UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

NEW MATERIALS

FOR CONTROL OF THE

MEALY PLUM APHID

LESLIE M. SMITH and CURTIS A. FERRIS

BULLETIN 671

October, 1942

UNIVERSITY OF CALIFORNIA
BERKELEY, CALIFORNIA

CONTENTS

PAGE

Annual cycle 3

Materials and methods used 5

Control studies, 1937-38 7

Control studies, 1938-39 9

Concentration and field efficiency of material no. 9 10

Use of dinitro-o-cyclohexylphenol without petroleum oil 11

Dinitro-o-cyclohexylphenol used with asphalt vs. paraffin oils 12

Use.of acid or base with dinitro-o-cyclohexylphenol 12

Mixtures prepared in the spray tank 13

Other materials tested in 1938-39 14

Control studies, 1939-40 15

Concentration and field efficiency of material no. 13A 15

Effect of wetting agent in no. 13A 15

Use of oil with material no. 13A 17

Comparison of materials no. 11 and no. 13A 17

Effect of rain on materials no. 13A and no. 13C 17

Other dinitro phenols tested in 1939-40 19

Control of two scale insects on plum trees 21

Control of brown apricot scale 21

Control of Italian pear scale 23

Effect of dinitro compounds on covercrops and trees 25

Care in handling dinitro cresols and phenols 28

Summary 28

Acknowledgments 30

NEW MATERIALS FOR CONTROL OF THE
MEALY PLUM APHID 1

LESLIE M. SMITH 2 and CURTIS A. FERRIS 3

The mealy plum aphid, Hyalopterus pruni (Geoff.), may injure plum
and prune orchards in three ways as discussed in Bulletin 606 4 : (1)
curling and stunting of the foliage, together with a reduced growth in
length of new wood and a general stunting of the trees; (2) soiling of
the surface and bloom of table fruits by aphid excrement and the fre-
quently associated black sooty molds ; (3) splitting of the fruit.

Control of the mealy plum aphid has been studied at the California
Agricultural Experiment Station since 1928. In Bulletin 606, spraying
with coal-tar distillates was presented to the growers as a cheap and
effective method of control on the basis of experiments conducted by
the senior author prior to 1936. The chief disadvantage is that tar sprays
are caustic to men.

Since this report was made, other materials have become commer-
cially available, some of which are allegedly aphid ovicides, while others
are not so described by the manufacturers. Among these are a number
of nitrated phenolic derivatives. One such material, 3, 5-dinitro-o-cresol
(reported by Tattersfield, Gimingham, and Morris 5 ), was tested at this
station as early as 1930-31 and found to be highly toxic to aphid eggs.
But at that time the only source for this compound was quoted at a
price of $10 a pound, so that the experiments were not continued. Present
prices of similar compounds, however, are not preclusive to their use.

During the winters of 1937-38, 1938-39, and 1939-40, a number of
new spray materials were tested. Some of these proved superior to coal-
tar-distillate sprays. This bulletin presents the results of that research.

ANNUAL CYCLE
Before control studies can be properly presented, however, the com-
plicated annual cycle of this aphid must be reviewed. This has been done
rather completely in previous papers 6 ; the following brief summary is
taken from Bulletin 606.

1 Received for publication August 7, 1941.

2 Assistant Entomologist in the Experiment Station.

3 Technical Assistant in Entomology; resigned June 30, 1940.

4 Smith, Leslie M. Control of the mealy plum aphid. California Agr. Exp. Sta. Bui.
606:1-34.1937.

5 Tattersfield, F., C. T. Gimingham, and H. M. Morris. Studies on contact insecti-
cides. Part III. Ann. Appl. Biol. 12:218. 1925.

6 For a more complete discussion of the life history of this pest see :

Smith, Leslie M. Biology of the mealy plum aphid, Hyalopterus pruni (Geoff roy).
Hilgardia 10(7) H67-211. 1936.

Smith, Leslie M. Growth, reproduction, feeding, and wing development of the
mealy plum aphid in relation to climatic factors. Jour. Agr. Res. 54(5) :345-64. 1937.

[3]

4 University of California — Experiment Station

The mealy plum aphids pass the winter in the egg stage on the plum trees. The eggs
(fig. 1) are found near the bases of the buds, and most commonly between the bud
and the twig. They hatch in the spring shortly after the buds start to swell, and are
practically all hatched by the time 5 per cent of the flowers are in bloom. The aphids
which emerge from the overwintered eggs are known as the stem mothers. They are
wingless, green in color, and match the color of the young leaves. Unlike the genera-

Fig. 1. — Egg of the mealy plum aphid, Hyalopterus
pruni (Geoff.), at the base of a bud. (From Hilgardia vol.
10, no. 7.)

tions that follow, they are devoid of the white waxy powder which is characteristic
of this species and which has given rise to its common name. All of the aphids from
the overwintered eggs are females and give birth parthenogenetically (that is, with-
out fertilization) to other wingless, parthenogenetic females.

Several similar generations (3 to 7) occur on the plum trees, but with the advent
of warm summer weather in June and July, the young, when matured, have wings
and can no longer feed on the plum tree. These winged females fly to reed grass or
cattails, where they give birth parthenogenetically to wingless aphids, identical in
appearance to those of the spring generations on the plum. Here several generations
of wingless females mature during the late summer and fall.

In the latter part of October and throughout November, winged aphids are pro-

Bul. 671] New Materials for Control of the Mealy Plum Aphid 5

duced on the secondary hosts. They are unable to feed on the secondary hosts, after
reaching maturity, and must fly back to the plum trees. The first winged aphids that
are produced are all parthenogenetic females, which after arriving on the plum give
birth to young that mature to small, wingless, sexual females. The winged aphids
produced somewhat later on the secondary hosts are males, which fly to the plums
and mate with the wingless sexual females. After mating, these females lay the
overwintering eggs.

The movement of aphids from tree to tree and from orchard to orchard is of pri-
mary importance in any consideration of control. Contrary to the popular belief, the
winged aphids developed on the plum are incapable of feeding on or producing young
on the plum and must migrate to the secondary hosts. This has been demonstrated
by repeated cage tests and by field evidence.

In certain orchards the aphids are found year after year on certain trees while
other trees are always free from aphids. This fact has given rise to the popular mis-
conception that the aphids complete their annual cycle on the plum, and doubt is
thereby thrown on the necessity for secondary hosts. In cases of this kind, it can
generally be shown that the infested trees are near a windbreak, such as a barn or
row of tall trees. The aphids, returning from the secondary hosts in the fall, settle
on trees in such sheltered situations. Conclusive proof has been obtained that the
aphids cannot complete their annual cycle without passing a part of the year on a
secondary host. 7

MATERIALS AND METHODS USED

All of the control measures studied and reported in this bulletin con-
sist of ovicidal sprays applied in the winter, or when the trees are fully
dormant. The materials tested are as follows :

1. A proprietary petroleum-oil emulsion, said to contain secret toxic
materials which might act as an aphid ovicide.

2. Phenothiazine (or thiodiphenylamine).

3. Dinitro-o-cyclohexylphenol.

4. Sodium salt of dinitro-o-cyclohexylphenol.

5. A solution of 2.5 per cent o-nitrophenol in an emulsive dormant oil.

6. Tar-oil vapor spray applied as an inverted emulsion.

7. A proprietary coal-tar-distillate emulsion.

8. Another proprietary coal-tar-distillate emulsion.

9. A proprietary solution of 4 per cent dinitro-o-cyclohexylphenol in
dormant-grade, eastern, petroleum oil.

10. o-Nitrophenol.

11. Sodium dinitrophenolate, as a solution and suspension in water,
containing 20 per cent by weight of sodium dinitrophenolate, and 10
per cent by weight of a secret "penetrant," hereinafter called a wetting
agent.

