GREENHOUSE
PESTS

AND THEIR CONTROL

A. EARL PRITCHARD
BULLETIN 713 MAY?

CALIFORNIA AGRICULTURAL

STATION

THE COLttEGT OF AGRICULTURE
UNIVERSITY OF CALIFORNIA

BERKELEY

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The Greenhouse Pests PAGE

Spider Mites (Red-Spiders) 6

False Spider Mites 8

Thread-Footed Mites 9

Louse Mites 10

Fungus Mites 10

Springtails 11

Earwigs 12

Termites 12

PAGE

Thrips 13

Aphids 16

Whiteflies 19

Mealybugs 21

Ensign Scales 24

Giant Scales 24

Woolly-Sac Scales 25

Soft Scales 25

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(AN INDEX OF SPE<
INFORMATION

Armored Scales ....

Plume Moths

Loopers

Leaf Blotch Miners .

Leaf Tiers

Leaf Rollers

Cutworms

Weevils 36

Fungus Gnats 37

Gall Midges 38

Bulb Flies 39

Leaf Miners 40

Sawflies 41

Stem Wasps 41

Ants 42

Millipedes 42

Garden Centipedes 43

Slugs and Snails 44

Pillbugs and Sowbugs 44

Nematodes 45

Methods of Control 46

Biological Control 46

Heat Treatment 46

Chemical Control 47

PAGE

. 53
. 54
. 54
. 54
. 54
. 54
. 54

The Insecticides 48

Arsenicals 48

Lead Arsenates 48

Calcium Arsenate 48

Paris Green 48

Arsenic Trioxide 49

Sodium Arsenite 49

Azobenzene 49

Benzene Hexachloride 50

Carbon Disulfide 50

Chlordane 51

Chloropicrin 51

Cyanide 51

DDT and Related Compounds .... 52

DDT 52

Methoxychlor 52

DDD 52

Dichlorobenzenes 53

Paradichlorobenzene 53

Orthodichlorobenzene 53

Dichloroethyl Ether 53

Dichloropropane-Dichloropropene . 53

WARNING

The organic phosphates (parathion,
hexaethyl tetraphosphate and tet-
raethyl pyrophosphate) are exceed-
ingly dangerous to human beings in
extremely minute amounts when
ingested, inhaled or absorbed
through the skin. The precautionary
statements contained in this publi-
cation concerning these materials

may not be wholly adequate.

Metaldehyde 54

Methyl Bromide 55

Naphthalene 56

Oils 56

Petroleum Oils 56

Vegetable Oils 56

Organic Phosphates 56

Hexaethyl Tetraphosphate 56

Tetraethyl Pyrophosphate 56

Parathion 57

Organic Thiocyanates 58

Plant Derivatives 58

Nicotine 58

Rotenone 58

Pyrethrum 59

Sabadilla 59

Selenium Compounds 59

Sodium Selenate 59

Sulfur 59

Elemental Sulfur 59

Lime-Sulfur 60

Ammonium Polysulfide 60

Tartar Emetic 60

Toxaphene 60

Methods for Applying

Insecticides 61

Dusts 61

Sprays 61

Fogs 63

Liquefied-Gas Aerosols 64

Smokes 65

Gaseous Fumigation 65

Soil Treatment 66

Baits 66

General References 66

Index &

Tabfes of Equivalents 72

At left: The Conservatory, Golden Gate Park, San Francisco.

This Bulletin

has been prepared as a source of information for the California green-
houseman in his fight against insect pests.

Investigation and observation in some of the most extensive com-
mercial greenhouses in California have formed the basis of this pub-
lication. In the survey work, as well as in conducting experiments on
the use of insecticides, the author has had access to the crops of a large
number of successful greenhouse operators. These growers have given
invaluable assistance to the studies.

The section on THE GREENHOUSE PESTS, with the many
original photographs, will give the greenhouseman complete material
to help him identify insect pests on his crops. This section clears up
much of the confusion which has existed concerning the occurrence
and the relative importance of certain species of insects and mites.
Some species, not previously known to occur in California, are reported
here for the first time.

It is important for the greenhouseman to learn to recognize the
specific insect pests. This is true not only in understanding the actual
importance of the pest involved, but also for deciding on the best
measures for control. The newer insecticides in particular are often
specific in their action, being effective for the control of one pest while
not affecting a closely related species.

The sections on KINDS OF CONTROL and METHODS FOR
APPLYING INSECTICIDES are intended as practical aids in carry-
ing out the pest-control program. These sections are presented to pro-
vide an understanding of the methods involved.

The section on INSECTICIDES is believed to be as complete
as possible in the light of present information. It describes all of the
chemical controls which are in common use, as well as those which the
greenhouseman may have heard about or those which he may have
seen on labels of commercial products. It gives an evaluation of each
with respect to its use in the greenhouse.

The reader is reminded that the /ecommendations for control should
not be considered complete or final. The entire field of chemical con-
trol is constantly undergoing refinement, and information concerning
the preparation and use of new materials is being augmented daily.

GREENHOUSE PESTS AND THEIR CONTROL

A. Earl Pritchard

Assistant Professor of Entomology and

Assistant Entomologist in the Experiment Station

The cultivation of flowering and other
ornamental plants has become a tremen-
dous industry in California during recent
years. The cut-flower industry in the San
Francisco Bay region alone has been esti-
mated at $25,000,000 a year. A large
amount of these crops are grown under
glass. The San Francisco Bay region is
particularly favored for greenhouse crops
because of the comparatively mild climate
throughout the year and the ready access
to airplane transportation for eastern
markets. About 8 million square feet of
greenhouse space are located near San
Francisco Bay.

In Los Angeles County there are over
2 million square feet of greenhouse space.
While most of the cut flowers are grown
out of doors, still those grown commer-
cially under glass are worth about a mil-
lion dollars annually.

There are also many amateur green-
house-gardeners in the state. Near Los
Angeles, particularly in the Hollywood
hills and Pasadena, and along the penin-
sula south of San Francisco there are
probably two thousand privately owned
glasshouses, more than half of which are
devoted to orchids.

Greenhouse Conditions Favor Pests

Ornamental plants are subject to the
depredations of mite, insect, and other
animal pests. The hothouse crops are
grown under warm and humid conditions
which favor the survival and development
of many species which have been im-
ported from tropical or semitropical

regions. Such pests may be found exclu-
sively in greenhouses, although many of
these are found outdoors in the coastal
and southern sections of California.
Greenhouses are also subject to the inva-
sion of native or established agricultural
pests of the local neighborhood. Some
may be infrequent or unimportant visi-
tors, while others may become more
serious because of the opportunity for
year-around reproduction and protection
from their natural enemies. This bulletin
pertains to the important greenhouse
pests which are introduced mainly by in-
fested stock and also to the more impor-
tant pests which are immigrants from
outdoors.

Limitations of this Study

Certain woody plants, such as camellia
and boxwood, are not generally consid-
ered to be greenhouse crops, although
their propagation may be carried on in
the greenhouse and pests attacking this
stock may be found on the cuttings. A
discussion of pests which are restricted
to such plants is not included in this bul-
letin.

The treatment of the greenhouse pests
and their control as given in this bulletin
is intended to serve as an over-all guide.
It has not been possible to include long
host lists which are often available for
many of the mites and insects. There is
still a need for publications dealing with
specific greenhouse crops, their individ-
ual pests, and specific control programs
in relation to the crops.

[5

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SPIDER MITES

(Red-Spiders)

Importance: Spider mites, or red-
spiders as they are commonly called, are
among the most serious pests of orna-
mental plants. Because of their very small
size and the general habit of feeding on
the undersurface of leaves, their presence
often escapes detection by the greenhouse-
man until they are exceedingly numerous
and plant damage is obvious.

The needlelike mouthparts are used to
puncture the tissues, and a speckled ap-
pearance of the leaves and flowers results.
In the case of severe infestations, entire
leaves may become bleached and curled,
and leaf drop occurs.

Appearance: Spider mites are soft
bodied, more or less elliptical, with the
back arched and bearing bristles. The
adult female is less than 1/50 inch in
length. They are colored greenish, yel-
lowish, or reddish, and often have dark
spots on each side. The eggs are globular
or flattened above and are pearly, amber,
or red in color.

Fine strands of silk are spun by spider
mites, although the webs may not be de-
tected readily except when large numbers
are present. When an infestation is very
severe, parts of the plant may become
completely enveloped in sheets of web-
bing, and masses of mites may hang from
the tips of the leaves.

Development: Eggs are laid singly on
the surface of leaves. An adult female may
lay several or more eggs a day, producing
as high as 50 to 100 eggs. During the
course of development of the female three
resting stages occur, each prior to shed-
ding the skin. In a warm greenhouse an
entire generation may be completed in

from 7 days (at 80° F) to 14 days (at 70°
F) ; but under cooler conditions a period
of two or more months may be required.

Important Greenhouse Species

Two-spotted spider mite (common red-
spider) , Tetranychus telarius (Linnaeus) ,
is greenish or yellowish, with a large,
blackish spot on each side, or else reddish
in color. It is the most general feeder and
the most troublesome of the spider mites
encountered by the floriculturist. Carna-
tions, cymbidium orchids, gardenias, hy-
drangeas, and roses are greenhouse crops
which are constantly subject to attack.
Many other flowering and ornamental
plants, as well as weeds, are susceptible
to injury. This mite is found in abundance
on many plants outside the greenhouse
during the warmer part of the year.

It has been estimated that one female
is capable of giving rise in one month's
time to a progeny of 20 mites at 60° F,
about 13,000 mites at 70° F, and well over
13 million mites at 80° F constant temper-
ature. It is thus easy to see why multipli-
cation is so rapid on hothouse crops and
why control measures must be thorough.

Fig. 1. The two-spotted spider mite: adult fe-
male.

6]

Fig. 2. Hydrangea enveloped in sheets of webbing made by an infestation of spider mites.

Other Species Found

In California Greenhouses

Luden spider mite, Tetranychus ludeniZacher,
is bright reddish in color. Frequently it is
found in greenhouses and is common outdoors
in southern California. A number of flowering
plants serve as hosts, of which lantana appears
to be a favorite.

Palm spider mite, Septanychus tumidus
(Banks), resembles the Luden spider mite but
is considerably smaller. It often is a serious pest
to greenhouse palms as well as to a few other
plants such as maranta. .

Asparagus spider mite, Schizotetranychus
asparagi (Oudemans), is very small, pinkish,
with dusky markings along each side. It is found
only on asparagus ferns, causing the plants to
become speckled or whitish.

Oxalis spider mite, Tetranychina harti
(Ewing), is reddish, with bristle-bearing tuber-
cles above and with very long forelegs. It occurs
commonly on oxalis in greenhouses but does not
transfer to other hosts.

CONTROL

Control of spider mites has long been
a major problem in connection with
greenhouse-grown cut flowers. Several
rather recently developed acaricides have
proved the most satisfactory, although
each is subject to limitations. These in-
clude :

1. Azobenzene fumigation : high degree
of control of all stages. (See page 49.)

2. Sodium selenate: excellent control
over a long period of time on carnations.
(See page 59.)

3. Tetraethyl pyrophosphate : effective
for active stages. (See page 56.)

4. Parathion: excellent control. (See
page 57.)

7]

FALSE SPIDER MITES

Importance: The false spider mites are
closely related to the spider mites, and
they similarly injure foliage. Leaves show
signs of their feeding by forming dis-
colored flecks or depressions, and this
may be followed by general discoloration
and leaf drop.

Appearance: They are exceedingly
small, flattened, red or yellowish mites.
Adults are less than 1/100 inch in length.
The eggs are elliptical, bright red, and
are sometimes seen more readily than
the mites. Unlike the spider mites, they
do not spin silken webs.

Development: Eggs are laid singly on
leaf surfaces. Under warm conditions, the
eggs hatch in several days, and the life
cycle may be completed in two weeks.

Fig. 4. Deep pits and silvering of the leaf
caused by the phalaenopsis mite.

Fig. 3. The privet mite: adult female.

Important Greenhouse Species

Privet mite, Brevipalpus inornatus
(Banks). Adult is bright red with a cen-
tral darkening which forms two eye-like
spots. The privet mite occurs on the un-
dersurface of leaves. It is particularly
destructive to azaleas and fuchsias in Cali-
fornia greenhouses, although a number
of other hosts have been noted.

Moderate to severe damage has been
observed by a closely related species
which feeds on several different orchids,
while still another species is a pest of
greenhouse palms.

Other Species Found

In California Greenhouses

Phalaenopsis mite, Tenuipalpus pacificus
Baker, is yellowish or reddish in color. It occurs
only on phalaenopsis orchids, forming deep pits
on the upper surface of the leaves. This species
is found infrequently in California greenhouses,
but it is a serious pest when present.

CONTROL

The false spider mites are not affected
by the organic phosphate acaricides that
are so effective for spider mites. Very little
information on their control is available.
Dimethyl carbinol has proved to give ex-
cellent control experimentally.

1. Sulfur or lime-sulfur: reported to
give satisfactory control. (See page 59.)

2. Light oil with rotenone: effective
control. (See page 56.)

[8]

THREAD-FOOTED MITES

Importance: The thread-footed mites
comprise a small group which contains a
few serious pests of ornamental plants.
Growing tips of plants and young leaflets
are characteristically deformed as a re-
sult of their feeding. The presence of these
tiny mites in a greenhouse is seldom de-
tected until a severe infestation has de-
veloped. Economic losses are due not only
to the plant damage incurred but also to
the labor and materials wasted in ineffec-
tive efforts for control.

Several species of thread-footed mites
which are found in greenhouses are not
known to be of economic importance.
These are presumed to feed on decaying
organic material or insects.

Appearance: Adult mites are elliptical
in shape, more or less flattened, brownish,
and shining. They are not over 1/100 inch
in length. The immature stages are white.
The eggs are elliptical and white. It is by
the characteristic damage that the pres-
ence of these mites is usually suspected.

Development: The eggs are laid on
protected surfaces of the plant tissues
where the mites are feeding. These hatch
into six-legged larvae in from 3 to 7 days.
The larval period is completed in from
1 to 4 days. A resting stage follows which
lasts from 2 to 7 days before the adult
emerges. The adult female may lay from
1 to 3 eggs during a day, and the total
number laid by a single female ranges
from 12 to 16. Breeding continues
throughout the year under greenhouse
conditions.

Important Greenhouse Species

Cyclamen mite, Tarsonemus pallidus
Banks, feeds characteristically at the ori-
gin of new plant growth, in the buds or
unfolding leaflets so that the leaves or
flowers formed are aborted and mis-

Fig. 5. The cyclamen mite: adult female.

Fig. 6. Crippled terminal growth of Hahn's ivy caused by the cyclamen mite.

9]

shapen. In the case of plants such as Afri-
can violet, gloxinia, and gynura, the
"eyes" become whitish and growth is cur-
tailed or stopped.

Optimum conditions for development
of the mite are found in greenhouses
where the temperature is moderately
warm (60° to 80° F) and the relative
humidity is very high (80 to 90 per cent) .
Lath house infestations are not apt to be
severe.

The host range of the cyclamen mite
is rather wide. English ivy is very com-
monly infested, and other plants such as
aralia, fuchsia, azalea, pepper plant, and
fibrous begonia are often infested. The
only agricultural crop that is attacked is
strawberry.

Other Species Found

In California Greenhouses

Broad mite, Hemitarsonemus latus (Banks),
is similar to the cyclamen mite in appearance
and host range. It differs principally by occur-
ring more generally over the plant and by feed-
ing on the undersurface of leaves. This impor-
tant pest of ornamentals is rarely encountered in
California.

Bulb scale mite, Tarsonemus laticeps Halbert,
infests the bulbs, stems, and leaves of narcissus.
Damage is caused principally to the bulbs. This
species is found only occasionally in California.

CONTROL

Control of the cyclamen mite is one of
the most difficult problems encountered
by growers of potted plants. The use of
lauryl thiocyanate, ammonium polysul-
fide, lime-sulfur, or rotenone prepara-
tions, has not proved to give effective
control in California. Dimethyl carbinol
has shown some promise experimentally.

1. Parathion: considerable control
when used as a wettable-powder spray.
Several applications at weekly intervals
are necessary. (See page 57.)

2. Hot water or vapor-heat treatment:
effective when such treatment is practical.
(See page 46.)

3. Methyl bromide fumigation : excel-
lent control. (See page 55.)

LOUSE MITES

Importance: The louse mites constitute
a small group which is closely allied to
the thread-footed mites. They are often
found on grasses or grains, but one of
the common species feeds on injurious
insects or sometimes annoys humans. The
only species which is of importance in
greenhouses is one which distributes
spores of a fungus disease.

Appearance: These are soft-bodied
mites. The abdomen of the female swells
enormously, forming an egg-shaped or
globular ball. They are whitish and be-
come about 1/50 inch long.

Development: As many as 200 eggs
are developed within the female mite.
These eggs hatch and the young mites de-
velop to maturity before they emerge
from the parent.

Species Found

In California Greenhouses

Grass mite, Pediculopsis gramineum Reuter,
burrows into carnation buds to feed on the
stamens and pistils. As they travel from plant
to plant, they act as the principal agent for
distribution of spores of the fungus causing
carnation bud rot and "silver top" of grasses.
This mite is found infrequently in California.

CONTROL

Manual picking and burning of infested
buds constitutes the control measure
which has been generally recommended.
No information is available on the use of
new acaricides.

FUNGUS MITES

Importance: Fungus mites are found
commonly in rotting leaves and plant
debris. Under greenhouse conditions
where the relative humidity is high and
the soil rich in decaying organic material
and fungi, large numbers of these mites
often occur. Generally they are associated
with the soil or moldy plant tissue, but
they also may be found crawling over the
foliage. Only one member of this group
is believed to be of economic importance
to the floriculturist.

10

Fig. 7. Bulb mite: top and bottom views.

Appearance: These mites are some-
what egg-shaped, soft-bodied, with long
bristles on the back. They are whitish and
generally bear a pair of conspicuous
brownish spots on the back part of the
body. Adults may be as large as 1/50 inch
in length.

Development: Eggs are laid singly
where the adults are feeding, each female
laying from 50 to 100 eggs. The eggs
hatch within a few days, and the young
mature in about two weeks. They are
spread from place to place by means of a
special form of the young which attaches
itself to flies and other insects.

Important Greenhouse Species

Bulb mite, Rhizoglyphus echinopus
(Fumouze and Robin) , is similar to other
fungus mites but larger and with short,
stubby legs. This mite is found univer-
sally in many kinds of bulbs and tubers.
It has been reported that healthy bulbs
are attacked under certain conditions,
but mite injury possibly follows a plant
disorder. A fungus disease causing rot
may be carried by the mite, however.

CONTROL

No information is available on the use
of new acaricides on fungus mites. Eggs
of the bulb mite are reported to withstand
methyl bromide treatment.

1. Hot water or vapor-heat treatment:
effective for bulb mite control. (See page
46.)

SPRINGTAILS

Importance: Springtails are found or-
dinarily under damp conditions where
there is an abundance of humus. In green-
houses they may be common in the beds,
in potting material, or under flower pots.
Ordinarily their food consists of decay-
ing organic material, fungi, or algae, but
certain species may be responsible for
injury to seedlings or young, tender
plants. Only one species is known to be
injurious in greenhouses. Many other
species also occur which are not known
to cause damage but which may become
so abundant as to be a nuisance.

Appearance: Springtails are small,
wingless insects, usually less than 1/5
inch in length. The immature stages are
usually whitish. The adults are sometimes
whitish, but often bluish, purplish, or yel-
lowish with dark spots. Many species are
able to jump by means of a lever which is
attached underneath the body.

Development: Globular eggs are laid
in small batches in the soil. As the young
mature, they change only in size and color.

Important Greenhouse Species

Armed springtail, Achorutes armatus
(Nicolet), is variable in color, but adults
often are bluish or grayish. They are able
to jump. This species is known to attack
germinating seeds of greenhouse plants
and particularly young ferns.

Fig. 8. A springtail insect which may be found
where there is an abundance of humus.

[n

CONTROL

Nicotine sulfate is effective against
springtails which are contacted with the
spray. More satisfactory control, how-
ever, may be obtained with certain of the
newer insecticides.

1. Benzene hexachloride. (See page
50.)

2. Chlordane. (See page 51.)

3. Parathion. (See page 57.)

EARWIGS

Importance: Earwigs are usually scav-
engers, feeding on decaying plant mate-
rial or on animal matter both dead and
alive. One species, however, is a nuisance
because it also chews all types of living
plants in the gardens and greenhouses.
Two other species occur in California
greenhouses, but they are not known to
be injurious.

Appearance: Earwigs are brownish,
slender, and medium-sized, about 1/2 to
3/4 inch long. They possess a conspicuous
pair of pincers at the back end. Wing
covers, when present, are short and
leathery.

Development: Earwigs are nocturnal
in activity, hiding in the daytime in the
soil or under trash, boards, or foliage.
The females lay masses of oval, white eggs

Fig. 9. The European earwig. The male, at
left, bears larger, strongly-curved forceps.

in small nests in the soil and then care
for the eggs and young. There is one gen-
eration each year, reproduction occurring
in the winter or spring.

Important Greenhouse Species

European earwig, Forficula auricularia
Linnaeus, is brownish and black with pale
wing covers, legs, and antennae. This is
an introduced species which has become a
considerable pest during recent years.

CONTROL

Proprietary earwig baits give partial
control of earwigs, but certain of the
newer organic insecticides give excellent
control.

l.DDT. (See page 52.)

2. Chlordane. (See page 51.)

3. Benzene hexachloride. (See page
50.)

TERMITES

Importance: Termites are sometimes
reported to be greenhouse pests, not only
by destroying benches and other wooden
structures, but by gnawing and killing
thick-stemmed plants such as geranium,
chrysanthemum, begonia, and rose. They
attack the mainstalk of the root just below
the surface of the ground, tunneling it
out or girdling it.

Appearance: The workers and soldiers
are pale, soft-bodied, and wingless, about
Y^ inch in length. The soldier may be
recognized by having the head and jaws
strongly enlarged. Reproductive forms
are black, about 1/2 inch in length, and
they develop wings in the fall. Termites
may be distinguished readily from ants
by the lack of a slender waist.

