrips
emerging.
Feb. 13 0
16 20
19 37 |
22 30
26 110
Mar. 2 615
5 679
10 752
12 273
16 65
20 33
| 22 4
27 11
|
|

1910.

Number

Date. of thrips
emerging.

Feb. 21 1
23 4

25 23

27 36
Mar. 1 56

3 237

5 1,170

i 2,110

9 892

11 1,778

13 557

15 198

17 71

19 3

21 6

27 5

TaBLE III.—Emergence of thrips from soil samples taken from
December and kept in cages at laboratory, Walnut

|
1909. 1910.
Number |, Number
Date. of thrips Date. of thrips
out. out.
|

Feb. 12 3 Feb. 18 11
15 42 20 16
16 56 22 0
17 38 24 12
18 56 |) 26 30
20 89 28 75
23 125 | Mar. 2 377
25 185 || 4 918
27 246 |) 6 937
Mar. 1 196 8 165
4 237 || 10 114
7 51 || 12 47
10 D2] 14 0
14 13 16 4

19 0

22 0

orchard in November and
Creek, Cal.

EMERGENCE REcoRD FOR SOLANO County, 1910.

TABLE IV.—Emergence of thrips from cages placed in ground under trees in orchards,
Suisun, Cal.

Date.

Number
of thrips
emerging.

rOoOCOow

Number
Date. of thrips
emerging.
Feb. 27 20
Mar. 1 47
3 121
10 484
16 1

TaBLE V.—Emerge

HOW TO

CONTROL THE PEAR THRIPS. 5

nce of thrips from samples taken from orchard in November and Decem-
ber and kept in cages at laboratory, Suisun, Cal.

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 destroyed and the trees

fail entirely to bloom.

Eqgs.—As soon as the first leaf surfaces
or fruit stems are exposed egg laying usually
begins, depending somewhat on the variety

Fig. 4.—The pear thrips: Larva,

greatly enlarged.

(Original.)

of fruit attacked.
The first eggs are
deposited the last
days of February
and oviposition
continues till near the middle of April, being
at its maximum, however, from the 10th of
March to the 1st of April. Most of the eggs
(fig. 3) are deposited just under the epidermis
in the fruit stems, young fruit, and leaf
stems. The eggs require from five to seven-
teen days to hatch, the average time being
about eight days.

Larve.—By the time the trees are break-
ing into full bloom the adults have done
most of the damage caused by their feeding,
and oviposition is at its height. Many of
the earlier appearing adults are dying off and
larve (fig. 4) are beginning to appear in
numbers. The very first larve can usually
be found about March 20, and are in maxi-

Fia. 3.—The pear thrips: Eggs, high-
ly magnified. (Original.)

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 larvee drop from the trees, of their accord or with falling
calyces, or are blown by wind or knocked off by rain. After the

6 HOW TO CONTROL THE PEAR THRIPS.

middle of April the number on the trees diminishes rapidly, and by
the last of April all the larve 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.

Pupz.—The larve mostly remain as such in these cells till Sep-
tember, when pupation begins, pupe (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 larve,
pupe, and adults in the ground.

CONTROL MEASURES.

The pear thrips is in some respects
an unusual insect in that it remains
in a dormant or semidormant condi-
tion for about ten months of the year.
Although on the trees for only two
months out of the twelve, it is able
in this short time, in the absence of
treatment, to completely destroy all
prospects of a crop of fruit, im many
cases within a very few days. The
trees are attacked at the period of
bud swelling and blossoming, when
they are most susceptible to injury.
These minute insects come literally

Fic. 5.—The pear thrips: Pupa, greatly in swarms, and may, if left alone,
ee ae 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 experiments with soil fumigants, fertilizers, and irrigation
were made with the hope of killing the thrips while in the ground,

HOW TO CONTROL THE PEAR THRIPS. 4

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 80 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 thrips, as both adults and larve 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 had to be abandoned because the dust
sprays failed to kill and the rapid swelling 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, unsafe 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 abandoned 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° Baumé 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

8 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 2? 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 ina 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 and the nico-

tine solutions.
DISTILLATE-OIL EMULSION.