12. A proprietary oil emulsion containing certain nitro compounds
and said to contain 75 per cent petroleum oil.

13. A solution and suspension in water of sodium dinitro-o-cresolate,

7 Smith, Leslie M. Control of the mealy plum aphid. California Agr. Exp. Sta. Bul.
606:3-5. 1937.

6 University of California — Experiment Station

20 per cent by weight, with the remainder being water and wetting
agent. The manufacturers furnished three types of sodium dinitro-o-
cresolate mixtures : no. 13C, containing no wetting agent; no. 13H, con-
taining 5 per cent wetting agent ; and no. 13A, containing 10 per cent
wetting agent. (Nos. 13C and 13H were experimental mixtures and
no.'13A was the proprietary mixture as marketed.)

14. Similar to no. 13A, except that the concentration of sodium dinitro-
o-cresolate was 30 per cent and no wetting agent was added.

15. A triethanolamine salt of dinitro-o-cyclohexylphenol.

16. A proprietary mixture of 2,4-dinitrophenol (2,6 isomer less than
3 per cent) dissolved at the rate of 1.86 ounces of dinitrophenol per
gallon of oil and emulsified.

17. Similar to no. 16, but with twice the concentration (3.72 ounces
per gallon) of dinitrophenol.

18. A proprietary mixture of 2,4-dinitrophenol dissolved in oil at the
rate of 3.0 ounces per gallon and emulsified.

These materials are referred to elsewhere in the text by number.
Materials 1 to 9 were tested during the winter of 1937-38 ; materials 10
to 14 during the winter of 1938-39; and materials 15 to 18 during
1939-40.

The stock mixtures were prepared in the following manner : 300 grams
of phenothiazine (material no. 2) was mixed with 8 liters of tank-mix
oil with a specific gravity of 0.9. The phenothiazine was worked in 200
cc of oil to a thick paste with an electric mixer. The paste was worked
through a % 4 -inch-mesh screen into the bulk of the oil. How much of
the phenothiazine went into solution in the oil is not known, but prob-
ably not more than 10 per cent by weight. The remainder was sus-
pended in the oil by stirring, then poured into the spray tank with the
agitator running.

Dinitro-o-cyclohexylphenol crystals were added to cold tank-mix oil
until a concentration of 3 per cent was reached. No more powder would
dissolve in the oil.

The sodium salt of dinitro-o-cyclohexylphenol (1,296 grams) was dis-
solved in 9 quarts of acetone to which 163 grams of a wetting agent was
added. When 2 quarts of this mixture was used per 100 gallons of- water,
the molal concentration of the sodium salt was the same as when 2%
gallons of 3 per cent dinitro-o-cyclohexylphenol was used per 100 gallons.

In the field, dinitro-o-cyclohexylphenol crystals were added to the
spray tank with the agitator running. Little, if any, of the crystals
dissolved. Caustic soda was added slowly until all of the crystals dis-
solved. When this was accomplished, 6 ounces of caustic soda per 100
gallons had been added. The dinitro-o-cyclohexylphenol reacts chemi-

Bul. 671] New Materials for Control of the Mealy Plum Aphid 7

cally with the caustic soda to form the sodium salt. This salt is reddish
orange, and when dry it is very irritating to the nose and throat. The
method of preparing the sodium salt of dinitro-o-cyclohexylphenol in
the spray tank is preferable to using the dry powder for this reason.

In one case of the dinitro-o-cyclohexyphenol tests (plat 6, table 1)
wherein the crystals were dissolved in the petroleum oil, oxalic acid was

TABLE 1

Angier Orchard, Sprayed February 16 and 24, 1938

Plat

Material and amount per 100 gallons
of water (except as noted)

sprayed

Amount
of spray
per tree

Trees

Heavily
infested

Lightly
infested

Clean

None, check

No. 5, 2 gals

None, check

4 per cent no. 5 in oil, 5 gals.; water,

5 gals, only

No. 6, 10 gals.; water, 10 gals, only

3 per cent no. 3 in tank-mix oil, 1Yi gals. ;
blood albumin, 6 oz.; oxalic acid, 4 oz.. .

No. 4 in acetone plus wetting agent, 2 qts.

None, check

No. 9, 2 l A gals.; blood albumin, 6 oz.;

oxalic acid, 4 oz

None, check

Tank-mix oil, 2H gals. ; blood albumin, 6 oz

No. 1,2^ gals

None, check

4 per cent no. 2 in tank-mix oil, 2 l A gals. ;
blood albumin, 6 oz

No. 3, \i lb.; caustic soda, 6 oz

No. 8, 3 gals

number
17
33
17

26
34

36
32
18

gallons
5.76

0.23
0.35

5.15
2.34

4.17
4.44

4.72
4.32

per cent
100.0
100
100.0

100.0
3.0

0.0

100.0

0.0
100.0
100.0
94.4
93.9

100.0
0.0
19.0

per cent
0.0
0.0
0.0

0.0

26.6

19.4
3.1
0.0

3.8
0.0
0.0
5.6
6.1

0.0

2.3

23.0

per cent
0.0
0.0
0.0

0.0
70.4

80.6

96.9

0.0

96.2
0.0
0.0
0.0
0.0

0.0

97.7
58.0

* Dashes indicate data not available.

added to the water in the spray tank to neutralize any base present and
thereby prevent the dinitro-o-cyclohexylphenol from leaving the oil and
going into solution in the water.

CONTROL STUDIES, 1937-38
The materials tested during the first winter were materials nos. 1 to 9.
The sprays were applied to President plums on the Angier orchard at
Lodi, San Joaquin County (table 1), and to Grand Duke and Diamond
plums on the Lynwood (table 2) and Highland (table 3) orchards at
Penryn, Placer County. Counts were made from May 1 to 15. Each tree
was carefully inspected, and if no aphids were found, it was counted as
"clean" ; if from one to three colonies were found, the tree was counted
as "lightly infested" ; and if four or more colonies were found, the tree
was counted as "heavily infested."

8 University of California — Experiment Station

In considering the data in tables 1 to 3, more dependence can be placed
on the Angier tests than those on Lynwood and Highland. The infesta-
tion on the Angier orchard at Lodi was heavy and uniform, whereas at

TABLE 2
Lynwood Orchard, Sprayed February 24, 1938

Plat
no.

Material and amount per
100 gallons of water

Trees
sprayed

Amount
of spray
per tree

Trees

Heavily
infested

Lightly
infested

Clean

1
2
3

None, check

number
20
38
34
36
31
34

gallons

2.79
2.22
2.74
2.94

per cent
100.0
86.9
32.4
0.0
77.4
14.7

per cent
0.0
10.5
38.2
19.4
16.1
26.5

per cent

0.0

2.6

29.4

4
5

No. 9, 2y<i gals.; blood albumin, 8 oz

No. 1, 2^2 gals

80.6
6.5

No. 4 in acetone + wetting agent, 2 qts

58.8

TABLE 3

Highland Orchard, Sprayed February 24, 1938

Plat
no.

Material and amount per
100 gallons of water

Trees
sprayed

Amount
of spray
per tree

Trees

Heavily
infested

Lightly
infested

Clean

number
23
27

27
20

gallons
3.70
3.07

2.56
3.75

per cent
78.3
55.6

29.6
75.0

10.3

33.3

0.0

per cent
21.7
37.0

48.2
15.0

15.4
41.7
33.3
21.1

per cent

2
3

Tank-mix oil, 2 X A gals. ; blood albumin, 6 oz.
4 per cent no. 2 in tank-mix oil 2J^ gals. ;
blood albumin, 6 oz

7.4
22.2

None, check

10.0

3 per cent no. 3 in tank-mix oil, 23^ gals.;
blood albumin, 6 oz

74.3

No. 5, 2V 2 gals

None, check

66.7

No. 7, 3 gals

78 9

Dash indicates data not available.