Development: The workers and sol-
diers live in darkness, traveling in tun-
nels in the earth or wood or else in
passageways which have been constructed
with soil. Flying reproductive forms ap-
pear in the light after the first fall rains.
These soon drop their wings and attempt
the start of new colonies.

[12]

Fig. 10. The western termite. Left, a swarming individual, which will lose its wings when it has
paired. Right, a member of the wingless, blind, and sterile soldier caste.

Species Found

In California Greenhouses

Western termite, Reticulitermes hesperus
Banks. The soldier of this species has a long and
narrow, pale head. This is the common subter-
ranean termite along the coast.

Black-legged termite, Reticulitermes tibialis
Banks, is similar in appearance to the western
termite, but the head of the soldier is short,
broad, and yellow. This species is found char-
acteristically in the more arid sections of Cali-
fornia.

CONTROL

Plants may be protected against ter-
mite injury with certain of the newer in-
secticides which may be mixed with the
soil.

1. DDT: excellent control. (See page
52.)

THRIPS

Importance: Thrips are important
pests of ornamental plants. Either the foli-
age or buds and flowers are most com-
monly attacked, but bulbs and seeds also
may be damaged. They feed on plant tis-
sues by puncturing the surface and then
sucking the liberated juices. A silvering
of the leaves results. This may be accom-
panied by premature defoliation or else
the flowers may be seriously blotched and
streaked.

Certain species of thrips— the western
flower thrips, the Moulton flower thrips,
and the onion thrips— are of further im-
portance because they serve as carriers of
spotted wilt, a serious virus disease of
many flowering plants. The nymphs of
these thrips acquire the virus by feeding
on an infected plant, and they are able to

transmit the disease about one week later,
after becoming adults.

Aside from the plant-feeding thrips
which are found in greenhouses, there are
several other species which are beneficial
inasmuch as they feed on various pests.

Appearance: Thrips are slender, very
small insects, ranging from 1/50 to 1/25
inch in length when grown. Adults are
usually colored dark brown or yellowish,
and the wings are banded with white in
some species. Immature stages are usually
whitish or yellowish with red eyes.

Thrips sometimes run rapidly, and
some are able to hop. Adults are usually
able to fly, although the very slender,
feather-like wings may not be noted when
they are folded over the back.

The presence of thrips on foliage may
be recognized by the small black dots of
excrement which they leave where they
feed. These black dots are absent on
leaves stippled by spider mites.

Development: From two weeks to two
months are required for the completion
of a generation, and breeding in green-
houses is continuous throughout the year.
The tiny, bean-shaped eggs are laid within
the more tender plant tissues, each female
laying from 25 to 50 eggs. The eggs hatch
in from 4 to 20 days, and two nymphal
stages follow which last from 7 to 20 days.
Two resting stages then occur, and these
may be found where the nymphs were
feeding or else in the ground below the
plant. The resting stages together last
from 4 to 14 days before the adult thrips
appear.

[13

Fig. 11. Left, silvering of the leaf is a characteristic result of thrips damage. This pest may simi-
larly attack flower, bud, seed or bulb. Right, a healthy leaf and leaves affected by spotted wilt, a
virus disease transmitted by thrips.

Fig. 13. The greenhouse thrips: adult female.

Fig. 12. Immature stages in the development
of thrips: A, egg; B, newly emerged nymph; C, Fig. 14. Adults and immature greenhouse

full-grown nymph; D, first resting stage; E, thrips. Leaf blisters show where eggs have been

second resting stage. laid in the tissue.

[14]

Important Greenhouse Species

Greenhouse thrips, Heliothrips hae-
morrhoidalis (Bouche) , has the body dark
brown with the back part much lighter
in color; legs light yellow; and wings uni-
formly dusky except at base. The front
portion of the body is covered with a
strong network of lines. This thrips feeds
almost entirely on the foliage, and large
colonies may build up to cause severe
damage. Although azaleas and fuchsias
are particularly liable to attack, a wide va-
riety of plants serve as hosts. Infestations
are found outdoors in the coastal regions,
but the adults rarely fly and migration is
slow.

Western flower thrips, Frankliniella
occidentalis (Pergande) , is a tiny, yellow-
ish species which enters the developing
flowers of practically all types of plants.
The blooms of cut flowers such as roses
and carnations are particularly suscepti-
ble to malformation or streaking due to
their feeding. When the outside flowers
and weeds begin to dry up, definite migra-
tions of the flower thrips occur, and
greenhouses become infested.

Moulton flower thrips, Frankliniella
moultoni Hood, is very similar to the
western flower thrips, but generally dark
brown. The two species are commonly
found together.

Onion thrips, Thrips tabaci Lindeman,
is very similar to western flower thrips in
appearance and habits. It is apt to be
present in larger numbers during the
winter.

Other Species Found

In California Greenhouses

Banded greenhouse thrips (sugar beet thrips) ,
Hercinothrips femoralis (Reuter), is similar in
appearance to the greenhouse thrips, but has
three white bands on the forewings and the legs
have dark brown basal segments. It is primarily
a greenhouse pest, attacking the foliage of a
wide variety of plants.

Dracaena thrips, Parthenothrips dracaenae
Heeger, is similar in appearance to the banded
greenhouse thrips, but paler and having only a
single, complete black band on the forewings.
This species is primarily a greenhouse pest,

being found on the foliage of plants such as
dracaena, palms, rubber plant, and philoden-
dron.

Chrysanthemum thrips, Thrips nigropilosus
(Uzel) , is similar to the onion thrips, but bearing
X-shaped flecks on the front part of the body.
This species is found occasionally in the flowers
of plants such as chrysanthemum and gloxinia.

Composite thrips, Microcephalothrips ab-
dominalis (Crawford) is a uniform chocolate
brown with light brown wings. It is frequently
found in the flowers of various composite plants,
particularly injuring the seeds.

Gladiolus thrips, Taeniothrips simplex (Mori-
son) , is very dark brown with the wings lighter
at the base to give the appearance of a grayish
band near the middle of the body. It is primarily
a pest of gladiolus, feeding on the leaves, stems,
and flowers. Minor infestations are found occa-
sionally on other bulbous plants.

Lily thrips, Liothrips vaneeckei Priesner, is
glossy black with silvery white wings. This
species is found occasionally on lily bulbs.

Long-winged thrips, Scirtothrips longipennis
(Bagnall), is orange yellow with dusky wings
that extend well beyond the body. Feeding
causes brown, corky lines on the leaves and
stems and malformed flowers resembling injury
by the cyclamen mite. Begonia and cyclamen
are preferred hosts, but other plants may be at-
tacked. It is found infrequently in California.

Yellow orchid thrips, Taeniothrips xanthius
(Williams) , is uniform pale yellow with brown
wings. It feeds on the upper surface of cattleya
leaves, and is found occasionally in California.

California orchid thrips, Anaphothrips or-
chidii (Moulton) , is bright yellowish with light
brown wings. It is occasionally found in Cali-
fornia greenhouses on various orchids and
plants similar to philodendron.

English orchid thrips, Anaphothrips orchi-
daceous Bagnall, is yellowish with brown cross-
bands on the abdomen. It is found occasionally
in California, occurring on a wide variety of
orchids.

CONTROL

In view of the fact that eggs are laid
within plant tissues and the transforma-
tion stages may occur in the ground, the
most satisfactory control of thrips is by
means of an insecticide which possesses
considerable residual action. Tartar
emetic and brown sugar sprays are sel-
dom used at the present.

1. DDT. (See page 52.)

2. Benzene hexachloride. (See page
50.)

3. Parathion. (See page 57.)

[15

APHIDS

Importance: Aphids, or plant-lice, are
well-known insects that infest nearly all
types of plants. They are commonly found
in colonies on the shoots of new growth,
but they also occur under leaves, on
stems, or on bulbs and roots. They injure
the plants by sucking the juices with a
long beak, and the new leaves are curled
and crinkled by their feeding.

They also excrete a honeydew which
may be produced in such quantities as to
form a glistening coating on the leaves
and branches. This honeydew attracts
ants and promotes the growth of the black
smut fungus.

Aphids also serve as the agents for
transmission of a large number of plant
virus diseases. The green peach aphid is
known to transmit carnation streak, lily
mottle virus, pansy and viola flower
breaking, gladiolus mosaic, stock mosaic,
ornithogalum mosaic, as well as mosaics
in tritonia, babiana, ixia, sparaxis, strep-

tanthera, and watsonia. The potato aphid,
the cotton or melon aphid, the bean or
dock aphid, the lily aphid, and the fox-
glove aphid also transmit certain of these
viruses. Several other plant virus diseases
such as narcissus mosaic, narcissus white
streak, tigridia mosaic, and Easter lily
necrotic fleck, are transmitted by certain
of the latter aphids.

Appearance: Aphids are soft-bodied,
usually with long legs and antennae, and
ordinarily possessing a pair of tubes near
the end of the body which are called cor-
nicles. Adults are generally from 1/12 to
1/8 inch in length, and they are colored
greenish, yellowish, pink, purplish, brown
or black. Most species have winged as
well as wingless forms.

Development: The life cycle of aphids
is often complicated, and various species
may differ considerably in details of de-
velopment. Most of the aphids found in
greenhouses, however, omit the egg stage
entirely, and reproduction is continuous

Fig. 1 5. Effect of stock mosaic, a
virus disease transmitted by cer-
tain aphids. Left, infected plant;
right, healthy plant.

[16

Fig. 16. Species of aphids of most importance in the greenhouse. A, pea aphid; B, cotton or
melon aphid; C, foxglove aphid; D, lily aphid; E, ornate aphid; F, green peach aphid.

from unfertilized females. When the col-
ony becomes overcrowded, winged forms
may appear, and these fly to new food
plants.

A single female may produce from 60
to 100 progeny before dying at an age of
20 to 30 days. The young in turn may
mature in from 6 to 7 days after birth.

Important Greenhouse Species

Green peach aphid, Myzus persicae
(Sulzer). The wingless form is slender
and greenish. The winged form has a con-
spicuous, large, dusky blotch on the body.
The cornicles are long and slender,
slightly swollen before the tip. Nearly all
of the greenhouse plants are subject to at-
tack by this common aphid.

Lily aphid, Myzus circumflexus (Buck-
ton) , is similar to the green peach aphid,
but the wingless form has a characteristic,
horseshoe-shaped black marking on the
back. This aphid is primarily a green-
house pest. Although Easter lilies and
tulips are particularly subject to attack,
infestations are found commonly on a
wide variety of other plants.

Ornate aphid, Myzus ornatus Laing.
The wingless form is similar to the green

peach aphid, but with interrupted, dusky
lines across the back. This aphid is a com-
mon greenhouse pest, occurring on a wide
variety of hosts.

Foxglove aphid, Myzus solani (Kalten-
bach) . The wingless form is similar to the
green peach aphid, but with a dark green-
ish spot at the base of each cornicle. This
aphid is a common, omnivorous feeder
on greenhouse plants.

Cotton or melon aphid, Aphis gossypii
Glover, is a small, rounded species which
is greenish, yellowish, or mottled to black-
ish in color. The cornicles are short and
dark. This species is very common, both
in greenhouses and outside on a very wide
variety of plants.

Bean or dock aphid, Aphis rumicis Lin-
naeus, is similar to the cotton or melon
aphid, but always dull black and often
with whitish spots on the back. Summer
forms of this aphid enter greenhouses
where they infest a wide variety of plants.
Winter forms are restricted to dock, nas-
turtium, and several other plants.

Potato aphid, Macrosiphum solanifolii
(Ashmead), is a large, slender aphid,
usually either pink or green in color and
often with a darker ridge down the back.

[17]

The cornicles are long and slender with
black ends. Summer forms enter green-
houses to feed on a large variety of plants.
The favorite winter host is rose.

Other Species Found

In California Greenhouses

Chrysanthemum aphid, Macrosiphum san-
borni (Gillette), is a large, slender, shining
dark brown or black species. The cornicles are
short, somewhat bottle-shaped. It is common,
but infests only chrysanthemum.

Geranium aphid, Macrosiphum pelargonii
(Kaltenbach), is similar to the potato aphid,
but only green in color. It is restricted to ger-
anium and is often abundant on the growing
tips.

Pea aphid, Macrosiphum pisi (Kaltenbach),
is similar to the potato aphid, but only green in
color. It is restricted to legumes, often being in-
jurious to sweet peas.

Rose aphid, Macrosiphum rosae (Linnaeus),
is similar to the potato aphid, but the cornicles
are black. It is found commonly on roses, either
outside or in greenhouses, preferring the tender
shoots and buds.

Small green rose aphid, Myzaphis rosarum
Walker, is much smaller than the rose aphid,
plumper, and always greenish in color. It is more
likely to be distributed over the plant, rather
than preferring new shoots. Attacks are con-
fined to certain varieties of roses.

Fern aphid, Idiopterus nephrolepidis Davis, is
a small, black species with whitish legs and
clouded wing veins. It is often taken on maiden-
hair, holly, Boston, and brake ferns, occurring
both in greenhouses and outside.

Violet aphid, Micromyzus violae (Pergande),
is dark reddish or brownish, with clouded wing
veins and club-shaped cornicles. Although it is
widely distributed, infestations are restricted to
violets. It is sometimes a serious pest.

Black citrus aphid, Toxoptera aurantii (Fons-
colombe), is a plump, dark brown aphid with
distinctive wing venation. It is a common pest
of camellias which sometimes enters green-
houses to feed on gardenias and various tropical
plants.

Banana aphid, Pentalonia nigronervosa Co-
querel, is a peculiar species with clouded wing
veins. It is found occasionally in greenhouses on
various tropical plants.

Tulip leaf aphid, Amphorophora tulipaella
(Theobald), is a bright green species with the
cornicles dark green and strongly swollen near
the middle. It was introduced on tulip bulbs,
originally from Holland, and it is sometimes a
pest to this crop.

Periwinkle aphid, Rhopalosiphoninus latysi-
phon (Davidson), is similar to the tulip leaf
aphid, but the cornicles are paler and with the
swelling very abrupt. This aphid is frequently a
pest of tulips.

Ivy aphid, Aphis hederae Kaltenbach, is simi-
lar to the cotton or melon aphid, but dark pur-

Fig. 17. The ivy aphid on terminal growth of English ivy. The enlarged, pale aphids are para-
sitized.

plish, dark greenish, or blackish. It is found
commonly on the tender tips of English ivy
both in the greenhouse and outside.

Leaf-curl plum aphid, Aphis helichrysi Kal
tenbach, is similar to the cotton or melon aphid
but only pale green in color. The summer forms
deform the leaves and buds of chrysanthemum
cineraria, and other composite plants, particu
larly in southern California.

Tulip bulb or iris root aphid, Aphis tulipae
(Fonscolombe) , is similar to the cotton or melon
aphid, but the wingless forms are covered with
a fine, white, powdery wax. It infests many
liliaceous plants, feeding chiefly under the leaf
sheaths at the base of the plant and on bulbs
and rootstalks. This aphid is common through-
out California, and it is particularly injurious
to bulbs in storage.

Aster root aphid, Aphis middletonii Thomas,
is similar to the cotton or melon aphid, but dark
green. It commonly infests the roots of various
composite plants.

Apple-grain aphid, Rhopalosiphum pruni-
foliae (Fitch) , is similar to the cotton or melon
aphid, but greenish with reddish areas at the
back end. It is frequently found on tulips, stre-
litzia, and similar plants under greenhouse con-
ditions.

Latania aphid, Cerataphis lataniae (Boisdu-
val) , is a wingless form with very short legs and
a dark, elliptical body which bears a dense, mar-
ginal fringe of white, waxy threads. This form
bears more resemblance to a young whitefly than
it does to an aphid. A winged form is found
occasionally, however, which bears more resem-
blance to aphids. This species is found only in
greenhouses, occurring frequently on orchids,
palms, and ferns.

CONTROL

Aphids often are very easy to kill,
although repeated applications may be
necessary to keep them controlled. The
newer insecticides frequently are effective
only against certain species.

1. Nicotine: most commonly used as a
spray or a smoke. (See page 58.)

2. Light-oil emulsions, containing ro-
tenone, nicotine, or pyrethrum: more
often used outdoors. (See page 56.)

3. Calcium cyanide fumigation: an im-
portant method of control. (See page 51.)

4. Tetraethyl pyrophosphate : kills most
aphids very rapidly. (See page 56.)

5. Benzene hexachloride : effective for
certain species and possesses a residual
action. (See page 50.)

• • :S

l|l

Fig. 18. The latania aphid is found on orchids,
palms, and ferns.

6. Parathion : excellent control with
some residual action. (See page 57.)

7. DDT : effective for the pea aphid.
(See page 52.)

WHITEFLIES

Importance: Whiteflies feed exclu-
sively on leaves, nearly always occurring
on the undersurface. They suck juices
from the plants, and also excrete large
quantities of honeydew in which sooty
mold grows.

Appearance: The adults are moth-like
and covered with white, waxy powder.
They are about 1/16 of an inch in length.
The immature stages resemble miniature
scale insects. They are flat and oval, light
yellowish or greenish, and often provided
with a fringe of wax threads.

Development: The oval eggs are at-
tached to the leaves by means of short
stalks, and they are sometimes arranged
in circles. Hatching takes place in 10 to
14 days, and the young crawl a short dis-
tance before settling down. After feeding
for about two weeks, a transformation
stage is formed which lasts another two

[19]

Fig. 19. Immature stages and adults of the greenhouse whitefly on underside of geranium leaf.

weeks. The adult female lives about one
month, laying from 50 to 150 eggs.

Important Greenhouse Species

Greenhouse whitefly, Trialeurodes va-
porariorum (Westwood). Immature stages
are pale greenish, semitransparent, and
the covering of the transformation stage
is armed with long and short transparent
threads. Adults are pure white. It is a
common greenhouse pest throughout the
country, and in California also is found
in lath houses and gardens. A very wide
variety of plants may be infested, particu-
larly pelargonium, fuchsia, bouvardia,
hibiscus, and lantana.

Other Species Found

In California Greenhouses

Iris whitefly, Aleyrodes spiraeoides Quain-
tance. Covering of transformation stage is yel-
low, devoid of any fringe. Adults are white with
two dusky spots on each of the fore wings and
one spot on each of the hind wings. Although
primarily a pest of iris, it also infests a variety
of other ornamental plants and weeds. This
species is common, being most abundant out-
doors in the late summer and fall.

Fern whitefly, Aleurotulus nephrolepidis
Quaintance. Covering of transformation stage
is bright yellow, without any fringe. Adults are
pure white. This species is found infrequently
on various ferns in greenhouses and homes.

Azalea whitefly, Aleyrodes azaleae Baker and

Moles. Covering of transformation stage is light
yellowish, without waxy secretions. Adults are
uniform pale yellow. Although found on azaleas
throughout California, it does not appear to be
a very serious pest.

Citrus whitefly, Dialeurodes citri (Riley and
Howard) , is similar in appearance to the green-
house whitefly, except lacking the threads on
the covering of the transformation stage. It is
a serious pest to citrus and many ornamentals.
It has been introduced into California several
times, but eradication measures are employed
whenever it is found. This whitefly is commonly
intercepted in quarantine and may be regarded
as a potential greenhouse pest.

CONTROL

Until recently whiteflies have been dif-
ficult to control except with considerable
effort.

1. Calcium cyanide fumigation: the
method most commonly employed. (See
page 51.)

2. Nicotine sprays or oil combinations
with nicotine or pyrethrum : some degree
of success. (See page 58.)

3. Tetraethyl pyrophosphate: effective
against adults only. (See page 56.)

4. DDT: effective against adults or
against all stages when combined with
oil. (See page 52.)

5. Parathion : excellent control when
used as a spray; kills only adults when
used as an aerosol. (See page 57.)

20]

MEALYBUGS

Importance: Mealybugs are among the
most serious of greenhouse pests. They
injure plants by sucking the sap with their
needle-like mouthparts. The masses of
wax from their bodies and their cottony
egg sacs or cocoons render the plants un-
sightly. The honeydew they excrete at-
tracts ants and serves as a medium of
growth for sooty mold, making the flow-
ers or plants even more unsalable. The
constantly recurring use of insecticides
and labor for their control has made their
cost to the grower still greater.

Appearance: Mealybugs are soft-
bodied scale insects which are more or
less covered with a whitish or yellowish,
powdery wax. They are usually from 1/5
to 1/3 inch in length when mature. Waxy
filaments are often formed around the
body, or, in some cases, humps of wax
are formed. Mealybugs retain their legs
and are able to move around, although
slowly, throughout life.

Development: Females may lay masses
of several hundred yellowish or orange
eggs in white, cottony sacs. In some
species, however, living young are pro-

duced. Egg laying, when this occurs, ex-
tends over a period of about ten days,
and the eggs commence to hatch in about
two weeks. From six weeks to two months
are required for the young females to
reach maturity. The young male forms a
cottony cocoon two or three weeks after
emerging from the egg stage and therein
develops into a transformation stage. The
adult male which emerges in a week or
ten days has a pair of delicate wings and
is able to fly to the females for fertiliza-
tion. All stages ordinarily may be found
under greenhouse conditions, due to the
constant overlapping of generations.

Important Greenhouse Species

Citrus mealybug, Pseudococcus citri
(Risso), is heavily and evenly covered
with white, powdery wax except for a
fainter, narrow streak down the middle.
Short filaments are present along the
sides, the hind ones being about one
fourth the length of the body. Irregular,
cottony egg masses are laid which con-
tain as many as 500 eggs. This mealybug
is the one most commonly found on gar-
denia, bouvardia, and stephanotis, but

Fig. 20. The citrus mealybug, which has a large host range on ornamental plants.

4--:%,

its host range on ornamental plants is
very large.

Mexican mealybug, Phenacoccus gos-
sypii (Townsend and Cockerell), is cov-
ered with white, powdery wax except for
four rows of thinly waxed depressions
down the back. Short filaments are present
along the sides, the hind ones being about
one fourth the length of the body. A gray-
ish, watery fluid is ejected from pores
on the back when it is irritated. The cot-
tony egg masses are large and uniform.
This species is found commonly on pelar-
gonium and fuchsia, as well as a wide
variety of other host plants.