Homemade 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 dealers.

Directions for making.—To make soap use this formula or some
multiple of same:

WiatliehetecSen seh soe hges to Se Se eee Bee ee 6 gallons.
Lave (OS. per Cent) 2. sen sten stem eee ee emia 2 aes oe 2 pounds.
LFTs so | SR git ARS ce OS in eee ou oe an co a 1} gallons.

Put the water in a caldron or boiler and add the lye. When the lye
is thoroughly dissolved and 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 cautioned 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 distillate emul-
sions made by using animal-oil soap as the emulsifier. The cost of
the soap is $0.0165 per pound made from fish oil at 35 cents a gallon.

The distillate-oil stock emulsion should be made as follows:

Formula:@
EHot water. <5 2: sch: eee eee aoe eee 12 gallons.
Fish-oil orwhale-oil suap: sscase eee ets. ee ee 30 pounds.
Distillate’ oil. (raw) 30° to 34°. Banmeé 22272 ss 20 gallons.

@ For a spray tank of 200 gallons capacity, five times this formula can be made at
one time.

HOW TO CONTROL THE PEAR THRIPS. 9

Have the water boiling hot whem 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 used 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
54 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-
made 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 the 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°
Baumé 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 distillates—that is, the first
distillate after the naphtha, gasolines, etc., have been removed.
This kind of oil when running 32° to 34° Baumé should under all cir-
cumstances be given preference. The ordinary stove distillates
have not, as a rule, given as good satisfaction, possibly because they

10 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 the 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. The 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 Willows 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 the branches now
overlap between the rows. The orchard has very heavy sandy loam
and has been well cultivated and usually irrigated twice each year.
Thrips 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 (undried) prunes the
entire 16 acres produced only 18 tons of green fruit. Injury by the
thrips was worse in 1908, the yield that year being only 10 tons of
green prunes.

DEMONSTRATION FOR 1909.

In the fall of 1908, under direction of the Bureau of Entomology,
Mr. Landon plowed and cross plowed this orchard to a depth of 9
inches, with thorough harrowing after each plowing. Thrips were
very abundant in the soil, there og sometimes as many as 3,000
to the square foot.

The following table, giving the emergence of adults in spring from
samples of soil fen before and after plowing, shows that approxi-
mately 70 per cent of the thrips were killed by cultivation:

HOW TO CONTROL THE PEAR THRIPS. Ab |

TaBLE VI.—Number of adult thrips emerging from cages containing samples of soil
taken before and after plowing—Landon prune orchard, 1908-9.

Plowed and cross plowed. Before plowing.
ba £4 ——_____

Cage I. Cage IT. Cage III. | Cage IV. Cage V. | Cage VI. |

475 389 | 607 | 115 1,175 | 1,474 |
Average number of thrips per cage before 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 in un-

LRGAe Me omO Ut Cue eet = hed Were Up ee Rt cern te rena, eee rere See per cent... 30
AMMroOMmnaALespereentage deed: 2). cia. 28 O00) ASS oe ot Sete doze 70

In the spring of 1909, 54 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

Fic. 6.—Power sprayer at work in Landon prune orchard, 1909. (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 the recommended 3 per cent homemade distillate-

1 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 5} acres, or
$44.54 per acre, an average of $0.449 per tree.

The 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 IJ.—The rest of the orchard, comprising 103 acres, and which
only had the plowing and cross plowing in the fall of 1908, at the cost

BRE TAN

names

a b c

Fic. 7.—Diagram 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, 85.65 boxes, value $74.85 per acre; c, check block, 7 boxes, value $6.65 per acre. (Original.)

of $5 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, check.—This plat, embracing 5 acres of the prune orchard
belonging to Mr. F. Cottle, and immediately adjoming the Landon
orchard and of the same kind of soil and with similar trees in regard
to size and previous care, received no treatment for thrips. The total
yield was 1,750 pounds of green prunes, or an average yield of 350
pounds 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
diagrammatically in figure 7.

The average gain per acre upon Plat I was obtained after adding
the total cost of treatment per acre to the value of the crop per acre
from the check plat, and subtracting that amount from the value of

HOW TO CONTROL THE PEAR THRIPS. 13

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.