Penryn it was light and spotted. About one fourth of a tree at Lodi was
examined microscopically during the winter of 1937-38, and 6,000 aphid
eggs were counted. This would mean 24,000 eggs per tree. At Penryn,
occasional check trees were free from aphids, which means that no eggs
were laid on them. The average infestation in Penryn was estimated at
about 10 eggs per tree. Furthermore, the spraying at Lodi was done
under good weather conditions, whereas at Penryn some of the sprays
were applied while a wind was blowing.

The materials no. 5 (either as an inverted or standard emulsion) , no. 1,
and no. 2 were not effective.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 9

Dinitro-o-cyclohexylphenol and its sodium salt (materials nos. 3 and
4) were highly effective, and for the most part surpassed tar sprays
(materials nos. 6, 7, and 8). Best results were secured with no. 9, using
2% gallons per 100 gallons of water. At Lodi, however (which is the
more conclusive test), the best results were secured with % pound
dinitro-o-cyclohexylphenol (material no. 3) per 100 gallons of water
plus 6 ounces of caustic soda. All combinations of this nitrated phenol
injured the covercrop, however. None produced injury to the spray
crew. The sodium salt was somewhat irritating to the throat during
spraying, but was not highly objectionable.

CONTROL STUDIES, 1938-39

In view of the excellent control obtained with dinitro-o-cyclohexyl-
phenol during the winter of 1937-38, several aspects of the use of this
material were studied during the next winter. The points investigated
were : (1) the relation of concentration of various mixtures to field effi-
ciency; (2) the value of using dinitro-o-cyclohexylphenol without petro-
leum oil ; (3) relative efficiency of western, asphalt-base oils as compared
with eastern, paraffin-base oils when used with dinitro-o-cyclohexyl-
phenol ; (4) the relation of the pH of the spray water to field efficiency ;
and (5) the efficiency of solutions prepared in the spray tank, as com-
pared to concentrated stock solutions. These factors were studied pri-
marily from the standpoint of mealy-plum-aphid control; but where
possible, data were also taken on the control of brown apricot scale, algae
and lichens, and the effect of the sprays on the covercrop, and stimulation
or injury to the trees.

The tests were conducted on sixteen different orchards, located in
El Dorado, Placer, Sacramento, San Joaquin, Santa Clara, Santa Cruz,
Solano, and Sonoma counties. Various types of spray rigs and spray
crews were used, which probably represent the average machinery and
spraying efficiency now in use. During the course of this work, sprays
were applied to President, Diamond, Grand Duke, and Tragedy plums ;
and to French (Agen), Hungarian (Pond Hungarian), Imperial (Im-
perial Epineuse) , Sugar, and Robe de Sergeant (Sergeant) prunes.

During the spring of 1939, an unusual emergence of several species
of Podabrus occurred, and these predators in some cases destroyed entire
colonies of aphids when the colonies each covered from five to ten leaves.
This made it impossible to count whole trees as was done the preceding
year, and instead, counts of colonies were made in which the locations
of former colonies were detected by curled, yellowed, wax-smeared
leaves. These were counted as were those colonies having heavy popu-
lations.

University of California — Experiment Station

Concentration and Field Efficiency of Material No. 9. s — Various
concentrations of material no. 9 (a proprietary solution of 4 per cent
dinitro-o-cyclohexylphenol in dormant type, eastern, paraffin-base oil)
were applied on the Franklin, Barton, Solari, and McDonell orchards
(table 4).

On the Franklin orchard, located at Penryn, Diamond plums were
sprayed on February 8, 1939, at a pressure of 375 pounds per square inch

TABLE 4

Field Efficiency of Material No. 9 at Different Concentrations

Orchard and amount of material per
100 gallons of water

Franklin orchard :

0.5 gal

1.0 gal

1.5 gals

2.0 gals

Barton orchard:

0.5 gal

1.0 gal

1.5 gals

2.0 gals

Solari orchard :

1.0 gal

1.5 gals

2.0 gals.

McDonell orchard
2.5 gals

Trees
sprayed

number

47
36
47
20

Amount of
spray per tree

gallons

2.6
2.1
2.3
3.2

5.5
3.5
3.8
4.1

2.7
3.0
2.8

Control"

per cent

* Computed as a percentage reduction in colonies from adjacent unsprayed trees,
t Dash indicates data not available.

with a Royal Bean no. 20 spray rig. Guns with four nozzles each were
handled by men riding on the rig. Each row of trees was sprayed from
two sides. The temperature at the time of spraying was 40° to 45° F,
followed by freezing temperatures at night. A slight breeze was blowing.
No rain fell until 8 p.m., February 9.

On the Barton orchard, located at Escalon, French prune trees were
sprayed on February 20 and 21, 1939, at a pressure of 250 pounds with
a Royal Bean spray rig. Guns with three nozzles each were handled by
men walking. The temperature at the time of spraying was 60° to 65° F.
No rain fell for several days after spraying.

On the Solari orchard, near Linden, French and Sugar prune trees
were sprayed on February 14 and 15, at a pressure of 400 pounds with
a Hardy Master Mongul. Guns with four nozzles each were handled by

8 Dowspray Dormant, manufactured by the Dow Chemical Co.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 11

men riding on the rig. Each row was sprayed from two sides. The tem-
perature was 50° to 60° F. No rain fell for several days after spraying.

Material no. 9 was emulsified as a tank mix with 1V4 pounds of emulsi-
fier per 100 gallons of water. The emulsifier was a proprietary mixture 9
prepared especially for use with material no. 9. The results are given
in table 4.

A study of the data in table 4 indicate that 2 gallons of material no. 9
per 100 gallons of water was necessary for satisfactory control.

TABLE 5
Efficiency of Dinitro-o-cyclohexylphenol (Material No. 3) without Oil

Orchard and amount of material per
100 gallons of water*

Trees
sprayed

Amount of
spray per tree

Control

Solari orchard f:
2 oz

number

25
22

gallons

3.2
3.5

3.2

4.5

per cent
41

4 oz

Barton orchard :
2oz

Highland orchard :
4 oz

* Unmodified well water with a pH of about 8.0 was used on these orchards.

t On the Solari orchard, no. 9 emulsifier was employed at \\i pounds per 100 gallons of water as aspreader
with no. 3.

Use of Dinitro-o-cyclohexylphenol without Petroleum Oil. — Tests were
conducted to determine the field efficiency of an emulsified oil solution of
dinitro-o-cyclohexylphenol (material no. 9), as compared to an aqueous
solution and suspension of this dinitro compound (material no. 3) with-
out oil. These tests were conducted on the Solari, Barton, and Highland
orchards. The spraying conditions on the Solari and Barton orchards
are described on page 10. On the Highland orchard, located at Penryn,
Grand Duke and Diamond plums were sprayed on February 9, 1939,
at a pressure of 375 pounds with a Royal Bean no. 20 spray rig. Guns
with four nozzles each were handled by men riding on the rig. The tem-
perature was 34° F. There was no wind and the day was overcast. Light
rain fell 8 hours after spraying was finished.

The dinitro-o-cyclohexylphenol used was a fine, yellow powder, prac-
tically chemically pure. It was very difficult to wet with water and had
to be worked into a stiff paste with water, before being added to the spray
tank. Approximately 1.74 ounces of this powder will dissolve in 100
gallons of neutral water, so that probably a considerable remainder was
in suspension. The results are given in table 5 and may be compared with
those in table 4.

Dowspray Dormant Emulsifier, manufactured by the Dow Chemical Co.

University of California — Experiment Station

Dinitro-o-cyclohexylphenol Used with Asphalt vs. Paraffin Oils. —
Solutions of 2 and 4 per cent by weight of dinitro-o-cyclohexylphenol in
asphalt-base and in paraffin-base oil were prepared as tank-mix emul-
sions, using 4 ounces of blood albumin per 100 gallons of water. The re-
sults of tests on the Solari and Barton orchards are given in table 6.

