Concentrate spraying in deciduous orchards

Publication 1020 February 1958

CONCENTRATE SPRAYING
IN DECIDUOUS ORCHARDS

by
JAMES MARSHALL

CANADA DEPARTMENT OF AGRICULTURE
£30 u, OTTAWA, ONTARIO

P. IOZLO

Publication 1020 February 1958

CONCENTRATE SPRAYING
IN DECIDUOUS ORCHARDS

by
JAMES MARSHALL

Entomology Laboratory
Summerland, British Columbia

SCIENCE SERVICE, ENTOMOLOGY DIVISION

CANADA DEPARTMENT OF AGRICULTURE

OTTAWA, ONTARIO

Price: $1.00

4500-23139-2:58
95319—1

CONTENTS

Page

Introduction 3

History of concentrate spraying 5

Types of sprayers 7

Effectiveness of concentrate spraying 12

Spray injury 14

Factors affecting efficiency of sprayers 15

Air stream 15

Blower scroll and air vent 15

Liquid manifold 16

Atomization of spray liquid 17

Type of nozzle 20

Angle of emission of spray liquid 22

Rate of travel 23

Spray coverage 25

Surface-active adjuvants (surfactants) 26

Physical characteristics of spray liquid 26

Homogeneity 26

Volatility 27

Viscosity and density 27

Surface activity 28

Experiments with surfactants 29

Type and quantity of surfactant necessary 31

Function of surfactants 33

Contamination of soil by spray chemicals 33

Present status of concentrate spraying 34

Assessment of sprayers 36

Recommendations for spraying 40

Summary 42

Acknowledgments 43

References 44

INTRODUCTION

Concentrate, or low-volume, spraying is a more complex procedure than
the high-volume method that it has replaced in British Columbia, and which
it is in process of replacing in a number of other fruit growing areas of the
world. The new practice has been in commercial use in orchards for less than
ten years, but has been the subject of a considerable number of technical and
popular articles. Since none of these articles has dealt with the subject as a
whole, it is timely to bring together and discuss the varied aspects of concen-
trate spraying in a single publication.

This bulletin is written for enquiring fruit growers as well as for technical
workers. It deals as directly as possible, therefore, with the more distinctive
features of concentrate spraying. Special consideration is given the use of
surfactants because they are likely to be used widely in concentrate spraying
though they are now used only in British Columbia. The literature on concen-
trate spraying is reviewed and pertinent information is added from experiments,
or from experience, in British Columbia. Except for spray recommendations,
tabular material is omitted.

In the approach to the problem it was necessary to deal empirically with
many of the important features of the work. Large differences were sought;
small differences were disregarded. As the British Columbia fruit industry
was the first to mechanize its spraying operations with concentrate equipment,
the development of the procedure should be of interest, and possibly of help,
elsewhere.

In the 67-year history of the British Columbia tree fruit industry it is
doubtful whether any production method has contributed so much to the
welfare of the fruit grower as concentrate spraying. The new method of
applying pesticides reduced the cost of controlling insects and diseases to about
half that of the high-volume, hand-gun spraying of earlier days, and trans-
formed a foul and irksome job into a relatively simple, routine operation. Five
years after concentrate spraying was officially approved, it had been adopted
by most of British Columbia's 3,500 fruit growers.

The course of spraying methods in other fruit growing areas of North
America indicates that the orchardists of British Columbia have mechanized
their spraying operations with unusual speed and unanimity. There was little
debate about the relative merits of high-volume and low-volume spraying.
Reasons for the growers ready acceptance of concentrate spraying were:

(a) British Columbia's orchards are far removed from the principal fruit
markets. Since high, fixed freight charges must be added to the cost of produc-
tion, every care has to be taken to keep the cost of production to a minimum.

(b) As the orchards average less than 10 acres in area, most of them cannot
support heavy capital investment, e.g., large and expensive air-blast sprayers.

(c) Few of the orchard tractors are capable of hauling heavy spray equipment
at slow speed in the predominantly hilly orchards, (d) The horticulturists of
the area are averse to hauling very heavy equipment through the orchards
because of suspected ill effects of soil compaction, (e) Although many of the
fruit trees of the area are about 20 feet high and 30 feet in diameter, they
are pruned to allow adequate air circulation and entry of light; hence they
are adapted to concentrate spraying with modestly powered machines, (f) Local

95319— li

manufacturers, who had no previous experience with spray applicators and
hence nothing to unlearn, sensed the significance of the new method of spraying
and quickly built the type of equipment that had been officially approved, and
that the growers were beginning to demand, (g) Official advisers were nearly
unanimous on the merits of concentrate spraying.

Nowadays the literature on orchard spraying is characterized by such
trims as bulk spraying, high-volume spraying, low-volume spraying, high-
pressure spraying, air-blast spraying, mist spraying, concentrate spraying, and
so forth. In England, where there is special interest in ultra low-volume
spraying (3 to 10 gallons per acre), it has been proposed that what is generally
referred to as concentrate spraying in North America should be more precisely
described. Specific names should be given to spraying at dosages of up to 20
gallons per acre, 20 to 50 gallons per acre, and over 50 gallons per acre.

A simpler way of dealing with the confused terminology is to group orchard
air-blast sprayers into two categories; high-volume sprayers and low-volume,
or concentrate, sprayers. On this basis, a high-volume sprayer is one that
induces dripping of spray liquid from the trees; a low- volume, or concentrate,
sprayer is one that does not induce dripping. This distinction is advanced
because perhaps the most important factor in orchard spraying is whether drip,
or run-off occurs. The character of a spray deposit alters radically after the
spray droplets coalesce and begin to move downwards. From a discrete, or
spotted, deposit a blotched, or filmed, deposit takes form. Particularly in the
control of fungus diseases, as discussed later, the character of the deposit is
important. Equally important, spray injury to foliage or fruit is commonly
intensified when the drip-point is almost reached or passed. If the trees are
dry, the drip-point occurs in a mature British Columbia apple orchard when
more than about 75 imperial gallons of spray liquid per acre are applied by an
efficient concentrate sprayer. Inefficient machines, however, by heavily over-
spraying the lower limbs, can induce dripping with a considerably lower
per-acre output. By the definition, such machines, though they may apply
60 gallons, or even less per acre, are not concentrate sprayers.

HISTORY OF CONCENTRATE SPRAYING

What seems to have been the first serious attempt to get rid of the high-
pressure spray gun was made in 1925 by the Niagara Sprayer and Chemical
Co., Middleport, New York. In that year the company introduced the Rex
Liqui-Duster — (Private communication, Niagara Sprayer and Chemical Divi-
sion, F.M.C., Middleport, New York, U.S.A.). The Liqui-Duster was equipped
with a centrifugal blower and a low-pressure, centrifugal pump, both powered
by a 12-horsepower gasoline engine. The machine developed an air stream
with a velocity of 150 miles per hour at the nozzle of a four-inch, manually
operated, metallic hose. The spray liquid was pumped into the air stream at
a pressure of 40 pounds per square inch. The Liqui-Duster never became
popular despite its appeal to the mechanically minded. In those days labor
was cheap, and perhaps the ear-splitting wail of the blower was disconcerting.

In 1933 Parker (49) described a machine that atomized an oil solution
of an insecticide and distributed it at 2.5 U.S. gallons per acre by means of
an air stream from a fixed vent. The machine was successfully used in vine-
yards and prune orchards to control "leaf-hoppers, the brown apricot scale,
red spider, and thrips." Oddly enough, although this pioneer work on con-
centrate spraying was done in California, the fruit growers of that state appear
to be more hesitant about adopting the method than those in most other fruit
growing areas.

Seven years later, Potts (51), who may aptly be termed the father of
concentrate spraying, reported on the use of concentrated spray mixtures on
forest, shade, and orchard trees. Using eight gallons of spray liquid per acre,
he claimed satisfactory control of pests, and less foliage injury than from
high- volume spraying. In 1942 French (19) mentioned that ground sprayers
of the compressed-air type, ground sprayers of the blower type, and aircraft
had been successfully used to apply concentrate spray liquids to various crops.

Potts and Friend (53) worked with a fixed- vent machine having an air
output of 8,730 cubic feet per minute at a velocity of 124 miles per hour. The
machine was fitted with a gear pump developing a pressure of 80 pounds per
square inch. Reporting in 1946, these authors appear to have been the first
to apply a clockwork mechanism to the study of droplet sizes and spray deposits
in concentrate spraying. Their device exposed coated glass slides to the spray
mist for predetermined periods of time.

Much of the pioneer work in concentrate spraying was done at Cornell
University. Pratt (55) described a machine known as the Cornell experimental
spray-duster that was the outcome of experiments begun in 1940. This machine
was eventually produced commercially, and operated with success by many
eastern and middle-western fruit growers. It featured a large, fixed "fish-
tail" so constructed as to direct the air-stream upwards through the trees at
an angle of about 45 degrees. The Cornell type of concentrate sprayer is
considerably larger and more powerful than those manufactured in British
Columbia.

Brann (7, 10), has been responsible for a good share of the research on
concentrate spraying. Having designed a spray nozzle for the purpose, he
experimented with ultra low-volume applications. Using dormant oil at con-
centrations varying from 100 per cent downwards, he concluded that 25 per cent
oil represented an optimum concentration. In controlling the European red

mite, Metatetranychus ulmi (Koch), Brann et al. (8) determined that oil
applied as a mist at 25 per cent concentration was two to three times as
effective as an equal quantity of oil applied in a high-volume spray.

From Michigan, Mitchell (40, 42) reported on concentrate spraying
investigations begun in 1947, and on the commercial application of the
procedure. The fruit growers in that state have had generally satisfactory
results from concentrate spraying, perhaps because they have not lacked
authoritative information on the importance of adequate pruning, and on the
relation of per-acre output, and rate of travel, to size and type of machine.
The trend in Michigan is to an increased concentration of toxicants.

Burrell (13) noted that, in eastern New York State, concentrate spraying
was the prevailing method; but in the western part of the state most of the
fruit acreage was sprayed with large, high-volume machines. He warned
against the purchase of conversion units ("hang-on" blowers) mounted on
old, high-pressure sprayers, pointing out that such devices were generally
inadequate.

A word of criticism of official caution about concentrate spraying was
expressed in 1951 by Ring (57), a grower operating 200 acres of apple orchard
in eastern United States: "In my travels round the country. . . there are many
growers much confused about mist concentrates. They are afraid to try them.
I believe this was good in the past but now growers need the advantages of
concentrates more than ever to help to keep down the cost of production".

~je*.

Figure 1 — Okanagan experimental sprayer, the prototype of concentrate sprayers in

British Columbia.

The first Canadian work on concentrate spraying in deciduous orchards was
mentioned briefly by Marshall in 1946 (35). The following year Marshall and
Miles (36) described experiments in applying spray concentrates with five types
of mobile machines. Although none of the machines was satisfactory the authors
wrote; "there is little reason to doubt that conventional, high-pressure sprayers
will shortly be supplanted by light, high-speed equipment". After listing what

they considered the necessary features of a light, "automatic" sprayer, they
mentioned that an experimental machine embodying these features was to be
built at once. In a paper presented to the Seventh Pacific Science Congress in
1949, Marshall and Miles (38) described the performance of the Okanagan
experimental sprayer (Fig. 1). It had proved so successful that it was serving
as a prototype for two commercial concentrate sprayers being built in British
Columbia.

Progress in concentrate spraying in Ontario and the Maritime Provinces
of Canada, and also in Great Britain, Europe, and the Antipodes, has been
discussed by Marshall (39). In Australia and New Zealand, where machines of
Canadian design are now manufactured, the method is being rapidly adopted;
but in the other areas just mentioned, acceptance is slower. The same applies
to the western fruit growing areas of the United States. So far, little if any
work on concentrate spraying has been done in South Africa.

TYPES OF SPRAYERS

Concentrate sprayers may be grouped in three types: —

1. Air nozzle manually operated (two-man machines).

2. Air nozzle or nozzles mechanically oscillated or rotated.

3. Air nozzle fixed.

Types 2 and 3 are available for one-side and two-side spraying. They are
operated by one man, the tractor driver. Some manufacturers of large, high-
volume sprayers claim that, by fitting nozzles with very small orifices, their
machines become concentrate sprayers. As a rule such sprayers are equipped
with low-pressure, centrifugal pumps that, with the type of nozzle generally
used, are incapable of atomizing the spray liquid to the degree necessary for
safe and efficient concentrate spraying. Furthermore, the blowers of the large
machines produce an air stream of high volume but relatively low velocity,
and such an air stream is of no value in reducing the size of the spray droplets
unless the spray stream is forced directly into the air stream; generally that is
not the case.

Experience of the last ten years in British Columbia has shown the logic
of designing spray equipment to meet specific needs. There is no point in
using an expensive, two-ton machine to do a job that can be done well by a
relatively inexpensive machine of less than half the weight.

The concentrate sprayers now being manufactured in this province have
fixed air vents, and most of them are one-side machines. They look puny
indeed beside machines of the high-volume, air-blast type, many of which
are over twice as heavy and four times as powerful as the locally built ones.

Concerning sprayer design, Hoare (31) summed up the situation in these
words: "The world problem of spraying is contained in a room through which
you enter by three consecutive doors the keys of which are held separately by
the engineer, the chemist and the biologist, . . . the writer believes that, at the
moment [1952], the closed door which requires opening first is under the control
of the engineer . . .". A number of years previously Davies and Smythe-
Homewood (17) had written: "Manufacturers . . . have done much to introduce
improved machinery but the amount of time they can devote to research is
necessarily limited and so they tend to produce what is demanded by the
growers". To some extent that observation still holds; but the type of spray

8

applicator demanded nowadays in many fruit growing districts is conditioned
to a considerable degree by advertising, by the adequacy of local research in
spraying techniques, and by the current preoccupation with super-powered
and supersized equipment of all kinds.