Resutts, 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.

Prowina RESULTS.

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

Total
Cage No. | Treatment. number Fe ecie
| thrips. ee
LU sce Si PS Ss a eee Before: plowilP<J-- see e 2, 813 0
NERY eS Soe | ee ee cee errant eee ee ae Plowedioncess7 ees 353 87
rear e PR acs ctorrcet oie wba as Rae see Before plowinga = 2- see eee oe 3,379 0
IWS 2, ace BeOS ea ae eee SA Be eee Plowedionce.2-22 44 2 en eee 1,306 61
{hs obec ae Ee eee Ae Before plowing ec a -seeeen cea seese ETO 0
Lee. BARE ape Oe Ree re a ees | Plowing and cross-plowing........ 27 98

The average percentage of thrips killed by one plowing was 71 per
cent and the average number killed by plowing and cross plowing
98 per cent.

No spraying was done in 1910, except a few trees for other experi-
ments.

Results 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 larve 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.

14 HOW TO CONTROL THE PEAR THRIPS.

The prunes averaged 57 to the pound, and computations made on
the basis of 5 cents oe 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 580 trees, or $3.63 per tree or $392.04 an acre.

Plat II—Sprayed for larve 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 $214.92 per acre. (This was part of Plat IL in 1909.)

Plat I1I—Remainder of orchard, consisting of 10 acres, not sprayed
in 1909.—This block yielded 74 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-
siderable benefit extends into the second year.

DEMONSTRATIONS FOR 1910.

The 64-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 the fall plowing, this block of 300 trees
received three applications of commercial tobacco extract No. 1 com-
bined at the rate of 1 to 66 with 3 per cent homemade distillate-oil
emulsion. 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 the petals were showing. The third application, which
was for the larvae, was made April 6, after most of the petals had
fallen. In all of the spraying an effort was made to direct the spray
into 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.

Results.—The first application was made too late to obtain best
results, and a large number of buds was so far advanced that it was
difficult to reach all of the thrips. A series of counts showed that all
of the exposed thrips were killed and about 30 per cent of those
within the buds. The second application killed practically all the
thrips left on the trees (over 90 per cent), as the bud clusters were
spreading at thistime. A fair portion of the blossoms set fruit on the

HOW TO CONTROL THE PEAR THRIPS. LS

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 diagrammatically in 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 tree.

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 480 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.

Fic. 8.—Diagram showing yield per acre in green prunes, Curry orchard, 1910: a, Sprayed and plowed,
136.08 boxes, value $190.08 per acre; b, plowed block, 26.46 boxes, value $34.02 per acre; c, check block,
2 boxes, value $2.59 per acre. (Original.)

Scabbiness.—An examination and count was made of all the fruit
from 5 trees on the sprayed block and from 5 trees in the unsprayed
block, giving the following results:

It will be seen from the above table that the sprayed fruit was prac-
tically free from scab (the 4 per cent that was scabby being only very
slightly marked), while the unsprayed fruit was all badly scabbed.

Size of frwit—Comparisons of the sprayed and unsprayed fruit
when dried showed the former to average 50 prunes to the pound and
the unsprayed 60 to the pound, making a difference 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 was sold
for more em the above quotation and premiums were given for the
large size and quality of the fruit.

16 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 spraying.—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 due 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 product 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-
ment 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 applied 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 hundred per cent
on the investment.

PEARS, CONTRA COSTA COUNTY.

An orchard consisting of about 54 acres of Bartlett pears belonging
to John Swett & Sons, in the Alhambra Valley, near Martinez, Cal.,
had been badly damaged by thrips for three years, causing almost
total failure of crop.