In the cases of the asphalt-base oil, the 1.2 ounces of dinitro-o-cyclo-
hexylphenol per 100 gallons of water was obtained by using ^ gallon of
4 per cent solution per 100 ; the 2.4 ounces by using 1 gallon of 2 per cent

TABLE 6
Material No. 3 in Asphalt- vs. Paraftin-Base Oils

Orchard

and amount of material
100 gallons of water

Control with oil base

per

Paraffin

Asphalt

Barton orchard:

1.2 oz

per cent

69.9

72.4
92.3

per cent
74

2.4 oz

Solari orchard:
4.8 oz

9.6 oz

solution ; the 4.8 ounces by using 2 gallons of 2 per cent solution ; and the
9.6 ounces by using 2 gallons of 4 per cent solution. In the cases of the
paraffin-base oil, an emulsion of a 4 per cent solution was used.

Use of Acid or Base with Dinitro-o-cyclohexylphenol. — The dinitro-o-
cyclohexylphenol powder was mixed into a paste with a little water and
added to the spray tank. Then this was made acidic with commercial
oxalic acid ; or basic (or alkaline) with caustic soda. The results of these
tests are given in table 7. When these results are compared with those
obtained when 2 and 4 ounces of dinitro-o-cyclohexylphenol were used
in unmodified well water (see table 5), it can be seen that the addition
of acid had practically no effect on the efficiency of the dinitro-o-cyclo-
hexylphenol and the addition of caustic soda increased the efficiency.

Material no. 9 and a homemade oil solution of dinitro-o-cyclohexyl-
phenol were also tested in combination with acid and base as indicated
in table 7. On each orchard the results obtained from the use of caustic
soda, exceeded the results obtained with oxalic acid. This is in agreement
with the other tests in table 7, wherein the dinitro-o-cyclohexylphenol
powder gave better results when combined with base than with acid. On
the Barton orchard no test was made of the homemade solution at 1
gallon per 100 gallons in unmodified water, so that no comparison can
be made on that orchard of the efficiency of unmodified water.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 13

TABLE 7

Effect of Acid or Base on Efficiency of Dinitro o-cyclohexylphenol and

of Emulsions of Dinitro-o-cyclohexylphenol Oil Solutions

Material, orchard, acid or base, and amounts

Trees

Amount of

Control*

per 100 gallons of water

sprayed

spray per tree

number

gallons

per cent

No, 3, 2oz.:

Solar i orchard f:

3.3
3.1

Barton orchard J:

3.7
3.2

Bellevue orchard J:

Caustic soda, 2 oz

— §

No. 3, 4oz.:

Solari orchard f:

Oxalic acid, 1 oz

2.8

Caustic soda, 4 oz

3.6

Bellevue orchard J:

Caustic soda, 4 oz

— §

No. 9, 1 gal.:

Solari orchard f:

2.8
2.9

Caustic soda, 4 oz

None, normal

2.7

Highland orchard f:

Oxalic acid, 6 oz

29
24

3.3
4.1

Caustic soda, 6 oz

Franklin orchard f:

None, normal

2.1

Barton orchard f:

None, normal

3.5

Homemade oil solution of dinitro-o-cyclohexylphenoll,

lgal.:

Barton orchard :

Oxalic acid, 4 oz

3.7

3.6

* Computed as a percentage reduction in colonies from adjacent unsprayed trees.
t 1% pounds spreader per 100 gallons of water used.
X No spreader used.
§ Dashes indicate data not available.

^ A solution of 4 per cent by weight of dinitro-o-cyclohexylphenol in western tank-mix oil, emulsified
in the spray tank with blood albumin.

Mixtures Prepared in the Spray Tank. — The possibility of mixing
dinitro-o-cyclohexylphenol powder with an oil emulsion in the spray
tank was investigated. Several tanks of this spray were applied, but
because of a biological control of aphids, data could not be obtained,
except in two plats on the Barton orchard. In the first of these a 2 per
cent tank-mix-oil emulsion was prepared, and then 2 ounces of dinitro-
o-cyclohexylphenol was added to the tank with the agitator running.

University of California — Experiment Station

Twenty-eight trees were sprayed, the average amount of spray used
being 3.4 gallons per tree. This yielded a control of 53.9 per cent. The
second plat was similar to the first except that 4 ounces of dinitro-o-
cyclohexylphenol was added to the tank. In this case twenty-six trees
were sprayed ; an average of 3.5 gallons per tree was used. This yielded a
control of 73.9 per cent. While these data are not conclusive, they

TABLE 8
Other Mixtures Tested, 1938-39

Orchard, material, and amount
per 100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

Spencer orchard:
No. 10, Yi lb.; caustic soda, Yi lb

Highland orchard:
No. 11, 12oz.f

Palms orchard:

No. 10, \i lb.; caustic soda, \i lb

No. 12, 5 gals

No. 13A, 1 qt

No. 14, 12oz.j

Barton orchard:

No. 10, y 2 lb

No. 12, 2 gals

No. 13A, 1 qt

No. 14, 12oz.f

Rubke orchard:

No. 13A, 1 qt

Coal-tar-distillate emulsion,! 2 l / 2 gal;

number
60

gallons

140

per cent
Negative

2.1

1.9

2.2

2.0

4.8

3.4

Negative

3.8

100

4.0

100

* Not measured.
t Dry- weight basis.

t Coal-tar distillate is not one of the materials tested in this study, but is merely put in here to show
a comparison with previous tests reported in Bui. 606.

indicate that under certain conditions, good results may be secured by
adding dinitro-o-cyclohexylphenol powder to oil emulsions in the spray
tank.

Other Materials Tested in 1938-39. — Several other proprietary dini-
tro derivatives of phenol or cresol were tested during the winter of
1938-39. These materials were nos. 10 to 14. The results of the tests
are presented in table 8. Material no. 10 (o-nitrophenol) produced no
control at all when used with caustic soda, and when used alone the
results were not satisfactory from the commercial standpoint. Material
no. 12 was ineffective and, even when used at the rate of 5 gallons per
100, failed to yield a commercial control. The success of materials nos.
13 and 14 led to further testing of them during the winter of 1939-40.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 15

CONTROL STUDIES, 1939-40

During the winter of 1939-40, several questions pertinent to the prac-
tical use of sodium dinitro-o-cresolate (material no. 13) were investi-
gated. These questions were: (1) the relation of the concentration of
sodium dinitro-o-cresolate to field efficiency; (2) the effect of wetting
agent; (3) the value of using petroleum oil with sodium dinitro-o-
cresolate ; (4) the efficiency of sodium dinitrophenolate (material no. 11)
as compared to sodium dinitro-o-cresolate (material no. 13) ; and (5) the
relation of time of application to field efficiency.

These points were investigated from the standpoint of mealy-plum-
aphid control, but whenever possible, data were also taken on the control
of brown apricot scale, algae and lichens, and effect on the covercrop
and on the trees.

Tests were conducted in about the same localities and on many of the
same orchards as in 1938-39. The majority of the spraying was done at
500 pounds of pressure with a Royal Bean no. 20 spray rig ; two single-
nozzled guns were handled by operators walking.

Concentration and Field Efficiency of Material No. 13 A. 10 — The rela-
tion of concentration of material no. 13A to field efficiency was tested on
the Club orchard at Penryn, the McDonell orchard at Sacramento, and
the Sheldon orchard at Fairfield. Sprays were applied on the Club
orchard on Diamond and President plums, February 7, 1940, at 400
pounds pressure with a Bean spray rig. Single-nozzled guns were han-
dled by men walking. The temperature was 43° F. No rain occurred for
several days after spraying. On the McDonell orchard the sprays were
applied on French prunes, February 12, 19, and 20, 1940, at 500 pounds
pressure with a Royal Bean no. 20 spray rig. Single-nozzled guns were
handled by men walking. No rain fell for some time after spraying. On
the Sheldon orchard the sprays were applied on French prunes, Febru-
ary 8, 1940, with a Niagara Liqui-Duster ; the operators rode on the rig.
The temperature was 55° F, and no rain fell for several days after
spraying.