Grape mealybug (Baker mealybug),
Pseudococcus maritimus (Ehrhorn), has
the body thickly and evenly covered with
white, powdery wax, the segments being
rather sharply defined. The marginal fila-
ments are short, although the terminal
ones are one half as long as the body or
longer. The egg masses are large and ir-
regular. The grape mealybug is a common
greenhouse pest, occurring on a wide va-
riety of plants but particularly on Boston
ferns. It is of special importance because
it usually occurs on the roots as well as
on the foliage.

Long-tailed mealybug, Pseudococcus
adonidum (Linnaeus) , has the body thin-
ly covered with white wax with a broad,
fainter stripe down the middle. Filaments
along the sides are often one half the
width of the body, and the terminal ones
are as long as the body or longer. No
eggs are laid, and living young are pro-
duced. This species is chiefly a green-
house pest, although it is common out-
doors in southern California. Dracaena
is a favorite host, but it may occur on a
wide variety of plants.

Ground mealybug, Rhizoecus falcifer
Kiinkel, is very small with the body evenly
covered with white wax and without fila-
ments. It is found in the soil, working on
the roots of a large variety of plants.
Palms and cacti are favored hosts under
greenhouse conditions.

Fig. 21 . The Mexican mealybug on geranium.

Fig. 22. The grape (or Baker) mealybug.

Fig. 23. The long-tailed mealybug on dra-

Fig. 24. The ground mealybug works on roots.

Fig. 25. The palm mealybug on a Kentia palm
leaflet. Immature stages, adult females, and
male cocoons are shown.

Fig. 26. The striped mealybug on nephthytis.

Other Species Found

In California Greenhouses

Citrophilus mealybug, Pseudococcus gahani
Green, is similar in appearance to the Mexican
mealybug in having four rows of thinly waxed
depressions down the back, of which the middle
pair is most conspicuous. The body fluid, how-
ever, is clear and red. Large egg masses are laid.
This species prefers cooler temperatures, and
is more apt to be a serious pest outdoors. It is
often found in greenhouses, however, on such
hosts as English ivy and rubber plant.

Palm mealybug (coconut mealybug), Pseu-
dococcus nipae (Maskell) , has the body covered
with cream-colored or yellowish wax which forms
rows of humps. Filaments are absent. No eggs
are laid. The palm mealybug is found particu-
larly on palms, although other tropical plants
sometimes serve as hosts. It is found chiefly in
greenhouses, but is common outdoors in south-
ern California.

Striped mealybug, Ferrisia virgatus (Cock-
erell) . The body is dark purple and thinly cov-
ered with white powder except for two black,
broken lines down the back. Numerous long and
very delicate filaments are secreted. It ordinarily
rests with most of the body held elevated from
the plant. No eggs are laid. This species is found
occasionally in California greenhouses on such
plants as nephthytis and croton. It is eradicated
whenever recognized.

Amaryllis mealybug, Trionymus peregrinus
(Green). The body is grayish with a coating of
white, powdery wax except for thinner cross-
bands. This species is found infrequently, oc-
curring only on clivia or related amaryllis-like
plants. It lies concealed between the bases of
the leaves, surrounded by masses of wax.

CONTROL

Mealybugs are often very difficult to
control, particularly those species which
lay eggs. High-pressure sprays are most
satisfactory, and water alone will often
check a serious infestation. Ant control
(see page 42) should be practiced in con-
nection with mealybug control. It is
worthy of note that the citrus mealybug
has been eliminated from some gardenia
ranges which have been regularly treated
with DDT.

1. Light-oil emulsions: nicotine or
other plant derivatives are often included.
(See page 56.)

2. Parathion. (See page 57.)

3. Biological control: cryptolaemus
beetles. (See page 46.)

23]

ENSIGN SCALES

Importance: The ensign scales are a
small group of mealybug-like insects
which feed on plants by sucking the
juices. They also excrete honey dew. Only
one species is of importance in green-
houses.

Appearance: They are dark colored
with long legs and with conspicuous,
snow-white plates symmetrically arranged
on the body. Adults are about 1/12 of an
inch in length. The characteristic egg sac
is slender with longitudinal ridges, com-
posed of white wax and attached to the
back end of the insect.

Development: There are about five
generations in a year. The female is about
nine weeks old when eggs are first laid.

Species Found

In California Greenhouses

Greenhouse orthezia, Orthezia insignis Doug-
las, is dark green or brown with broad, white
plates along each side and in two rows down
the back. Its egg sac is about twice the length
of the body. It is found infrequently in Califor-
nia greenhouses and also occurs outdoors in
southern California. A wide variety of plants are
subject to infestation.

CONTROL

The control measures which are used
for mealybugs are used also for the green-
house orthezia.

Fig. 27. The cottony-cushion scale on Japa-
nese pittosporum.

Fig. 28. Young and adult females of the
greenhouse orthezia on bignonia.

GIANT SCALES

Importance: The giant scales are
mealybug-like insects which feed on
plants by sucking the juices. They also
excrete large quantities of honeydew.
Only one species is of importance as a
pest of ornamentals.

Appearance: Adult females of the pest
considered here are about 1/3 inch in
length, reddish in color, and more or less
covered with a whitish powder. The char-
acteristic egg sac is very large and broad
with longitudinal ridges. It is composed
of white, cottony wax.

Development: From 500 to 800 eggs
are laid by a single female. The young
settle on the branches and leaves and
mature in about four months.

Species Found

In California Greenhouses

Cottony-cushion scale, Icerya purchasi Mas-
kell, was introduced into California from Aus-
tralia, following which it became a serious pest
of citrus and many ornamentals. Its general
spread and build-up have been remarkably con-
trolled by means of the Australian ladybird
beetle and a cryptochaetum fly parasite. It is
found infrequently in greenhouses on such
plants as croton, geranium, ivy, and poinsettia.
Japanese pittosporum is a favorite host.

CONTROL

The cottony-cushion scale is very dim-
cult to control with insecticides except for
one of the new organic phosphates:

l.Parathion: excellent control. (See
page 57.)

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Fig. 29. Cottony sacs of the woolly cactus
scale.

WOOLLY-SAC SCALES

Importance: The woolly-sac scales are
a small group of mealybug-like insects
which injure ornamentals by sucking the
plant sap. No honeydew is excreted by
the greenhouse species.

Appearance: Active stages are pur-
plish or reddish and more or less coated
with a whitish, powdery wax. The full-
grown female is enclosed in an elliptical,
woolly sac, about 1/8 inch in length, while
the male cocoons are noticeably smaller.

Development: From 50 to 200 eggs
are laid in the sac covering the adult fe-
male. The young crawl to the stems or
axils of the leaves and grow very slowly.
There is but one generation each year,
although all stages are usually present
under greenhouse conditions.

Species Found

In California Greenhouses

Woolly azalea scale, Eriococcus azaleae Com-
stock. Azaleas and rhododendrons are the usual
hosts. This species has been reported from Cali-
fornia several times.

Woolly cactus scale, Eriococcus coccineus
Cockerell. Various cacti serve as hosts, the cot-
tony sacs occurring commonly on the spines.
It is a common pest in California, both outside
or under greenhouse conditions.

CONTROL

The only satisfactory control of woolly-
sac scales has been obtained with one of
the new organic insecticides.

l.Parathion: excellent control. (See
page 57.)

SOFT SCALES

Importance: Soft scales are important
greenhouse pests, not only because they
suck the plant juices, but also because of
the sooty mold which grows in the honey-
dew that they excrete. They are often
present in large numbers.

Appearance: Partially grown individ-
uals are flattened, elliptical, shining, and
rubbery. Adult females may be rubbery
or hardened, and flattened or globular in
shape. They are from 1/12 to 1/3 inch
in length. A cottony, white egg sac is
formed in certain species.

Development: As many as several
thousand eggs may be laid by one female
over a period of six weeks to two months.
These are usually deposited under the
body, although a cottony egg sac is some-
times formed. Eggs usually hatch in from
1 to 3 weeks after they are laid. In certain
cases, living young are produced. The
crawlers wander over the plant for several
days before settling down. Gradual growth
then takes place, the females maturing in
a period of from several months to nearly
a year. The ability to move about some-
times occurs throughout a large part of
the development.

Important Greenhouse Species

Soft brown scale, Coccus hesperidum
Linnaeus. The adult female is rather flat-
tened, soft and pliable, and shining yel-
lowish or brownish with a somewhat

Fig. 30. Adults and young of the soft brown
scale. Sooty mold grows on the insect excretions.

25

Fig. 31. Adult females of the hemispherical scale on fern.

mottled appearance. Living young are
produced. It is primarily a greenhouse
pest, although it also is destructive out-
doors in California. Practically all types
of greenhouse plants serve as hosts.

Hemispherical scale, Saissetia hemis-
phaerica (Targioni). Adult females are
strongly convex, hard, brown, smooth
and shining. The skin is covered with
tiny, round, pale areas. The undersurface
of the female forms a cup as a tremen-
dous number of eggs piles up. A great
many plants are subject to attack, ferns
being one of the favorites.

Other Species Found

In California Greenhouses

Elongate soft scale, Coccus elongatus (Sig-
noret), is similar in appearance to the soft
brown scale, but the body is considerably more
elongate as a rule. Living young are produced.
It is not as commonly encountered as that
species, and it is more restricted to greenhouses.
A variety of tropical plants serve as hosts, palms
being one of the favorites.

Orchid soft scale, Coccus pseudohesperidum
(Cockerell). Adult female is elliptical and flat-
tened, leathery, black, with a narrow yellowish
margin, and with thin patches of wax on the
back. Living young are produced. This scale is
generally distributed on orchids in California
greenhouses, dendrobium being a favorite.

Fig. 32. The orchid soft scale on leaf of den-
drobium orchid.

Tessellated scale, Eucalymnatus tessellatus
(Signoret). The adult female is elliptical and
flattened, greenish black and with a network of
pale lines. Reproduction is by eggs, but the
young emerge from the thin shells immediately
after deposition. It is found almost entirely in
greenhouses on various tropical plants.

Nigra scale, Saissetia nigra (Nietner) . The
adult female is elliptical, flattened, hardened,
and black, the skin being covered with small, ir-
regularly divided pale areas. A large number of
eggs are laid beneath the female during the pe-
riod of June until February. This species is fre-
quently found in greenhouses, although it is a
serious pest outdoors along the coast. Woody
plants, such as ivy, holly, and Japanese aralia,
are preferred hosts.

Black scale, Saissetia oleae (Bernard). The
adult females are globular, hardened, and with

[26

ridges on the back that form the letter "H."
The skin is covered with tiny, rounded, pale
areas. Very large numbers of eggs are laid
beneath the body of the female. Although fre-
quently found in greenhouses, it is a more
serious pest outdoors. A very wide variety of
plants are attacked, but woody stems are pre-
ferred.

Pyriform scale, Protopulvinaria pyriformis
(Cockerell). The adult female resembles the

Fig. 34. The cottony orchid scale with its egg
sac on a leaf of dendrobium.

soft brown scale but forms a cottony sac which
appears as a white fringe around the body. An
infestation of this pest was recently found in a
greenhouse in southern California, although it
was probably eradicated. Woody ornamentals
are favored hosts.

Cottony camellia scale, Pulvinaria floccifera
Westwood. Mature females are light brownish,
elliptical, flattened, and soft. A characteristic
long and slender, usually curved egg sac is
formed from a white, cottony material. Camel-
lias are the preferred host, but it has been found
on ferns and podocarpus under greenhouse con-
ditions.

Cottony hydrangea scale, Pulvinaria hydran-
geae Steinweden. Resembles the cottony camel-
lia scale, but is found characteristically on
hydrangea throughout California.

Cottony orchid scale, Pulvinaria phaiae Lull.
Resembles the cottony camellia scale, but oc-
curs only on orchids. It is found occasionally in
California.

Cottony guava scale (green shield scale) , Pul-
vinaria psidii Maskell. Closely resembles the
cottony camellia scale. A serious pest of guava
and certain woody ornamentals which is occa-
sionally found in California greenhouses.

CONTROL

Soft scale insects are very difficult to
control, particularly under greenhouse
conditions where the young are not pro-
duced at definite seasons.

1. Light-oil emulsion: the most effec-
tive spray where this can be used. (See
page 56.)

2. Calcium cyanide fumigation : some
degree of control. (See page 51.)

3. Parathion: effective against young
of soft scales, but not effective for "rub-
bery" stages. (See page 57.)

Fig. 35. Adult females of the black scale on English holly.

ARMORED SCALES

Importance: Armored scales are very
serious pests of ornamental plants. They
not only suck the plant sap, but their feed-
ing is often accompanied by a toxic ef-
fect to the plant. No honeydew is excreted.

Appearance: Armored scales are char-
acterized by possessing a hardened shield,
or scale, above the body. The shields are
more or less flattened, usually about 1/12
to 1/8 inch in diameter. They are circular
in shape, or else elliptical or oystershell-
like.

Development: Reproduction may be
by eggs, from several dozen to several
hundred being laid beneath the shield
over a period of a month or two. In some
cases, living young are produced. The
newly emerged crawlers are active for
several hours or for a day or two. After
settling down, they lose their legs and re-
main stationary for the rest of their de-
velopment. There are commonly from 3
to 7 generations a year.

In the course of female development,
the discarded skin of the settled crawler
forms the nipple of the shield. The cover-
ing of the second stage forms a ring
around this. The larger part of the shield
ordinarily is secreted by the third stage
which becomes the mature female. The
shape, color, and texture of the shield,
together with the position of the nipple
and comparative sizes of the rings, are
useful in recognizing the species.

The nipple, together with the secretion
of the second immature stage, forms the
covering of the male. Adults of this sex
emerge as delicate, winged insects. The
male shields are smaller and more elon-
gate than those of the female. They either
resemble the female shield in color and
texture or else they are cottony white with
three longitudinal ridges.

Important Greenhouse Species

Ivy scale (oleander scale), Aspidiotus
hederae ( Vallot) . The shield of the female
is more or less circular, flattened, whitish

in color, and with the nipple more or less
central. Shield of the male is similar but
smaller and more elongate. This scale is a
very common pest, both in greenhouses
and outside. The leaves and stems of a
wide variety of plants may be infested.

Florida red scale, Chrysomphalus ficus
Ashmead. The shield of the female is thin,
circular, flat, with a central nipple, and
dark mahogany red in color. Shield of the
male is smaller, more or less oval, some-
what lighter in color. It is common in
greenhouses throughout California. It is
found on the leaves of a wide variety of
plants, particularly palms and rubber
plant.

Fig. 36. Above, the ivy scale. Below, the aspi-
distra scale, showing white, elongate males and
brown, oystershell-shaped females.

28

Fig. 37. The false Florida red scale on aspi-
distra.

Boisduval scale, Diaspis boisduvalii
Signoret. The shield of the female is more
or less circular, flat, thin, whitish, and with
the nipple more or less central. Shield of
the male is small, elongate, white, bearing
three ridges, and with nipple terminal.
The males are found commonly clustered
together in a cottony mass. Cattleya and
cymbidium serve as the most common
hosts, although other orchids and certain
tropical plants may be attacked. This spe-
cies often encrusts the stems, and heavily
infested leaves turn yellow and die.

Aspidistra scale (fern scale), Pinnaspis
aspidistrae (Signoret). The shield of the
female is brown, broadly oystershell-
shaped with terminal nipple. Male shield
is small, elongate, and felted white. This
is a common greenhouse pest, occurring
on a wide variety of plants but particu-
larly aspidistra and ferns.

Other Species Found

In California Greenhouses

Cyanophyllum scale, Hemiberlesia cyano-
phylli (Signoret), closely resembles the ivy
scale. It is often found in greenhouses, but also
occurs outdoors in southern California. A large
number of tropical plants may be infested.

Latania scale, Hemiberlesia lataniae (Sig-
noret), closely resembles the ivy scale, except
the female shield is evenly and strongly convex
and the body of the insect usually remains in

the shield when it is removed. It is sometimes
abundant on palms, but a wide variety of other
plants are attacked.

Greedy scale, Hemiberlesia rapax (Corn-
stock) , resembles the ivy scale except the female
shield is strongly convex with the apex of the
hump off to one side. Primarily a greenhouse
pest in many parts of the United States, but
found more commonly outdoors in California. It
occurs on a wide variety of woody ornamental
plants, chiefly infesting the stems and particu-
larly the axils of the leaves and bases of the
buds.

Dictyospermum scale (Spanish red scale),
Chrysomphalus dictyospermi (Morgan) , is simi-
lar to the Florida red scale, but the shield of
the female is yellowish or light brownish. It is
primarily a greenhouse pest, although occurring
outdoors in southern California. It has been
noted on various palms, as well as a wide variety
of other plants.

False Florida red scale, Chrysomphalus bifas-
ciculatus Ferris. Shield of the female is very
similar to that of the Florida red scale, but dark
chocolate brown in color. It is frequently found
both in greenhouses and outdoors over most of
California. Aspidistra is a favorite host, al-
though many other plants may be infested.

California red scale, Aonidiella aurantii
(Maskell) . The shield of the female is similar to
that of the Florida red scale, but bright reddish
in color. Body of female is bean-shaped. It is an
important pest of citrus which is sometimes
found on various greenhouse plants throughout
California.

Yellow scale, Aonidiella citrina (Coquillett),
is similar to the California red scale, but its
shield is yellowish in color. It is similarly a citrus
pest but may be found occasionally on peren-
nial greenhouse plants.

West Indian red scale (rufous scale) , Selenas-
pidus articulatus (Morgan) . Shield of the fe-
male resembles the Florida red scale, but is
grayish brown or yellowish brown with the mar-
ginal portion distinctly lighter. It is regarded as
a serious pest of citrus in tropical countries, and
also infests a wide variety of ornamentals. Infes-
tations have been found twice in California, on
greenhouse crotons, and it was eradicated each
time.

Mexican red scale, Acutaspis albopicta (Cock-
erell), resembles the Florida red scale, but the
shield of the female is dark brown in color.
It is rarely found in California on such plants as
philodendron, and is eradicated whenever de-
tected.

Rose scale, Aulacaspis rosae (Bouche), re-
sembles the Boisduval scale, but the female
shield has the nipple on one side. It is a common
pest on rose and bramble stems, both outdoors
and in greenhouses.

[29

Cactus scale, Diaspis echinocacti (Bouche),
closely resembles the Boisduval scale but is
found only on various cacti. It is a common pest
in California, both in the greenhouses and out-
side.

Mining scale, Howardia biclavis (Comstock) .
Shield of the female is whitish, circular, convex,
with terminal nipple. It has the habit of bur-
rowing beneath the outer bark, so that it is usu-
ally recognized by the nodular stem swellings
on older wood and roots. It is a species which
occurs on various tropical plants and has been
found in several localities in California.

Cycad scale, Furcadiaspis zamiae (Morgan).
Shield of the female is circular, slightly convex,
with marginal nipple, and with outer ring cot-
tony white. It occurs on the leaves of various cy-
cads and is frequently found in California.

Lesser snow scale, Pinnaspis strachani (Coo-
ley) , is very similar to the aspidistra scale, but
the shield of the female is white. This species
has been found in California several times, par-
ticularly on sansevieria, ferns, and cycads. It is
eradicated when detected.

Purple scale, Lepidosaphes beckii (Newman).
Shield of the female is oystershell-shaped, elon-
gate and generally curved, purplish or brownish
in color. Shield of the male is similar but smaller
and more elongate. Although primarily a pest of
citrus, it is occasionally found on various orna-
mentals in greenhouses and outside.

Cymbidium scale, Lepidosaphes machili
(Maskell), closely resembles other oystershell
scales, but is found only on cymbidium orchids.
Severe infestations are occasionally found in
California greenhouses.

Mackie scale, Lepidosaphes mackiana Mc-
Kenzie, closely resembles other oystershell scales,
but is found beneath the sheath on stems of
dendrobium orchids. It has been found several
times in southern California greenhouses.

Noxious scale, Lepidosaphes noxia McKenzie,
closely resembles the Mackie scale and also
occurs only on dendrobium orchids. One infes-
tation has been found in a northern California
greenhouse.

Croton scale, Lepidosaphes tokionis (Ku-
wana) , closely resembles the other oystershell
scales, but occurs only on croton. It has been
found twice in northern California greenhouses.

Proteus scale (sansevieria scale), Parlatoria
proteus (Curtis). Shield of the female is elon-
gate-oval, somewhat convex, thin and delicate,
with nipple terminal and middle ring very large.
Shield of the male is similar but smaller and
more elongate. Occasionally it is found in Cali-
fornia greenhouses on such hosts as sansevieria,
various orchids, and palms. Eradication meas-
ures are taken when it is found.

Chaff scale, Parlatoria pergandei Comstock, is
similar in appearance to the proteus scale, but

Fig. 38. The cactus scale: subcircular females
and smaller, elongate males.

r

r

Fig. 39. Left, the cymbidium scale on cymbid-
ium orchid; right, the proteus scale on vanda
orchid.

[30]

the shield of the female is thick and the middle
ring is smaller. Primarily it is a pest of citrus,
but is occasionally taken on various ornamentals
both in greenhouses and outside.

False parlatoria scale, Pseudoparlatoria par-
latorioides (Comstock). Shield of the female is
semitransparent yellowish, more or less circular,
with nipple marginal. Shield of the male is simi-
lar, but smaller and oval. Occasionally it is
found in California greenhouses, particularly on
phoenix palms and cypripedium orchids. Eradi-
cation measures are taken whenever it is found.

Palm fiorinia scale, Fiorinia fioriniae (Tar-
gioni) . Shield of the female is elliptical, thin,
yellowish or brownish, with nipple terminal and
remainder of shield formed by second skin
which bears a longitudinal ridge. Shield of the
male is white and felted. It is found occasionally
in California greenhouses, especially favoring
palms.

CONTROL

Control of armored scales is often very
difficult because of the protection af-
forded by the shield over the body.

1. Light-oil emulsion: may give control
where it can be used. Applied most effec-
tively when crawlers are active. (See page

56.)

2. Calcium cyanide fumigation : gives
very good control for most species, but
the California red scale may be resistant.
(Seepage 51.)