In the spring of 1910 Mr. Frank T. Swett had 550 of the trees
sprayed twice for adults, and a portion of these received a third
application or larval treatment. All spraying consisted of the rec-
ommended material (commercial tobacco extract No. 1 diluted 1 part
to 66 in 3 per cent homemade distillate-oil emulsion) put on the trees
with good pressure, using gasoline-power outfit with 8-foot tower,
thus enabling one man to cover thoroughly the tops of the trees and

HOW TO CONTROL THE PEAR THRIPS. iyi

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 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

F1G. 9.—Swett pear orchard at time of blooming. Sprayed trees. (After Swett.)

shows the condition of a sprayed tree at blossoming time. The 550
sprayed trees gave a yield of 1,700 boxes of No. 1 pears 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 the 150 boxes of No. 2 pears, at
50 cents per box, gives $75, making a total of $1,435, the value of the
crop from 550 sprayed trees, or practically $2.60 per tree.

18 HOW TO CONTROL THE PEAR THRIPS.

Figure 10 shows an unsprayed tree at blossoming time. The
unsprayed trees cave a yield of less than one-fourth box per tree, all
of which was scarred, misshapen, and unmerchantable; but counting
them as No. 2 peats, at 50 cents per box, gives a return of about
124 cents per tree. |

According to Mr. Swett, the spraying, including material, labor,
and all expenses connected with the operation, cost less than 25 cents

Fic. 10.—Swett pear orchard at time of blooming. Unsprayed trees, sprayed portion of
orchard in background. (After Swett.)

per tree for the 550 trees. This, plus the value of the crop (124 cents)
from the check trees, gives 37} cents. Subtracting this from the $2.60,
value of the crop per tree in the sprayed block, leaves a net gain of
$2.125 per tree, or approximately $225 per acre, or a return of over
900 per cent on the investment.

j 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 the 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 nozzles. 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, SACRAMENTO COUNTY.

A good demonstration showing the possibility of control and the
commercial advantage by spraying cherries was given by Mr. T. W.
Dean, near Courtland, Cal. Mr. Dean has about 14 acres or 180 trees
in bearing, which were sprayed upon an average four times in the
spring of 1910 (some of the trees sprayed five times and the remainder
only three times). The cost of the spraying was approximately $90,
or 50 cents per tree. Mr. Dean shipped 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 $8.99 per tree.

Sixty-five trees belonging to Mr. I. G. Doty and immediately
adjoining the above orchard were not sprayed. The 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 the crop per tree in the sprayed orchard. The
difference is $7.49 per tree, or approximately $898.80 per acre,
the net gain due to spraying paying 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 deciduous fruit trees in California.
However, to spray successfully involves an entirely different concep-
tion of the operation than as ordinarily practiced against other orchard
insects. Only the most efficient spray materials should be used,
namely, the combination of distillate-oil emulsion and tobacco extract
or distillate-oil emulsion and nicotine solutions. The spraying must
be thoroughly done and put on the 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 drench 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

20 HOW TO CONTROL THE PEAR THRIPS.

must be held close to the bud clusters to force the spray directly into
the ends of the 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; more liquid is required for large prune trees; large cherry trees
may require 7 to 8 gallons per tree for satisfactory results. Only two
rows should be sprayed at a time, using three men, one on the tower
to spray the tops of the trees, thus reaching all buds pointing upward,
and two men on the ground (one to each row) to spray the lower
buds and those pointing downward or laterally.

Fig. 11.—Power outfit ready for use in spraying experiments in pear orchards, Contra Costa County,
Cal., 1910. (Original.)

TIMING THE APPLICATIONS.

The spraying must be done on time, and for best results all the trees
should be treated within a few days. During the season of 1910 more
of the failure to get satisfactory results was due to lateness of applica-
tion than to any other one cause. Thrips were in the trees and in
great numbers before many of the growers purchased their spraying
supplies, and in many cases half the buds were entirely destroyed and
the others badly injured before the trees had been given even the first
application. The grower should have everything in readiness, all
materials on hand, concentrated emulsion made up, and spray machin-
ery in perfect working order by the first of March and have all other
orchard work in such shape that when the thrips appear in numbers

HOW TO CONTROL THE PEAR THRIPS. 21

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 pear thrips. Two of these sprayings
should be directed against the adults and one against the larve, and
to obtain satisfactory 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 March, 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, depending some-
what on variety of Fig. 12.—Bartlett pear cluster buds showing stage of earliest buds at

: time of first spraying against.thrips. (Original.)
fruit, stage of bud
development, and 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 be held close to the bud clusters and the spray directed into
the ends of the buds. This makes it necessary that the spraying be
done mostly from above.