The results of these tests are given in table 9. These data indicate that
12 ounces, dry weight, of sodium dinitro-o-cresolate per 100 gallons of
water are necessary for an effective control.

Effect of Wetting Agent in No. 13 A. — As supplied to the trade, no.
13A contains 10 per cent by weight of a so-called "penetrant," or wetting
agent, which is said to be incorporated into the mixture during the manu-
facturing process so that it becomes intimately associated with the salt
in some chemical or physical manner.

]0 Elgetol, manufactured by the Standard Agricultural Chemicals Co.

University of California — Experiment Station

TABLE 9

Field Efficiency of Material No. 13A at Different Concentrations

Orchard and amount* of material
per 100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

Club orchard:

4 oz

8 oz

number

19
21
16
21

21
22
24

24
24

gallons

3.4
3.3
3.4
3.2

4.8
4.6
4.2

4.2
4.2
4.2

per cent

85
83

12 oz

16 oz

100
100

McDonell orchard:

8oz

12 oz

16 oz

Sheldon orchard:

8oz

12 oz

16 oz

100

91
96
100

* Dry weight of sodium dinitro-o-cresolate.

TABLE 10

Efficiency of Wetting Agent at 0, 5, and 10 Per Cent, as Contained in

Materials Nos. 13C, 13H, and 13A, Respectively

Orchard and amount* of material
per 100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

McDonell orchard:
No. 13A:

8.0 oz

number

21
22
24

19
18

19
21
16
21

22
19
20

gallons

4.8
4.6
4.2

4.8
5.6

5.3
5.6

3.4
3.3
3.4
3.2

3.4
3.1
3.2
3.2

per cent
90

12.0 oz

16.0 oz

100

No. 13H:

9.0 oz

13.5 oz.

100

No. 13C:

9.0 oz

13.5 oz.

100
100

Club orchard:
No. 13A:

4.0 oz

8.0 oz

12.0 oz.

16.0 oz

No. 13C:

83
100
100

9.0 oz

13.5 oz.

18.0 oz

94
99
99

Dry-weight basis.

Bul. 671 ] New Materials for Control op the Mealy Plum Aphid 17

The three mixtures, nos. 13 A, 13C, and 13H (see p. 6), were tested
on the McDonell orchard and nos. 13A and 13C on the Club orchard
as shown in table 10. These data indicate that the efficiency of the sodium
dinitro-o-cresolate has been reduced in some manner by the incorpora-
tion of the wetting agent. It can be seen, however, that at dosages above
12 ounces (that is, the concentration herein recommended) the differ-
ences in control due to the wetting agent are slight and may be ignored
from a practical standpoint.

Use of Oil with Material No. 13 A. — Various amounts of material no.
13A were tested with various amounts of petroleum oil. The oil used in
each case was a winter grade of tank-mix oil with an unsulfonatable
residue of 70 per cent. It was emulsified in the spray tank with 4 ounces
of blood-albumin spreader per 100 gallons of water. Material no. 13A
was added last, with the agitator running. The results of these tests are
presented in table 11.

In some cases, such as the 12-ounce series on the Sheldon and Osterli
orchards the control ranged from 94 to 100 per cent, so that the effect
of the various amounts of oil could not be measured. The 4-ounce series
on the Sheldon orchard failed to produce any control, and again no
effect of the oil could be measured. The most interesting series was the
8-ounce series on the Sheldon orchard, wherein the addition of oil
appeared to reduce the efficiency of the mixture, but as the oil concen-
tration was increased the efficiency of the mixture increased, until at
a concentration of 2 gallons of oil per 100 gallons of water the efficiency
was nearly equal to that of material 13A when used without oil.

Tests of materials nos. 13C and 13H with and without oil, as shown in
table 12, approximated 100 per cent control, but a slight decrease in
control occurred when oil was added to material no. 13H at the rate of
1.5 gallons per 100 gallons of water.

Comparison of Materials No. 11 and No. 13 A. — Materials no. 11
(sodium dinitrophenolate) and no. 13A (sodium dinitro-0-cresolate) were
tested on three orchards, and the results obtained are given in table 13.
These data indicate that no. 11 as used in these tests was less effective
than no. 13A. On the McDonell orchard, no. 11 was also tested in com-
bination with iy 2 gallons of oil per 100 gallons of water, using 7.3 and
11.0 ounces of no. 11. These applications yielded 77 and 88 per cent
control.

Effect of Rain on Materials No. 13 A and No. 13G. — A number of tests
using materials nos. 13A and 13C at various concentrations were applied
on the Barton orchard. Rain followed these applications within a few
hours. The humidity was high, and prior to the rainfall, the sprays
dried very slowly on the trees. The results of these tests are given in

University of California — Experiment Station

TABLE 11

Use of Oil with Material No. 13A

Orchard, amount of no. 13A*, and amount
of tank-mix oil per 100 gallons of water

Trees
sprayed

Amount of
spray per tree

Sheldon orchard :
Check, oil alone:

2.0 gals. oil...
4 oz. no. 13A:

1.0 gal. oil

1.5 gals. oil.

2.0 gals. oil.
8 oz. no. 13A:

0.0 gal. oil

1.0 gal. oil

1.5 gals. oil. .

2.0 gals, oil ... .
12 oz. no. 13A:

0.0 gal. oil

1.0 gal. oil

1.5 gals, oil

2.0 gals. oil...

McDonell orchard:
8 oz. no. 13A:

0.0 gal. oil

1.5 gals, oil

12 oz. no. 13A:

0.0 gal. oil

1.5 gals, oil

Barton orchard :
4 oz. no. 13A:

2.0 gals. oil.
8 oz. no. 13A:

2.0 gals, oil
12 oz. no. 13A:

2.0 gals. oil.

Osterli orchard :
4 oz. no. 13A:

0.5 gal. oil .

1.0 gal. oil

1.5 gals. oil.

2.0 gals, oil . .
8 oz. no. 13A:

0.5 gal. oil...

1.0 gal. oil

1.5 gals. oil. .

2.0 gals. oil..
12 oz. no. 13A:

0.5 gal. oil. . .

1.0 gal. oil...

1.5 gals, oil .

2.0 gals. oil. .

number

gallons

4.2

4.8

4.6

4 4

6.6
8.0
8.2

4.4

5.0

3.5

4.4

4.0

4.8

5.1

4.6

3.4

4.0

3.4

Dry-weight basis.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 19

table 14. The higher concentrations were not so adversely affected as
the lower ones, though in both the A and C series the lower concentra-
tions had longer drying time. This test indicates that the spray must

TABLE 12

Tests of Materials No. 13C and 13H with and without Oil

Material and tank-mix oil per 100
gallons of water

Trees
sprayed

Amount of
spray per tree

Control

No. 13C, 9.0 oz.:
Without oil

number

19
19

18
20

20
22

gallons

5.3
4.5

5.6
4.9

4.8
4.1

5.6

per cent
100

With 1.5 gals, oil

100

No. 13C, 13.5 oz.:

Without oil

100

With 1.5 gals, oil

100

No. 13H,9.0oz.:

Without oil

With 1.5 gals, oil

No. 13H, 13.5 oz.:

Without oil

100

TABLE 13

Comparison of Materials No. 13A and No. 11

Orchard, material, and amount per
100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

Barton orchard :
No. 11, 14.6 oz.*.. ..

number

22
23

18
18
20
21
22

23
20
22

gallons

8.1
6.5

5 5
5.5
5.0

4.8
4.6

4.4
5
4.6

per cent

No. 13A, 16.0 oz

McDonell orchard:

No. 11, 7.3 oz

No. 11, 11.0 oz

No. 11, 14.6 oz

No. 13A, 8.0 oz

83
92
91
90

No. 13A, 12.0 oz

Osterli orchard:
No. 11, 7.3 oz

No. 11, 11.0 oz

No. 11, 14.6 oz

Dry-weight basis.

dry on the trees if the control of aphids is to be satisfactory, and if rain
occurs before the trees are dry, the spraying should be repeated.