3. DDT: sprays have given effective
control of crawlers of some species and
have been used extensively against the
Boisduval scale. It is necessary to main-
tain a residual on the plants until older
scales have died, so applications are re-
peated every 3 or 4 months. (See page
52.)

4. Parathion : excellent control of many
species, although mature forms may not
appear dead for several weeks after ap-
plication. (See page 57.)

PLUME MOTHS

Importance: The caterpillars of several
species of plume moths cause damage of
economic importance in California. Al-
though they may chew on any part of the
plant, the most noticeable injury is to
the developing flowers.

Appearance: The caterpillars are yel-
lowish, greenish, or purplish, with a black
head, about 1 inch long when grown.

Adult moths are small, tan, with a wing
expanse of about 1 inch. The wings are
very slender and are held outstretched
when at rest. Actually each wing is sub-
divided so as to resemble a series of
plumes.

Development: Each female lays one
hundred to two hundred eggs individually
underneath the leaves. They hatch in 1
or 2 weeks, and the young caterpillars
mine into tender buds or leaves. As they
grow, they burrow into the stems or feed
among terminal leaves and developing
flowers. They mature in 1 or 2 months.
The transformation stage is formed where
they have been feeding, and this stage
lasts 3 or 4 weeks. Adult moths are from
several days to a week old before they
start laying eggs.

Fig. 40. A fiorinia scale on podocarpus leaf. Fig. 41. The snapdragon plume moth.

[31]

Species Found

In California Greenhouses

Snapdragon plume moth, Platyptilia antir-
rhina Lange, often is a serious pest of snap-
dragons in southern and central California.

Geranium plume moth, Platyptilia pica Wals-
ingham, is similar to snapdragon plume moth,
but particularly prevalent on geranium in the
coastal region of southern California.

CONTROL

Information concerning the use of
newer insecticides is not available for the
plume moths. Nicotine sulfate, rotenone,
lead arsenate, and cryolite have not given
adequate control. A pyrethrum and me-
dium-oil spray has given control of ex-
posed caterpillars and adults.

LOOPERS

Importance: Loopers, or measuring
worms, are familiar caterpillars which eat
the leaves of a wide variety of ornamental
shrubs and trees. Only one species is of
economic importance in California green-
houses.

Appearance: The caterpillars may be
recognized by the series of looping move-
ments which they make when they crawl.
They frequently rest by holding on with
the hind legs and straightening the body
out. The caterpillars are variously col-
ored, about 3/4 inch long when grown.

The moths have a slender body and
broad, rather delicate wings. The wings
are about 1 inch long and are held partly
outstretched when at rest.

Development: Eggs are usually laid in
small clusters on the foliage. As the cater-
pillars grow up, large portions of the
leaves are consumed. They often fasten
leaves together in which to hide during
the day, and pass the transformation stage
within such a shelter. There are several
generations a year.

Species Found

In California Greenhouses

Omnivorous looper, Sabulodes caberata
Guenee. Caterpillars usually are yellowish or
orange with narrow, green and black stripes.
The moth is pale tan in color. The caterpillars

Fig. 42. Injury to snapdragons by caterpillars
of the snapdragon plume moth.

are general feeders, attacking a wide variety of
ornamental plants outdoors. They often invade
greenhouses, particularly during the fall when
they are most abundant.

CONTROL

1. DDT: effective control. (See page

52.)

LEAF BLOTCH MINERS

Importance: The leaf blotch miners
are small caterpillars which usually feed
within or curl the leaves of various orna-
mental shrubs and trees. Injured portions
die. Only one species has been found in
California greenhouses, but it often
causes considerable trouble.

Appearance: The caterpillars are pale,
about 1/2 inch long when grown. They
are generally recognized by the charac-
teristic blotches which they make in
leaves when they are young, together with
their pellets of frass.

Adults are small, slender moths, about
1/3 inch long. At rest, the wings are
folded along the sides, and the front end
of the body is held up high.

Development: Eggs are laid on the
foliage. The newly emerged caterpillars

32

mine within the leaf tissues, forming an
irregular blotch. As they mature, they
emerge, curl over a portion of the leaf
with silken threads, and feed on the inner
surface. The transformation stage is
formed where they have been feeding.

Important Greenhouse Species

Azalea leaf miner, Gracilaria azaleella
Brants. Adults are prettily marked with
bright purple and yellow. The caterpillars
commonly infest greenhouse azaleas, but
they do not appear to build up under lath
house or garden conditions.

CONTROL

Both lead arsenate and nicotine or
other plant product preparations are re-
ported to give effective control. Certain
of the newer insecticides appear to be
preferable, however.

1. DDT: excellent control. (See page
52.)

2. Parathion: excellent control. (See
page 57.)

LEAF TIERS

Importance: The leaf tiers belong to a
group of caterpillars which are often im-
portant feeders on plants. Only one
species, however, is found ordinarily in
greenhouses.

Appearance: The caterpillars are pale
in color, about 3/4 inch long when grown.
They are generally found within leaves
which are folded over or tied together for
protection.

The moths are somber colored, about
1/2 inch long when at rest. The wings are
held along the sides to give a triangular
appearance.

Development: Eggs are laid singly or
in small groups on the underside of
leaves. They hatch in 1 or 2 weeks. The
caterpillars feed almost entirely on the
underside of leaves, chewing off the sur-
face in irregular patches when they are
young and eating holes when they are
larger. The larval stage lasts about three
weeks. The transformation stage occurs

Fig. 43. Azalea leaves showing damage by the azalea leaf miner.

r 33 1

in a slight cocoon among the foliage, and
this stage lasts about three weeks. Multi-
plication is continuous in greenhouses,
the generations overlapping.

Species Found

In California Greenhouses

Greenhouse leaf tier (celery leaf tier) , Phlyc-
taenia rubigalis (Guenee). The caterpillar is
yellowish with a narrow green stripe down the
back and a broader greenish stripe along each
side. The wings of the moth are crossed with
narrow, wavy, dark lines. This species is a com-
mon outdoor pest on garden crops and orna-
mental plants. It readily invades greenhouses
to feed on a wide variety of crops.

CONTROL

Control measures which are employed
for the omnivorous looper are also used
for the greenhouse leaf tier.

LEAF ROLLERS

Importance: The leaf rollers are a very
destructive group of caterpillars. They
not only tie together and feed on the ter-
minal leaves but they often bore into
flower buds and terminal shoots. They
are very persistent pests when they be-
come established in greenhouses.

Appearance: The caterpillars are yel-
lowish or pale greenish with a yellowish
to black head. They are about 1/2 inch
long when mature. When disturbed they
wriggle violently, escaping backwards
into their shelter or dropping by a silken
thread.

Adults are more or less tan in color,
the wings having an oblique, dark band
across the middle and usually a spot be-
yond this on the front margin. They are

Fig. 44. Terminal growth of carnation showing injury by the carnation leaf roller.

[34]

about 3/8 inch long when at rest, the
wings being folded along the back to give
a bell-shaped appearance.

Development: Eggs are laid in over-
lapping masses on the leaves, and they
hatch in 1 to 3 weeks. The caterpillars
curl leaves over or web them together for
protection, or else burrow into buds or
tender shoots. Feeding continues for 3 or
4 weeks. A transformation stage is then
formed in the leaf rolls or buds. Adult
moths emerge in another 2 weeks, and the
adult female may lay several hundred
eggs. There may be from 1 to 5 genera-
tions annually, depending on the species.

Important Greenhouse Species

Orange tortrix, Argyrotaenia citrana
(Fernald). Hind wings of the moth are
white in color. It is a very common pest of
fruit trees, berries, and many ornamental
plants. Rose is a favorite host.

Carnation leaf roller, Platynota stul-
tana Walsingham.The moth has very long
palps projecting in front to resemble a
long snout. It is a very serious pest of
carnations, but other flowering plants are
sometimes attacked.

Other Species Found

In California Greenhouses

Apple skinworm, Argyrotaenia franciscana
(Walsingham). The moth has hind wings gray
in color. This species is of particular importance
in northern California, infesting a wide variety
of flowering plants.

Cyclamen leaf roller, Clepsis buskana Keifer.
Front wings of the moth are golden in color.
The overwintering caterpillars which mature in
the early spring cause the most damage. It is
occasionally found in greenhouses, particularly
on cyclamen in northern California.

Oblique-banded leaf roller, Choristoneura
rosaceana (Harris). The caterpillar is larger
than the other leaf rollers. The moth has three
oblique bands on front wing. It is a troublesome
pest of flowering plants in many parts of the
United States, and it readily adapts itself to
greenhouse conditions. It is seldom found in
California.

CONTROL

The leaf rollers are difficult to control,
particularly because of protection af-

forded by the buds in which many of the
caterpillars live. DDT is not effective
against many species.

1. Cryolite: considerable control. (See
page 54.)

2. Pyrethrum dusts : reported to be ef-
fective when a second application is made
after a 30-minute interval. The first ap-
plication serves to drive the caterpillars
from concealment. (See page 59.)

3. DDD: effective control. (See page
52.)

4. Parathion: effective control. (See
page 57.)

CUTWORMS

Importance: Cutworms, and army-
worms, are destructive caterpillars which
feed on many agricultural ornamental
crops. Younger plants are often killed
overnight by being cut off at the base, or,
in other cases, the foliage may be eaten
so extensively that they are ruined. They
often eat into buds.

Appearance: Cutworms are shining,
fat caterpillars, about 1 or 2 inches long
when mature. They are gray, brown,
greenish or yellowish, with darker mark-
ings. They hide in the daytime, usually in
the ground, and come out at night to feed.

The adults are medium-sized, stocky,
and somber-colored moths. They are com-
monly seen around lights at night. When
at rest, the wings are folded over the body
to give the insect a triangular outline.

Development: The eggs are laid singly
or in clusters on the foliage, and they
hatch in about one week. The caterpillars
feed for 3 or 4 weeks. The transformation
stage is usually in a cell in the soil, and it
lasts for 2 or 3 weeks. The adult female
lays several hundred eggs. There are sev-
eral generations a year as a rule.

Important Greenhouse Species

Variegated cutworm, Peridroma mar-
garitosa (Haworth). Caterpillar is gray
or brown with darker markings and with
a row of yellow dots down the middle of
the back. It is a common pest throughout

35

California, often entering greenhouses to
feed on young gardenias, carnations, and
many other flowering plants.

Other Species Found

In California Greenhouses

Tobacco budworm, Heliothis virescens (Fa-
bricius) . The caterpillar is greenish with longi-
tudinal pale stripes. This is a common pest of
geranium and pelargonium in southern Cali-
fornia. Caterpillars feed on the buds and un-
folded leaves so that they are ragged as they
expand.

Corn earworm, Heliothis obsoleta (Fabri-
cius). The caterpillar is light green to dark
brown with light and dark longitudinal stripes.
It is a common vegetable pest which occasionally
becomes established in greenhouses, feeding on
various flowering plants.

Beet armyworm, Laphygma exigua Hiibner.
Caterpillars vary from green to having black and
white stripes along the back and sides. A peri-
odic pest of truck crops, it has been noted feed-
ing on greenhouse cinerarias in northern Cali-
fornia.

Fern cutworm, Euplexia lucipara (Linnaeus) .
Caterpillars are green, matching the color of
the ferns on which they feed. A European
species which occurs rarely in California.

CONTROL

Although cutworms have been satisfac-
torily controlled with poison baits (see
page 66) in the past, certain of the newer
organic insecticides are better for green-
house use.

1. DDT: excellent control. (See page
52.)

WEEVILS

Importance: There are a large number
of species of weevils, and many of these
are serious pests to plants. The adults
commonly chew on the foliage or flowers,
and the grubs generally eat on the roots
or else feed in the stems, buds, or fruits.

Appearance: The grubs are fleshy,
strongly arched, and sluggish. They are
pale colored with a distinct head. The size
varies considerably according to the
species but commonly ranges from about
1/12 to 1/2 inch in length.

Adult weevils are hard-shelled insects
which have the front portion of the head
more or less prolonged to form a snout.

Fig. 45. Grub and adult of the black vine
weevil.

They are often dark in color, and are
commonly from 1/12 to 1/2 inch in
length.

Development: Eggs may be dropped
on the soil or laid on the plants. The grubs
feed on the plant tissues and when mature
enter a transformation stage in a cell in
the soil or within the plant where they
have been feeding. The adult weevils
may live a considerable length of time as
they continue to feed at night over the
plants. The biology varies considerably
according to the species.

Important Greenhouse Species

Fuller rose weevil, Pantomorus god-
mani (Crotch). Adults are grayish with
an oblique, whitish line on each wing
cover. They are moderately large, and
with the snout short and broad. They are
commonly found hiding in the foliage in
the daytime, and they chew on the leaves
at night. The eggs are laid in elongate
masses near the tips of branches or near
the base of the plant, and the grubs feed
on the rootlets. This common species is
particularly destructive to gardenias and
roses, although a wide variety of plants
may be attacked, either in greenhouses
or outdoors.

Black vine weevil, Brachyrhinus sulca-
tus (Fabricius). Adults are brownish
with golden flecks on the wing covers,
otherwise similar in general appearance
to the Fuller rose weevil. Adults hide in
debris on the ground, coming out at night
to scallop the leaves in a characteristic
fashion. The eggs are dropped on the soil,
ordinarily in the summer, and they hatch

36

in about two weeks. Young grubs feed on
the tender rootlets, but as they become
larger, in the winter or early spring, they
may girdle the crowns of smaller plants.
The transformation stage is passed in a
cell in the ground. The adults emerge in
the spring, and they may live for two
years, laying several hundred eggs.

A very wide variety of plants are at-
tacked, although azaleas and camellias
are killed the most often. Infestations in
greenhouses are usually initiated by
bringing in infested soil, but invasion
may result from the slowly crawling
adults. Several other species of Brachy-
rhinus have been introduced into Califor-
nia, but they have not been found yet in
greenhouses.

Of her Species Found

In California Greenhouses

Vegetable weevil, Listroderes obliquus Klug.
Adult is moderate sized and brownish; each
wing cover has an oblique pale marking and a
tubercle near the back end; the snout is short
and broad. The grubs are greenish. Both the

-■■

Fig. 46. The cattleya weevil feeding on bud
of cattleya orchid.

adults and grubs feed on the foliage, and the
grubs also feed on the roots. Eggs are laid mostly
in the fall, and damage is found mostly during
the winter and spring. Although principally a
pest of vegetables, it is occasionally found in
greenhouses feeding on various plants such as
cyclamen in seedling flats.

Orchid weevil, Diorymerellus laevimargo
Champion, is small, shiny black, with a long,
curved snout. The adults feed on the flower buds,
petals, and young leaves at night and hide in
the daytime at the leaf bases or in the potting
material. The grubs feed inside the new roots,
causing them to blacken and die. Formerly it
was a very common and very destructive pest of
cattleya and dendrobium orchids in California.

Cattleya weevil, Cholus cattleyae Champion,
is large and black with conspicuous, white
markings on the wing covers, and with a long
snout. It is a South American immigrant which
is seldom found in California. When present,
however, it causes serious damage to cattleya
orchids, both by the adult feeding punctures in
the pseudobulbs and the larval feeding within
the pseudobulbs, stems, or leaves.

CONTROL

The most satisfactory control of weevils
is obtained with certain of the newer or-
ganic insecticides, although proprietary
poison apple baits have been widely used
for adults of the black vine weevil. For
control of ground-inhabiting grubs, the
insecticide usually must be mixed with
the soil.

1. DDT: effective control. (See page
52.)

2. Benzene hexachloride : effective con-
trol of adults or grubs. (See page 50.)

FUNGUS GNATS

Importance: Fungus gnats are com-
mon greenhouse inhabitants, often occur-
ring in such large numbers as to be a
nuisance. The maggots ordinarily feed
among decaying organic material in the
soil. As a general rule they are not con-
sidered to be of economic importance,
but there are a number of instances in
which larval injury to roots of greenhouse
plants has been reported in other parts
of the United States.

Appearance: The young are slender,
legless maggots which are white with a

37

black head. When mature they are about
1/4 inch long.

The adults are slender, blackish gnats,
about 1/8 inch long. They run rapidly
over the foliage, soil, and windows.

Development: Eggs are laid in the soil.
Hatching takes place in about one week,
and the maggots feed for about two weeks.
A transformation stage is then passed in
the soil which lasts about 1 week. Each
female lays about 100 eggs.

CONTROL

Fungus gnats are effectively controlled
with certain of the newer organic com-
pounds.

1. DDT: effective for adults. (See page
52.)

2. Chlordane : excellent control of mag-
gots and adults. (See page 51.)

3. Benzene hexachloride : effective for
maggots and adults. (See page 50.)

GALL MIDGES

Importance: Gall midges comprise a
large group which contains a number of
important pests of ornamental plants.
They generally make characteristic galls
on the foliage or deform the buds and
flowers. Several species, such as the rose
midges, violet midges, and orchid midges,
are important greenhouse pests in other
parts of the country, but these have not
been observed in California. The chrys-
anthemum gall midge, however, is a com-
mon and persistent pest.

Some species of gall midges are fungus
feeders, and those belonging to the genus
Mycophila in particular, have been ob-
served in numbers in greenhouses, breed-
ing among flower pots. These do no
damage. Other species are beneficial, the
larvae preying on destructive midges,
mites, aphids, mealybugs and other scale
insects. Several of these have been ob-
served in California greenhouses.

I

,

■

Fig. 47. Galls of the chrysanthemum gall midge on chrysanthemum leaves.

r 38 1

Appearance: The larvae are small,
fleshy maggots, without a head, and often
yellowish or orange in color. They are
commonly about 1/12 inch in length.

The adults are very delicate midges,
usually reddish in color, and less than
1/12 inch in length.

Development: Eggs of gall-making
species are laid on the new growth. The
galls develop around the maggots as they
feed. The transformation stage is usually
found in the gall. The adult midges live
only a day or so. The period from egg to
adult is about one month in the case of
the chrysanthemum gall midge, and the
adult female may lay as many as 100 eggs.

Important Greenhouse Species

Chrysanthemum gall midge, Diarthron-
omyia chrysanthemi Ahlberg. Individual
cone-shaped galls are formed on the
leaves and stems. These may be so abun-
dant that the leaves are deformed and
the stems gnarled and misshapen. Only
chrysanthemums are attacked, although
some varieties are more susceptible to
injury than others. It is a common green-
house pest, although outside infestations
also occur along the coast.

CONTROL

Until recently the chrysanthemum
gall midge has been very difficult to con-
trol. Certain of the newer insecticides,
however, are very effective.

1. DDT: adult control. (See page 52.)

2. Benzene hexachloride : excellent con-
trol of adults and immature stages within
the galls. (See page 50.)

BULB FLIES

Importance: The maggots of several
species of bulb flies are found commonly
in association with bulbs of all types. One
of these species is of considerable im-
portance in destroying bulbs. Certain
others may be secondary, the maggots
preferring to feed on diseased or infested
rootstocks. Bulb flies are primarily pests
under field conditions, but infested bulbs
are transferred to greenhouses.

Appearance: Bulb fly maggots are
fleshy, whitish or dirty gray, without legs
or a head but with a short, brown tube
at the back end. They are from 1/2 to 3/4
inch long when mature.

Adults are medium-sized flies, about
1/3 or 1/2 inch long, dark in color with
pale markings or hairs.

Development: Eggs are laid at or near
the bases of plants or on exposed bulbs,
and the maggots work into the bulbs. The
transformation stage is passed in a brown
case in the bulb or in the nearby soil.
Adults are most active on warm, sunny
days.

Important Greenhouse Species

Narcissus bulb fly, Lampetia equestris
(Fabricius). The maggot is large, work-
ing in the center of the bulb and usually
only one in each bulb. Adult is large and
stocky, the body densely covered with
hairs which are yellowish except for a
variable black band which is often present
across the middle. It is a common pest,
and a wide variety of bulbs are subject
to attack.

Other Species Found

In California Greenhouses

Lesser bulb fly, Citibaena tuber culata (Ron-
dani) . These maggots are smaller than those of
the narcissus bulb fly, and a large number are

Fig. 48. Maggot of the narcissus bulb fly
working in the center of a bulb.

39]

usually present in an individual bulb. Adults
are slender, blackish green with pale markings.
Although this species is very common on decay-
ing bulbs, it would appear that primary injury is
not generally caused.

Least bulb fly, Citibaena narcissi (Smith), is
very similar to the lesser bulb fly and sometimes
found in association with that species. Its occur-
rence is more limited, however.

CONTROL

Many bulb treatments have been tried
with moderate success. These include fu-
migation with paradichlorobenzene, car-
bon disulfide, mercuric chloride, and
calcium cyanide. Certain of the newer in-
secticides might be effective for bulb fly
control, but information on their use is
not available.

1. Methyl bromide: very effective bulb
treatment. (See page 55.)

2. Hot water or vapor-heat treatment:
effective for control of bulb infestations.
(See page 46.)

3. Chlordane : reported to be effective
for prevention of infestation of planted
bulbs. (See page 51.)

LEAF MINERS

Importance: The maggots of leaf min-
ers are found commonly tunneling within
the leaves and stems of a wide variety of
plants. The foliage is rendered unsightly
by the larval mines and by the feeding
punctures of adults. In the case of heavy
infestations leaf drop follows.

Appearance: The larvae are soft,
white maggots, with black mouth hooks.
They are about 1/10 inch long when ma-
ture. Their tunnels are long and winding
or else blotch-like.

The adult flies are stocky, about 1/12
inch long, and are blackish, sometimes
marked with yellow. They are very active,
flying among the plants and walking over
the foliage.

Development: Eggs are deposited in
small feeding holes made by the adults in
the leaf tissues. Hatching takes place in
5 or 6 days, and the maggots feed in the
leaves for about two weeks. The transfor-

mation stage is formed in the mine or in
the ground, and it lasts about two weeks.
The adults may live for 2 or 3 weeks, each
female laying about 100 eggs.

Important Greenhouse Species

Chrysanthemum leaf miner, Phyto-
myza atricornis Meigen. Larvae make
conspicuous, serpentine mines in the
leaves, and the case of the transformation
stage is whitish and occurs within the
mine. The adult is uniform blackish. A
wide variety of composite plants serve as
hosts, chrysanthemum, cineraria, and
marguerite being favorites. Although pri-
marily a greenhouse pest in other parts
of the United States, it is common both
under glass or outside in California.