Davies and Smythe-Homewood mentioned that it is logical to carry out
research in sprayer design in the heart of a fruit growing district where the
engineer can have the advantage of close collaboration with entomologists,
chemists, and technical advisers as well as fruit growers. It was under such
conditions that concentrate sprayers were developed in British Columbia
(Fig. 2). As reported by Marshall (39), a group of entomologists, chemists,
and horticulturists and, later, an agricultural engineer, teamed with machinists
in designing spray equipment to meet a specific need. The available information
on spray chemicals, how they are formulated and how they function, was taken
into account, as well as that on methods of atomization, and types of blowers
and gasoline engines. Abrasion and corrosion-resistant materials were exam-
ined, and consideration given to the most effective droplet sizes. Good
horticultural practice, and the economics of the fruit industry were kept in
mind. The outcome was a one-man sprayer capable of doing what the British
Columbia fruit growers wanted at a price most of them could afford.

Figure 2 — Entomology Laboratory, Summerland, British Columbia.

Since the introduction in 1949 of the first commercial concentrate sprayers
by two British Columbia manufacturers, and one United States manufacturer,
there have been many improvements in design (Fig. 3). The weight of the
single-side machines has remained under one ton, but they have become
lower and more carefully streamlined in order to pass more readily beneath
overhanging branches (Fig.4). They are available with either two- wheel or
four-wheel mounting. Although more expensive, the latter is preferred be-
cause of lighter draft, less tendency to compact the soil, and more nearly
uniform spray application when travelling over rough ground.

One of the more troublesome problems in concentrate spraying has been
corrosion and scaling of steel tanks, and consequent plugging of screens and
nozzles. The problem has been largely overcome by using stainless-steel or
fiberglass-plastic tanks.

Figure 3 — The first concentrate sprayer commercially built in British Columbia, in 1949.

Figure 4 — Turbine-type, one-side concentrate sprayer, 1955 model, made in

British Columbia.

95319—2

10

One of the British Columbia machines has a turbine-type blower producing
a linear-flow air stream of 6,500 to 7,000 cubic feet per minute at a velocity
of 105 to 120 miles per hour. The other has an axial fan that moves about
21,000 cubic feet of air per minute at 93 miles per hour (Fig. 5). When hauled
at the rate of 1 mile per hour both machines have given adequate penetration
of full-foliaged, well-pruned fruit trees up to 30 feet in diameter and 15 to 18
feet high.

Figure 5 — Axial-flow, one-side concentrate sprayer, 1956 model, made in

British Columbia.

Because of the importance of adequate atomization, piston-type, high-
pressure pumps are used on both Canadian-built machines in preference to
less expensive, low-pressure, centrifugal pumps or to gear pumps. The spray
nozzles are of the hollow-cone, swirl type and are fitted with orifice discs and
swirl plates made of that exceedingly hard substance sintered tungsten carbide.
One of the manufacturers has been fitting the pressure-relief valve with tung-
sten carbide inserts at the points of greatest wear. Although both machines
are equipped with air-cooled engines, the performance of an experimental
model fitted with a liquid-cooled, overhead-valve engine has been such as to
suggest that liquid-cooled engines may shortly be optional. In New Zealand
light, liquid-cooled, overhead-valve automobile engines, of British manu-
facture, have been giving satisfactory results with the turbine type of Canadian
concentrate sprayer.

To meet the requirements of some operators of large acreages "two-side"
machines are being built by both of the British Columbia manufacturers.
Unlike the "single-side" unit, which is generally operated somewhat beneath
the overhanging branches, the two-side machine must travel midway between
the two rows of trees. Consequently, unless the rows are less than 30 feet
apart, or the trees are of modest size, or are exceptionally well pruned, adequate

11

penetration of heavy foliage is more difficult to attain. Evidently somewhat
more than double the power input is necessary for equivalent penetration of
foliage (Figs. 6 and 7).

\V

'■>£,-

"k

iptr»

Figure 6 — Turbine-type, two-side concentrate sprayer with stainless steel tank,

1956 model.

Figure 7 — Axial-flow, two-side concentrate sprayer with fiberglass-plastic tank,

strainer and hood, 1956 model.

95319— 2i

12

EFFECTIVENESS OF CONCENTRATE SPRAYING

Courshee (15) sums up orchard spraying techniques thus: "As yet no
method and program has been shown to be successful on a sufficiently wide-
spread scale to be certain that it works under all conditions". Whether light,
concentrate sprayers will eventually displace heavy, high-volume machines
entirely is, of course, debatable. But, as greater attention is paid to the devel-
opment of less phytotoxic spray chemicals, as more information becomes avail-
able on sprayer design, and as more regional and local research is undertaken
to evaluate spraying procedures, doubtless the logic of using minimum quant-
ities of water to distribute spray chemicals will be ever harder to dispute.

Marshall and Miles (36) conducted experiments in British Columbia to
determine whether either wet or dry dusting is as effective against orchard
pests and diseases as concentrate spraying. They concluded that dusting was
inadequate. Evidently a similar conclusion was reached at Cornell University,
where Pratt (55) reported on an investigation of dusting versus concentrate
spraying begun in 1940.

That there are decided differences of opinion on the effectiveness of con-
centrate spraying, even within a limited area, is shown by reports from the
State of New York. Glass and Lienk (23) say: "Our data indicate that there
is no saving in material, and further, there is some indication that more
material may be required to get the same results that are obtained with dilute
spraying". But Burrell (13) points out that concentrate spraying is gaining
acceptance in New York State because of its savings in man- and machine-
hours.

In a study of the cost and effectiveness of spraying methods, Von Oppen-
feld et al. (63), also of New York, concluded that, regardless of type of
machine, pest control was inferior on trees over 20 feet high. Poor control was
frequently associated directly with excessive rate of travel. In other instances
it was indirectly associated with a very rapid output of spray liquid; a high
output tended to induce a hurried job. Concentrate spraying was the least
expensive method.

Garman (22) mentions that small, cheaply constructed concentrate spray-
ers have proved unsatisfactory, but well-designed mist blowers have given
just as good results as hydraulic, high-volume machines in Connecticut. He
does not favor automatically oscillated or rotated, air vents, considering that
they add little to the effectiveness of a sprayer although they complicate its
design.

In England, as in North America, there are differences of opinion on con-
centrate spraying. Beskine (5), for example, states that "single-shot", i.e.,
fixed air-vent spraying, is too wasteful and expensive. He favors the manually
operated nozzle of the two-man machine as developed in Holland and Great
Britain. Kearns (34), on the other hand, thinks that machines with "guided
nozzles" are of debatable value, the ultimate aim being the development of
fully automatic spray machinery. He emphasizes that growers who wish to use
automatic applicators should see that their trees are kept to a size within the
capacity of their spray equipment.

It is pointless to expect that a light, concentrate sprayer powered, for
example, with a 25-horsepower engine will be capable of producing adequate
spray coverage in apple trees 25 feet high and 35 or 40 feet in diameter. That
is a job for a large, high-powered machine and, preferably, for high-volume
application. When such very large trees are poorly pruned, or when their
branches sweep the ground, the problem is doubly difficult; for it is under such

13

conditions that apple scab and many insects and mites nourish best, and spray
penetration is poorest. In Michigan, Mitchell (41) has repeatedly stressed to
the owners of concentrate sprayers the importance of good pruning. He re-
ported no reduction in yield from adequately pruned trees, but, as compared
with high-volume spraying, a reduction in the amount of spray chemicals in
concentrate spraying, and lower cost of spray application.

Using equal quantities of insecticide per acre, Waddell and McArthur (64)
compared spray deposits on British Columbia apple trees from thorough high-
volume, hand-gun spraying and those from concentrate spraying with a 25-
horsepower turbine machine. The trees, 25 feet in diameter and 20 feet high,
were of two types; some were pruned, some not pruned. Waddell and Mc-
Arthur summarized thus: (a) In the dormant period, oil deposits in the non-
pruned trees were equal to those in the pruned trees, whether hand-sprayed or
concentrate-sprayed, (b) With an equal quantity of oil per acre, concentrate
spraying produced treetop deposits of dormant oil four times as great as hand
spraying, (c) After the foliage had fully developed, treetop deposits of DDT
from concentrate spraying were about 50 per cent lighter in non-pruned trees
than in pruned trees; with the hand spraying there was no difference. (d)
Despite the reduction in treetop deposits of DDT from concentrate spraying in
non-pruned trees, the deposits were, nevertheless, as heavy as from hand
spraying with an equal per-acre quantity of DDT. The authors concluded that
concentrate spraying is a more efficient means of applying spray chemicals
than hand spraying, and that concentrate spraying emphasizes the importance
of good pruning.

Cutright (16) found that the control of orchard mites in Ohio was as
good from an acaricide suspension applied at 100 gallons per acre as at 1,000
gallons. Experimental work reported by Marshall and Miles (38), later work
at Summerland (unpublished), and commercial results have shown that an
efficient concentrate sprayer, well operated, provides as good control of the
most important pests of British Columbia orchards as commercial high-volume,
hand-gun spraying. Among those pests are the European red mite, Metatetrany-
chus ulmi (Koch); the two-spotted mite, Tetranychus telarius (L.); the yellow
spider mite, Eotetranychus carpini (Oudms.); the brown mite, Bryobia arborea
M. & A., formerly not distinguished from the clover mite, Bryobia praetiosa
Koch; the McDaniel mite, Tetranychus mcdanieli McG.; the codling moth,
Carpocapsa pomonella (L.); the San Jose scale, Aspidiotus perniciosus Comst.;
lygus bugs, the peach twig borer, Anarsia lineatella ZelL; the apple aphid,
Aphis pomi DeG.; the woolly apple aphid, Eriosoma lanigerum (Hausm.); the
black cherry aphid, Myzus cerasi (F.); and the pear psylla, Psylla pyricola
Foerst.

On the other hand, the control of apple scab and of apple powdery mildew
is not so good as would be expected from the high deposits of fungicides that
are obtained. Pratt (56) noted that, in New York State, the control of apple
scab with an efficient concentrate sprayer was as good as with hand spraying,
but the fungicide deposits were much higher, hence evidently less efficient.
Presumably the type of spray deposit most effective in controlling fungus
diseases differs from that needed to control insects and mites. This point is
discussed further under the heading "Surface-active Adjuvants".

Relatively little work appears to have been done on concentrate spraying
in citrus groves. In Florida, Griffiths et al. (26) compared insect control on
orange trees from high- volume spraying and concentrate spraying (£ of
high-volume). Control of rust mites and scale insects was equally good by
the two methods. In Australia, on the other hand, Mr. C. Brickhill, Department
of Agriculture, New South Wales, (private communication) found that an
efficient concentrate sprayer of the turbine type was measurably less effective

14

than high-volume spraying in controlling the California red scale, Aonidiella
aurantii (Mask.) with oil application. Brickhill's findings have some support
in experiments in British Columbia against the San Jose scale, Aspidiotus
perniciosus Comst., on apple. There is evidence that heavy infestations of
that pest may be more effectively dealt with by applying 150 gallons of spray
liquid per acre from four sides of each tree than 75 gallons from two sides, the
amounts of toxicant per acre being the same. Presumably that is because it
is difficult to wet well-protected insects in the larger crotches of the trees. Light
to moderate infestations of the San Jose scale, however, have been adequately
controlled at the smaller dosage.

SPRAY INJURY

Critics of concentrate spraying generally disapprove of it on two counts: It
is not sufficiently effective; it is too likely to cause spray injury. Perhaps the
first criticism arises from lack of information. It is not generally appreciated
that many of the so-called concentrate sprayers, or conversion or attachment
units now in use, are incapable of applying concentrate sprays (less than 75
gallons per acre) safely or uniformly. They were evidently manufactured
and sold on the assumption that concentrate spraying merely means decreased
output of spray liquid, and correspondingly increased concentration of spray
chemical; and that almost any makeshift equipment capable of projecting air
and liquid simultaneously can be called a concentrate sprayer. Fortunately
those misconceptions are being corrected; but a certain amount of poor equip-
ment is still being sold to growers who are more concerned about low cost than
efficiency.

As for spray injury the evidence is not entirely one-sided. Spray
chemicals that have a tendency to be phytotoxic may be particularly likely to
cause injury at high concentration. Certainly they should not be applied by
so-called concentrate sprayers having poor atomization, faulty distribution of
spray liquid in the air stream, inadequate blowers, or inadequate agitation. But
the best of today's concentrate sprayers, properly operated, are capable of
handling any of the spray chemicals in general use for high-volume spraying.
There is another consideration: in view of the wide selection of acaricides,
insecticides, and fungicides now available, it is questionable whether it
should be necessary to use any that are known to be hazardous to the tree,
to the operator, or to the consumer of the fruit.

Let us look now at the other side of the evidence. Ingerson (33), referring
to the effects of standard spray schedules, reported less injury from concentrate
spraying than from dilute spraying. Mitchell (41) mentioned that fruit rus-
setting decreased with increased concentration of spray chemicals, and Harley
(28) agreed. Moore (44) found that undiluted lime-sulphur, applied to apple
trees as very fine droplets, caused no injury; applied as a spray of larger drop-
lets, it caused pronounced injury.

It may seem remarkable that lime-sulphur, that excellent but caustic
insecticide-acaricide-fungicide of long standing, should be more likely to cause
injury to fruit or foliage if applied highly diluted than highly concentrated, at
the same per-acre dosage. Evidently it is entirely a matter of the rate of
drying of the spray deposit; the sooner the spray deposit dries the less the
likelihood of injury by lime-sulphur. A tree drenched by high-volume spray-
ing takes considerably longer to dry than one that has been sprayed by the
fine mist of a concentrate machine. The observation that the concentration
of lime-sulphur may have little to do wTith spray injury was made in British

15

Columbia in 1947 with spray concentrates containing from 10 per cent to 20 per
cent lime-sulphur of 32° Be. gravity, compared with high- volume spraying
with one per cent lime-sulphur; that observation has been verified repeatedly.
Needless to say, concentrated lime-sulphur should never be applied to wet
trees.

FACTORS AFFECTING THE EFFICIENCY OF SPRAYERS

Air Stream

Concentrate sprayers are equipped with either of two general types of
blowers, axial-flow or centrifugal. Axial-flow blowers vary in form from
few-bladed to multibladed, and from what is commonly considered a typical
fan to an air turbine. An axial-flow blower delivers the air parallel to its
axis or shaft; consequently, if the air stream is directed into the double vent
of a two-side sprayer, the characteristics of the two halves of the air stream
are similar. As the number of blades is increased, and the clearance between
rotor and casing diminishes, the characteristics of the air stream change.
Static pressure increases and turbulence decreases until, with the multibladed
air turbine, what has been referred to as a "hard", or linear-flow, air stream
is produced. Experiments at Summerland have indicated that such an air
stream penetrates heavy foliage better than a turbulent air stream of equal
volume.