Other Dinitro Phenols Tested in 1939-40. — During the winter of
1939-40, a few other dinitro phenols were tested. These were materials
nos. 15 to 18. The results of these tests are given in table 15. Material

University of California — Experiment Station

TABLE 14
Effect of Rain on Materials No. 13A and 13C, Barton Orchard, 1939-40

Amount* of material per 100
gallons of water

Rain,

hours after
spraying

Actual
control

Expectancy!
control

Loss in

control

from rain

Material no. 13 A:

4.0 oz _

hours
4
2H

per cent

13
21

47
54

67
100

per cent

85
88
97
100

91t
94
99
99

per cent

8.0 oz. . .

12.0 oz.

16.0 oz

Material no. 13C:

4.5 oz

9.0 oz.

91
94

13.5 oz

18.0 oz

* Dry-weight basis.
t From table 9.
% From table 11.

TABLE 15
Other Materials Tested, 1939-40

Orchard, material, and amount per
100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

Osterli orchard:
No. 15, 1 pt

number

23
21
23
22
23
23
22

gallons

3.7
3.6
3.8
4.6
3.8
3.9
4 3

8.9

per cent
98

No. 15, 2 pts

No. 15, 3 pts

No. 18, 3 gals. . .

No. 17, 2 gals

No. 17, 2H gals

No. 17, 3 gals

Barton orchard :
No. 16, 3 gals

no. 15 (triethanolamine salt of dinitro-o-cyclohexylphenol 11 ) is a dark
liquid containing 30 per cent of the salt and is readily soluble in water.
It was used alone, without added oil or spreader. A slight excess of tri-
ethanolamine is said to be present, which acts as a spreading agent. Ap-
parently, the 1-pint concentration of material no. 15 approximated a
complete control. The aphid infestation on the Osterli orchard was not
heavy, and spraying conditions were excellent, all of which contributed
to a high field efficiency for the material. Under more difficult conditions,
1 pint per 100 gallons may not produce sufficient control and a higher
concentration may be necessary.

As a check, or comparison, no. 9 and coal-tar distillate were applied
on some orchards during 1939^0. The results of these applications are

11 Dowspray Dormant No. 2, manufactured by the Dow Chemical Co.

Bul. 671] New Materials for Control op the Mealy Plum Aphid 21

given in table 16. The figures for material no. 9 agree fairly well with

the control obtained in 1938-39 as presented in table 4, except for the

1-gallon application on the Club orchard. In this case the trees were

small, which facilitated thorough spraying and may account for the

better control.

TABLE 16

Tests with Material No. 9 and Coal-Tar Distillate, 1939-40

Orchard and amount of material per
100 gallons of water

Trees
sprayed

Amount of
spray per tree

Control

Osterli orchard:

No. 9, 2 gals

Coal-tar distillate*, 2 gals.
Coal-tar distillate*, 3 gals.

Barton orchard:
No. 9, 2 gals

number

23
24
21

gallons

4.1
4.5
4.3

10.2

per cent

97
91
97

100

Club orchard:
No. 9, 1 gal. .
No. 9, 2 gals.

McDonell orchard:
No. 9, 2 gals

Sheldon orchard :
No. 9, 2 gals. . .

3.4
3.1

4.8

4.2

97
100

100

or.

* Coal-tar-distillate emulsion is not one of the materials tested in this study, but is merely put in here
to show a comparison with previous tests reported in Bul. 606.

CONTROL OF TWO SCALE INSECTS ON PLUM TREES

Control of Brown Apricot Scale. — Counts on the control of brown
apricot scale, Lecanium corni Bouche, were made on some of the plats
during the summer. The control was measured by counting the number
of scale on ten twigs of uniform size on each of ten trees. Thus a hundred
twigs on each plat were counted. The counts averaged as follows :

Number of scale
Orchard per plat

McDonell 800

Barton 5,000

Nicolaus 1,000

Siemas 800

Sheldon 2,000

The percentage control was computed as a percentage reduction in
population from adjacent checks.

Material no. 9 gave a very good control of brown apricot scale with
concentrations as low as 1 gallon per 100 gallons of water. Dinitro-o-
cyclohexylphenol (material no. 3) without oil, on the other hand, gave

22 University of California — Experiment Station

poor results, whether used alone or with acid or base. The results with
dinitro-o-cyclohexylphenol with oil (material no. 9) and without oil
(material no. 3) were as follows :

Orchard, materials, and

amount per 100 gallons Control,

of water per cent

Barton orchard :

No. 9, no acid or base :

0.5 gal 92

1.0 gal : . . 97

1.5 gals 98

2.0 gals 99

No. 3, 2 oz.:

No acid or base 36

With 4 oz. caustic soda 31

With 4 oz. oxalic acid Negative

Seimas orchard :

No. 9, no acid or base :

1.25 gals 97

2.5 gals 98

No. 3, 4 oz. with 4 oz. caustic soda 0.7

Sheldon orchard:

No. 9, 1.67 gals., no acid or base 97

McDonell orchard :

No. 9, 2.5 gals., no acid or base : 99

No. 3, 4 oz., with 4 oz. caustic soda 38

Nicolaus orchard :

No. 3, 2 oz., no acid or base 21

When this compound was dissolved in western, asphalt-base oil, the
control was as good as that obtained with the eastern, paraffin-base-oil
solution, no. 9.

In one test on the Barton orchard, the concentration of dinitro-o-
cyclohexylphenol was held constant at 2.4 ounces per 100 gallons of
water while the oil solvent was used at 1 and 2 gallons per 100 gallons
of water. In this test, 2 gallons of oil, plus 2.4 ounces of dinitro-o-cyclo-
hexylphenol per 100 gallons of water gave 94 per cent control, whereas
1 gallon of oil, plus 2.4 ounces of dinitro-o-cyclohexylphenol per 100
gallons of water gave 86 per cent control. In this case the addition of
one more gallon of oil produced an important gain in efficiency.

On the Nicolaus orchard, near Mountain View, Santa Clara County,
dinitro-o-cyclohexylphenol was used at 2 and 4 ounces with 2 gallons
of tank-mix oil per 100 gallons of water in unmodified, in acidified, and
in basic water. The results are given on the following page.

Bul. 671 ] New Materials for Control of the Mealy Plum Aphid 23

Dinitro-o-cyclohexylphenol, in
ounces per 100 gallons of

water with 2 gallons Control, in

of tank-mix oil Acid or base added per cent

2 None 94.0

2 Caustic soda, 4 oz 86.3

2 Oxalic acid, 4 oz 89.0

4 None 97.3

4 Caustic soda, 4 oz 83.5

4 Oxalic acid, 4 oz 86.4

The pH of the unmodified well water on this orchard was 8.09. The order
of mixing in the spray tank was : ( 1 ) about half of the desired amount
of water, (2) blood-albumin emulsifier (or a proprietary emulsifier in
those cases where caustic soda was used), (3) tank-mix oil, (4) dinitro-o-
cyclohexylphenol powder previously worked into a paste with a small
amount of water, (5) acid or base, (6) rest of the water. The agitator
of the spray rig ran constantly during mixing and spraying.

The above data indicate that best results were obtained with unmodi-
fied water, that both acid and base reduced the efficiency, and that the
base reduced the efficiency slightly more than the acid.

In one test, material no. 10 (o-nitrophenol) was used at 8 ounces of
powder per 100 gallons of water, and in another test 2 gallons of tank-
mix oil was added to 8 ounces of this compound. The powder alone
yielded no control at all, and when used with oil the control of scale was
60 per cent. Material no. 6 (a tar-oil vapor spray) applied on the same
orchard at the same time killed 96 per cent of the scale.