Other Species Found

In California Greenhouses

Serpentine leaf miner, Liriomyza subpusilla
(Frost). Larvae make narrow, twisting mines
in the leaves, but the case of the transformation
stage is brown and occurs in the soil. The adult
fly is blackish with conspicuous yellow mark-
ings. It is a very common outdoor pest on many

Fig. 49. Tunnels of the chrysanthemum leaf
miner in a cineraria leaf.

40

field crops and frequently enters greenhouses to
attack a wide variety of plants.

Burdock leaf miner, Dizygomyza maculosa
(Malloch). The larvae form irregular blotch
mines, the transformation stage occurring in the
ground. The adult fly is comparatively large, and
uniformly black. Burdock, chrysanthemum, and
various composites are commonly attacked out-
doors, and occasional greenhouse infestations
are found.

CONTROL

Until recently the leaf miners have been
very difficult to control, because of the
protection afforded the maggots within
their mines.

l.Chlordane: effective control. (See
page 51.)

2. Benzene hexachloride : effective con-
trol. (See page 50.)

SAWFLIES

Importance: Sawflies constitute a
rather large group of insects, the imma-
ture stages of which feed on leaves or
bore in stems. Several species are pests of
ornamental plants, and two of these have
been found in California greenhouses.
The bristly rose slug is another common
species in the state, but it has been found
only outdoors.

Appearance: The larval stage of saw-
flies often resembles a caterpillar very
closely, but a pair of fleshy legs are found
on the first segment behind the three pairs
of true legs at the front end of the body.
They are commonly about 1/2 inch long
when mature, and some species are
prettily colored.

The adult sawflies are wasp-like insects
but do not have a narrow waist. They are
often black or marked with yellow or or-
ange and about 1/2 inch in length.

Development: Eggs are laid in punc-
tures within the plant tissues, and they
hatch in about two weeks. The larvae feed
on the plants for about one month, usually
either skeletonizing leaves or eating the
margins, or else mining in the stems. The
mature larva makes a cocoon, usually
within the stalk of a pithy plant, and many
months may pass before the transforma-
tion stage is formed and the adults

emerge. There is usually but a single gen-
eration annually, but some species have
two generations each year.

Species Found

In California Greenhouses

Western rose stem sawfly, Hartigia cressoni
(Kirby) . A pest of roses and brambles, the
whitish larvae boring within the pith of terminal
shoots. A common outdoor pest which frequently
invades rose greenhouses and kills the terminal
growth.

Violet sawfly, Ametastegia pallipes (Spinola) .
Larvae dark greenish with small white spots.
They occur only on pansies and violets and are
found infrequently in greenhouses. The young
larvae feed on the underside of leaves making
small holes, but as they become larger they rest
in the daytime and come out at night to devour
the margins.

CONTROL

Sawfly larvae are easy to control when
they are exposed on leaves by use of the
insecticides listed below. When they bore
within the stems, however, it is necessary
to cut off and burn the shoots as soon as
the injury is discovered.

1. Basic lead arsenate. (See page 48.)

2. Cryolite. (See page 54.)

3. Parathion. (See page 57.)

STEM WASPS

Importance: The stem wasps comprise
a group of tiny wasps. The larvae of a
number of species are found in the stems
of plants, often forming galls, or else in-
festing seeds. Certain species, however,
are parasitic on other insects. Only one
species is a pest to greenhouse plants, and
it is restricted to orchids.

Appearance: The larvae are white,
fleshy, without legs or a distinct head.
They are about 1/6 inch long when grown.

The adult is a slender, black wasp, with
clear wings, and it is about 1/7 inch in
length.

Development: Individual eggs are in-
serted into the plant tissue, and the larvae
burrow out cavities, causing the infested
parts to become darkened and swollen.
The transformation stage occurs within
the burrow, and the life cycle is completed
in about two months.

41

Species Found

In California Greenhouses

Cattleyafly, Eurytoma orchidearum (West-
wood), occurs within the small flower buds or
pseudobulbs of cattleya orchids. Infested buds
never bloom. An important pest of these plants
which often has been encountered in California.

CONTROL

The cattleyafly has ceased to be a prob-
lem in orchid houses that have been
sprayed three or four times annually with
DDT. Prior to the use of this material,
the infested parts were removed and
burned, and repeated fumigations for ex-
tended periods were directed against the
adults.

ANTS

Importance: Ants are of particular im-
portance to the grower of ornamental
plants, because many species are fond of
the honeydew excreted by aphids, mealy-
bugs, and soft scales. They may tend and
pasture these pests and guard them from
their enemies. Infestation of the honey-
dew-excreting insects may originate or
spread by ants moving them from plant
to plant. Sweet plant exudates such as
secreted by many orchids, are also attrac-
tive to ants. Certain species may be of im-
portance in directly attacking plants.

Appearance: Ants are wasp-like in-
sects, having a narrow waist. They are
reddish, brown, or black in color. The
forms most commonly seen are the work-
ers which are wingless and usually about
1/10 to 1/5 inch in length.

Development: Ants are social insects
which live in colonies. Their nests are
often simple and located either in the
ground outside or in greenhouse beds and
potting material. The eggs and worm-like
larvae are found in the nests where they
are cared for by the workers. At mating
time swarms of winged males and females
come out to start new colonies.

Important Greenhouse Species

Argentine ant, Iridomyrmex humilis
Mayr is a small, brown ant which follows

[42

definite trails. The workers are fond of
sweets and readily enter greenhouses for
honeydew. It has become a widespread
and serious pest since its introduction into
California.

Other Species Found

In California Greenhouses

California fire ant, Solenopsis xyloni maniosa
Wheeler, is yellowish red with a black abdomen.
It feeds upon greenhouse plants, steals seeds,
and tends honeydew-excreting insects.

California honey ant, Prenolepis imparls cali-
fornica Wheeler, is shining brownish black. The
abdomen is greatly distended after feeding. It is
commonly found throughout the state and often
enters greenhouses to feed on honeydew and
plant exudates.

California brown field ant, Formica cinerea
Mayr, is a brown, medium-sized species. It fre-
quently invades greenhouses to tend honeydew-
excreting insects.

Western pavement ant, Tetramorium pacifi-
cum Mayr, is a large, red ant. It has been found
frequently in orchid houses.

CONTROL

The use of liquid ant baits containing
sodium arsenite is being replaced by one
of the newer organic compounds which
may give control for many months as a
result of a single application.

l.Chlordane: excellent control with
applications to lower walls of greenhouse
and sides and supports of benches. (See
page 51.)

MILLIPEDES

Importance: Millipedes are found com-
monly in damp soil or leaf mold where
they feed on decaying organic material.
Several species, however, are known to
feed occasionally on sprouting seeds or
roots.

Appearance: Millipedes are long,
worm-like animals that are related to cen-
tipedes but differ in having two pairs of
legs on each segment. Their bodies are
hardened, dark colored, about 1/2 to 1
inch in length. They coil in a character-
istic manner and are active only at night.

Development: Eggs are laid in large
clusters in the soil, and they hatch in

about three weeks. The young grow grad-
ually in size, adding segments and legs
until mature. There is one generation
each year.

Important Greenhouse Species

Greenhouse millipede, Orthomorpha
gracilis Koch, is brown with pale sides. It
is a common greenhouse inhabitant al-
though it also occurs outdoors in Califor-
nia. A variety of flowering plants have
been reported to be injured.

Other Species Found

In California Greenhouses

Common millipede, Diploiulus luscus (Mein-
ert) , is small and brown. It is a common species
outdoors in California and occasionally found
in greenhouses. It has been reported to be in-
jurious to begonia tubers.

Bulb millipede, Nopoiulus minutus (Brandt) ,
is brownish with a row of black spots on each
side. It is found eating into bulbs occasionally.

CONTROL

Millipedes are very easily controlled
with certain of the newer organic prepa-
rations.

l.DDT. (See page 52.)

2. Chlordane. (See page 51.)

3. Benzene hexachloride. (See page
50.)

4. Parathion. (See page 57.)

GARDEN CENTIPEDES

Importance: Garden centipedes occur
in damp, loose soil or ground debris.
Most of the species feed on algae and
fungi, but one species eats the tender
roots of plants. It is often a serious pest
in greenhouses.

Appearance: Garden centipedes are
soft, white, and elongate, about 1/2 inch
long when grown. They bear one pair of
legs on each segment, the adults having
twelve pairs.

Development: Eggs are laid in small
batches, and they hatch in about two
weeks. The young gradually increase in
size and gain legs, and they mature in sev-
eral months. Adults may live for several
years, wandering at different levels in the
soil from the surface to a depth of over
four feet.

Important Greenhouse Species

Garden centipede, Scutigerella immac-
ulata (Newport), has longer legs and is
more active than related species. Damage
is caused to various plants but particu-
larly to bedding plants such as snap-
dragons under greenhouse conditions.

CONTROL

In view of the fact that the garden cen-
tipede occurs commonly at considerable
depths in the soil, steam sterilization of
earth beds does not effect control. A soil
fumigant with considerable residual ac-
tion is needed in such cases.

1. D-D or EDB: most satisfactory for
soil fumigation before planting. (See
pages 53 and 54.)

2. Benzene hexachloride: affords pro-
tection of established plants. (See page
50.)

Fig. 50. The garden centipede. Above, adult;
below, eggs and young.

[43]

SLUGS and SNAILS

Importance: Slugs and snails are com-
mon greenhouse pests where the humidity
is high. They often feed on the leaves,
stems, or roots of various plants, scraping
off the surface or making irregular holes.

Appearance: Snails and slugs are ani-
mals that are related to clams and oysters.
Their bodies are soft, covered with slime,
and they are commonly from 1/2 to 2
inches long. Snails form a hard shell into
which they can retreat, while slugs do not
have this protective covering. Both come
out at night to feed and leave a character-
istic trail of slime over the path.

Development: Eggs are laid in small
masses, and under favorable conditions
they hatch in about one month. Growth
is slow and gradual, maturity being
reached in from several months to two
years.

Important Greenhouse Species

Greenhouse slug, Milax gagates (Mul-
ler), is black or dark gray with a longi-
tudinal ridge down the back. It is a very
destructive species and is commonly
found in greenhouses and gardens.

Gray garden slug, Agriolimax agrestis
(Linnaeus), is light grayish with scattered
darker spots. It is a common garden pest
which also is found commonly in green-
houses feeding on orchids and various
other plants.

Other Species Found

In California Greenhouses

European brown snail, Helix aspersa (Miil-
Icr) . The shell is large and brownish with spiral
dark bands which are broken by light cross
streaks. This snail is common throughout Cali-
fornia and frequently found in greenhouses. A
wide variety of low plants are attacked.

Bush snail, Zonitoides arboreus Say. The shell
is small, brown, nearly flat. Common throughout
the United States and sometimes found in Cali-
fornia greenhouses on orchids and other plants.

Cellar snail, Oxy chillis cellularis (Miiller) .
The shell is medium sized, pale brownish or
whitish, and nearly flat. This species is widely
distributed on the Pacific Coast and occasionally
is found in greenhouses.

Drapernald snail, Oxychilus drapernaldi
(Beck), is similar to the cellar snail but some-
what larger. It is established in gardens and
greenhouses in northern California.

CONTROL

None of the newer insecticide materials
has been found to be effective for slug and
snail control.

1. Metaldehyde and calcium arsenate
bait: checks infestations. (See page 66.)

PILLBUGS and SOWBUGS

Importance: Pillbugs and sowbugs are
common greenhouse inhabitants which
usually feed on decaying organic mate-
rial. In fact, they may devour the manure
used for fertilizer. At times, however, they
also feed on the tender shoots of young
plants.

Appearance: Pillbugs and sowbugs are
related to shrimp and crayfish and simi-
larly breathe by gills. They are more or
less gray, elliptical, about 1/2 inch in
length. The back is covered by a series of
plates, and seven pairs of legs are present.
They are active at night, hiding in the
soil and under flower pots in the daytime.

Development: The young hatch from
eggs held in a pouch in the female, and
they gradually increase in size, maturing
in about one year. Damp greenhouse con-
ditions favor their development.

Important Greenhouse Species

Greenhouse pillbug, Armadillidium
vulgar e (Latreille) , rolls into a ball when
disturbed. A common greenhouse and
outdoor pest which has been introduced
into California, it is particularly destruc-
tive to bedding plants such as asparagus
fern.

Dooryard sowbug, Porcellio laevis
Koch, runs into hiding when disturbed.
It is found commonly in greenhouses and
outdoors and has been reported to injure
plants.

CONTROL

Pillbugs and sowbugs formerly were
controlled with baits. Certain of the newer

[44]

insecticides are more satisfactory, how-
ever. They are applied to the surface of
the soil, either as sprays or dusts.

1. DDT. (See page 52.)

2. Chlordane. (See page 51.)

3. Benzene hexachloride. (See page
50.)

4. Parathion. (See page 57.)

NEMATODES

Importance: Nematodes which infest
plants are very destructive. They injure
the plants by killing tissues or by produc-
ing abnormal growth. Several species are
found occasionally in California green-
houses.

Appearance: Nematodes are round
worms, without body segments. The ones
which infest plants are very small, mature
females being about 1/20 inch long. Ex-
ceedingly large numbers may be present.
It is by their characteristic injury that the
presence of nematodes is suspected.

Development: Eggs are laid where
they feed, and the worms mature in from
two to four weeks. Adult females may
each lay several hundred eggs.

Species Found

In California Greenhouses

Root-knot nematode, Heterodera marioni
(Cornu) , works in the roots, causing gall forma-
tions which interfere with the transportation
system of the plant. Infested plants become
stunted, sickly, and often die. Young larvae
which wander through the soil are responsible
for new attacks. A very wide variety of green-
house plants are subject to infestation.

Foliar nematode, Aphelenchoides olesistus
(Ritzema Bos) , works in fleshy leaf tissues, pro-
ducing irregular, blackened patches. Adults are
able to wander over the surface of the plant in
films of moisture, and they are capable of re-
maining dormant for some time. A number of
greenhouse plants are subject to infestation,
common ones being African violet and pepero-
mia. Birds-nest fern is often infested by a simi-
lar form.

Bulb and stem nematode, Ditylenchus dipsacl
(Kiihn) , works in bulbs, stems, or leaves, pro-
ducing swellings, twisting, and stunted growth.
The mature larvae may wander through the soil
to infest new plants, and this stage may remain
inactive for several years. There are distinct
forms which are restricted to a given type of
plant, but the host list is large.

Fig. 51. Symptoms of the foliar nematode on
birds-nest fern.

CONTROL

Nematodes are serious pests and their
control is difficult. Infested plants should
be completely discarded.

1. Steam sterilization: effective for
treatment of soil and pots. (See page 46.)

2. D-D or EDB : effective soil treatment.
(See pages 53 and 54.)

3. Heat treatment : effective for control
of bulb infestations. (See page 46.)

45

TUetfauU o£ (fatfaol

BIOLOGICAL CONTROL

The insect pests occurring in green-
houses are likely to be isolated from the
natural enemies which accomplish vary-
ing degrees of control under outdoor con-
ditions. Biological control in greenhouses
consists for the most part of artificially
rearing and liberating certain of these
enemies. The use of such predators and
parasites is impractical when they are
killed by insecticides which may be used
for the control of other pests.

The ladybird beetle, Cryptolaemus
montrouzieri Mulsant, is a voracious
feeder on mealybugs in both larval and
adult stages. This beetle was originally
collected in Australia, and colonies were
liberated in California citrus orchards
many years ago. A number of growers
have used them in gardenia ranges. Their
results have been variable, but in general
the mealybug populations have been con-
siderably decreased but not eliminated.
Conditions unfavorable for the develop-
ment of the beetles may occur during the
winter, and new liberations are then
necessary in the spring.

The Sicilian parasite, Leptomastidea
abnormis (Girault), also has been re-
leased to a limited extent in gardenia
ranges for control of the citrus mealybug.

In other parts of the country parasitic
wasps, Encarsia formosa Gahan, have
been released in greenhouses infested
with the greenhouse whitefly. Very satis-
factory control has been reported.

HEAT TREATMENT

Steam Sterilization

Sterilization of the soil with steam is a
well-known practice for the control of
many pests. Many plant disease organ-
isms and weed seeds also may be killed by
steam, and conditions more favorable in
general to plant growth may be produced.

Fig. 52. Larvae of a ladybird beetle which
feeds on mealybugs.

The soil should be dry and loose at the
time of steaming. The type and condition
of the soil and the amount of steam avail-
able per unit area are important consid-
erations for the length of time necessary
for sterilization. From 2 to 10 hours may
be required, and a soil temperature of
140° F to 150° F should be attained.

For the treatment of small quantities
of soil for flats or potting purposes, vari-
ous types of box sterilizers are used.

The inverted pan system and the buried
pipe or tile system are used for steam ap-
plications to the beds.

Inverted Pan. In this system a rectan-
gular galvanized-iron pan, 6 to 9 inches
deep, is inverted over the soil, and steam

[46]

is admitted under pressure through con-
nections in the pan. This method is fairly
satisfactory, with killing temperatures
being produced at depths of 5 to 10
inches.

Buried Pipe. The more efficient method
of steam sterilization is the use of buried
perforated pipes or tiles. The pipes are
from 1% to 2 inches in diameter, per-
forated at 6- to 12-inch intervals with
holes about % inch in diameter. They
are laid at a depth of 6 to 12 inches with
spacings of 12- to 16-inch intervals. One
end of each pipe is bent to protrude from
the ground and is provided with a union
to a crossheader which is connected with
the steam pipe. Both 3- and 4-inch irriga-
tion tile are used commonly in place of
the pipe. The tile lines are buried from
12 to 18 inches deep and from 18 to 24
inches apart. Steam from a high-pressure
boiler (80 or more pounds pressure) is
admitted to the pipes or tile lines, while
the soil is covered above with a tarpaulin.

Hot Water Sterilization

Hot water treatments of ground soil
have not proved successful, but this
method often has been used for the con-
trol of bulb pests, such as nematodes,
mites, maggots, and aphids, and also for
the control of the cyclamen mite.

Bulb treatment consists of submersion
in water ranging in temperature from
110° to 111° F, for a period of 2*/2 to 3
hours. For the control of the cyclamen
mite, the plant material is immersed for
only 15 to 20 minutes.

The water should be agitated or circu-
lated to insure a constant and uniform
temperature after the plant material is
submerged. Temperatures over 111.5° F
are apt to result in plant injury.

Vapor-heat Treatment

The vapor-heat method of bulb treat-
ment involves the use of a treating room
equipped with a conditioning machine
which circulates water-mist and air satu-
rated with water vapor at the desired tem-

perature. Similar to the hot water treat-
ment, a temperature of 110° to 111° F
is the most favorable. Periods of bulb
exposure vary from % to 1% hours for
mite and fly control to 8 hours for nema-
tode control. Bulbs intended for green-
house flower production should be treated
early in the fall, after at least three weeks
of drying. For control of the cyclamen
mite, the plant material is exposed for
30 to 60 minutes.

CHEMICAL CONTROL

There are three considerations which
may be stressed with regard to the chemi-
cal control of greenhouse pests :

1. Use the proper insecticide against
the specific pest involved. Practically all
of the insecticides are specific against
certain pests or groups of pests. The insect
should be recognized, and the selection
of an insecticide for its control should be
based on a knowledge of its value against
that insect, as well as the more obvious
considerations of plant tolerance, ease of
application, objectionable residue, rela-
tive danger to humans, and cost.

2. The treatment should be thorough.
Wherever possible the pest should be
eliminated, and this is more readily pos-
sible since recently developed materials
have become available to augment the
older insecticides.

3. The grower should be alert to recog-
nize incipient infestations and to employ
timely treatment. The problems of control
are more easily solved before widespread
destruction occurs and large numbers of
pests are present. In this connection it
is important to examine carefully and to
decontaminate when necessary any new
plant or other material before it is intro-
duced into a greenhouse. This is the only
source of infestation of a large number
of greenhouse pests.

Many new insecticides have been ap-
pearing on the market since the war. The
grower should learn to recognize these by
the chemical name which is given on the
label as the active ingredient.

47

76c*)*t4ecticide4,

Insecticides are nearly always poison-
ous to humans, and the newer ones are
released before their hazards are well un-
derstood. For this reason, the grower
should handle the materials with great
care. This is particularly true of concen-
trated forms of the insecticides.

The synthetic organic insecticides
which have recently come on the market
are continually undergoing change and
improvement, with regard to both the
technical material and the formulations.
Other new insecticides are being evalu-
ated, and some of these will become com-
mercially available.

These materials are released before
they are tested extensively on the ex-
tremely wide range of greenhouse plants,
their numerous varieties, and under all
the possible growing conditions. These
insecticides, however, are often very valu-
able for pest control, and the grower
should satisfy himself as to the tolerance
of the particular plants to be treated.

Accuracy of dosage is essential with
modern chemicals. Not only are accurate
measures of the insecticides necessary to
minimize the danger of plant injury, but
they also are necessary to ensure effective
control.

ARSENICALS

Lead Arsenates

Arsenicals containing lead have been
used extensively for the control of leaf-
chewing insects such as caterpillars and
beetles. There are two types of such com-
pounds, standard lead arsenate and basic
lead arsenate.

Standard lead arsenate contains a
higher percentage of arsenic than the
basic type, and it is a stronger poison,
acting more quickly. It is also more sus-
ceptible to the action of other chemicals,
particularly those of an alkaline nature
(such as soaps) , and is more or less de-

composed by them when used in the
spray. The soluble arsenic so formed may
lead to severe burning of tender foliage.
Under moist greenhouse conditions, con-
siderable foliage injury may result when
standard lead arsenate is used alone.

Basic lead arsenate, although a weaker
poison with slower action, is not appreci-
ably decomposed by moisture or slightly
alkaline materials. This type may be used
with safety on most foliage. When applied
as a spray, basic lead arsenate is used at
the rate of 2% to 5 pounds to 100 gallons
of water.