Centrifugal blowers are characterized by the fact that they deliver the
air radially. Since the air comes off the tips of the blades there is a tendency
to pulsation and, with two-sided blower scrolls, to an uneven delivery; the
air tends to travel upwards on one side of the machine and downwards on the
other, in the direction of the blower's rotation.

Opinions differ as to the most desirable air velocity and air volume for
applying spray concentrates. When spraying to one side in a mature 30-foot
planting of apple trees, with an output of 12,000 to 20,000 cubic feet of air
per minute, a minimum air velocity of 90 miles per hour appears to be desirable.
With an output of only 7,000 cubic feet of air per minute the minimum velocity,
evidently, should be at least 110 miles per hour, and the air stream should be
of the linear-flow type.

Some workers, notably in California, have expressed the opinion that an
efficient spray job demands the complete displacement of the air within the
outline of the tree. Akesson (1) has calculated that, at a speed of one mile
per hour, an air output of 5,000 cubic feet per minute is required for 10-foot
trees, 20,000 cubic feet for 20-foot trees, and 50,000 cubic feet for 30-foot trees.
Such is the reasoning behind the use of the huge, high-volume, air-blast
sprayer of which Beskine (5) is critical. As he puts it: "They are designed to
saturate the whole of the atmosphere around the trees. This may appear
impressive to the uninitiated but it is not, .... Effective blast spraying can be
obtained with a modest expenditure of fuel, a reasonably small engine, and
little wastage of chemicals". Byass (6) agrees with Beskine. Experiments
in Great Britain, he writes, indicate that a high-volume, low-velocity air stream
is not necessarily better than a low-volume, high-velocity air stream in
producing good spray coverage. The Summerland work supports Beskine
and Byass; it is discussed later under the heading "Rate of Travel".

Blower Scroll and Air Vent

The design of the air vent plays an important part in the performance
of an orchard concentrate sprayer; but air vents vary so widely in shape and
in dimensions that more research is apparently needed in relating type of air

16

ven.1 to type of blower. Some machines, e.g., Kiekens Whirl-vind (Holland)1
and R.S.M. (Denmark)2, employ a stationary air vent made up of several
circular orifices, one above the other. An American machine (Lawrence
Mist-o-matic)8, uses three circular vents mounted on a rotating head. Another
American machine (Iron Age)4 uses a fixed "key-hole" type of air vent, the
middle part with a wider cross section than the ends; a Canadian machine
(Turbo-Mist)"' has a somewhat similar air vent. Seen from front or rear, most
air vents are of the arc-of-circle type, but a very efficient concentrate sprayer,
the Hardie Orchard Mist", is fitted with a projecting rectangular air vent eight
feet long and four inches wide, that is carried at a 45-degree angle to the
vertical. The Turbo-Mist of Australia7 and New Zealand* uses a similar but
smaller air vent, as does the Air Mist of Australia1'.

It has been claimed that good penetration of foliage by an air stream is
assured by an oscillating air vent, as on the American-made Myers10 con-
centrate sprayer, a machine on which the entire blower scroll is oscillated
through an arc of some 30 degrees. The Myers machine, as do most other
concentrate sprayers, delivers air at right angles to the line of travel; but the
Kiekens Whirlwind, which uses more highly concentrated spray mixtures,
delivers the air at a distinct angle to the rear. The manufacturers claim that,
otherwise, there wTould be a risk of overspraying the lower parts of the trees.
The Trump concentrate sprayer (Canada)11 directs the air stream at about
a 10-degree angle to the rear.

Referring to the experimental concentrate sprayer developed at Cornell
University, Parker and Pratt (47) emphasize the importance of directing the
air stream at approximately a 45-degree angle to the vertical. They found that
a horizontal delivery tended to drive the outer branches backwards against
the inner ones, whereas a vertically directed air blast resulted in excessive
under-leaf spray deposition. They contended, furthermore, that the spray-
should be directed exactly at right angles to the line of travel. Marshall
and Miles (38), arrived, independently, at the same conclusions. Their
Okanagan experimental sprayer had, in fact, air delivery very similar to that
of the Cornell machine except that the volume of air was little more than one
third as great. On the other hand, the Okanagan sprayer was designed to
operate at a speed of one mile per hour in a mature 30-foot planting, whereas
the Cornell one was operated at two to three miles per hour. The actual
volumes of spray-laden air to which the trees were subjected were, therefore,
fairly similar.

Liquid Manifold

In the early days of air-blast spraying, hydraulic machines with fixed
air vents were usually fitted with multi-nozzled liquid manifolds. Although,
in those days, they were a nuisance from the standpoint of nozzle obstruction,
multi-nozzled manifolds, with small disc orifices, were considered necessary
for adequate atomization. The work of Davies and Smythe-Homewood (17),

^iekens-Whirlwind-Holland, Bommelweg 43-44, Wadenoyen, Holland.

2R. Sigvardt Motorfabriken, Orehoved, Denmark.

'Lawrence Aero-Mist Sprayer Company Incorporated, Greenfield, Massachusetts, U.S.A.

■*A. B. Farquhar Division, Oliver Corporation, York, Pennsylvania, U.S.A.

•r,Okanagan Turbo Sprayers Limited, Penticton, B.C., Canada.

"Hardie Manufacturing Company, Hudson, Michigan, U.S.A.

7Ronaldson Brothers & Tippett Limited, Ballarat, Victoria, Australia.

8Fruit Growers Chemical Company, Port Mapua, Nelson, New Zealand.

"Metters Limited, Mile End, Adelaide, Australia.

10F. E. Myers & Brothers Company, Ashland, Ohio, U.S.A.

"Trump Sales Limited, Oliver, B.C., Canada.

17

Taylor (62), and French (19) had shown, however, that within practical
limits the size of the orifice of a swirl nozzle has little or no bearing on the
degree of atomization of the spray liquid. The point was investigated by
Messrs. D. B. Waddell and J. M. McArthur (unpublished work) at Summerland.
They fitted an experimental turbine sprayer with a ten-nozzle manifold, and,
by blocking off certain nozzles and increasing the orifice diameter of others,
examined various nozzle arrangements. They concluded that a three-nozzle
arrangement was capable of producing an effective spray pattern. Since the
cost of a three-nozzle manifold is considerably less than that of a multi-nozzle
one (tungsten carbide swirl plates and orifice plates are expensive), and since,
because of large orifices in two of the three nozzles, the three-nozzle manifold
is less likely to give trouble from blockage, it is now standard equipment on
one of the Canadian-built concentrate sprayers. The other sprayer is fitted
with a five- or six-nozzle manifold.

In spraying large fruit trees it is important that the amount of spray liquid
directed at the upper branches be considerably greater than that at the lower
branches — according to Brann (10), five to six times as much and, according
to Moore et al. (43), perhaps 10 times as much. In order to ensure adequate
treetop deposits, therefore, the upper two nozzles of the three-nozzle manifold
have larger orifices than the lower ones. In applying 75 gallons of spray liquid
per acre at a pressure of 300 pounds per square inch, the orifice diameter of
the topmost nozzle, (dealing with the upper branches of the near side of the
tree) is 0.094 inch; that of the center nozzle (dealing with the middle branches
of the near side of the tree and the upper branches of the far side), 0.125 inch;
and that of the bottom nozzle, 0.050 inch. In applying 50 gallons per acre the
respective orifice diameters are 0.050 inch, 0.094 inch, and 0.040 inch. The
nozzles are fitted with standard swirl plates with two orifices, each orifice
1/16 inch in diameter and inclined at an angle of 45 degrees to the face of the
plate.

Atonaizatioii of Spray Liquid

In the days of high-volume spraying, whether with spray gun or air-blast
machine, little thought was given to the droplet spectrum. Since the trees
were sprayed to dripping, the important point was an adequate distribution
of the spray liquid; large droplets, or a wide variation in droplet size were not
necessarily detrimental. It is otherwise with concentrate spraying. If sprayed
to dripping, highly concentrated insecticide or fungicide mixtures may injure
fruit or foliage, so that it becomes a matter of covering the sprayed surfaces
as completely as possible short of coalescence of the droplets to cause drip,
or "run-off". Unless modified by the presence of a surfactant, as discussed
later, coverage of that kind requires very small droplets, the more nearly
uniform in size the better. Goossen (24) has mentioned that a threefold
increase in drop diameter produces an equivalent decrease in coverage.
Droplets 270 microns in diameter, as in high-volume spraying for example,
cover only one third as much of leaf or fruit as an equal volume of liquid in
the form of 90-micron droplets, as in concentrate spraying: Goossen and Eue
(25) have defined the reduction of a spray liquid to droplets of less than
150 microns in diameter as atomization.

Kearns (34) and Edwards and Ripper (18) have pointed out that, with
low-volume sprays, the smaller the droplet size the better the penetration of
dense foliage. Yeomans and Rogers (66), quoting Sell (58), state that the
maximum penetration of foliage is accomplished by maintaining a low efficiency
of deposition on the nearer parts of the tree: "For penetration through the
95319—3

18

lower branches the particle size should be reduced to less than 50 microns mass
median diameter". But penetration is only part of the story. If the droplets
are too fine they will not impinge on the surface to be protected. According
to Potts (54): "A field of resistance surrounds all objects... and repels
droplets smaller than approximately 30 microns in diameter". For concentrate
spraying with ground equipment he gives an optimum droplet size range of
30 to 80 microns. Beskine (5) claims that 50 microns is the minimum droplet
diameter for effective work. Garman (22) mentions that, for mist-blowers,
droplet size should be from 50 to 100 microns. He notes that smaller droplets
do not impinge readily, and larger droplets fall out too quickly. Recognizing
the undesirability of ultra-fine droplets, Goossen and Eue (25) point out that
a decrease in the size of the droplets must be accompanied by an increase in
the velocity with which they leave the machine; otherwise they will not come
to rest where intended.

Working at the Summerland laboratory with a 25-horsepower, turbine,
concentrate sprayer, Mr. D. B. Waddell (unpublished work) found that,
although 98 per cent of the spray droplets were below 100 microns in diameter,
the remaining two per cent constituted about 50 per cent of the spray liquid.
One of the most important jobs in the development of concentrate spraying is
to reduce the relatively few large droplets to more efficient dimensions, or to
increase their covering capacity in some other way. Some British and European
sprayer manufacturers claim to have solved the problem by mechanical means.
One overseas machine, for which uniformly fine atomization is claimed, has
been examined at Summerland, but only with liquid output of 10 to 15 gallons
per acre did it achieve exceptionally fine atomization. Consequently, its use
appears to be restricted to the application of highly concentrated liquid pesti-
cides; and such formulations are generally more prone to cause plant injury
than the wettable powders that are favored in British Columbia. On the other
hand, several overseas manufacturers indicate that it is feasible to get adequate
spray coverage from exceedingly fine mists without necessarily overspraying
branches close to the machine, and hence running undue risk of injury. The
experimental work at Summerland has not yet shown how that can be accom-
plished. This point is discussed later under the heading "Surface-Active
Adjuvants".

The reduction of a sprav liquid to droplets fine enough for concentrate
spraying may be accomplished by projecting the liquid at low speed into
rapidly moving air or other gas, or by projecting the liquid at high speed into
relatively slowly moving air. Atomization of the first type has been achieved
with compressed air, and with high-pressure steam. French (19) wrote that
such methods produce smaller droplets than other types of atomization. Air at
a pressure of 20 pounds per square inch, for example, produced droplets
averaging 55 microns in diameter; at 80 pounds per square inch, the droplets
averaged 35 microns in diameter. Steam generators such as the Besler12 of the
Second World War, are capable of reducing liquids to an extremely fine state
of subdivision, to produce true fogs. With such equipment, later adapted to
apply pesticides, the size of the spray droplets can be modified by the simple
adjustment of a thermo-regulator. In experiments at the Summerland labora-
tory between 1946 and 1949, atomization by steam proved to be a somewhat
more complex and more expensive procedure than atomization by hydraulic
pressure. Steam atomization did not come into general favor with the fruit
growers.

Compressed-air atomization, as mentioned by French (19), was used
between 1930 and 1932 in spraying California vineyards with quantities of
liquid as low as two to four U.S. gallons per acre. Recently there has been a

:2Besler Engineering Corporation, Emeryville, California, U.S.A.

19

revival of this procedure in Great Britain with, it is claimed, excellent results.
The compressed-air method of atomization has not yet been examined at
Summerland. The subject is mentioned further under the heading "Type of
Nozzle".

In concentrate spraying the usual methods of atomization are by hydraulic
pressure, or by a combination of hydraulic pressure and high-velocity air.
Hydraulic pumps may be grouped in three categories: rotary, diaphragm, and
piston pumps. The first two types usually operate at relatively low pressures
(up to about 100 pounds per square inch); piston pumps are generally used
when higher pressures are required. Most rotary and diaphragm pumps do
not develop sufficient pressure to produce the fine droplets necessary in con-
centrate spraying. That shortcoming however, may be minimized or overcome
by the use of a special nozzle, by an exceptionally high-velocity airstream,
or, perhaps, by the addition of a surfactant to the spray concentrate. According
to French (19), air moving at 125 to 150 miles per hour exerts a considerable
shearing action on a spray liquid. Experiments at Summerland suggest that,
with conventional nozzles, the air velocities developed by most concentrate
sprayers (less than 150 miles per hour) are too low to play a significant role
in atomizing the spray liquid.