Third application.—The third spraying is for larve and properly
comes just as most of the petals are falling from the trees, depending
somewhat upon the variety of fruit. In any case the small, white,
active larve can be easily seen, and when they first become abun-
dant spraying should be done. In this larval spraying on cherries
and prunes where there is a large amount of leaf surface exposed, the

oo, 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 larvee 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 coming into contact with the spray. Angle nozzles of
the type 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° Baumé, and the nicotine solutions,

a b
Fig. 13.—a, French prune buds; 6, Imperial prune buds; showing stage of earliest
buds at time of first application against thrips. (Original.)

is given preference over all other sprays used so far. To dilute,
measure out 54 gallons of the stock emulsion for each 100-gallon
spray tank, or 11 gallons for a 200-gallon tank; start the engine; pour
the stock emulsion into the spray tank, and while the agitator is
running, add the water to fill up the tank, putting in the strong
nicotine solution last and after the stock emulsion has been diluted.
For spraying in the interior counties add to this dilute oil-emulsion

HOW TO CONTROL THE PEAR THRIPS. 23

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 light-colored 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. Thisform ofthe nicotine
has been highly efficient and will in
all probability be more satisfactory
than the former. By reason of its
greater concentration the handling
and transportation charges will be
much less; also, the nicotine contained
in this preparation is much less vola-
tile, thus allowing the use of asmaller
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, evapo-
ration there being much less at this
time than in the interior counties Fie. 14.—Buds of Black Tartarian cherry at
where the atmosphereisdrier. Grow-_ . time of first application against thrips.
c About one-half natural size. (Original.)

ers in the Santa Clara Valley are
advised to use the 3 per cent distillate-oil emulsion, with tobacco
extract No. 1 added 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
larvee and on all varieties of deciduous
fruits attacked by the pearthrips. No or-
chards should be sprayed, however, when
the trees are in full bloom. Allspraying
for adults should be done before the blos-
soms appear and spraying for larve after
a large proportion of the petals have

fallen.
credit In the prune orchards of Santa Clara
per type used in spraying experiments. Valley deep fall plowing and cross-plow-
ree) ing has 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 proper condition plow with disk plows to a depth of 7 or

24 HOW TO CONTROL THE PEAR THRIPS.

8 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.

Plowing has not proved satisfactory as even a partial means of
controlling the thrips in the pear orchards of the interior counties.
This is due, perhaps, to several conditions, one of which is the differ-
ent type of soil, and another, the fact that the area of soil infested
with thrips around pear trees is very much less than around prune
trees, the branches of which spread farther, covering a greater surface
of ground. The larve in leaving the trees fall to the ground directly
from the foliage and young fruit, rather than crawl down the trunks
of the trees; hence in a prune orchard they are more widely distrib-
uted throughout the soil between the trees and can be reached by the
plows, while in a pear orchard most of the larvee in the ground are
close around the base of the trees.

SUMMARY.

The pear thrips can be controlled by thorough spraymg on any
variety of the deciduous fruits grown in the 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 returns of from $100 to $600 per acre more
than was peace from adjoining untreated areas.

The thrips work rapidly and may destroy all prospects of a crop
in less than a week’s time. Spraying, to be successful, must be done
thoroughly and at the time to kill the thrips before the fruit buds
have been destroyed.

Those who can do so successfully are advised to irrigate and plow
in the fall. This is to be followed by thorough spraying the follow-
ing spring.

When the thrips begin to appear on the trees in numbers, spraying
should be done thoroughly, using high pressure, holding nozzles close
to buds, and directing the spray directly into the ends of the buds, and
not against the sides.

Growers should not attempt to spray too many trees with one
machine. More profitable returns will be gained by spraying half of
the orchard thoroughly and at the propertimes than byspraying all the
orchard poorly one time. Results of the work in 1909 and 1910 show
conclusively that one application is not sufficient when the thrips are
abundant.

TT
3 9088 01272 8010

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