In preparing a spray a thin paste
should be made before final dilution.
Pastes which are commercially available
contain approximately half as much ar-
senic as the corresponding powders and
should be used at twice the dosage. A
spreader should be used with the lead
arsenates, unless one has been added in
the commercial formulation.

When combined with a carrier such as
sulfur and used as a dust, lead arsenate
is used at a rate of 10 per cent by weight.

Calcium Arsenate

Calcium arsenate is somewhat similar
to the lead arsenates. It contains a rather
high proportion of soluble arsenic, there-
fore it is not used as a spray. It also has
a high lime content and so is incompatible
with many insecticides. It has been used
to some extent by floriculturists in cut-
worm baits, but chiefly in slug and snail
baits. (See Metaldehyde, page 54.)

Paris Green

Paris green was formerly used exten-
sively in greenhouses for the control of
chewing insects because it is inconspicu-
ous on green foliage. It contains, how-
ever, a high and variable content of water-
soluble arsenic, and is therefore likely to
cause burning.

48

As a spray, Paris green is mixed with
twice its weight of hydrated lime to neu-
tralize the soluble arsenic, and diluted at
the rate of about 1 pound to 100 gallons
of water. It has also been used in 5 to 10
per cent dusts. Paris green sometimes has
been substituted for arsenic trioxide or
sodium arsenite in baits, using about
double the proportions given for the latter
compounds.

Arsenic Trioxide

Arsenic trioxide or "white arsenic" has
been used in baits for the control of pests
such as cutworms, the black vine weevil,
sowbugs, pillbugs, and millipedes. The
basic formula is 1 pound of arsenic tri-
oxide to 25 pounds of bran (2 teaspoons
of arsenic trioxide to 1 pound of bran) .

These ingredients are mixed dry and
then sufficiently moistened to make a soft
mash. Alfalfa meal, shorts, dried beet
pulp, or rice meal may be substituted for
the bran. Molasses, banana oil, or finely
ground lemons or oranges are sometimes
added in an effort to make the bait more
attractive. The bait is scattered thinly
over the soil and is applied in the evening
for nocturnal pests.

Sodium Arsenite

Sodium arsenite is very soluble, and
it is extremely poisonous to plants and
animals. It is the poison which is most
commonly employed in commercial ant
baits and is sometimes used in other baits.
Because it may be made by heating ar-
senic trioxide with washing soda (sodium
carbonate) or lye (sodium hydroxide),
it is sometimes called "arsenite of soda."

Caution. Baits containing sodium arse-
nite or other arsenicals should be handled
with care and should not be placed within
access of children and pets.

AZOBENZENE

During the past few years azobenzene
fumigation has played an important role
in the control of spider mites on gar-
denias, roses, and other crops. The mites,

including the eggs, die over a period of
several days to a week following treat-
ment, and a single application generally
gives from 95 to 99 per cent control.

Steam-pipe vaporization of 70 per cent
azobenzene powder has been the general
method of fumigation, although a 90 per
cent powder is now available. The stand-
ard dosage with the 70 per cent material
is 1 pound per 40,000 cubic feet of space.
It is mixed with water to form a paste,
painted onto the pipes throughout the
house, and the steam is then turned on,
first in one set of pipes and an hour or
so later in the other set. Fumigation
should be carried on under warm tem-
peratures (70° to 95° F) , preferably 75°
F, and the house should remain closed
for six hours before ventilating and slow
cooling.

The pure azobenzene crystals may also
be used for vaporization, either with hot
plates, lamps, or steam-pipe boxes, and
the standard dosage with this material is
1 pound to 57,000 cubic feet (2 ounces
per 7,000 cubic feet) , evaporated over a
two- or three-hour period.

Azobenzene also is available in a pow-
der form ("pressure fumigator") which
is released with the smoke when the mate-
rial is ignited in the can. This type of
fumigation is convenient and is apt to
produce less-injurious effects on the
plants. One pound of this material is used
for each 10,000 cubic feet. Slow-burning
azobenzene candles also have been pro-
duced, and this chemical has been used to
some extent as micronized dusts.

In general, azobenzene has a good rec-
ord of foliage safety, although in some
cases tipburn of young leaves and bleach-
ing or dropping of mature leaves occurs.
The greatest objection has been to the
discoloration of red flowers. It is possible
that azobenzene serves as a stimulant to
plant growth. In addition to gardenias
and roses, a number of other crops have
been fumigated successfully, including
carnations, chrysanthemums, and snap-
dragons.

49

BENZENE HEXACHLORIDE

Benzene hexachloride, commonly short-
ened to "BHC," is the generally accepted
name for the chemical hexachlorocyclo-
hexane, a recently developed insecticide
which was first known as "666." Its insec-
ticidal properties were discovered in
France in 1941, independently in England
in 1942, and commercial quantities were
available in the United States in 1947.

Outstanding uses of the material ap-
pear to be for the control of such soil
pests as the garden centipede, millipedes,
sowbugs, springtails, wireworms, grubs,
and for the control of gall midges, leaf
miners and other maggots. It is effective
for the control of many beetles, aphids,
and thrips, as well as certain caterpillars
and other insects.

Commercial preparations of benzene
hexachloride are composed of various
forms of this compound and also impuri-
ties. The form which is known as the
"gamma isomer" is accepted to be the
principal toxic ingredient, and insecti-
cidal considerations are based on this
form. Benzene hexachloride is insoluble
in water, but soluble in certain organic
solvents. The residue is effective for 1
or 2 weeks, and an insecticidal vapor is
slowly released.

Commercial material has been avail-
able principally in two forms, dusts and
wettable powders. Dusts containing from
0.5 to 4 per cent gamma isomer are spread
on or worked into the soil. The rate of
usage is 1 to 3 ounces of the 1 per cent
gamma isomer per 100 square feet. The
chemical may be dispersed over the foli-
age at the rate of 1 ounce of the 1 per
cent material per 100 square feet.

Wettable powders containing approxi-
mately 6 to 12 per cent gamma isomer
have been used the most widely. These
are applied at the rate of 1 to 2 pounds
of the 6 per cent gamma isomer, or % to
1 pound of the 12 per cent gamma isomer,
per 100 gallons of water. These prepara-

tions possess a persistent and obnoxious
odor.

More purified wettable powders, con-
taining approximately 25 to 36 per cent
gamma isomer, have been more recently
available, and these are applied at the
rate of about 1 pound per 100 gallons
of water. Preparations containing this
higher amount of gamma isomer are
preferable for use with ornamentals, be-
cause the objectionable odor is consider-
ably reduced and because isomers which
are believed to be of greatest toxicity to
plants are reduced.

Benzene hexachloride is available also
as a liquefied-gas aerosol.

Because of the possibility of plant in-
jury, caution should be followed in the
use of benzene hexachloride. Consider-
able burning of stocks has resulted with
heavier applications of dusts, and seed-
lings may be injured, or stunting may
occur, when it is used excessively in the
soil. Benzene hexachloride is one of the
newer materials which has not been tested
very extensively on ornamental plants,
and the grower should treat only a small
sample first to assure himself with regard
to the tolerance of the crop to be treated.

Caution. Benzene hexachloride is poi-
sonous to man. Care should be taken to
avoid inhalation of the dust or spray.
Liquefied-gas aerosols of this chemical
should be applied only while wearing a
gas mask with filter for organic vapors,
and protective clothing should be worn.

CARBON DISULFIDE

Carbon disulfide is very toxic to plants,
but it has been used to some extent on
bare soil as a fumigant for the control of
such pests as the garden centipede and
soil mealybugs. It is a colorless, ill-
smelling liquid which evaporates quickly
when exposed to the air. It is heavier than
air and penetrates downward into the soil.

Commercial preparations consist of a
rather unstable emulsion which is diluted
to from 0.25 to 0.5 per cent actual mate-
rial (1 quart to 2 quarts actual carbon

[50]

disulfide per 100 gallons of water), and
applied to the surface of the soil at the
rate of about 5 gallons per square yard.
Caution. Carbon disulfide is poisonous
and should be handled with care. The
vapor is highly inflammable, and even
hot steam pipes may ignite the gas.

CHLORDANE

Chlordane is a recently developed in-
secticide which is particularly effective
for the control of ants. It also is promis-
ing for the control of leaf miners and
other maggots, earwigs, certain caterpil-
lars, and grubs.

The technical material contains several
chlorinated hydrocarbons of which the
form containing seven chlorine atoms is
now believed to be the most toxic. Chlor-
dane is an oily liquid, completely soluble
in common organic solvents but insoluble
in water. The residue slowly vaporizes,
but a residual action persists for about
one week. It is formulated as a dust, wet-
table powder, emulsion, or solution.

Dusts are generally used at 5 to 10 per
cent strength, and at the rate of 1 ounce
per 100 square feet. Wettable powders
(containing 50 per cent chlordane) and
emulsion concentrates (1 quart of con-
centrate containing 45 per cent actual
material or approximately 1 pound chlor-
dane) are used at the rate of from 1 to 2
pounds actual chlordane per 100 gallons
water.

A 2 per cent oil solution also is avail-
able for ant control. In this form the ma-
terial is applied only to the walls, walks,
floors, and sides of the benches.

There appears to be considerable plant
tolerance to the above concentrations,
but comparatively little information is
available with regard to the tolerance of
greenhouse crops. For this reason the
grower first should treat only a sample
of plants to satisfy himself as to the toler-
ance of the crops needing treatment.

Caution. Chlordane is poisonous and
care should be taken to avoid inhalation
of the dust or spray.

CHLOROPICRIN

Chloropicrin is a poisonous tear gas
which has been used to a limited extent
as a soil fumigant for the garden centi-
pede, nematodes, and certain other soil
pests. It is a very heavy gas which pene-
trates downward, and it is relatively non-
inflammable.

Chloropicrin cannot be used at all with
growing plants, and it will injure ger-
mination of certain kinds of seeds. Bare
soil should be treated ten days before
planting.

CYANIDE

Hydrogen cyanide is a very deadly gas
which has been used for many years as a
greenhouse fumigant for the control of
aphids, thrips, whiteflies, and certain
scale insects.

Liquefied hydrogen cyanide may be
obtained in heavy steel cylinders from
which the gas is liberated when the pres-
sure is released. Sodium or potassium
cyanide, when treated with sulfuric acid,
quickly releases the gas, and the combi-
nation of these materials in earthen pots
has been used for greenhouse fumigation.
The use of calcium cyanide as a source of
hydrogen cyanide gas is the easiest and
the most generally accepted method for
such fumigation.

Commercial calcium cyanide is a dark
gray dust yielding up to about 50 per cent
by weight of hydrogen cyanide. The ac-
tion of moisture from the atmosphere
readily liberates the gas from this mate-
rial. From % to 1 ounce per 1,000 cubic
feet are the dosages in general use, and
it is advisable to test the lighter amount
first.

The proper amount of material is
evenly scattered along the walks late in
the evening (at dark), and the house is
ventilated early the following morning
(before sunrise). High humidity in-
creases the risk of plant injury, so the
house should not be watered from 12 to
24 hours preceding fumigation. The tem-
perature should not fall during fumiga-

51

tion because of condensation on the
foliage, and it should be within the range
of 52° to 70° F.

Caution. Hydrogen cyanide is a deadly
poison, and great care should be exercised
to prevent inhalation of the gas. It is not
safe to enter a house while fumigation is
in progress nor until the house has been
thoroughly ventilated.

DDT

DDT AND RELATED
COMPOUNDS

DDT is the common name for the white,
crystalline compound dichloro-diphenyl-
trichloroethane. Technical grade prepa-
rations also contain closely related com-
pounds which are less toxic to insects. In
1939, a Swiss firm reported this material
to be an effective insecticide, and in 1943,
it was first available in the United States
for extensive experimental work. It has
since become widely known, but there is
much to be learned concerning its use on
ornamentals.

DDT is highly effective for the control
of many caterpillars, the grubs and adults
of many beetles, thrips, adults of midges
and many other flies, plant bugs, leaf-
hoppers, crawlers of certain scale insects,
ants, pillbugs, termites, and certain other
pests of ornamental plants. It is not an
ovicide but possesses insecticidal proper-
ties over a long period of time after ap-
plication (up to three months under
protected conditions), thus killing the
immature forms as they hatch.

In some cases the use of DDT outdoors
has appeared to cause an increase in the
numbers of certain pests. A considerable
increase of spider mites, certain aphids,
and other insects has been observed.

Dust preparations containing from 1
to 10 per cent DDT are sometimes used
in greenhouses and for soil treatment.
One ounce of a 5% dust is used per 100
square feet. A longer residual action is
obtained with the use of spray material,
and most growers prefer such applica-
tions.

The wettable powder preparations are
safer for spraying on plants inasmuch as
there is no danger of plant injury by the
solvent. In order to avoid unsightly resi-
due the wettable powders containing high
percentages of DDT (50 to 90 per cent)
are desirable, and these are used at the
rate of about 1 pound actual DDT per
100 gallons.

The emulsions of DDT are made with
a large number of organic solvents. Some
of these, like xylene solutions, are formu-
lated primarily for spraying walls for fly
or ant control. Emulsion concentrates
(generally 25 per cent DDT) are diluted
at the rate of about 1 pint per 100 gallons
water for application to plants.

Certain plants, such as kalanchoe, are
readily injured by DDT. Several varieties
of camellias (particularly Cheerful and
Everet R. Rust) and at least one variety
of rose (Eclipse) are reported to be sus-
ceptible to considerable injury. It is pos-
sible that the accumulation of DDT in the
soil over long periods of time may pro-
duce injurious effects on plants.

Caution. Care should be taken to avoid
inhalation of DDT dust or mist, and ab-
sorption of the emulsion through the skin.

Methoxychlor

Methoxychlor is the name used in refer-
ence to methoxyphenyl- (or dianisyl-)
trichloroethane. It is closely related to
DDT, but is less effective against some
insects and more effective against others.
It is considerably less toxic than DDT to
mammals. Advantages of methoxychlor
for greenhouse use have not been deter-
mined.

DDD

DDD (or TDE) is a name used to re-
fer to dichloro-diphenyl-dichloroethane.
It is very similar to DDT, but is more
toxic to certain insects and less toxic to
other insects and to man. The advantages
of DDD in controlling greenhouse insects
have not been determined, except in the
case of orange tortrix. To control this

52

pest DDD may be applied as a spray,
using 2 pounds of 50 per cent wettable
material to 100 gallons of water.

DICHLOROBENZENES

Paradichlorobenzene

Paradichlorobenzene is a white, crys-
talline compound which volatilizes at
room temperatures. It has been used to
some extent as a soil fumigant for the
control of root aphids, grubs, and wire-
worms, but it must not be used on plants.
At one time the crystals were sprinkled on
orchid pots for the control of orchid wee-
vils, but plant injury was later noted.

Orthodichlorobenzene

This compound is similar to para-
dichlorobenzene, but it is a liquid. It has
been reported to give good control of
mealybugs on phoenix palm roots, and it
has also been used successfully for ter-
mite control. This material is also gen-
erally toxic to plants.

DICHLOROETHYL ETHER

There are two forms of dichloroethyl
ether, of which the /?-/?' form is the most
common commercially. It has a definite
odor, and is irritating to the eyes, nose,
and throat. The principal use of dichloro-
ethyl ether has been as a soil fumigant
where it has been used with some success
for the control of soil mealybugs, root
aphids, garden centipedes, wireworms,
and maggots.

It is used as an emulsion which is di-
luted to from 0.3 to 0.5 per cent of actual
material ( 1 pint to 1 quart of actual ma-
terial to 100 gallons of water). The rate
of application is such as to wet the soil
down (about 3 gallons per square yard) .
Many plants may be injured by this treat-
ment.

Dichloroethyl ether also has been used
experimentally for greenhouse fumiga-
tion, the pure material being volatilized
by an electric fan. Such fumigation is
reported to be effective for aphids, spider

mites, thrips, and adult whitefly, but foli-
age burning and flower bleaching are
caused on many plants.

DICHLOROPROPANE-
DICHLOROPROPENE

A mixture consisting mainly of dichlo-
ropropane and dichloropropene (1 part
of the former to 2 parts of the latter) is
commonly known as D-D. It has been de-
veloped recently as a soil fumigant which
gives effective control of the garden centi-
pede, wireworms, nematodes, and certain
other soil insects and pathogens.

D-D is a dark liquid which is applied
most effectively by means of a hand-type
injector regulated to give an individual
dosage of 3.5 ml. (cc.) at 12-inch spac-
ings and 6 to 8 inches depth. The soil
should be friable and moist.

D-D is not suitable for use with living
plants, and the beds should not be planted
for two to three weeks following treat-
ment, or longer if a strong odor of the
fumigant is detected in the soil.

Caution. D-D is poisonous and should
be handled with care.

DIMETHYL CARBINOL

Di(p-chlorophenyl) methyl carbinol
(DMC) is one of the new organic com-
pounds which has shown some promise
for mite control. It is reported to give
considerable control of spider mites on
deciduous fruit trees. It is effective
against the false spider mites and shows
some promise against the cyclamen mite.

DMC possesses considerable residual
action. Emulsion concentrates (25%
technical DMC) are available, and these
are used at the rate of V2 to 1 pint per 100
gallons of water.

Very little is known concerning the
plant toxicity of this chemical. A number
of woody plants appear to be tolerant, but
begonias, ferns, and other tender plants
are apt to be severely injured.

Caution. Dimethyl carbinol is poison-
ous and should be handled with care.

[53

Spray particles should not be inhaled, and
the eyes and skin should be protected.

DINITRO-PHENOL
COMPOUNDS

Dinitro-phenol compounds have been
used to some extent for the control of
spider mites. The dusts and spray materi-
als available consist of dinitro-ortho-
cyclohexylphenol or the dicyclohexyl-
amine salt of this compound.

Two applications, about ten days apart,
are reported to give satisfactory control
of spider mites, the kill being slow.
Considerable damage, however, may be
expected to the foliage and flowers of
greenhouse crops, particularly under con-
ditions of high temperature and humidity.
Caution. The dinitro-phenol com-
pounds are poisonous and should be han-
dled with care. Spray or dust particles
should not be inhaled.

ETHYLENE DIBROMIDE

Ethylene dibromide, commonly re-
ferred to as EDB, is one of the most
promising of the new soil fumigants, but
it cannot be used with living plants. It
has been effective in controlling the gar-
den centipede, wireworms, nematodes,
and other soil pests.

It is a colorless liquid which is com-
mercially available as a 10 to 25 per cent
solution in petroleum thinners. It is most
effectively used in beds by means of a
hand applicator which injects measured
quantities into the soil. About 2 ml. (cc.)
of 10 per cent material is drilled 6 or 8
inches into the soil at 12-inch intervals.
The soil should be in a condition ready
for planting, moist but not wet. Crops
should not be planted for a week to ten
days following treatment.

Caution. EDB is poisonous and should
be handled with care.

FLUORINE COMPOUNDS

Cryolite

Cryolite is a complex fluoride contain-
ing both sodium and aluminum, and it is

[54

often called "sodium fluoaluminate." It
is mined from natural deposits, but syn-
thetic material also is available commer-
cially.

Cryolite is only slightly soluble in water
but may cause burning under moist
greenhouse conditions. It has been used
to some extent against earwigs and cer-
tain beetles and caterpillars, usually as a
40 or 50 per cent dust or as a 50 to 90
per cent wettable powder. The 90 per cent
material is used at a rate of from 3 to 5
pounds per 100 gallons of water.

Sodium Fluosilicate

Sodium fluosilicate has often been used
as the toxic ingredient of baits, particu-
larly for earwigs and cutworms. It is used
in about the same proportion as that
given for arsenic trioxide.

Caution. Fluorine compounds are poi-
sonous and should be handled with care.

MERCURIC CHLORIDE

Mercuric chloride, also called corro-
sive sublimate, is an extremely poisonous
compound which has been used for cer-
tain soil pests such as root maggots. It
is used at a dilution of 1:1,000 (1 ounce
mercuric chloride per 8 gallons of water)
when it is sprinkled over the soil. Tablets
may be obtained at a drugstore which will
make 1 pint of solution. Dilution should
be made with distilled water, and the so-
lution must not be kept in a metal con-
tainer.

Care should be taken during applica-
tion to keep the liquid off foliage. Its
deleterious effects on plants may not be
evident for many months.

Caution. Mercuric chloride must be
handled carefully because of its great
toxicity to man and animals.

METALDEHYDE

The use of metaldehyde has been con-
fined to baits and to the control of slugs
and snails. The most satisfactory mix-
tures for this purpose consist of 1.5 to
2.5 per cent of powdered metaldehyde and

5 per cent calcium arsenate in bran, along
with other ingredients such as fruit pulp,
molasses, raisins, or boiled potatoes. The
mixture is moistened to form a mash and
broadcast lightly over the soil, but not
on the plants. Many commercial slug and
snail baits are available in pellet, granu-
lar, or powder form, and these are usually
successful in keeping the populations
down.

METHYL BROMIDE

Methyl bromide is a fumigant of con-
siderable importance for the treatment
of greenhouse plants, nursery stock, and
bulbs. It is a gas at ordinary tempera-
tures, but it is easily liquefied. This prod-
uct is commercially available in %- or 1-
pound cans or in quantities of 10, 50, and
150 pounds in light metal cylinders. The
vapor is heavier than air, and it is nonex-
plosive. It is very toxic to man and lacks
a distinctive odor at low but toxic concen-
trations.

It is less injurious to plants than most
fumigants and highly toxic to all forms
of insect life including the eggs, but evi-
dence of its insecticidal action may be
delayed for as long as several weeks fol-
lowing fumigation. Methyl bromide has
proved to be outstanding for the control
of scale insects, mealybugs, cyclamen
mite, and other pests which are difficult
to control.

Fumigation Chambers. Because
methyl bromide readily dissipates from
small leaks, it is usually used in air-tight
fumigation chambers. Such chambers
should be equipped with a heater to per-
mit temperature control, and insulated to
avoid temperature fluctuations. Methyl
bromide is introduced from outside the
chamber through copper tubing which
enters near the ceiling, and stratification
of the vapors will result unless fans are
provided for air circulation. The cham-
ber should be loaded so as not to interfere
with the circulation. A humidifier should
be used, since a relative humidity of 75
per cent or higher lessens considerably

the danger of plant injury and probably
enhances the insecticidal action. Caution
should be used to avoid exposure of hu-
mans to the gas following fumigation,
and for this reason an evacuator should
be provided for the chamber.