Another device to improve atomization is the "reversed" nozzle. As
pointed out by Akesson (1) the degree of atomization produced upon intro-
duction of a liquid stream into an air stream is a function of the difference in
velocity, so that the greatest break-up of liquid occurs when the spray nozzle
is directed against the air stream. A disadvantage of the reversed nozzle
arrangement, however, is that the type of nozzle generally used offers an
obstruction to the air stream and tends to create excessive turbulence; the
Summerland studies have indicated that a turbulent air stream has less pene-
trating power than a linear-flow air stream. A second consideration is that, by
directing the liquid stream against the air stream, the energy inherent in the
rapidly moving liquid is absorbed by that of the air stream instead of added
to it. Although that may seem a minor matter there is measurable kinetic
energy in a liquid emitted at two to three gallons per minute under a pressure
of 300 pounds per square inch, and the fact is that most light, concentrate
sprayers require all the air-liquid energy their engines, blowers, and pumps
are capable of delivering. A third consideration in using reversed nozzles is
that, with narrow, rectangular air vents, it is difficult to contain the spray
cone within the air stream. In the work at Summerland a considerable number
of pumps of various types have been examined by Mr. A. D. McMechan. He is
of the opinion that a suitable method of using a low liquid pressure will
eventually be developed for the rugged and simply designed concentrate spray-
ers that are favored by British Columbia fruit growers.

High-pressure pumps have several shortcomings. They are expensive, and
most of them are fairly heavy and bulky. Spray concentrates containing
wettable powders may be very abrasive when ejected under high pressure;
consequently, high-pressure pumps necessitate the use of tungsten carbide
parts at points of greatest wear, e.g., nozzle discs and swirl plates. On the other
hand, the use of high pressure is, perhaps, the simplest method of reducing the
size of spray droplets to the degree that appears to be necessary in concentrate
spraying. Davies and Smythe-Homewood (17) listed pressure as the first factor
influencing the degree of atomization. French (19) noted that, to reduce the
size of spray droplets by one half, the pressure had to be increased four times.
At a pressure of 300 pounds per square inch he recorded an average droplet
diameter of 350 microns; at 500 pounds the droplet diameter was 250 microns.
He concluded: "Pressure is the primary factor controlling the degree of
atomization". A few years later Akesson (1) stated that the average droplet
95319— 3£

20

diameter of the spray from a high-pressure spray gun was 400 microns at
400 pounds' pressure per square inch, and 200 microns at 800 pounds per square
inch; in other words, doubling the pressure halved the droplet size.

Early experiments on the control of orchard mites with the Bean Mist-
Duster1'1 in British Columbia showed that neither perforated-tube manifolds,
nor conventional nozzles operated at low pressure, were adequate for concen-
trate spraying. The machine, as received, was equipped with a rotary pump
that developed a pressure of 20 pounds per square inch; the liquid manifold
was a simple perforated brass tube inserted across the mouth of the air vent,
in which position it caused pronounced turbulence in the air stream. The
droplet spectrum, even at an air velocity of 120 miles per hour, was very wide,
much of the liquid being projected as droplets over 400 microns in diameter.
The perforated tube was replaced by a swirl-nozzle manifold attached to the
outer edge of the blower scroll, in order to avoid unnnecessary air turbulence.
The new manfold was so inclined that its 6 nozzles directed the spray forward
into the air stream at an angle of 45 degrees. Although the droplets became
smaller and more nearly uniform in size, atomization was still unsatisfactory
for concentrate spray coverage; the dinitro phenol derivative that was being
used as an acaricide caused foliage injury in the lower parts of the trees. When
the rotary pump was replaced by a piston pump operated at a pressure of 300
pounds per square inch, atomization was further improved, spray injury was
almost eliminated, and the control of mites was satisfactory throughout the
trees.

Experiments with the Buffalo Turbine sprayer-duster14 in 1946 and 1947
confirmed these results. The low-pressure gear pump, and the perforated-tube
manifold with which the machine was fitted, proved unsuitable for applying
spray concentrates.

Type of Nozzle

Failure of the perforated-tube manifold emphasized the need for more
information on the atomization of spray liquids. Writing of their pioneer work
in Great Britain 22 years ago, Da vies and Smythe-Homewood (17) said about
swirl nozzles: "One popular misconception to be dispelled by these researches
was that smaller disc orifices produce finer sprays. They do not." They found
that the factors that do influence the degree of atomization are pressure, depth
of swirl chamber, and size of vortex holes in the swirl plate. A decrease in
the depth of the swirl chamber, or in the diameter of the vortex holes, produced
smaller droplets and decreased the output of the nozzle; an increase in pressure
produced smaller droplets but increased the output. Taylor (62) of New Zealand
elaborated on the earlier work. He found that, at relatively low pressures,
as the diameter of the disc orifices was increased the average diameter of the
spray droplets increased; at high pressures, however, there was no change.
According to Akesson (1), at orifice diameters above 0.05 inch the droplet
sizes remain fairly constant, but below 0.05 inch the size of the droplets
apparently becomes an increasing function of the orifice size; smaller orifices
produce smaller droplets. Perhaps that is the reason for subsequent contradic-
tory statements on the relationship between orifice diameter and droplet size.
Taylor (62) noted that thicker swirl plates produced narrower spray cones and
larger droplets, that an increase in the angle of the vortex openings produced
slightly smaller droplets, and, the output being the same, four vortex openings
appeared preferable to two, at least from the standpoint of droplet size.

13Food Machinery Corporation, Bean Division, San Jose, California, U.S.A.
14Buffalo Turbine Agricultural Equipment Company, Gowanda, New York, U.S.A.

21

The two types of orchard concentrate sprayers manufactured in British
Columbia depend upon high liquid pressure (300 to 400 pounds per square inch)
and swirl nozzles to obtain the degree of atomization necessary in applying,
from fixed air vents, as little as 50 gallons of spray concentrate per acre. One
of the machines generates a linear-flow air stream with a velocity of about
110 miles per hour; the other, with considerably greater air volume but more
turbulence, has an air velocity of about 90 miles per hour. The Summerland
investigations have shown no appreciable reduction in the size of the spray
droplets by either type of air stream.

Since it has been found that liquid spray formulations containing organic
solvents are generally more prone to injure fruit or foliage than wettable
powders, most of the orchard spraying in British Columbia is with the latter.
But wettable powders applied at high pressure, and in high concentration, may
be exceedingly abrasive. In the early days of concentrate spraying, faulty
application was commonly traced to worn orifice discs or swirl plates and, less
frequently, to worn pressure regulators or relief valves. Marshall (37) made
a laboratory study of substances that might be used in the fabrication of
orifice discs; he examined ceramics, natural rubber, plastics, various types of
steel, and tungsten carbide, but only the last gave adequate resistance to abra-
sion. In commercial operations he compared stainless steel orifice discs, at
that time in fairly general use, with tungsten carbide discs. The stainless
steel discs were commonly ruined within 10 hours but, just as commonly, the
tungsten carbide discs were still serviceable at the end of the season. Nowadays
the nozzles of all concentrate sprayers manufactured in British Columbia are
factory-equipped with tungsten carbide orifice discs and swirl plates. Australian
and New Zealand manufacturers evidently follow the same practice.

With the swirl nozzle, according to Byass (6), 50 gallons per acre is the
lowest volume of liquid that is feasible for mature orchards. He describes two
compressed-air nozzles that, he claims, are capable of applying quantities as
low as five gallons per acre. The more promising of the two nozzles consists
of a number of tubes projecting at right angles into a circular opening through
which compressed air passes at high velocity. Spray liquid, presumably mov-
ing at little pressure through the tubes, is atomized by the air stream. Com-
pressed-air nozzles have not yet been examined at Summerland.

When it became evident that concentrate spraying was more than just
a passing fad, several manufacturers hurriedly devised and marketed bizarre
bits of equipment that they labelled concentrate sprayers. Evidently, in the
interests of simplicity and low cost, some of these were equipped with the
flat- jet, or fan, type of nozzle. Experiments at the Summerland laboratory
and in the orchard have shown that fan nozzles do not atomize the spray
liquid well enough to be satisfactory for concentrate spraying.

An efficient device for atomizing liquids is the whirling disc nozzle. Essen-
tially it consists of a circular plate rotated at high speed. Spray liquid flowing
onto this plate is thrown to the periphery in a fine sheet by centrifugal force.
The sheet of liquid is fractured as it leaves the edge of the plate, and the fine
droplets so produced are caught up and dissipated by the air stream of the
sprayer. The whirling disc nozzle has two advantages over conventional
nozzles: it is capable of producing unusually small and uniform spray droplets;
and, since it operates at very low liquid pressure, it necessitates only a simple
and inexpensive centrifugal pump. One disadvantage of the whirling disc
nozzle is that, although simple in principle, it is not simple in construction;
hence it is expensive and, it is suspected, somewhat liable to breakage or
maladjustment. A second limitation is that, in all likelihood, the use of the
whirling disc nozzle will be restricted to circular air vents, because, for efficient
operation, it must be rotated by a high-velocity air stream. A modification

22

of the whirling disc nozzle is fitted on a British-built concentrate sprayer
recently examined at the Summerland laboratory. According to Mr. A. D.
McMechan it produces droplets of more nearly uniform size and of lower mass
median diameter, than most of the other nozzles so far examined.

A nozzle used to some extent in high-volume, air-blast spraying is the
opposed-jet type. Two liquid jets from the orifices of this nozzle impinge on
one another to produce a spray. At the Summerland laboratory, experimental
work with the most widely used make of opposed-jet nozzle indicated that
it was not adapted for concentrate spraying; apart from its high cost, which
would be even higher if the nozzle were fitted with tungsten carbide orifice
tips, it did not atomize the spray liquid sufficiently and its output was too
great.

Another spray nozzle now being studied by Mr. A. D. McMechan at
Summerland is the so-called anvil type, a device that reduces a jet of liquid
to droplets by impingement on the end of a wirelike "anvil". This nozzle
has the considerable advantage of simplicity, always a desirable feature in
agricultural machinery; but it does not appear to provide sufficiently fine
atomization for concentrate spraying, and the position of the anvil, or pin,
is so critical that there is likelihood of misalignment.

In other fruit growing areas, special nozzles have been advocated, or are
in use, for applying spray concentrates. Among the first investigators to study
nozzles for the application of spray concentrates were Brann et al. (8), who
developed a streamlined nozzle through which spray liquid was forced at a
pressure of 100 pounds per square inch directly against the air blast. The
nozzle, placed in the center of a circular air vent, was capable of applying
spray liquid at various rates without the need of changing either nozzle orifice
or pressure; the rate of application was varied by the adjustment of a flow
valve. This type of nozzle, the use of which appears to be limited to circular
air vents, has been fitted by manufacturers of concentrate sprayers in the
United States and, apparently, in England. A Danish manufacturer has devised
a nozzle that may be directed either with the air stream or against it. As with
the other machines that depend, to some degree, on the atomizing effect of
high velocity air stream, the blower scroll of the Danish one is formed of
several circular vents.

Angle of Emission of Spray Liquid

Like high-volume, air-blast sprayers, some concentrate machines deliver
the spray stream at a zero angle to the air stream. If, on such machines,
the air vents are circular, a nozzle may be placed in the center of each; if
rectangular, several nozzles are placed along the mid-line. The chief advantage
of this arrangement seems to be that it streamlines the machine. Another
benefit might be that it fully utilizes the kinetic energy of the spray droplets.
No work has yet been done, however, to determine the significance of kinetic
energy at outputs of less than 100 gallons per acre. A disadvantage is that,
unless specifically designed to function in an air stream, the nozzles obstruct
it and induce turbulence. Air velocity measurements show that the air speed
for some distance outwards from an ordinary swirl nozzle is reduced almost to
zero. If the blower develops a turbulent, high-volume air stream, the added
turbulence induced by interposed spray nozzles is presumably of little con-
sequence. In a low-volume, high-velocity, linear-flow air stream, however,
nozzle-induced turbulence may lower the efficiency of the machine.

Other orchard concentrate sprayers deliver the spray stream at an angle
of 180 degrees to the air stream, i.e., directly against it. The advantage of this
method is that the greatest possible friction is generated between liquid and

23

air, and the size of the spray droplets is reduced to a minimum. With a high-
velocity air stream, the use of the inverted nozzle makes it feasible to employ
a low liquid pressure, and hence a small, inexpensive pump. A disadvantage
of this type of nozzle is that its use appears to be restricted to circular air vents.
Rectangular air vents are generally so narrow that inverted nozzles tend to
drive some of the spray droplets to the sides of the blower scroll. The resultant
sheet of liquid is reconstituted by the air stream into droplets at the edge of
the blower scroll but these are too large to be very effective in concentrate
spraying. Circular vents can be used to advantage when they are manually
directed; but, when mounted one above the other to form a fixed, multi-vent
blower scroll for one-man operation, there may be complications. Unpublished
records of Mr. A. D. McMechan of the Summerland laboratory showed that
each of the four circular air streams from such a blower scroll maintained its
identity, although to a decreasing degree, for a distance of 20 feet. Four
distinct air streams are less likely to apply a uniform spray coverage than the
single air stream emitted from a well-designed, rectangular air vent.

A third method of injecting the spray droplets into the air stream is a
compromise between the other two. The spray liquid manifold is attached
to the outer side of the blower scroll, and the nozzles are so inclined as to direct
the atomized liquid at an angle of approximately 45 degrees into the air stream.
This arrangement has the advantage of offering no obstruction to the air stream
and, since the spray droplets are projected at a forward angle, their momentum
may be somewhat greater than if they were projected directly against the air
stream. On the other hand, the Summerland investigations indicate that the
injection of spray liquid at a 45 -degree angle into air streams moving at 90
to 115 miles per hour, such as are in general use in British Columbia, results
in little if any reduction in the size of the droplets. The ultimate size of the
droplets from the two British Columbia — built orchard concentrate sprayers
is determined, therefore, by the type and pressure of the spray liquid and the
type and arrangement of the spray nozzles.

Rate of Travel

Much of the uncertainty about concentrate spraying in some of the
deciduous fruit industries of North America is undoubtedly due to lack of
information on rate of travel. There have been many occasions on which light,
concentrate sprayers, with very modest output of air, have been hauled twice
to three times as rapidly as the manufacturer intended, and the unsatisfactory
results blamed on the machine or the method. On the other hand, in the race
for sales, manufacturers or their agents have sometimes oversold their machines,
and extravagant claims for performance have not been substantiated in the
orchard.