Three pints of material no. 13A (that is, 12 ounces of sodium dinitro-o-
cresolate on dry- weight basis) per 100 gallons of water has been shown
in this paper to yield a good control of mealy-plum-aphid eggs. This
concentration was studied for control of brown apricot scale on the
Seimas orchard, as indicated in table 17. These data indicate that nos.
13A and 13C alone are not satisfactory for control. As shown in the
table, however, 3 pints of either no. 13A or 13C combined with 2 gallons
of tank-mix oil are effective. The relation of the more standard mixtures
is shown graphically in figure 2.

Control of Italian Pear Scale. — Old French prune trees on the Hor-
warth orchard, San Jose, were sprayed on January 12, 1940, with no.
13A, with and without oil. These trees were very mossy, that is, thickly
covered with lichens and algae. In many places solid incrustations of
Italian pear scale, Diaspis piricola (Del Guercio), occurred. Previous to
spraying, the ratio of living to dead scales was 2:1. Plat 1 was sprayed
with 1 gallon of no. 13A per 100 gallons of water, and plat 2 was sprayed
with 2 quarts of no. 13A plus 2 gallons of oil per 100 gallons of water.
Both plats were examined on March 18. No control of scale occurred.

University of California — Experiment Station

At San Jose, French prune trees were sprayed on February 15, 1940,
with no. 13A at 0.38, 4.0, and 10.7 gallons per 100 gallons of water.
These trees were moderately mossy and supported a moderate infesta-

TABLE 17
Control of Brown Apricot Scale, Seimas Orchard

Material and amount per
100 gallons of water

No. 13A, 3 pts

No. 13C, 3 pts

No. 13A, 3 pts. ; tank-mix oil, 2 gals. ;

blood albumin, 4 oz

No. 13C, 3 pts. ; tank-mix oil, 2 gals. ;

blood albumin, 4 oz

No. 9, 2 gals.; no. 9 emulsifier,

IK lbs

Dinitro
compound*

per 100
gallons of
of water

ounces
12
13.5

12.0

13.5

Control after spraying on the following dates

Nov. 28

per cent
72
■ ■t

• •t

• t
..t

On
Dec. 15

per cent
74
50

100

Jan. 15

per cent
74

99
100

On
Mar. 4

per cent
61
57

100

Average

per cent
70
64

100
98

*Dry-weight basis.

t These sprays were not applied on these particular dates.

PER CENT CONTROL
40 50 60

Fig. 2. — Control of brown apricot scale with dinitro compounds
alone and combined with oil.

tion of Italian pear scale. Counts made three weeks after spraying
showed that the 0.38 per cent application had killed none, the 4.0 per
cent application had killed 17 per cent, and the 10.7 per cent application
had killed 88 per cent of the scale.

Bul. 671] New Materials for Control of the Mealy Plum Aphid 25

At the Grace orchard near Santa Kosa, tests with material no. 9 at
1.0 and 1.8 gallons per 100 gallons of water were made on French prune
trees infested with Italian pear scale. No microscopic counts were made
on these plats, but examination with a hand lens six weeks after spraying
showed many scales still alive. This inspection indicated that few scales,
if any, had been killed by the spray.

The above tests indicate that these dinitro compounds, either alone
or with oil, are not highly effective against the Italian pear scale. As
indicated later, however, they are effective against lichens and algae.
The removal of these plants deprives the scale of their natural cover and
the subsequent mortality due to predators and adverse weather may be
high. This action was not measured during the course of this study.

EFFECT OF DINITRO COMPOUNDS ON COVERCROPS AND TREES

No general statement can be made forecasting the effect of dinitro
phenols and cresols on covercrops. The injury is most severe on young
plants in the rosette stage 12 and is less severe on plants that have devel-
oped stems. Different species of plants vary markedly in their suscepti-
bility to injury. The dinitro phenols and cresols used in this study
injured the covercrop in some instances. Injury was divided into five
classes with numerical ratings. Rating 1 was used to indicate very slight
damage and 5 to represent complete killing of most of the plants under
the sprayed trees. Ratings 2, 3, and 4 were intermediate and progressive
stages of injury. The following data on injury were taken :

Orchard and amount of material Rating of effect on

per 100 gallons covercrop

Barton orchard :

No. 9, 0.5 gal 2

No. 9, 1.0 gal 2

No. 9, 1.5 gals 4

No. 9, 2.0 gals 5

No. 3, 1.2 oz. 4- tank-mix oil, 0.25 gal 1

No. 3, 2.4 oz. 4- tank-mix oil, 1.0 gal 1

No. 3, 2.4 oz. 4- tank-mix oil, 2.0 gals 1

No. 3, 4.8 oz. 4- tank-mix oil, 1.0 gal. 4- caustic soda, 4.0 oz 1

No. 3, 4.8 oz. 4- tank-mix oil, 1.0 gal. 4- oxalic acid, 4.0 oz 3

No. 3, 2.0 oz. 4- tank-mix oil, 2.0 gals 2

No. 3, 4.0 oz. 4- tank-mix oil, 2.0 gals 1

No. 3, 2.0 oz 1

No. 3, 2.0 oz. 4- caustic soda, 4.0 oz 1

No. 3, 2.0 oz. 4- oxalic acid, 4.0 oz

No. 12, 2.0 gals 1

No. 14, 12.0 oz 5

No. 13A, 8.0 oz 4

No. 10, 8.0 oz 4

^Westgate, W. A., and R. N. Raynor. A new selective spray for the control of
certain weeds. California Agr. Exp. Sta. Bul. 634:1-36. 1940.

26 University of California — Experiment Station

Orchard and amount of material Rating of effect on

per 100 gallons covercrop

McDonell orchard (averages of duplicated plats) :

No. 13A, 8.0 oz 1.5

No. 13A, 12.0 oz 2.0

No. 13A, 8.0 oz. + tank-mix oil, 1.5 gals 2.0

No. 13A, 12.0 oz. + tank-mix oil, 1.5 gals 3.0

No. 13A, 8.0 oz. -f oil emulsion, 1.5 gals 3.0

No. 13A, 12.0 oz. + oil emulsion, 1.5 gals 4.5

No. 13C, 9.0 oz 2.0

No. 13C, 9.0 oz. + oil emulsion, 1.5 gals 4.0

No. 13C, 13.5 oz. + oil emulsion, 1.5 gals 5.0

No. 13H, 9.0 oz 5.0

No. 13H, 13.5 oz 4.5

No. 11, 7.3 oz 1.0

No. 11, 11.0 oz 1.5

No. 11, 14.6 oz : . . . . 2.0

No. 11, 7.3 oz. + oil emulsion, 1.5 gals 4.0

No. 9, 2.0 gals 5.0

On the Barton orchard, the covercrop consisted of natural growth —
mostly miner's lettuce, wild grasses, and a few scattered mustard plants.
No fall irrigation was applied. The spraying was done February 20,
1939, and data on covercrop were taken on March 7, 1939. On the
McDonell orchard, which was fall irrigated, the covercrop was vetch.
The spraying was done on February 12, 1940, and data on covercrop
were taken on March 19, 1940.

On the Seimas orchard the covercrop was horse bean (faba bean, or
broad bean) . A good stand was present at the time of spraying on March
4, 1940. The damage to this plant caused by either no. 13A or 13C at
3 pints combined with 2 gallons of tank-mix oil per 100 gallons of water
was very severe. When these materials were used alone at that concen-
tration, the damage was moderate to severe. Material no. 9 at 2 gallons
per 100 gallons of water produced very slight injury.

Stimulation of the trees as indicated by an advance in time of bloom-
ing was not observed in any of the plats. Maximum effect of this type
is obtained from petroleum-oil sprays when applied about the middle
of January. The majority of plats used in this study were sprayed in
February, and hence were probably applied too late to affect the time
of blooming.