Dosage. There is a close relationship
between the dosage used, the time of ex-
posure, and the temperature under which
the fumigation is carried out. The best
temperature for fumigation is between
80° and 85° F, although somewhat lower
temperatures may be used by increasing
the dosage or the time of exposure. In
this connection, one may consider %
pound of methyl bromide to be equivalent
to 10° F difference in temperature or %
hour exposure time, once the lethal dos-
age has been established for other given
conditions.

The dosage is also determined on a
basis of the specific pests to be controlled
and the tolerance of the plants to be fu-
migated. As a general rule, however,
greenhouse plants are fumigated with 2
pounds of methyl bromide per 1,000
cubic feet for two hours when the tem-
perature is from 80° to 85° F. For outside
nursery stock, or dormant plants being
brought into the greenhouse, 2% pounds
are often used under the same conditions.
In this case, it is important to warm for
several hours plants which have been in
cold outside temperatures. Dormant
bulbs may be subjected to 3 pounds under
the same conditions.

Plant Tolerance. A great many plants
are tolerant to methyl bromide fumiga-
tion, but banana, begonia, chrysanthe-
mum, coleus, fish geranium, maidenhair
fern, poinsettia, saintpaulia, stephanotis,
and certain other plants may be severely
injured. Plants which show initial injury
but soon recover are fuchsia, hibiscus,
hydrangea, and pelargonium.

Greenhouse Fumigation. Experi-
mental studies have been conducted on
the use of methyl bromide for fumigation
directly in the greenhouse. Vaporization
was obtained preferably by spraying the

[55

liquid material into the house. Satisfac-
tory control of a variety of pests was
reported.

Methyl bromide emulsion is a good soil
fumigant, particularly near living plants.
Soil may be treated with a hand injector,
and it may be planted safely within sev-
eral days.

Caution. Its extreme toxicity to man
makes great care necessary in the use of
tliis fumigant.

NAPHTHALENE

Naphthalene is a white crystalline com-
pound that may be obtained either as
flakes or mothballs. It was used against
spider mites in greenhouses in England
as early as 1923, and formerly it was used
to a considerable extent as a greenhouse
fumigant in this country.

As a fumigant, from 2 to 3 ounces per
1,000 cubic feet are vaporized by heat,
under temperatures between 75° and 85°
F, and relative humidities between 75 and
80 per cent to avoid recrystallization on
the plants. Several fumigations usually
are necessary, and many plants are sus-
ceptible to injury.

Naphthalene is also effective against
gladiolus thrips, and the flakes are used
with bulbs for control of these insects.

OILS

Petroleum Oils

Petroleum oils that are used for spray-
ing are derived from certain distillation
fractions which are refined by removing
most of the portion which reacts with
sulfuric acid. The oils which are less toxic
to foliage contain a higher percentage of
this unsulfonated residue, usually from
90 to 98 per cent in the "light oils" or
"foliage oils." The less volatile and more
viscous oils (medium and heavy oils) are
more effective as insecticides, but they
are also more toxic to plants. They are
used as dormant sprays on deciduous,
hardy plants outdoors.

In order to secure a uniform film over
the plant, oils are generally applied in

the form of an emulsion (with small glob-
ules of the oil evenly dispersed in water) .
To provide the emulsion, commercial
preparations usually contain an emulsify-
ing agent either dissolved in the oil
(emulsive type containing about 99 per
cent oil) or else forming a concentrated
stock emulsion (emulsion type containing
about 83 per cent oil). The type and
amount of emulsifying agent largely con-
trol the amount of oil that is deposited
in spraying, as well as its compatibility.

Applications. Light-oil emulsions are
used at a 1 to 2 per cent dilution for the
control of mealybugs, soft scales, armored
scales, and whiteflies in greenhouses. The
amount of oil needed may be consider-
ably reduced by the incorporation of an
oil-soluble toxicant such as rotenone,
nicotine, or DDT. These oil combinations
are the ones most commonly used by nur-
serymen, and many plants are tolerant to
several treatments a year. Certain tender
plants, however, may be readily injured
by oil.

Applications are generally in the form
of a fine spray. Potting plants are some-
times immersed into the agitated emul-
sion and then laid on their sides to drain.

Vegetable Oils

Vegetable oils, such as coconut oil, are
sometimes used instead of petroleum oils,
particularly when such plant derivatives
as rotenone are incorporated.

ORGANIC PHOSPHATES

Hexaethyl Tetraphosphate
Tetraethyl Pyrophosphate

The insecticidal value of hexaethyl
tetraphosphate or "HETP" was originally
discovered in Germany where a formu-
lation was called "Bladan." Then it was
believed that hexaethyl tetraphosphate
was the toxic material, and many com-
mercial preparations have referred to the
content of this chemical. It is now known
that the active ingredient is tetraethyl
pyrophosphate, which constitutes about
20 per cent of hexaethyl tetraphosphate.

56]

Technical material referring to tetra-
ethyl pyrophosphate, "TEP," or "TEPP,"
is composed of about 40 per cent of the
active ingredient.

TEP or HETP are effective insecticides
for many species of aphids and for the
active stages of spider mites. The insecti-
cidal phosphate breaks down rapidly in
the presence of water and loses its effec-
tiveness, and no residual action is ob-
tained.

Formulations used as a spray are usu-
ally diluted at the rate of about % pint
(for 20 per cent TEP) per 100 gallons of
water. Satisfactory results for greenhouse
use have been obtained with aerosol
applications, either by mechanically pro-
duced fogs or liquefied-gas aerosols.
Steam-pipe fumigation has been prac-
ticed to some extent with this material.

Care must be exercised in the use of
TEP to avoid plant injury. A wide variety
of plants are tolerant to the recommended
dosages, but heavier applications are apt
to cause considerable burning. Certain
plants such as cyclamen are very sensitive
to TEP.

Caution. TEP and HETP are very toxic
to man. The concentrate material must be
handled with extreme care. Protection is
necessary against the spray mist to avoid
inhalation, contact with the eyes, or wet-
ting of bare shin through which absorp-
tion may occur. Protective clothing and a
respirator are necessary when applying a
spray or mechanically -produced aerosol.
Liquefied-gas aerosols should be applied
only when using a gas mask provided with
a filter for organic vapors as well as pro-
tective clothing.

The greenhouse must be thoroughly
ventilated following aerosol or steam-pipe
fumigation.

Parathion

Parathion is the accepted common
name of diethyl-paranitrophenyl thio-
phosphate, and it also has been referred
to under other designations such as
"3422." The insecticidal value of para-

thion was originally discovered in Ger-
many during the war. It promises to be
one of the best insecticides yet developed
for many pests encountered by the flower
grower.

Parathion applications possess resi-
dual action for several days or for
longer periods of time against very sus-
ceptible insects, but its lethal action
against scale-like insects may not be evi-
dent for several weeks. Commercial prep-
arations have a musty odor. Both wettable
powders (15 and 25 per cent actual ma-
terial) and dusts (% to 5 per cent para-
thion) as well as liquefied-gas aerosols
are available.

As a wettable powder, used at a rate
of one pound of 15 per cent actual mate-
rial per 100 gallons of water, parathion
is effective for the control of all stages of
thrips, aphids, whiteflies, and caterpil-
lars. At the rate of 1% to 2 pounds of 15
per cent actual material per 100 gallons
of water, excellent control may be ob-
tained for all the spider mites, mealybugs,
active stages of the cyclamen mite under
exposed conditions, and young stages of
armored scales and soft scales.

Liquefied-gas aerosols are also avail-
able. Such an aerosol is used at the rate
of one pound of 10 per cent (by weight)
solution in methyl chloride per 50,000
cubic feet of greenhouse space.

Significant plant injury, including in-
jury to delicate blooms, has not been ob-
served with experimental materials on a
great variety and large number of plants
treated with parathion. However, maiden-
hair and Boston ferns, poinsettias, and
one variety of azalea (Christmas Star),
are susceptible to damage. Commercial
preparations have not been used exten-
sively, and the grower should treat a small
sample first to satisfy himself as to the
tolerance of the plants involved. It should
not be used when active sulfur is present
from sulfur fumigation, else considerable
leaf drop is possible.

Caution. Parathion is a very toxic ma-
terial and must be handled accordingly.

[57

Spray mists or dusts must not be inhaled,
and a respirator as well as protective
clothing should be worn for spray and
dust applications. In the case of using
liquefied-gas aerosols a gas mask pro-
vided with a filter for organic vapors must
be worn as well as protective clothing.
The greenhouse should be thoroughly
ventilated following use of parathion as a
spray or as an aerosol fumigant.

ORGANIC THIOCYANATES

A number of organic thiocyanates are
highly toxic to certain species of insects
and mites and their action is very rapid.
They are relatively nontoxic to man. The
simplest one of practical value is lauryl
thiocyanate, and this compound has
shown some promise in the control of the
cyclamen mite. The commercial prepara-
tion is used at the rate of % pint to 1 pint
per 100 gallons of water.

The most widely used organic thiocya-
nate is ft— butoxy— ft' thiocyanodiethyl
ether. A 50 per cent solution of this com-
pound in kerosene is sold as a fly spray
concentrate, while a water-miscible con-
centrate has been prepared for green-
house uses against such pests as mealy-
bugs and whiteflies.

The thiocyanates are apt to be very in-
jurious to plants at effective concentra-
tions, but this danger may be reduced
somewhat by syringing with water after
each application.

PLANT DERIVATIVES

Nicotine

Nicotine is one of the oldest and best
known insecticides. It is effective for
many aphids, certain caterpillars, leaf-
hoppers, and thrips. It is derived from
various species of tobacco. Nicotine itself
is a fairly volatile and very toxic liquid
which is readily absorbed by the human
skin. It reacts with many substances to
form compounds which are nonvolatile
and relatively nontoxic as long as they
remain undecomposed. Alkaline sub-

stances cause the liberation of nicotine
from its compounds.

Nicotine sulfate (40 per cent nicotine)
is the chief form in which nicotine is
used. This form is applied as a spray at
the rate of about 1 pint per 100 gallons,
with the addition of a liberal amount of
soap (such as 1 gallon liquid fish-oil
soap) or other spreaders and stickers. It is
also commonly used in oil preparations.

A wide variety of nicotine dusts are
available, with different strengths of nico-
tine (usually 1 to 4 per cent) and with a
large assortment of carriers. The alkaline
carriers cause a more rapid liberation of
the nicotine, while neutral carriers favor
a release which is slower and over a
longer period of time. High temperatures
favor the evolution of nicotine from the
dusts. Combination dusts are available in
which nicotine is included with other in-
secticides or fungicides.

Nicotine as a fumigant also has been
used in greenhouses. Liquid nicotine is
painted on cold steam pipes and then
volatilized by turning on the heat, or else
it is volatilized from special heating con-
tainers distributed throughout the house.
Nicotine powder preparations are also
available in cans which can be ignited to
release nicotine with the smoke.

Many delicate flowers and tender shoots
are subject to injury by nicotine as a
spray, dust, or fumigant.

Caution. Because nicotine is very toxic
to humans, it should be handled with
care. Acute illness may be caused by in-
halation of the fumes or by absorption
of nicotine through the skin.

Rotenone

Rotenone is derived from the roots of
certain legumes which occur in the trop-
ics. These plants sometimes are called
derris, cube, or timbo. It is not known
to be very harmful to humans, although
hypersensitive individuals may suffer
skin irritation.

Rotenone serves as either a contact or
stomach poison, and its action is slow.

[58

It is used against various insects includ-
ing aphids and certain caterpillars and
beetles. It is applied either as a spray or
as a dust, various concentrations being
present (usually 0.5 to 5.0 per cent) in
commercial products. It also is incorpo-
rated in oil sprays.

Pyrethrum

Pyrethrum is derived from the flowers
of the pyrethrum plant, a member of the
genus Chrysanthemum. It is not generally
toxic to man, and it is nontoxic to plants.
The insecticidal ingredients are four com-
plex compounds which are known as
pyrethrins and cinerins.

Pyrethrum is known particularly as
a household insecticide, but it also is
used for pests of ornamentals, including
aphids, thrips, and leaf tiers. The active
ingredients are volatile and deteriorate
rapidly, and they break down in the pres-
ence of alkalies. Spray concentrates and
dusts with varying pyrethrum content
(usually 0.1 to 3.0 per cent) are used,
as well as mixtures in oil or liquefied-gas
aerosols.

Sabadilla

Sabadilla is derived from the seeds of
a South American liliaceous plant. It has
been used to some extent for the control
of plant bugs and leafhoppers, as well as
certain caterpillars and fungus gnats.
Dusts (10 or 20 per cent) are used
mostly, but spray materials are also
available. Sabadilla is not toxic to plants
or animals, but it does cause sneezing.

SELENIUM COMPOUNDS

Sodium Selenate

Sodium selenate, when applied to the
soil, is taken up by plants and accumu-
lates in the foliage. It is used rather ex-
tensively on carnations for the control
of spider mites and aphids. Other crops
such as chrysanthemums, saintpaulias,
and hydrangeas are sometimes treated.
Sufficiently toxic quantities are not ac-

cumulated in woody plants to give pest
control.

Sodium selenate may be obtained in
pure form with which a stock solution
is prepared by dissolving 1 pound in 4%
gallons of water (100 grams per gallon) .
One quart of the stock solution is diluted
with 25 gallons of water and evenly sprin-
kled over 100 square feet of bench area.

A dry form is also available which
consists of 2 per cent sodium selenate
impregnated on superphosphate. Three
pounds of this solid material are broad-
cast evenly over 100 square feet of bench
area and watered into the soil carefully.

Treatment with sodium selenate either
as a solution or solid should not be made
until after plants are well established,
about one month after benching, and
from two weeks to two months are re-
quired for the plants to absorb insecti-
cidal quantities. A single application may
then remain effective for 9 to 12 months
on carnations. Great care should be taken
to give the proper dosage. In too large a
dose sodium selenate may produce stunt-
ing on chrysanthemums, and it will pro-
duce severe injury to plants such as
cyclamen and begonia.

Caution. Sodium selenate is very toxic
to humans, and it should be handled with
great care.

SULFUR

Elemental Sulfur

This form of sulfur has been used ex-
tensively for the control of spider mites.
Dusting sulfur is made free flowing by
the addition of a small amount of inert
powder, and it is often incorporated in
other insecticidal dusts. Extreme fineness
of the sulfur particles enhances the effec-
tiveness. Preparations of sulfur can be
obtained in which a wetting agent has
been added, so that water suspensions
may be used for spraying.

Sulfur may be injurious to plants, par-
ticularly under high temperatures, and
oil should not be used while sulfur is on
the plant.

[59

Lime-Sulfur

Lime-sulfur is a reactive solution of
lime and sulfur. It contains a high per-
centage of calcium polysulfides which
break down after spraying to form very
fine particles of sulfur. Both liquid con-
centrates and wettable powders are avail-
able commercially. It has been used to
some extent in greenhouses for cyclamen
mite control.

Lime-sulfur is very likely to cause fo-
liage injury, particularly in hot weather.
It will discolor paint or cement work.

Ammonium Poly sulfide

Commercial preparations of ammo-
nium polysulfide have been used to a
limited extent for control of the cyclamen
mite.

TARTAR EMETIC

Tartar emetic is an antimony com-
pound known as potassium antimonyl
tartrate. It has been used with brown
sugar incorporated into a spray as a
poisonous bait for the control of thrips,
and it has been used in ant baits.

Certain thrips, notably the citrus and
greenhouse thrips, apparently have de-
veloped resistance to tartar emetic, and
newer insecticides have for the most part
replaced it.

TOXAPHENE

Toxaphene, or chlorinated camphene,
is a chlorinated terpene hydrocarbon. It
is a cream-colored, waxy material with a
pine-like odor. It is readily soluble in
organic solvents, and is available as an
emulsion concentrate, wettable powder,
or dust.

Toxaphene is a relatively new insecti-
cide, and its advantages or usefulness on
greenhouse insects have not been deter-
mined. It is reported, however, to be
effective against a number of agricultural
pests such as certain beetles, caterpillars,
thrips, and leafhoppers. There is a con-
siderable residual action, and plant tol-
erance appears to be generally good.

Toxaphene is reported to be less toxic
to warm-blooded animals than DDT, but
it should be handled with care until the
hazards are better understood.

Tables of equivalents for diluting liquid and
solid insecticides in water are given on page 72.

60

METHODS FOR rffe^UlVtfl INSECTICIDES

DUSTS

In the preparation of dusts, finely
ground particles of a solid insecticide are
mixed with a suitable powdered diluent,
or else the insecticide is impregnated on
a powdered diluent carrier. Dust diluents
or carriers include such materials as
pyrophyllite, kaolin, bentonite, and talc.
Certain arsenicals, benzene hexachloride,
chlordane, DDT and related compounds,
parathion, plant derivatives, and sulfur
may be used as dusts. The insecticidal
concentration in dusts is generally from
0.5 to 10 per cent.

Dusting Equipment

Dusts are usually applied in green-
houses by means of hand-operated dust-
ers. Both the rotary type and the bellows
type are available, but the former is easier
to handle in narrow aisles. The dusting
apparatus must be adjusted so that an
even coverage is possible, and it should
be operated so that a very light but thor-
ough coverage is obtained. It is some-
times practical when dusting the soil in
small beds or individual pots to use a
shaker made from a fruit jar with small
holes punched in the lid.

SPRAYS

Nearly all of the insecticides which are
sprayed on plants are but sparingly solu-
ble in water. Special preparations are
necessary, therefore, in order to dilute
the insecticides with water to provide a
spray which will evenly distribute small
quantities of the material over the plants.
There are two general types of such spray
materials: wettable powders and emul-
sions.

Wettable powders are solid particles
either composed of or impregnated with
the insecticide to which has been added
a wetting agent. Such powders form sus-

pensions in the water with which they
are mixed. Lead arsenate, benzene hexa-
chloride, chlordane, DDT and related
compounds, parathion, and sulfur may
be obtained as wettable powders.

Emulsions are insecticides which are
dissolved in an organic solvent with the
addition of an emulsifying agent. These
emulsions form small globules in the
water with which they are mixed. Chlor-
dane, DDT and related compounds, or-
ganic phosphates, oils, and thiocyanates
are used commonly as emulsions.

Wettable powders or emulsions must
be thoroughly mixed and continually
agitated while spraying. Nicotine sulfate,
however, is readily soluble in water, and
it forms a true solution when diluted.

Spreaders and wetting agents are often
used in sprays to provide even coverage
of the foliage, but the use of too much
adjuvant of this type will result in ex-
cessive run-off. Stickers are used in
sprays to increase the persistence of the
deposit.

Spraying Equipment

Various types of spraying equipment
are in current use. The hand-operated
sprayers are convenient for small green-
houses or for spot treatment. A 3-gallon,
pressure type, knapsack sprayer is con-
venient for carrying along narrow aisles.
This type is pumped up by hand before
spraying, and must be repumped when
the pressure drops. It must be shaken
often because it contains no agitator.

A 15-gallon wheelbarrow-type sprayer
is often used for small jobs. With this
type of apparatus, one man operates the
handle of the pump while another does
the spraying.

A power-operated sprayer is an in-
dispensable piece of equipment for many
nurserymen. From 25- to 50-gallon port-
able models are satisfactory for most

[61]

Fig. 53. Dusting equipment of two satisfactory
types is shown above: at left, the rotary type which
is easy to handle in narrow aisles; at right, the bellows
type worn on the back.

Spraying equipment convenient for greenhouse
use includes the three shown here. Right, the 3-gallon
pressure type knapsack sprayer; below left, a power-
operated sprayer with larger capacity; below right, a
15-gallon wheelbarrow type.

Fig. 54. A portable model of fog-generating machine produces very fine particles, necessary in
this method of pest control.

greenhouse work. In some of the larger
establishments a sprayer with a much
larger capacity is installed, and outlet
pipes are laid to the various greenhouses.
The amount of pressure necessary for
satisfactory coverage varies mainly with
the type of spray equipment, the type and
number of nozzles, and the size of the
disc openings. In general, nozzles prefer-
able for greenhouse use are those which
give a fan-type spray or else a solid cone.

FOGS

Spray concentrate solutions may be
forced through an atomizer with the aid
of compressed air, so that very small drop-
lets are formed. These tiny droplets will
form an aerosol fog or mist when suffi-
cient compressed air is used for propul-
sion. Such insecticidal fogs have proved
to be effective means of control in green-
houses when the particles are very fine

and adequately dispersed. This method
has been particularly popular for appli-
cation of tetraethyl pyrophosphate.

Fog-generating Equipment

To produce fogs, a power-operated
compressor may be used with a conven-
tional atomizer. Small greenhouses can
be treated from the entrances with such
equipment. Hand-operated units for high-
pressure atomization are available, these
being carried through the greenhouse.
Fog-generating machines are made which
utilize the engine exhaust as an aid in
producing the fog. The portable models
of these machines must be pulled through
the greenhouse in order to obtain cov-
erage.

The discharge nozzle for fog fumigants
should be directed so as to avoid immedi-
ate contact with plants because the larger
droplets, which settle out first, may cause

[63

burning. Wind currents should be con-
sidered in the plan of release so that
uniform coverage of the house may be
obtained. In general the rate of applica-
tion is similar to that necessary with a
given amount of spray for the same
coverage.

The operator must take proper pre-
cautions when he may be exposed to fogs
of poisonous materials. A suitable gas
mask, protective clothing, hat, and gloves
must be worn. The same precautions are
necessary as in the application of lique-
fied-gas aerosols.

LIQUEFIED-GAS AEROSOLS

An aerosol is a dispersion of very fine
particles in the air. The term, however,
is applied particularly to the dispersion
obtained from release of a solution of
insecticide in a liquefied gas. When pres-
sure on the liquefied gas is released it is
vaporized and particles of the insecticide
are left suspended in the air. Freon-12
and methyl chloride are commonly used
as the solvents in aerosol preparations
for greenhouse purposes.