Although rate of travel is a matter of great importance, it is remarkable,
to judge from the literature, how little attention has been paid to it. Using
a high- velocity, concentrate sprayer, Brann (10) obtained better codling
moth control when the machine was moved at 1.5 miles per hour than at
2 miles per hour. Pearch (50) warned that, in mist-spraying large trees in
England, the rate of travel should not exceed 1 .5 miles per hour. Akesson (1),
whose views are typical of many operators of heavy equipment, has written:
"In order to obtain the full benefits of blower sprayer operation it is necessary
that the quantity of discharged air be sufficient to displace the air volume of
the row of trees being passed." Brann (9) disagrees: "Some authorities have
said that the air blast must have sufficient volume to displace the air in the
tree .... If the equipment is moved at two miles per hour the air that must
be displaced would be several times in excess of the air volume delivered
by any machine now available".

24

When hauled at a rate of one mile per hour, one type of British Columbia
concentrate sprayer with a high-velocity, linear-flow air stream of only 7,000
cubic feet per minute gives satisfactory coverage of well-pruned, full-foliaged
apple trees up to 30 feet in diameter and 18 feet high. If, to do so, it were
necessary to displace all the air within such trees, the machine would have
to be moved past them at a speed of approximately 0.2 mile per hour.
Apparently, then, it is unnecessary to displace all the air within a tree when
applying concentrate sprays with an air blast just as it is unnecessary to do
so when applying high-volume spray liquids with a hand gun. The air within
the tree, presumably, becomes mixed with that projected from the blower,
and the mixture, highly turbulent by reason of the interference of branches,
carries the spray droplets throughout the tree. It seems advisable, however,
to travel slowly enough for the air stream to set the air in motion to the far
side of the tree.

Various experiments have been carried out at the Summerland laboratory
on this aspect of concentrate spraying. In 1949, for example, a light, one-side,
air-blast sprayer, powered by a 5-horsepower engine and generating an air
stream of approximately 5500 cubic feet per minute at an average velocity of
60 miles per hour, was operated experimentally in the control of the European
red mite, Metatetranychus ulmi (Koch). It was hauled at one mile and two
miles per hour among full-foliaged, 12-year-old apple trees approximately 20
feet in diameter and 15 feet high. Concentration of the acaricide, the mono-
ethanolamine salt of dinitrocyclohexyl phenol, was the same at both speeds.
A week after spraying the average percentage survival of mites in five separate
trials was 27.7 where sprayed at two miles per hour, and 9.5 at one mile per
hour. In every case survival was greater at the higher speed. With the reduced
dosage of toxicant, clearly the machine in question was inadequate for spraying
even rather small apple trees in full foliage, when operated at a speed of two
miles per hour. On the other hand, at the same per-acre dosage of toxicant,
the mites were satisfactorily controlled by a 25-horsepower turbine-type
machine, travelling at two miles per hour and projecting approximately 7,000
cubic feet of air per minute at a velocity of 110 miles per hour.

In an experiment by Messrs. J. M. McArthur and A. D. McMechan
(unpublished records), well-pruned apple trees approximately 27 feet in
diameter and 18 feet high were sprayed at the pink-bud stage with methoxy-
chlor, and the foliage was sampled for chemical analysis as soon as it had
dried. The sprays were applied with the turbine, concentrate sprayer referred
to in the preceding paragraph. In this instance both the speed and the con-
centration of toxicant were varied so that the same amount of methoxychlor
was applied per acre, i.e., 12 pounds of 50 per cent wettable powder. The
deposit in the tops of the trees was 250 micrograms per leaf at a rate of travel
of one mile per hour (90 gallons per acre), and 278 micrograms at two miles
per hour (45 gallons per acre, double concentration). In the bottoms of the
trees the deposits were 233 and 281 micrograms respectively. It could not be
said, therefore, that the higher rate of travel resulted in lower spray deposits
in any part of the tree.

In another experiment with the turbine sprayer a lime-sulphur-dormant
oil mixture was applied to mature apple trees as a dormant spray at rates of
travel of one and two miles per hour, the per-acre dosages of oil and lime-
sulphur being the same for each speed. Deposits of oil on twigs in the tree tops
averaged 0.46 milligram per square centimeter at two miles per hour, and 0.51
milligram per square centimeter at one mile per hour. In the bottoms of the
trees the respective figures were 0.41 and 0.42 milligram. Control of the
European red mite was approximately the same in each instance. A pink-bud

25

spray of an Ovotran-methoxychlor mixture was applied at the two speeds to
other plots in the same orchard. Both the deposit of spray chemical and the
control of mites were similar to those in the preceding experiment.

Evidently the 25-horsepower, one-side, concentrate sprayer now being
manufactured in British Columbia may be operated throughout the spraying
season at a speed of two miles per hour among apple trees up to about 20 feet
in diameter and 15 feet high. In large, well-pruned trees, 30 feet in diameter
and 18 to 20 feet high, a speed of two miles per hour seems adequate from
dormant to pink-bud stage; for such trees in full foliage more information is
needed, and experiments to that end are now under way. In the meantime, the
official recommendation for British Columbia fruit growers (2) is to operate
concentrate sprayers at a speed of one mile per hour in mature plantings with
rows 30 feet apart, at 1| miles per hour in mature plantings with rows 20
feet apart, and at two miles per hour in plantings with rows 15 feet apart.
The growers have been notified, however, that it is feasible to increase the
speed measurably, up to the pink period of apple bud development, provided
they operate efficient, adequately powered concentrate sprayers.

SPRAY COVERAGE

Twenty-three years ago the British investigators Davies and Smythe-
Homewood (17) noted that biologists did not agree on the ideal type of spray
coverage. The plant pathologists favored a fine, mistlike coverage, whereas
the entomologists preferred a driving type of spray, even to the point of
dripping. But they added: "It appears that all would be satisfied if every
part of the sprayed objects were evenly covered with a finely divided, stippled
deposit". Beskine (5) mentioned that, although 150-micron droplets are
efficient enough for controlling insects, they are too large for fungi. In
spraying with mist concentrates, Brann (9) claimed the ideal cover is not a
continuous film, nor the blotchy type of deposit normally laid down by a
high-volume sprayer, but a finely spotted deposit. Wittwer and Muller (65)
found that the greatest resistance to weathering was from droplets 30 to 50
microns in diameter. Goossen (24) stressed the need for an unbroken filmlike
coverage of fungicide to control plant diseases, and emphasized that coverage
of the kind is more readily attained with high-volume than with concentrate
spraying.

Early in the commercial use of concentrate sprayers in British Columbia
it was observed that the growers were having more trouble in controlling
apple scab than the codling moth or phytophagous mites; yet the opposite had
been the case in the days of high-volume spraying. It was suspected that
the trouble lay in the tendency of even the most efficient concentrate sprayers
to overspray surfaces facing the air stream, and to underspray surfaces not
facing the air stream, such as the stem-basins of well developed fruit, i.e.,
there is a tendency to produce a "shadow" effect. Theoretically, a uniform,
filmlike deposit should be more important in dealing with a motionless organism
such as an apple scab spore than an active insect or mite. In the first instance,
the toxicant must be placed close to or in contact with the spore, a requirement
that can be met readily by the washing effect of high- volume spraying; in
the second, the object of the spray unwittingly seeks out the toxicant, so that
the deposition of the toxicant, even though relatively irregular, may be
adequate for the job.

A Netherlands manufacturer has developed a machine that is said to be
capable of producing droplets with an average diameter of approximately 50
microns. Droplets of that size, it is claimed (undated brochure of Kiekens
Whirlwind (London) Ltd.), are caught up in air eddies behind leaves and

26

fruit, and eventually come to rest in sufficient quantity to give protection
even on surfaces facing directly away from the sprayer. So far, the Summer-
land investigations have not shown how that can be accomplished, although
they have included experiments with steam-atomized and with hydraulically
atomized spray liquids, the average droplet sizes of which lay between 30 and
100 microns. Whether these droplets were projected in a turbulent air stream
or in a linear-flow air stream, only a very small percentage were deposited
on surfaces facing away from the machine.

Despite the fact that spray coverage on reverse surfaces was deficient,
however, chemical analyses repeatedly showed that concentrate spraying
resulted in higher spray deposition on the tree than high-volume spraying
with an equal quantity of toxicant. Obviously there was much room for
improvement in the uniformity and completeness of the spray coverage. Since
it appeared unlikely that the necessary improvement could be accomplished
by mechanical means, an investigation was begun to determine whether it
could be done chemically. Five years later the use of surface-active chemicals
to enhance the performance of concentrate spray mixtures became commercial
practice in British Columbia. Despite this development, however, the use of
such preparations in concentrate spraying is still a controversial subject.
Some investigators consider that the idea has possibilities; others say it is
out of the question because it will lead to excessive spray injury. The matter
is important enough to merit considerable discussion.

SURFACE-ACTIVE ADJUVANTS (SURFACTANTS)

Physical Characteristics of Spray Liquid

Recently Brann (11) commented: ". . . we can not go on solving problems
by building larger machines with more air blast. Progress lies in the direction
of more efficient application of the power we are now using through a better
understanding of the factors involved in getting the toxicant from the tank to
the plant". Among the most important of those factors are certain physical
characteristics of the spray liquid — homogeneity, volatility, viscosity, density,
and surface activity.

Homogeneity

In concentrate spraying it is important that the composition of the spray
liquid be constant from start to finish of the operation. Unlike high-volume
spraying, in which a variation of as much as 100 per cent in the concentration
of an ingredient probably might go unnoticed, any such variation in concentrate
spraying may have profound effects. Agitation of the concentrate spray liquid,
therefore, requires special consideration. Some manufacturers have fitted their
sprayers with tanks of rectangular, or approximately rectangular, cross section.
If the agitation is vigorous such tanks are satisfactory, but if for any reason it
should weaken, settling is likely to occur in the corners; consequently, round or
oval tanks are preferable.

The Summerland investigations have indicated that mechanical agitation is
preferable to hydraulic agitation. Mechanical agitation is the more reliable
method and has the added advantage that it does not necessitate a high-capacity
pump. Agitation should not be so great that air may be carried into the suction
line to cause air locks in the pump. For .mechanical agitation, flat paddles or
propeller-type paddles are generally used, the former, as a rule, being somewhat
more effective.

27
Volatility

The application of ultra low- volume sprays (3 to 20 gallons per acre)
necessitates exceptionally fine atomization. It appears, from several published
articles, that there is no trouble from evaporation of such spray droplets in
districts with relatively high atmospheric humidity and moderate temperatures.
But in semi-arid areas, such as the Okanagan Valley of British Columbia,
indications have been that spraying at the rate of 20 gallons per acre may, to
a degree, become dusting. It is to be expected that, in rapidly moving air at
a temperature of 100° F. or higher and a relative humidity of perhaps 15 or
20 per cent, minute droplets of water will be in a highly unstable condition.
Zimmer (69) remarks that "even in a temperate climate all small volume sprays
are susceptible to loss by evaporation. It is often necessary to minimize this by
preparing the solution in an oil of suitably high boiling point".

There has been a marked disinclination to use petroleum oils as foliage
sprays in British Columbia. The general adoption of concentrate spraying has
emphasized the hazards of the commonly used petroleum fractions, and it is
doubtful whether with the present machinery, even the phytonomic summer oils
will be employed. In any case, a dosage of 50 gallons per acre, as now sug-
gested, appears to be high enough to ensure that an adjuvant will not be needed
to minimize the effects of evaporation, yet low enough to give a substantial
saving through protracted operation between fillings. Investigations now in
progress indicate that a dosage of as little as 35 gallons per acre may be feasible
in British Columbia; but dosages of that order must be applied with special care
and with the best of equipment. Present indications are that such low dosages
may necessitate the use of a surfactant in the spray concentrate. The point is
discussed later.

Viscosity and Density

In calculating the size of spray droplets, Nukiyama and Tanasawa (46)
developed a formula in which the flow of liquid, the flow of air, the velocity of
gas and liquid relative to one another, the viscosity of the liquid, the density of
the liquid, and the surface tension of the liquid are variables. In the application
of oil sprays Potts and Friend (53) found that an increase in the viscosity of
oil from 50 to 200 seconds, as measured by the Saybolt Universal viscosimeter
at 100° F., resulted in an increase of nearly 100 per cent in the size of the spray
droplets. At Summerland a similar effect was observed in experiments in
which, as the viscosity of a DDT wettable powder spray concentrate was raised
by addition of carboxymethyl cellulose, the size of the spray droplets increased
and the spray coverage became irregular and spotty.

Although spray concentrates may contain more than a pound of finely
divided, suspended material per gallon, it is doubtful whether their viscosity
varies appreciably from that of water alone. On the other hand, their density is
generally greater than that of water; and as Nukiyama and Tanasawa have
pointed out, the greater the density of the spray liquid the larger the spray
droplets. It has to be remembered, though, that a spray concentrate may not
be a pure liquid, or even a solution, but a two- or three-phase system, so that
its behavior cannot be deduced by analogy from that of pure liquids of similar
density.

In any case, density appears to be a more important factor in concentrate
spraying than viscosity. It is also a more important factor in concentrate spray-
ing than in high-volume spraying. Any measures that might be taken to offset
the influence of high density, therefore, should be given due consideration. One
such measure is the modification of the surface tension of the spray liquid, or
the interfacial tension between the spray liquid and the sprayed surface, by the
addition of an appropriate surface-active preparation.

28

Surface Activity

Among the fust to examine the effects of surface-active materials in spray
concentrates were Potts (52), who stated that the droplet size in a concentrate
spray may be reduced 30 to 50 per cent by the addition of a good wetting
agent, and Pratt (55), who mentioned having used the non-ionic, water-dis-
persible surfactant Triton B 1956 (Rohm and Haas Co., Philadelphia, U.S.A.)
with water-wetted sulphur dust. The surfactant measurably increased the
amount of sulphur residue on fruit and foliage.

As concentrate spraying became more widely studied, references to wet-
ting agents and other surfactants became more frequent. Among those who
considered that surfactant should not be added to spray concentrates were
Besemer (4), Foulds et al., (20), Moore (45), Hey (30), and Young (67, 68).
These authors agreed that the spray droplets should not be allowed to spread
to the point of coalescence. Their disapproval of surfactants varied from the
opinion expressed by Young (67), "In the case of concentrate sprays, the low
gallonages and high concentrations of materials makes complete wetting of the
surfaces impossible. For this reason the matter of uniform distribution is more
strictly a function of the spray machine" to the categorical advice of Hey, "Do
not use wetting agents with low-volume sprays. . .".