No damage to the trees was caused by any of the sprays when applied
in the full dormant period. At San Jose, French prune trees sprayed
with no. 13A at 4.0 and 10.7 gallons per 100 gallons of water on February
15 showed no damage.

Dinitro phenols and cresols cannot be applied after the buds open
in the spring. Some French prune trees at San Jose were sprayed on

Bul. 671 ] New Materials for Control of the Mealy Plum Aphid 27

March 25. At this time about 35 per cent of the blossoms were in full
bloom and new leaves were about % inch long. One tree was sprayed
with no. 13 A at 4 pints per 100 gallons of water; one tree was sprayed
with no. 13A, at 4 pints and petroleum-oil emulsion, 2 gallons per 100
gallons of water ; one tree was sprayed with material no. 9 at 2 gallons
per 100 gallons of water. All three sprays produced damage to flowers
and leaves. The most severe damage was caused by no. 13A and oil.

Early-fall applications of dinitro phenols and cresols present interest-
ing possibilities. Two old French prune trees at San Jose were sprayed
with no. 13A at 3 pints per 100 gallons of water on November 28. Rainfall
prior to this date was :

Date Rainfall, in inches

Oct. 5 0.50

Oct. 6 16

Oct. 24 13

Nov. 25 0.17

This was soon lost by evaporation, and since no fall irrigation was
applied to these trees, they were fairly dry at the time of spraying. No
damage to the trees resulted from this spraying. On the Seimas orchard,
four trees were sprayed on the same date with the same spray mixture.
This orchard received the same rainfall as above, but in addition, was
fall-irrigated about October 10. No damage occurred to the trees as a
result of the sprays.

Early fall applications of petroleum-oil sprays applied while the
trees are dry are known to be injurious, and probably petroleum oil with
dinitro phenols or cresols in solution will be more dangerous to the trees.
From the above meager evidence, it seems that dinitro phenols and
cresols, without oil, may be applied when the trees are dry. In those years,
therefore, when fall rainfall is slight, and trees drop their leaves early,
it may be possible to spray while the ground is dry. This will have the
double advantage of ease of application, that is, freedom from mud, and
since covercrop seeds will not yet have germinated, no damage to the
covercrop can occur. Growers interested in fall applications of dinitro
sprays, before appreciable rain has fallen, should test this method in a
small way the first year to determine whether or not injury will result.

Dinitro phenols and cresols have considerable value in cleaning mossy
trees. The susceptibility of lichens and algae to injury seems to vary
considerably with the species of plant, the dinitro compound, and the
physiological conditions of the plants probably as determined by weather
conditions, chiefly rainfall and fog. It is believed that repeated annual
spraying, at dosages herein recommended for mealy-plum-aphid control,
will satisfactorily clean the trees.

28 University of California — Experiment Station

CARE IN HANDLING DINITRO CUE SOLS AND PHENOLS

Sodium dinitro-6>-cresolate (proprietary 20 per cent mixture in water)
is marketed in 1-gallon cans, which are about half full of solid material
that settles to the bottom. Before a representative sample is poured from
the can, the sodium dinitro-o-cresolate must be unif ormily suspended in
the solution. If the full cans are placed upside down on the spray rig,
vibration and movement of the rig will wash the heavy material from
the bottom of the can and deposit it loosely against the lid of the inverted
can. When the lid is removed, the solid material is then much more easily
mixed with the solution.

When it is allowed to dry completely, in thick layers or chunks, it is
highly flammable. Care must be taken, therefore, to avoid spilling the
concentrate around buildings; and spray rigs should be thoroughly
washed at the conclusion of the spray work. It should not be left in open
cans and allowed to dry. This material is a dye with a particular affinity
for woolen cloth. When strips of cloth were dyed in a saturated solution
of this chemical and dried, they burned more slowly than untreated
cloth.

The dinitro phenols and cresols discussed herein will dye human skin
and hair yellow. This can be removed only with difficulty by repeated
washings with soap.

SUMMARY

This study pertains exclusively to winter sprays, applied when the
trees are fully dormant, for the control of the mealy plum aphid, Hyalop-
terus pruni (Geoff.), which is present on the trees during the winter, in
the egg stage. Observations on scale control and effect on covercrop are
included.

Preliminary studies eliminated several diverse materials, and nar-
rowed the possibilities to certain dinitro compounds. Two of these,
namely, dinitro-o-cyclohexylphenol, and sodium dinitro-o-cresolate were
studied extensively.

Four per cent dinitro-o-cyclohexylphenol dissolved in petroleum oil
(material no. 9) and emulsified as a tank mix yields satisfactory control
when used at 2 gallons of this solution per 100 gallons of water.

Twenty per cent sodium dinitro-o-cresolate (material no. 13A), used
as a solution in water, yields a satisfactory control when used at 3 pints
(12 ounces dry weight) per 100 gallons of water.

Dinitro-o-cyclohexylphenol without oil (material no. 3) yielded better
control than when oil was used with it. When tested in eastern, paraffin-
base vs. western, asphalt-base oils, no difference in efficiency was found.

Dinitro-o-cyclohexylphenol (material no. 3) was tested in acidic, in

Bul. 671 ] New Materials for Control of the Mealy Plum Aphid 29

basic, and in unmodified water, and the efficiency increased with an
increase in pH.

Material no. 9 (a proprietary mixture of dinitro-o-cyclohexylphenol
in dormant oil) was most efficient in unmodified water, less efficient in
basic, and least efficient in acidified water.

Sodium dinitro-o-cresolate (20 per cent by weight), as marketed
(material no. 13A), contains 10 per cent "penetrant," or wetting agent.
Tests of sodium dinitro-o-cresolate containing 0, 5, and 10 per cent by
weight of wetting agent indicated that the wetting agent slightly reduces
the efficiency of this material.

Sodium dinitro-o-cresolate combined with oil was reduced in efficiency
— the less oil, the lower the efficiency until an undetermined low was
reached. The efficiency of this material with 2 gallons of oil per 100
gallons of water, however, nearly approximates that of the material
alone.

Sodium dinitrophenolate (material no. 11), was markedly inferior to
sodium dinitro-o-cresolate (material no. 13A).

The proprietary solution of 4 per cent dinitro-o-cyclohexylphenol in
petroleum oil (material no. 9) used at 1 gallon per 100 of water yields
a satisfactory control of brown apricot scale.

Dinitro-o-cyclohexylphenol at 2 and 4 ounces per 100 gallons of un-
modified, of acidic, or of basic water failed to yield a satisfactory control
of scale.

Dinitro-o-cyclohexylphenol at 4 ounces with 2 gallons of oil per 100
gallons yielded a satisfactory control of brown apricot scale. The addi-
tion of acid or base to the above mixture decreased the kill of scale.

Sodium dinitro-o-cresolate (20 per cent by weight) used alone at 3
pints per 100 gallons did not satisfactorily control brown apricot scale.
When this concentration was used with 2 gallons of oil per 100 gallons
of water, the control of scale was satisfactory.

Neither of these dinitro compounds was effective against the Italian
pear scale.

Both of these compounds injure the covercrop, and the extent of the
injury is determined by many variable factors.

No damage to the trees resulted from any dormant applications.
Severe injury occurred when these compounds were applied to trees
which were starting to bloom.

Early-fall applications of dinitro phenols and cresols, without oil,
present interesting possibilities in special cases.

30 University of California — Experiment Station

ACKNOWLEDGMENTS

The authors wish to express their appreciation to the several growers
mentioned in this paper, all of whom contributed valuable aid. The
Penryn Fruit Company assisted in tests on their orchards, Franklin,
Highland, Bellevue, Palms, and Club. Assistance was rendered through
Work Projects Administration Official Project No. 465-03-3-168.

12m-ll, '42(3176)