Among those who mention that surfactants might prove useful is Brann
(9), who, although stating that the ideal deposit in concentrate spraying is
not a continuous film, but a finely spotted deposit, nevertheless suggests the
use of a spreader such as vegetable oil or the non-ionic surfactant Triton B
1956 at the rate of four to six ounces per 100 U.S. gallons of spray liquid,
particularly if wettable powders are to be applied. In true concentrate spray-
ing, as defined earlier (not over 75 imperial gallons per acre of mature trees),
such an amount of either of these preparations is too small to produce a film
coverage.

Noting that the penetration of spray through thick foliage is best accom-
plished by small droplets, Edwards and Ripper (18) proposed the use of wet-
ting agents and high pressures to improve the atomization of the spray liquid
in herbicidal applications; but there is difference of opinion as to whether
wetting agents have any such effect. Parker (48) was one of the first workers
to emphasize that surfactants may be necessary if the potential effectiveness
of concentrate spraying is to be fully realized. In 1950 he wrote: "Spreaders
in the water seem to be important if this small amount of liquid is to provide
adequate coverage". He considered that the most pressing research problems
in concentrate spraying related to spray formulations. The following year
Hamilton (27) stated that, since high concentrations of solids produced con-
centrates that are difficult to "break up", a surfactant such as the water-soluble,
non-ionic Triton X100 (Rohm and Haas Co., Philadelphia, U.S.A.) may be
added to good effect at a concentration of one pint per 100 gallons of spray
concentrate.

The relationship between surface tension and size of droplet has been
mentioned by Potts and Friend (53) who stated that the addition of the sur-
factant Santomerse D (Monsanto Chemical Co., St. Louis, U.S.A.), at two per
cent by weight of the suspended solid, reduced the droplet size of a lead arsenate
spray concentrate by 20 per cent. Writing on the manner in which liquids are
reduced to droplets, Zimmer (69) claims, however, that a swirl nozzle forces
the liquid into a thin sheet which, as the result of air friction, breaks up into
rodlike ligaments. The ligaments in turn break up along their length into
droplets in a manner controlled mainly by the surface tension of the liquid. He
suggested that a surfactant could not influence the process because there would
be insufficient time for the surfactant to reach the new surfaces before the
process was completed.

29

As mentioned earlier, Mr. D. B. Waddell of the Summerland laboratory
found that the turbine type of concentrate sprayer, widely used in British
Columbia, produced a droplet spectrum in which only about two per cent of
the droplets were above the maximum wanted diameter of 100 microns. Those
few large droplets, however, represented about half of the volume of the spray
liquid. Various authors have stressed that, since spray concentrates are ap-
plied in relatively small amounts, the droplets must be very fine, and closely
and uniformly spaced. That being so, the detrimental effect to the spray cover-
age of the two per cent of large droplets must be considerable. But if, by
modifying the surface activity of the spray liquid, all the droplets coalesced
after impact to form a liquid film, then, provided the large droplets did not
fall away from the air stream too rapidly, and provided they were able to
penetrate the foliage canopy, the volume of spray material represented by the
large droplets might be as effective in protecting the foliage and fruit as an
equal volume in the form of small droplets.

Experiments with Surfactants

There are two reasons for caution in using a surfactant to improve the
efficiency of concentrate spray coverage. First, the addition of a surfactant,
in sufficient amount to produce a uniform liquid film on fruit or foliage, may
result in the formation of a heavy, objectionable residue at points from which
there is drip. Second, if a spray chemical has a tendency to be phytotoxic, the
tendency is aggravated by the formation of localized, heavy deposits.

The first of these difficulties can be avoided by attention to type of
machine, and method of operating it, and to dosage of spray concentrate. The
machine should apply the spray liquid in such a manner as to avoid unnecessary
overspraying of the lower parts of the trees. The quantity of spray liquid
should not exceed 75 gallons per acre of mature trees; as shown later, 50 gallons
per acre appears to be sufficient, particularly if a surfactant is used in the
spray concentrate. The same precautions will minimize the second difficulty;
avoidance of spray chemicals that are prone to cause injury will, of course,
eliminate it.

In British Columbia the first field experiments with surfactants in concen-
trate spraying were undertaken in 1952 against the codling moth. But neither
in that year nor in succeeding years, including 1956, were weather conditions
favorable enough for the insect to develop the heavy infestations that are
desirable in field experimentation. Nevertheless, repeated trials indicated
that control of the codling moth was improved when a surfactant was added to
the spray mixture. For example, 50 per cent DDT wettable powder was
applied at six pounds per acre, in five separate, large-scale experiments, in
plots of one-quarter to one-half acre. In each instance, codling moth infest-
ation at harvest was lower where a surfactant had been added to the DDT
concentrate. Where no surfactant had been used, the average infestation was
4.0 per cent; with surfactant it was 2.2 per cent. With three pounds of 50 per
cent DDT per acre the average infestation was 12.0 per cent without surfactant
and 7.9 per cent with surfactant; again the differences in separate experiments
were in favor of the surfactant mixture.

In recent years control of apple scab has been a serious problem for many
British Columbia fruit growers. It has been mentioned earlier that, although
concentrate spraying generally results in deposits of fungicides that are
adequate from the standpoint of chemical analysis, the deposits are not entirely
adequate from the standpoint of scab control. The difficulty, it was suspected,
arises from the irregularity of the spray coverage. Since it was known from

30

red ling moth experimentation that certain surfactants have the capacity to
eliminate "shadow effect", and produce a barely visible, film-type coverage
without loss of toxicant, it seemed reasonable to assume that, if inferior scab
control did indeed result from unprotected areas on the surface of fruit or
foliage, the addition of an appropriate surfactant to the fungicidal spray
mixture should render the mixtures more effective. As an outcome of dupli-
cated orchard experiments to test that theory, Swales and Williams (61)
reported that surfactants measurably improved the effectiveness of fungicidal
spray concentrates. Without surfactant a spray schedule of lime-sulphur,
ferbam, wettable sulphur (the fungicidal mixtures applied at 75 gallons per
acre in seven applications) resulted in an average of 11.7 per cent scabby fruits
at harvest. Plots sprayed with the same fungicides but with added surfactant
yielded 4.1 per cent scabby fruits. Where a fungicide schedule of ferbam,
wettable sulphur was followed throughout the season the respective figures
were 13.5 per cent and 7.7 per cent; non-sprayed check trees were largely
defoliated and the fruit was 100 per cent scabby. The differences were
consistent in the two orchards.

The following year the same investigators (unpublished work) reproduced
these results with a dosage of 75 gallons per acre, and showed that the dosage
might be reduced to 50 gallons per acre if a surfactant was added to the spray
mixture. In duplicate experiments, the idividual plots being about a third of
an acre in area and the dosage 50 gallons per acre, they found the average
scab infection at harvest to be: without surfactant, 54.4 per cent; with
surfactant, 26.1 per cent. Again the fruit on the non-sprayed check trees was
a total loss; again the differences were consistent in the two orchards. Scab
infection on the sprayed plots was abnormally high because of exceptionally
prolonged precipitation, which on one critical occasion seriously delayed the
spray application.

Ranking with the codling moth and apple scab as bugbears of the orchards
in British Columbia are several species of phytophagous mites. In field
experiments against the European red mite, Metatetranychus ulmi (Koch),
and the two-spotted mite, Tetranychus telarius (L.), acaricides applied with
and without surfactant have shown no measurable differences in control.
Presumably that is because with active organisms such as mites, a uniform
spray coverage is not necessary; the mites come in contact with the toxicant
during their wanderings whether it is deposited as a uniform film or as
discrete spots. A second consideration is that certain acaricides may be lethal
although not immediately in contact with the mites.

Aphids are also troublesome orchard pests in British Columbia; the apple
aphid, Aphis pomi DeG., and the woolly apple aphid, Eriosoma lanigerum
(Hausm.), are among the most prevalent and the most injurious. One of the
standard procedures in controlling both species is to anply, during warm
weather, a spray of nicotine sulphate at 0.5 gallon and sodium carbonate
(washing soda) at two pounds per acre. In an exoeriment, undertaken to
determine whether the addition of a surfactant affects the toxicity of the
nicotine mixture, several acres of mature orchard heavily infested by the
apple aphid were soraved with a standard mixture, and an equal area sprayed
with the same mixture to which a surfactant had been added. From the
commercial standpoint, control of the aphid was equally good with both spray
mixtures.

A few years ago it was thought that the woollv apple aphid was so well
protected by its waxy covering that only as a drenching spray could a toxicant
be brought into effective contact with the insect. Experience has shown that,
in warm or hot weather, the aphid is readily controlled by the application
of as little as 50 gallons of nicotine spray concentrate per acre, an amount

31

far short of that required to wet and penetrate the aphid wax in liquid form.
The addition of a surfactant has been of no evident benefit. Presumably there
is no point in adding a surfactant to concentrate spray mixtures of the fumigant
type, such as the one in question.

In many fruit growing areas, one of the more bothersome problems in
apple production nowadays is the control of apple powdery mildew. It has
been claimed by several writers, Sprague (59), Hunnam et al. (32), and
Hey (30), for example, that, even in high- volume spraying, the addition
of a wetting agent measurably improves the control of the disease by sulphur
sprays or Karathane (dinitrocapryl phenyl crotonate). It is logical to assume
that the beneficial effects of a surfactant would be even more pronounced
in concentrate spraying. Extensive field experiments were undertaken in 1956
and 1957 to determine whether that is so; but weather conditions reduced
mildew infection to such a low point that the results were inconclusive, and
the trials must be repeated.

Field experiments were undertaken to find out whether the addition of
a surfactant affects the scale-killing properties of dormant oil — lime-sulphur
spray concentrate. The oil, emulsified with soya flour, quickly separated from
the water phase of the emulsion after the regularly recommended, water-
dispersible, non-ionic surfactant, Triton B 1956, had been added to the spray
mixture; it was therefore necessary to substitute the water-soluble, non-ionic
preparation Triton X100 (Rohm and Haas Co., Philadelphia, U.S.A.). A month
later trees sprayed with standard dormant oil — lime-sulphur mixture (dormant
oil, 220 S.S.U. viscosity at 100° F., six gallons per acre, plus lime-sulphur,
32° Be., 12 gallons per acre) showed 99.4 per cent mortality of the San Jose
scale, Aspidiotus perniciosus Comst. ; trees sprayed with the same mixture
plus 0.25 per cent of Triton X100 showed 99.8 per cent scale mortality;
non-sprayed trees showed 65 . 7 per cent mortality. It is suspected that there
is little if any advantage in adding a water-soluble surfactant to a spray
mixture having the pronounced wetting capacity of petroleum oil — lime-sulphur.
It is difficult to find heavy infestations of the San Jose scale in British Columbia,
so that it has not been possible to repeat the experiment.

Type and Quantity of Surfactant Necessary

Experiments with such surface-active compounds as sodium lauryl sulphate,
triethanolamine oleate, saponin, soap bark, and certain commercial wetting
agents that are widely used in high-volume spraying showed that the require-
ments of concentrate spraying necessitated a new approach. Even in high
concentration the commonly used, detergent-type of surfactant failed to produce
a film coverage when added to a spray concentrate heavily charged with finely
divided solids. The low concentrations of the surfactants (wetters and spreaders)
common in high-volume spraying proved inadequate in concentrate spraying.
Anionic and cationic surfactants were evidently too likely to prove incompatible
with a number of the present-day pesticides. Water-soluble surfactants were
considered unsatisfactory because of their lack of resistance to heavy rainfall.
When present in relatively high concentration, and subjected to the strong
agitation necessary for spray concentrates, many surfactants foam heavily,
and cause air locks in high-pressure spray pumps; the result is a variable
output of spray liquid.

Eventually it was determined that the desired coverage could be obtained
by the use of the non-ionic, water-dispersible, low-foaming surfactants Triton
B 1956 (Rohm and Haas Co., Philadelphia, U.S.A.) and Colloidal Spray Modifier
(Colloidal Products Corp., San Francisco, U.S.A.). The latter was formulated
particularly for use with spray concentrates.

32

The impression of most writers who admit the possibility of using sur-
factants in concentrate spraying seems to be that the same concentration of
surfactant is required as in high-volume spraying. Hunnam et al. (32), for
mple, found that certain surfactants improved the control of apple powdery
mildew in high-volume spraying, and presumed they would do so in low-volume
spraying if used at the same concentration. For high-volume spraying the
surfactant Triton B 1956 is recommended by the manufacturers at one to two
ounces per 100 gallons; but, in concentrate spraying at 50 gallons per acre,
40 ounces per 100 gallons has proved necessary to provide a satisfactory film
coverage. Evidently, when spray droplets are very fine and the quantity of
liquid is insufficient to induce marked coalescence of droplets, the quantity of
surfactant necessary to produce a film coverage is much greater than would
be expected from experience with high-volume spraying. The point has been
mentioned by Srivastava and Srivastava (60), who determined that the con-
centration of soap required to produce complete wetting of foliage became
greater as the spray droplets became smaller.

Lacking an adjuvant, a concentrate spray mixture applied at 75 gallons
or less per acre of mature apple trees forms an obviously spotted deposit. When
an appropriate surfactant is added, the spray liquid forms a film, and the
resulting residue is barely visible (Fig. 8). According to Mr. K. Williams,
(unpublished work) of the Summerland laboratory, repeated analyses reveal
that the lack of deposit is merely apparent. In the application of DDT wettable
powder, for example, the amount of spray residue on the lower parts of large
trees, i.e., over 20 feet in diameter and over 15 feet high, or throughout small
trees, was approximately the same whether a surfactant had been added to
the spray mixture or not. In the tops of large trees, however, where adequate
spray coverage is generally hardest to achieve, the addition of a surfactant
consistently increased the amount of spray deposit; the increase has varied

Figure 8 — Mcintosh apples sprayed with 50 per cent DDT wettable powder at six
pounds in 65 gallons per acre. Left DDT-surfactant mixture; right, DDT alone.

from 20 per cent upwards. These analyses have special significance because
one of the shortcomings of concentrate spraying is the tendency to overspray
the lower parts of the trees. If a surfactant were to cause heavier spray
deposition in the lower parts of the trees, as it does in the upper parts of large
trees, that would be a serious handicap to its use. Perhaps the chief benefit

33

from the use of surfactants in controlling the codling moth and apple scab
has come from the improvement in the quality, or type, of the spray deposits.
But it seems probable, too, that the greater deposit in the tops of large trees
is important, because it is there that adequate coverage is most frequently
lacking.

Function of Surfactants

The way in which a water-dispersible surfactant improves spray coverage
is not yet well understood. Laboratory experiments by Mr. K. Williams,
(unpublished work) of the Summerland laboratory, suggest that the presence
of such a surfactant in a concentrate spray mixture increases the deposition of
spray liquid on surfaces exposed to the spray blast at angles of 45 degrees or
less. Possibly, when there is high interfacial tension between droplet and the
sprayed surface, the droplet has a tendency to ricochet when it impinges on an
inclined surface; that being the case, if the interfacial tension is reduced, as
by the addition of an appropriate surfactant, the droplet should be more likely
to adhere on impact and thus promote uniform spray coverage.

It has been observed that the surfactants now in commercial use in British
Columbia appear to increase the density of a concentrate spray mist. Experi-
ments with a commercial, turbine type of concentrate sprayer, on surfaces
exposed at an angle of 90 degrees to the spray stream, showed that no more
spray droplets were deposited from a Rhodamine B dye solution containing
the surfactant Triton B 1956 than from a solution lacking the surfactant.
Evidently the water-dispersible surfactant did not reduce the size of the spray
droplets and thus increase their number and hence the density of the spray
mist. Perhaps the apparent increase in the density of the spray mist is an
optical effect arising from the opacity imparted to the spray liquid by the
surfactant.

CONTAMINATION OF SOIL BY SPRAY CHEMICALS

In the spraying of orchards a problem not always given the consideration
it merits is contamination of the soil by spray chemicals. The serious losses
that occurred from the poisoning of orchard soils by lead arsenate in Colorado
and Washington in the '30's and early '40's were a warning that greater care
should be taken to minimize the amounts of persistent spray chemicals that
might reach the soil. Several experiments carried out by Dr. J. M. McArthur
and his associates (unpublished data) in the Okanagan Valley of British
Columbia have shown that concentrate spraying has a practical bearing on
the problem. In one case, for example, chemical analyses were made of the
cover crop in a mature apple orchard, with trees 30 feet apart, that had been
sprayed with 50 per cent wettable DDT powder, in part by high-volume spray-
ing at 0.22 pound of wettable powder per tree and in part by concentrate
spraying at 0.17 pound per tree. Since the trees nearly touched one another,
approximately 80 per cent of the orchard floor was beneath them. The following
figures represent, on a dry-weight basis, the parts per million of DDT on the
cover crop: — less than five feet from the tree trunk: high-volume spraying,
2,790; concentrate spraying, 580; five to 15 feet from the trunk: high-volume,
2,360; concentrate, 620; between trees: high-volume, 970; concentrate, 645.
Over the two sprayed areas there was on the average about 2.5 times as much
DDT on the cover crop for high-volume spraying as for concentrate spraying,
although not quite one-third more DDT was applied by the high-volume
procedure. Doubtless the chief reason for the difference in amounts of spray
chemical reaching the cover crop, or orchard floor, is the absence of drip, or
"run-off", from concentrate application.

34

Because of data such as these, and extensive experiments to determine
effective dosages, the recommended quantities of spray chemicals per acre are
generally markedly lower in British Columbia than in areas where insect and
disease control problems are similar but high- volume spraying is still the
general practice. Just how great the differences may be is shown in Table I,
which gives the quantities of some spray chemicals recommended per-acre for
concentrate spraying in the official spray recommendations for 1956 for British
Columbia (2) and for high- volume spraying in the neighboring State of
Washington (3).

Table I

Recommended Amounts of Spray Chemicals per Acre for Concentrate Spraying
in British Columbia and for High-Volume Spraying in Washington in 1956

Application

Dormant

Dormant

Pre-pink

Pink

Codling Moth

Chemical

Lime-sulphur
Lime-sulphur
Dormant oil .

Lime-sulphur

Karathane

DDT, 50%, plus.

(Parathion, 15%. .

Amount per acre (pounds or imperial gallons)

British Columbia
(Concentrate)

20 gal.

12 gal.

6 gal.

8 gal.

5 1b.

6 1b. plus 0.75 qt.

surfactant
none

Washington
(High- Volume)

73 gal. (88 U.S.)

19.9 gal. (24 U.S.)

9.9 gal. (12 U.S.)

16.6 gal. (20 U.S.)
8 1b.
16 lb.

3 to 8 lb.

PRESENT STATUS OF CONCENTRATE SPRAYING

It is probably significant that concentrate spraying is most sharply criti-
cized chiefly in the fruit growing areas where it has not been carefully
investigated. On the other hand, even with the admittedly second-rate con-
centrate sprayers commonly in operation, apparently few orchardists have
reverted from concentrate to high-volume spraying. The logic of the method
cannot be denied; light, low-priced equipment, minimum soil compaction,
minimum quantity of spray chemicals, minimum soil contamination, and mini-
mum water requirements, are features that the commercial fruit grower cannot
afford to overlook.

There have been, of course, frequent reports of poor pest or disease control
from concentrate spraying. Generally the trouble seems to have arisen from
faulty or underpowered equipment, or from failure to appreciate the importance
of proper dilution, nozzle adjustment, rate of travel, or tree pruning. But "Too
much spray injury" is the argument most often used against concentrate
spraying. On several occasions that argument has been traced to misinformation
as to what concentrate spraying actually is; on other occasions, to the exuber-
ance of sprayer salesmen; and sometimes it seems merely to have been a
matter of a common human tendency to resist change, or the urge to be
considered a cautious adviser.

Frequently "semiconcentrate" spraying, with from 150 to 300 gallons of
spray liquid per acre, is advanced as a means of reducing spray injury. Yet
semiconcentrate spraying results in drip, and to judge from the Summerland

35

investigations, only with highly dilute spray mixtures can drip be safely
permitted. As concentrate spraying becomes better understood and poor
machines are eliminated, it seems probable that semieoncentrate spraying will
be given up. Because there are, in British Columbia, a number of so-called
concentrate sprayers incapable of applying strictly concentrate sprays, semi-
concentrate spraying is still practised in this province; but concentrate spraying
is now the generally accepted method. Uncertainties as to effectiveness, spray
injury, and quantities of spray chemicals per acre have been largely cleared
up, although there is still some difference of opinion as to optimum amount
of spray liquid per acre. As inefficient machines become fewer, about 50 gal-
lons per acre of mature trees may become standard dosage (Fig. 9). Rate of
travel may vary somewhat, according to capacity of machines and according
to season, i.e., up to and including the pink-bud spray, the machines may travel
about twice as fast as for full-foliage sprays.

Figure 9 — One-side concentrate sprayer applying 50 gallons of spray concentrate per
acre. The spray mist can only be seen clearly when viewed against the sun.

Indications are that the deciduous fruit industries of Australia and New
Zealand will be the next to adopt concentrate spraying as standard procedure.
Already several hundred concentrate machines are operating in the Antipodes.
In Great Britain, Holland, and Denmark there appears to be increasing interest
in concentrate spraying, and several types of low-volume sprayers, as they are
commonly known overseas, are available. Sharp differences of opinion as to
dosages per acre appear to have led to some uncertainty about low-volume
spraying among fruit growers in Great Britain; but, whether the 50-gallon
dosage or the ultra low- volume three to 10 gallon dosage will eventually
prevail, there is reason to believe the new practice will steadily become more
popular.

The degree of acceptance of concentrate spraying in North America appears
to parallel its study. In New York State and New England, where most of
the recent United States research on orchard spray applicators has been done,

36

concentrate spraying is widely practised. But in the huge orchard areas of the
Pacific States, where there has been little research on the method, relatively
few fruit growers use it. In Canada the situation is reversed. Most of the
research has been done in the west, and most of the concentrate machines are
m the west. For the last several years the investigations at the Science
Service Laboratory, Kentville, Nova Scotia, have been giving reliable guidance
in concentrate spraying to the fruit growers of that province, and now, it is
understood, a turbine type of concentrate sprayer is to be built and marketed
there. The general mechanization of spraying by means of concentrate equip-
ment may be fairly close at hand in Nova Scotia and New Brunswick.

According to Mr. G. G. Dustan, Officer in Charge, Entomology Laboratory,
Vineland Station, Ontario, and Mr. A. A. Beaulieu, Officer in Charge, Science
Service Laboratory, St. Jean, Quebec, most apple growers in Ontario and
Quebec now use automatic sprayers of one kind or another. Machines without
fans are of the high- volume type; those with fans may be either high- or low-
volume. Fan-equipped machines have proved more efficient than those without
fans. Many growers now use low-volume, air-blast machines, but because of
their large orchards and densely foliated trees they prefer heavier, more highly
powered sprayers than are general in British Columbia. Growers who have
to spray more than about 15 acres of trees have found that it is less economical
to use a low-powered machine than a larger one; the larger machines do a
better job at high speeeds.

ASSESSMENT OF SPRAYERS

Suggesting the arbitrary level of 100 microns in droplet diameter to dif-
ferentiate between sprays and mists, Brown (12) mentions that the main
interest in orchard spraying now centers around the attainment of droplets with
mass median diameters between 50 and 100 microns, i.e., mists. He adds: "There
is a crying need for methods of obtaining droplet spectra of spray and mist
blowers". Experience at the Summerland laboratory supports Brown's views.
Indeed, what is needed is not merely a method, but a rapid method.

Ever since the project on concentrate spraying was begun in British
Columbia, efforts have been made to develop a simple yet reasonably accurate
means of assessing the performance of concentrate sprayers. In order to
screen new machines or devices, a two-dimensional trial was devised, largely

Figure 10 — Targets used in sprayer assessment; left, treated card; right, treated

microscope slide.

37

by Messrs. D. B. Waddell and J. M. McArthur. It consists in operating sprayers
past a frame 30 feet high and 30 feet wide, to the face of which are attached
small targets. The targets are mounted in pairs; one of each pair is a glass
microscope slide coated with a silicone preparation; the other, a white card
treated with a benzene solution of a high melting point wax (Fig. 10). The
slides and cards are so treated as to minimize the spreading of spray droplets
and the penetration of the spray liquid. Equidistant from one another, at the
five-foot level, are six pairs of such targets; six more pairs are directly above
them at the 10-foot level, and so on at five-foot intervals to the 25-foot level.
Thus, on the face of the frame are 30 pairs of targets. Charged with a water-
solution of the dye Rhodamine B, at known concentration, the sprayers are
driven past the spray frame at an angle of about 30 degrees, the first vertical
row of targets being sprayed when the machine is 15 feet from the frame, and
the last vertical row when the machine is five feet away (Fig. 11).

Figure 11 — Spray-frame used in assessing orchard
sprayers at the Entomology Laboratory, Summerland.

As soon as a trial run is completed the sprayed slides and cards are
removed to numbered holders, and replaced by fresh slides and cards. A
statistical analysis showed that reproducible results necessitate three runs for
each experimental machine or device. Since each assessment involves compari-
son with a reference machine, six sets of 30 pairs of targets are required.

38

After the spray droplets have dried, the microscope slides are washed in
distilled water to remove the dye, the quantity of which is determined by means
of a spectrophotometer. This procedure gives a reasonably accurate estimate
of the mass of the spray per unit of area at various distances from the ground
and from the sprayer. It does not, however, provide any information about
the size or uniformity of the spray droplets. That is done by microscopic
examination of the white target cards. Droplet diameter is approximated by
dividing stain diameter by a factor that represents the spread of the droplet
after impact.

Strips two inches by one inch in size are cut from the target cards, and
so mounted on black photographic album paper as to represent their relative

Figure 12 — Mounted cards showing performance of an efficient concentrate sprayer.

Note that all the targets received obvious spray coverage when the machine was

9 or 11 feet away from the spray frame.

39

positions on the spray frame. Examination of the 30 mounted sprayed strips
gives information on the spray pattern. Large stains on the lower cards, for
example, indicate coalescence of droplets and overspraying. Little or no
deposit on the uppermost cards indicates that the machine lacks capacity for
spraying treetops (Fig. 13). A uniform, finely stippled deposit from the five-
foot level to the 25-foot level, with the machine nine to 11 feet from the frame,
is evidence of efficient operation (Fig. 12). Sometimes only the white cards
are used in the assessment. But, when greater assurance is required, the glass
slides and chemical analyses are brought into play. Then, as a final step, the
evidence of performance from the mounted cards is compared with the data
from the chemical analyses.

Figure 13 — Mounted cards showing performance of an inefficient concentrate sprayer;
heavy overspraying at low levels, insufficient coverage at high levels.

40

III assessing concentrate spray equipment it is necessary to have a record
of atmospheric air movement while each run is being made. An observer is
stationed near the spray frame on a platform 10 feet high. While the sprayer
is being driven past the spray frame he notes the wind direction and, by means
of a velometer and an anemometer, the maximum wind velocity and the
number of feet of air movement. These data are taken into account when it
is desired to study the records of sprayer performance with particular care.

Use of the spray frame is restricted to preliminary screening trials. When
a new machine, or a new component, gives results on the spray frame obviously
inferior to those for the reference machine (a turbine-type, high-pressure,
concentrate sprayer developed from the Okanagan experimental sprayer; air
stream 6,700 to 7,000 c.f.m. at 110-115 m.p.h.), the new equipment is eliminated
without further ado. If, however, it appears to be as efficient as. or more
efficient than, the reference machine, it is subjected to orchard trials involving
chemical analyses of samples from various levels in the trees and, if feasible,
determination of effectiveness against whatever orchard insects or mites are
available in adequate number.

The foregoing procedure for assessing concentrate orchard sprayers has
proved most useful; but it is a laborious undertaking. The job of operating
the sprayer, taking wind measurements, and changing targets requires the
services of six people, and preparation of the targets and chemical and micro-
scopic analyses necessitate many hours of careful laboratory work. Although
the procedure does not provide highly accurate measurements of droplet size,
it is questionable whether great precision is necessary for work of the kind.
In assessing the performance of concentrate sprayers, the most obvious need,
as mentioned earlier, is for greater speed rather than greater precision.

RECOMMENDATIONS FOR SPRAYING

It has been observed that advisers, or operators, who are unfamiliar with
concentrate spraying, are prone to overestimate the amounts of spray chemicals
necessary for it. Overlooking the great wastage from the drip, or "run-off", in
high-volume spraying, they tend to assume that the quantities per acre for
concentrate spraying are the same as for the old procedure. Chemical analyses,
trials of effectiveness, and observations on phytotoxicity have shown that this
is not the case. In the days of high-volume spraying in British Columbia, for
example, 50 per cent DDT wettable powder was used at 1^ pounds per 100
gallons against the codling moth. Growers applied from 800 to 1600 gallons of
spray liquid per acre, i.e., from 12 to 24 pounds of DDT. If an appropriate
surfactant is added in the necessary amount, adequate deposits for all but the
heaviest infestations are obtained when six pounds of DDT per acre are applied
as spray concentrate. Again, in dormant spraying, a mixture of two gallons of
heavy dormant oil and four gallons of lime-sulphur per 100 gallons of spray
liquid was recommended in high-volume spraying against the San Jose scale,
Aspidiotus perniciosus Comst., and about 500 gallons of spray liquid might be
used per acre, i.e., 10 gallons of oil and 20 gallons of lime-sulphur. In con-
centrate spraying, on the other hand, similar results are obtained from six
gallons of oil and 12 gallons of lime-sulphur.

By repeated experiment and observation the appropriate per-acre dosages
of spray chemicals have been determined for British Columbia conditions.
Since 1949, official recommendations for concentrate spraying have been made
by the British Columbia and Canada Departments of Agriculture. The recom-
mendations are prepared without reference to high- volume spraying; hence
such terms as "8X" and "semiconcentrate" are avoided. Undoubtedly the

41

simplicity of these spray recommendations has been an important factor in the
rapid adoption of concentrate spraying in the Province. The 1957 recommenda-
tions (2) which, in general, should be applicable elsewhere, are in part as
follows:

"Speed of travel is most important in the successful operation of con-
centrate machines. For average size, mature trees, in full foliage applications,
speed should not exceed one mile per hour (90 feet per minute). Disk openings
should be checked frequently for any sign of wear. Use only materials listed
for concentrate sprays. Shut off spray while making turn at end of row. Use
smaller disks at lower end of nozzle-boom when excessive deposits are visible

Table II

Amounts of Spray Chemicals Recommended per Acre for Concentrate
Spraying in British Columbia in 1957

Spray Chemicals

Pounds or
Imperial Gallons

(Nicotine sulphate, 40%

^Sodium carbonate (washing soda)

Diazinon, 25% wettable powder

\ gal.
2 1b.

12 lb.

Malathion, 25% wettable powder

15 lb.

Aramite, 15% wettable powder

Sulphenone, 50% wettable powder

12 1b.
16 1b.

Fenson, 50% wettable powder

4 1b.

Ovex, 50% wettable powder

4 1b.

[Dormant oil, 200-220 S.S.U. Vis

[Dinitro-cresol wettable powder, 40%

6 gal. (8 gal. if 75%
emulsified oil is used)
4 1b.

/Dormant oil, 200-220 S.S.U. Vis

6 eal.

\ Lime-sulphur, 32° Be

12 gal.

Lime-sulphur (dormant spray)

20 gal.

Lime-sulphur (foliage spray)

Wettable sulphur

(Wettable sulphur

\Ferbam (Iron carbamate) or Ziram (zinc carbamate)

Bordeaux mixture

copper sulphate

8 gal.
10 1b.

15 1b.
5 1b.

25 lb.

hvdrated lime

40 lb.

Bordeaux mixture for fire blight

copper sulphate

hvdrated lime

3 lb.

3 lb.

DDT, 50% wettable powder

12 lb. (6 lb. if used with

Methoxychlor, 50% wettable powder

surfactant)

12 lb. (6 lb. if used with

surfactant)

on lower portions of trees, (there should be no visible run-off). Amounts of
chemicals for concentrate sprays . . . are recommended amounts per acre.
Determine tank output on acreage basis; e.g., if tank covers \\ acres use \\
times the material shown in concentrate column above."

42

Since "safe" chemicals are emphasized for concentrate spraying in British
Columbia, the use of organic pesticides in liquid form is not recommended,
and liquids formulated with organic solvents are generally avoided. Wettable
powders are preferred; their abrasive qualities have been fairly well taken care
of by the use of tungsten carbide nozzle discs and swirl plates; and the con-
spicuousness of their deposits, by surfactants. Restrictions as to type of formula-
tion have helped to simplify the spray recommendations, a desirable thing
when the recommendations otherwise tend to become more confusing year by
year. Unusually abrasive formulations are avoided, as are heavily foaming
preparations.

Table II shows that lime-sulphur has considerable prominence in the
British Columbia spray recommendations. Since, just before the introduction of
concentrate spraying, it had been largely superseded by less caustic, if less
effective and less versatile, preparations, that is an interesting point. Lime-
sulphur still ranks as one of the most useful and most economical spray
chemicals and, in re-establishing its general use, concentrate spraying has
conferred an unexpected dividend on the fruit growers.

SUMMARY

Experiments were begun in 1946 to reduce the labor and cost of spraying
operations in the orchards of British Columbia. By 1956 virtually all the
spraying was being done with light, concentrate sprayers modelled after the
Okanagan experimental sprayer built in 1948. The change-over to concentrate
spraying was accomplished without confusion, partly because most of the
machines were of the same type, and partly because the recommendations for
concentrate spraying were concise and easily interpreted.

Concentrate spraying is being rapidly adopted in the eastern and middle-
western United States and in Australia and New Zealand. Dutch, Danish, and
British fruit growers appear to be turning increasingly to the new procedure.

Concentrate sprayers are defined as machines that cause no drip from the
sprayed trees. They apply up to 75 imperial gallons of spray per acre of
mature trees. The preferred dosage for British Columbia is 50 gallons.

The type of machine that, to date, has proved most practical for the majority
of British Columbia fruit growers is a "one-side" sprayer weighing, with tank
empty, from 1,500 to 1,800 pounds. It has a high-pressure pump, generates a
linear-flow air stream, and is powered by a 25-horsepower gasoline engine.
Operators of 50 acres or more generally prefer "two-side machines with double
the capacity of the "one-side" models.

In British Columbia, concentrate spraying has proved as effective as com-
mercial, high-volume spraying against insects, mites, and diseases of deciduous
fruit trees, and has effected substantial savings in spray chemicals and labor;
it has eliminated the wet clothing, drudgery, and discomforts of high-volume
spraying.

The efficiency of concentrate sprayers is influenced by the velocity, the
volume, and the type (turbulent or linear-flow) of the air stream, the design
of the blower scroll and the air vent, the type of liquid manifold, the type of
spray nozzle, the arrangement of the nozzles, the angle of emission of the spray
liquid, the output of spray liquid, the pressure of the spray liquid (with swirl
nozzles), and the rate of travel.

The homogeneity, volatility, viscosity, density, and surface-activity of
spray concentrates have a bearing on atomization and on performance after
impact.

The type of spray coverage obtained with concentrate sprayers is less effi-
cient than would be expected from the amount of spray chemical that they

43

deposit. The coverage can be made more nearly uniform and more efficient
by the addition of certain non-ionic, water-dispersible, low-foaming, surface-
active preparations (surfactants). The percentage of surfactant necessary is
from 10 to 40 times as great as the percentage of wetter, or spreader, used in
high-volume spraying.

In concentrate spraying, surfactants have improved the control of apple
scab and the codling moth, but not of aphids nor of phytophagous mites.

With efficient, properly operated equipment, spray injury has not been
more troublesome with concentrate spraying than with high-volume spraying.
Lime-sulphur applied to dry trees has proved less prone to cause injury in
concentrate spraying than in high-volume spraying.

Soil contamination by spray chemicals is distinctly less from concentrate
spraying than from high-volume spraying.

A spray-tower technique has been developed for assessing the performance
of concentrate sprayers. Its purpose is to screen out inferior equipment.

Amounts of spray chemicals recommended for concentrate spraying in
British Columbia are considerably lower than for high-volume spraying.

Recommendations for concentrate spraying need be no more involved than
those for high- volume spraying. The 1957 spraying recommendations for
British Columbia are quoted to illustrate the point.

ACKNOWLEDGMENTS

Concentrate spraying could not have been quickly and soundly established
in British Columbia without the aid of all members of the staff of the Sum-
merland laboratory, the whole-hearted support of the Okanagan and Kootenay
horticulturists of the British Columbia Department of Agriculture, and the
confidence of the fruit growers. The entomologists, Messrs. R. S. Downing,
C. V. G. Morgan, M. D. Proverbs, and D. B. Waddell all contributed useful
observations and ideas. The chemists, Messrs. J. M. McArthur, J. R. W. Miles,
and K. Williams, with their assistants, Messrs. F. E. Brinton and G. A. Wardle,
carried out innumerable chemical analyses to determine spray deposits in the
orchards, and played a leading part in the spray-tower assessment of new
equipment.

Since 1955 Mr. A. D. McMechan, agricultural engineer at the laboratory,
has been doing valuable work on the mechanical side of concentrate spraying.
Messrs. G. D. Halvorson and G. F. Lewis, technicians, helped greatly by oper-
ating the various types of sprayers, experimental and otherwise, in the orchards,
and by contributing ideas on modifications to simplify or improve operation of
the equipment.

Mr. F. E. Owen, Defence Research Station, Suffield, Alberta, had much to
do with the preliminary investigations, and built the prototype of Canadian
concentrate machines, the Okanagan experimental sprayer. He deserves a
particular word of appreciation because, in doing the job, he did not have the
incentive of close association with the fruit industry.

Messrs. W. H. Robertson, Ben Hoy, and R. P. Murray, successive Provincial
Horticulturists, arranged for the funds that were needed to build the Okanagan
experimental sprayer, and have strongly supported the concentrate spraying
investigations since they were begun. Among the Provincial district horticul-
turists, all of whom have been most helpful, special thanks must go to Messrs.
E. C. Hunt, retired, and J. E. Swales, for the work they have done to establish
concentrate spraying in the Kootenay Valley.

A final word of thanks goes to the three sprayer manufacturers who
kindly contributed machines, and ideas, to further the investigations: Okana-
gan Turbo Sprayers Ltd., Penticton, British Columbia; Trump Ltd., Oliver,
British Columbia; and Besler Engineering Corp., Emeryville, California.

REFERENCES

1. Akesson, N. B. Blower sprayer equipment for pest control. Implement

Record 47: 27-30. 1950.

2 . Anonymous. Control of tree-fruit pests and diseases. British Columbia

Dept. Agr. poster, p. 1. 1957.

3. Anonymous. 1956 spray recommendations. State Coll. Washington

Ext. Bull. 419 (rev.). 35 pp. 1956.

4. Besemer, A. F. H. Faktoren die van Invloed zijn op het Ontstaan van

"Spuitbeschadigingen". Achtste Jaarlijks Symposium over Phyto-
pharmacie. Mededel. Landbouwhogeschool en Opzoekingsstations
StaatGent21: 483-496. 1956.

5. Beskine, J. M. The use of the low volume mist blower. World Crops 4:

338-343. 1952.

6. Byass, M. A. Concentrate spraying: Will this nozzle solve the problems?

The Grower 45: 1306-1307. 1956.

7. Brann, J. L., Jr. New methods for the application of insecticides to

fruit trees. New York State Hort. Soc, Proc. 93rd Ann. Meeting:
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8. Brann, J. L., Jr., A. W. Avens, and R. W. Dean. The application of dormant

oils as mists. J. Econ. Ent. 41: 180-185. 1948.

9. Brann, J.L., Jr. The use of mist concentrates on fruit trees. New York

State Hort. Soc, Proc. 95th Ann. Meeting: 96-104. 1950.

10. Brann, J. L., Jr. Mist concentrates on fruit trees. New York State Hort.

Soc, Proc. 96th Ann. Meeting: 100-107. 1951.

11. Brann, J. L., Jr. Apparatus for application of insecticides. Ann. Rev.

Ent. 1: 240-260. 1956.

12. Brown, A. W. A. Some principles of the application of liquid insecticides.

Pesticide Application Equip. Conf., Cornell Univ. Mimeo. 21 pp.
1955.

13. Burrell, A. B. Concentrate spraying in New York State during 1952.

New York State Hort. Soc, Proc. 98th Ann. Meeting: 142-148.
1953.

14. Burrell, A. B. Concentrate method prevails in eastern New York. American

Fruit Grower 73: 20, 44-47. 1953.

15. Courshee, R. J. How many gallons to the acre? The Grower 45: 338-341.

1956.

16. Cutright, C. R. Control of mites with concentrate sprays. Ohio State Hort.

Soc, Proc. 82nd Ann. Meeting: 89-93. 1949.

17. Davies, C, and G. Smythe-Homewood. Investigations on machinery used

in spraying. Part 1. Nozzles. J. South East Agr. Col. (Wye,
England) 3: 39-62. 1934.

18. Edwards, C. J., and W. E. Ripper. Droplet size, rates of application, and

the avoidance of spray drift. British Weed Control Con., pp.
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19. French, O. C. Spraying equipment for pest control. California Agr. Expt.

Sta. (Berkeley) Bull. 666: 1-42. 1942.

44

45

20. Foulds, R. M., G. L. Hey, and D. Hunnam. Low volume sprays for pest

and disease control. The Grower 43: 941, 943, 945. 1955.

21. Garman, P. Efficiency of various orchard spray machines. J. Econ. Ent.

45: 345-346. 1952.

22. Garman, P. A study of spray machines in Connecticut orchards. Connec-

ticut Agr. Expt. Sta. Bull. 567: 1-34. 1953.

23. Glass, E. H., and S. E. Lienk. Some problems in orchard spraying. New

York State Hort. Soc, Proc. 98th Ann. Meeting: 135-141. 1953.

24. Goossen, H. Welche biologischen Forderungen werden an Pflanzenschutz

gerate fur den Feldbau gestellt? Z. Pflanzenkrank. Pflanzensch.
60: 561-568. 1953.

25. Goossen, H., and L. Eue. Distribution, resistance to rain, and translocation

of spray and mist deposits in potato stands. Hofchen-Briefe
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