Liquid-gas aerosols are available which
contain benzene hexachloride, DDT, ro-
tenone, organic phosphates, and pyre-
thrum. Lauryl thiocyanate aerosols have
been used under experimental conditions.
These aerosols are especially suited to
enclosed conditions. Because of the ease,

Fig. 55. Right, fumigation of a greenhouse by
means of a liquefied-gas aerosol. Below, a hand
dispenser commonly used.

■~**^nMMm

speed, and efficiency of application, they
are expected to become of major impor-
tance for the control of greenhouse pests.

Dispensers

The hand dispensers which commonly
are used consist of metal cylinders pro-
vided with valve and nozzle and con-
taining the liquid-gas solution under high

64

Fig. 56. A pressure-fumigator can emitting
smoke for greenhouse fumigation.

pressure. Low-pressure cans, employing
other solvents, are being developed. Bot-
tles are also expected to become available
which will contain the liquid-gas solution
under relatively low pressure. Such bot-
tles are heated in an electric jacket to
raise the pressure for application, and
an applicator rod is inserted in the cap
for release.

Caution. Methyl chloride, as well as
such insecticides as the organic phos-
phates, is very poisonous. The operator
applying these materials must wear a gas
mask with a canister designed for pro-
tection against organic vapors (for ex-
ample, the industrial full-vision gas mask
made by the Mines Safety Appliance
Company, or similar Army or Navy gas
masks, provided with GMC-1 or GMA
canisters for organic vapors). Protective
clothing, rubber gloves, and hat also
should be worn.

SMOKES

Smokes are aerial suspensions of very
fine particles which are produced by the
incomplete combustion of organic ma-
terial. Smoldering powders that are com-
posed of tobacco powder and potassium
nitrate (saltpeter) and containing nico-
tine or azobenzene are often used in
greenhouses.

Preparations which are used in cans
are referred to as "pressure fumigators."
For application, scored holes are punched
in the can and the contents ignited. High
temperature and pressure are then de-
veloped in the can, and clouds of smoke
stream from the openings. Candles are
also available which slowly smolder to

produce the insecticidal smoke. Conden-
sation of the azobenzene or nicotine va-
pors on the smoke particles renders this
method of application somewhat safer on
plants than their use as a gas, particularly
when a sudden drop of temperature is
experienced.

GASEOUS FUMIGATION

A fumigant is an insecticide which acts
upon the insect as a gas. Liquid or crystal-
line materials which are used for green-
house fumigation must be volatile enough
to produce a toxic concentration of the
vapor.

Calcium cyanide is one of the most
widely used materials, and the toxic
fumes are released by moisture in the air.
Nicotine and naphthalene were formerly
used extensively, while azobenzene and
tetraethyl pyrophosphate have been used
during recent years. Ready vaporization
of these compounds is accomplished by
means of heat from hot plates or steam
pipes. Studies also have been made on
the use of dichloroethyl ether and
methyl bromide for greenhouse fumiga-
tion. Methyl bromide is a very effective
fumigant which ordinarily is employed
in fumigation chambers.

Successful greenhouse fumigation is
generally dependent upon proper tem-
perature and moisture conditions and
proper exposure time. The dosage of a
given material is subject to variation ac-
cording to the tightness of the greenhouse
and wind conditions. Gaseous fumigants
are poisonous, and every precaution
should be taken in their use.

65

SOIL TREATMENT

There are a number of materials which
have been used for the fumigation of soil
pests. Calcium cyanide, carbon disulfide,
dichloroethyl ether, naphthalene, para-
dichlorobenzene, chloropicrin, and others
have been used with varying degrees of
success. Applications of these chemicals
generally have been by spraying or
sprinkling the surface of the soil. Where
it is possible to treat bare soil, steam
sterilization is generally effective.

Ethylene dibromide and D-D have
proved to be the most satisfactory chemi-
cals for treatment of bare soil. Methyl
bromide emulsion can often be used when
living plants are nearby. These, as well
as other liquid soil fumigants, are most
satisfactorily applied by means of a hand-
operated gun which injects regulated
dosages into the earth.

Benzene hexachloride and chlordane
are the most promising materials for
many soil pests (except mealybugs and
nematodes) where treatment of the plants
is also involved. These soil fumigants
must be mixed with heavy soils, but they
may be dusted or sprayed on light soils
and watered in.

BAITS

Baits have been used extensively for
the control of such pests as earwigs,
sowbugs, cutworms, slugs, millipedes,
brachyrhinus weevils, and ants. Materials
such as the more soluble arsenicals and
fluorine compounds and tartar emetic
have been used as the toxic ingredients
of varous formulae. In general these baits
are effective in reducing populations, but
elimination of the pests is rarely obtained.
The newer insecticides, such as benzene
hexachloride, DDT, and chlordane dusts
or sprays, have largely replaced the baits
for all of these pests except snails and
slugs. The metaldehyde and calcium ar-
senate baits are still in general use for
their control.

In order that the information in our publica-
tions may be more intelligible it is sometimes
necessary to use trade names of products or
equipment rather than complicated descriptive
or chemical identifications. In so doing it is un-
avoidable in some cases that similar products
which are on the market under other trade
names may not be cited. No endorsement of
named products is intended, nor is criticism
implied of similar products which are not men-
tioned.

GENERAL REFERENCES

COMPTON, C. C.

1930. Greenhouse Pests. Illinois State Natural History Survey Circular 12, 112 pp.

Essie, E. 0.

1926. Insects of Western North America. 1035 pp. The Macmillan Company.

Essie, E. 0., and W. M. Hoskins.

1944. Insects and Other Pests Attacking Agricultural Crops. California Agricultural Exten-
sion Service, Circular 87, revised, 197 pp.
Gibson, Arthur, and W. A. Ross.

1940. Insects Affecting Greenhouse Plants. Dominion of Canada, Department of Agriculture
Publication 695, 87 pp.
McDaniel, E. I.

1931. Insect and Allied Pests of Plants Grown Under Glass. Michigan Agricultural Experi-
ment Station Special Bulletin 214, 117 pp.

Severin, H. C.

1924. Insects and Other Enemies Harmful to Greenhouse Plants. Fifteenth Annual Report of
the State Entomologist of South Dakota, pp. 10-63.
Weigel, C. A., and E. R. Sasscer.

Undated. Insects Injurious to Ornamental Greenhouse Plants. U. S. Department of Agricul-
ture, Farmers' Bulletin 1362, 80 pp.

r 66 1

INDEX

Achorutes armatus (Nicolet), 11

Acutaspis albopicta (Cockerell), 29

African violet, see Saintpaulia

Agriolimax agrestis (Linnaeus), 44

Agromyza maculosa Malloch, see Dizygomyza macu-
losa (Malloch)

Agromyza pusilla Meigen, see Ltriomyza subpusilla
Frost

Aleurotulus nephrolepidis Quaintance, 20

Aleyrodes azaleae Baker and Moles, 20

Aleyrodes spiraeoides Quaintance, 20

Amaryllis mealybug, 23

Ametastegia pallipes (Spinola), 41

Ammonium polysulfide, 60; for cyclamen mite, 10

Amphorophora tulipaella (Theobald), 18

Anaphothrips orchidaceous Bagnall, 15

Anaphothrips or chidii (Moulton), 15

Ants, 42; control of, 42; relation to mealybugs, 23;
species: Argentine, 42; California fire, 42; Cali-
fornia honey, 42; California brown field, 42;
western pavement, 42

Anuraphis, see Aphis

Aonidiella aurantii (Maskell), 29

Aonidiella citrina (Coquillett), 29

Aphelenchoides fragariae (Ritzema Bos), see
Aphelenchoides olesistus (Ritzema Bos)

Aphelenchoides olesistus (Ritzema Bos), 45

Aphids, 16; control of, 19; species: green peach, 17;
lily, 17; ornate, 17; foxglove, 17; cotton or melon,
17; bean or dock, 17; potato, 17; chrysanthemum,
18; geranium, 18; pea, 18; rose, 18; small green
rose, 18; fern, 18; violet, 18; black citrus, 18;
banana, 18; tulip leaf, 18; periwinkle, 18; ivy, 18;
leaf -curl plum, 19; tulip bulb, 19; ins root, 19;
aster root, 19; apple-grain, 19; latania, 19

Aphis gossypii Glover, 17

Aphis hederae Kaltenbach, 18

Aphis helichrysi Kaltenbach, 19

Aphis middletonii Thomas, 19

Aphis rumicis Linnaeus, 17

Aphis tulipae (Fonscolombe), 19

Apple-grain aphid, 19

Apple skinworm, 35 . . ,

Aralia, host for: cyclamen mite, 10; nigra scale, 26

Argentine ant, 42

Argyrotaenta citrana (Fernald), 35

Argyrotaenia franciscana (Walsingham), 35

Armadillidium vulgar e (Latreille), 44

Armed springtail, 11

Armored scales, 28; control of, 31; species: ivy, 28;
Florida red, 28; Boisduval, 29; aspidistra, 29;
cyanophyllum, 29; latania, 29; greedy, 29; dictyo-
spermum, 29; false Florida red, 29; California red,
29; yellow, 29; West Indian red, 29; Mexican
red, 29; rose, 29; cactus, 30; mining, 30; cycad,
30; lesser snow, 30; purple, 30; cymbidium, 30;
Mackie, 30; noxious, 30; croton, 30; proteus, 30;
chaff, 30; false parlatoria, 31; palm fionnia, 31

Arsenicals, 48

Arsenic trioxide, 49

Asparagus fern, host for: asparagus spider mite, 7;
greenhouse pillbug, 44

Asparagus spider mite, 7

Aspidiotus hederae (Vallot), 28

Aspidistra, host for: aspidistra scale, 29; false Flor-
ida red scale, 29

Aspidistra scale, 29

Aster root aphid, 19

Aulacaspis rosae (Bouche), 29

Azalea, host for: privet mite, 8; cyclamen mite, 10;
greenhouse thrips, 15; azalea whitefly, 20; woolly
azalea scale, 25; azalea leaf mine*, 33; black vine
weevil, 36

Azalea leaf miner, 33

Azalea whitefly, 20

Azobenzene, 49; for spider mites, 7

B

Baits, 66; for: earwigs, 12; cutworms, 36; weevils,

37; slugs and snails, 44
Baker mealybug, 22
Banana aphid, 18
Banded greenhouse thrips, 1 5
Bean or dock aphid, 17
Beet army worm, 36

Begonia, host for: cyclamen mite, 10; termites, 12;
long-winged thrips, 15; common millipede, 43

Benzene hexachloride, 50; for: springtails, 12; ear-
wigs, 12; thrips, 15; aphids, 19; weevils, 37; gall
midges, 39; leaf miners, 41; millipedes, 43; gar-
den centipedes, 43; pillbugs and sowbugs, 45

BHC, see benzene hexachloride

Biological control, 46; for: mealybugs, 23; cottony-
cushion scale, 24

Black citrus aphid, 18

Black-legged termite, 13

Black scale, 26

Black vine weevil, 36

Boisduval scale, 29

Bouvardia, host for: greenhouse whitefly, 20; citrus
mealybug, 21

Brachyrhinus sulcatus (Fabricius), 36

Brevipalpus inornatus (Banks), 8

Broad mite, 10

Bulb flies, 39; control of, 40; species: narcissus, 39;
lesser, 39; least, 40

Bulb millipede, 43

Bulb mite, 1 1

Bulb nematode, 45

Bulb scale mite, 10

Bulbs, pests attacking, 10, 11, 15, 39, 43, 45

Burdock leaf miner, 4 1

Bush snail, 44

Cactus, host for: ground mealybug, 22; woolly cactus
scale, 25; cactus scale, 30

Cactus scale, 30

Calcium arsenate, 48

Calcium cyanide, 51; for: aphids, 19; whiteflies, 20;
soft scales, 27; armored scales, 31; bulb flies, 40

California brown field ant, 42

California fire ant, 42

California honey ant, 42

California orchid thrips, 15

California red scale, 29

Camellia, host for: black citrus aphid, 18; cottony
camellia scale, 27; black vine weevil, 37

Carbon disulfide, 50; for: bulb flies, 40

Carnation, host for: two-spotted spider mite, 6; grass
mite, 10; western flower thrips, 15; carnation leaf
roller, 35; variegated cutworm, 36

Carnation leaf roller, 35

Carnation streak, transmitted by aphids, 16

Cattleyafly, 42

Cattleya orchid, host to: yellow orchid thrips, 15;
Boisduval scale, 29; orchid weevil, 37; cattleya
weevil, 37; cattleyafly, 42

Cattleya weevil, 37

Cerataphis lataniae (Boisduval), 19

Chaff scale, 30

Chemical control, 47

Chlordane, 51; for springtails, 12; earwigs, 12; fun-
gus gnats, 38; bulb flies, 40; leaf miners, 41; ants,
42; millipede, 43; pillbugs and sowbugs, 45

Chlorinated camphene, see toxaphene

Chloropicrin, 51

Cholus cattleyae Champion, 37

Choristoneura rosaceana (Harris), 35

Chrysanthemum aphid, 18

Chrysanthemum, host for: termites, 12; thrips, 15;
chrysanthemum aphid, 18; leaf -curl plum aphid,
19; chrysanthemum gall midge, 39; chrysanthe-
mum leaf miner, 40; burdock leaf miner, 41

Chrysanthemum gall midge, 39

Chrysanthemum leaf miner, 40

Chrysanthemum thrips, 15

Chrysomphalus aonidum (Linnaeus), see Chrysom-
phalus ficus Ashmead

Chrysomphalus bifasciculatus Ferris, 29

Chrysomphalus dictyospermi (Morgan), 29

Chrysomphalus ficus Ashmead, 28

Celery leaf tier, 34

Cellar snail, 44

Cineraria, host for: leaf -curl plum aphid, 19; beet
armyworm, 36; chrysanthemum leaf miner, 40

Citibaena narcissi (Smith), 40

Citibaena tuber culata (Rondani), 39

Citrophilus mealybug, 23

Citrus, host for: citrus whitefly, 20; California red
scale, 29; yellow scale, 29; purple scale, 30; chaff
scale, 30

[67

Citrus mealybug, 2 1

Citrus whitefly, 20

Clepsis buskana Keifer, 35

Clivia, host for: amaryllis mealybug, 23

Coccus elongatus (Signoret), 26

Coccus hesperidum Linnaeus, 25

Coccus pseudohesperidum (Cockerell), 26

Coconut mealybug, 23

Common millipede, 43

Composite thrips, 15

Corn earworm, 36

Cotton or melon aphid, 17

Cottony camellia scale, 27

Cottony-cushion scale, 24

Cottony guava scale, 27

Cottony hydrangea scale, 27

Cottony orchid scale, 27

Crescent-marked lily aphid, see lily aphid

Croton, host for: striped mealybug, 23; cottony-
cushion scale, 24; West Indian red scale, 29;
croton scale, 30

Croton scale, 30

Cryolite, 54; for: leaf rollers, 35; sawflies, 41

Cutworms, 35; control of, 36; species: variegated,
35; tobacco bud worm, 36; corn earworm, 36; beet
armyworm, 36; fern, 36

Cyanide, 5 1

Cyanophyllum scale, 29

Cycad, host for: cycad scale, 30; lesser snow scale, 30

Cycad scale, 30

Cyclamen, host for: long-winged thrips, 15; cycla-
men leaf roller, 35; vegetable weevil, 37

Cyclamen leaf roller, 35

Cyclamen mite, 9

Cymbidium orchid, host for: two-spotted spider
mite, 6; Boisduval scale, 29; cymbidium scale, 30

Cymbidium scale, 30

Cypripedium orchid, host for: false parlatoria scale,
31

D-D, see dichloropropane-dichloropropene

DDD, 52; for: leaf rollers, 35

DDT, 52; for: earwigs, 12; termites, 13; thrips, 15;
aphids, 19; whiteflies, 20; armored scales, 31;
omnivorous looper, 32; leaf blotch miners, 33;
leaf rollers, 35; cutworms, 36; weevils, 37; fungus
gnats, 38; gall midges, 39; cattleyafly, 42; milli-
pede, 43; pillbugs and sowbugs, 45

Dendrobium orchid, host for: Mackie scale, 30; nox-
ious scale, 30; orchid weevil, 37

Dialeurodes citri (Riley and Howard), 20

Diarthronomyia chrysanthemi Ahlberg, 39

Diarthronomyia hypogaea Low, see Diarthronomyia
chrysanthemi Ahlberg

Diaspis boisduvalii Signoret, 29

Diaspis echinocacti (Bouche), 30

Dichlorobenzenes, 53

Dichloroethyl ether, 53

Dichloro-diphenyl-dichloroethane, see DDD

Dichloro-diphenyl-trichloroethane, see DDT

Dichloropropane-Dichloropropene (D-D), 53; for:
garden centipedes, 43; nematodes, 45

Dictyospermum scale, 29

Dimethyl carbinol, 53; for: false spider mites, 8;
cyclamen mite, 10

Dinitro-phenol compounds, 54

Diorymerellus laevimargo Champion, 37

Diploiulus luscus (Meinert), 43

Ditylenchus dipsaci (Kiihn), 45

Divarinychus ftoridensis McGregor, see Schizotetrany-
chus asparagi Oudemans

Dizygomyza maculosa (Malloch), 41

DMC, see dimethyl carbinol

Dooryard sowbug, 44

Dracaena, host for: thrips, 15; long-tailed mealybug,
22

Dracaena thrips, 15

Drapernald snail, 44

Dusts, 61

Earwigs, 12; control of, 12; species: European ear-
wig, 12

Easter lily, host for: lily aphid, 17

Easter lily necrotic fleck, disease transmitted by aph-
ids, 16

Elongate soft scale, 26

English orchid thrips, 15

Ensign Scales, 24; control of, 24; species: greenhouse
orthezia, 24

Eriococcus azaleae Comstock, 25

Eriococcus coccineus Cockerell, 25

Ethylene dibromide (EDB), 54; for garden centi-
pedes, 43; nematodes, 45

Eucalymnatus tessellatus (Signoret), 26

Eumerus, see Citibaena

Euplexia lucipara (Linnaeus), 36

European brown snail, 44

European earwig, 12

Eurytoma orchidearum (Westwood), 42

False Florida red scale, 29

False parlatoria scale, 3 1

False spider mites, 8; control of, 8; species: privet,
8; phalaenopsis, 8

Fern aphid, 18

Fern cutworm, 36

Fern, host for: armed springtail, 11; fern aphid, 18;
latania aphid, 19; fern whitefly, 20; grape mealy-
bug, 22; hemispherical scale, 26; cottony camellia
scale, 27; aspidistra scale, 29; lesser snow scale,
30; foliar nematode, 45

Fern scale, 29

Fern whitefly, 20

Ferrisia virgatus (Cockerell), 23

Fiorinia fioriniae (Targioni), 31

Florida red scale, 28

Fluorine compounds, 54

Fogs, 63

Foliar nematode, 45

Forficula auricularia Linnaeus, 12

Formica cinerea Mayr, 42

Foxglove aphid, 17

Frankliniella moultoni Hood, 1 5

Frankliniella Occident alis (Pergande), 15

Fuchsia, host for: privet mite, 8; cyclamen mite, 10;
greenhouse thrips, 15; greenhouse whitefly, 20;
Mexican mealybug, 22

Fuller rose weevil, 36

Fungus gnats, 37; control of, 38

Fungus mites, 10; control of, 11; species: bulb mite,
11

Furcadiaspis zamiae (Morgan), 30

Gall midges, 38; control of, 39; species: chrysanthe-
mum, 39

Garden centipede, 43; control of, 43

Gardenia, host for: two-spotted spider mite, 6; black
citrus aphid, 18; citrus mealybug, 21; variegated
cutworm, 36; Fuller rose weevil, 36

Gaseous fumigation, 65

Geranium aphid, 18

Geranium, host for: termites, 12; geranium aphid,
18; cottony-cushion scale, 24; geranium plume
moth, 32; tobacco budworm, 36

Geranium plume moth, 32

Giant scales, 24; control of, 24; species: cottony-
cushion scale, 24

Gladiolus, host for: thrips, 15

Gladiolus mosaic, transmitted by aphids, 16

Gladiolus thrips, 15

Gloxinia, host for: cyclamen mite, 10; thrips, 15

Gracilaria azaleella Brants, 33

Grape mealybug, 22

Grass mite, 10

Gray garden slug, 44

Greedy scale, 29

Greenhouse leaf tier, 34

Greenhouse millipede, 43

Greenhouse orthezia, 24

Greenhouse pillbug, 44

Greenhouse slug, 44

Greenhouse thrips, 1 5

Greenhouse whitefly, 20

Green peach aphid, 17

Green shield scale, 27

Ground mealybug, 22

Guava, host for: cottony guava scale, 27

Gynura, host for: cyclamen mite, 10

H

Hartigia cressoni (Kirby), 41

Heat treatment, 46', for: thread-footed mites, 10;
bulb mites, 11; bulb flies, 40; nematodes, 45

68

Heliothis obsoleta (Fabricius), 36
Heliothis virescens (Fabricius), 36
Heliothrips haemorrhoidalis (Bouche), 15
Helix aspersa (Miiller), 44
Hemiberlesia cyanophylli (Signoret), 29
Hemiberlesia I at ant ae (Signoret), 29
Hemiberlesia rapax (Comstock), 29
Hemispherical scale, 26
Hemitarsonemus latus (Banks), 10
Hercinothrips femoralis (Reuter), 15
Heterodera marioni (Cornu), 45
HETP, see hexaethyl tetraphosphate
Hexaethyl tetraphosphate, 56
Hibiscus, host for: greenhouse whitefly, 20
Holly, host for: nigra scale, 26
Houardia biclavis (Comstock), 30
Hydrangea, host for: two-spotted spider mite, 6; cot-
tony hydrangea scale, 27

Icerya purchasi Maskell, 24

Idiopterus nephrolepidis Davis, 18

Iridomyrmex humilis Mayr, 42

Iris, host for: iris whitefly, 20

Iris root aphid, 19

Iris whitefly, 20

Ivy aphid, 18

Ivy, host for: cyclamen mite, 10; ivy aphid, 19;

citrophilus mealybug, 23; cottony-cushion scale,

24; nigra scale, 26
Ivy scale, 28

Ladybird beetle, for mealybug control, 46

Lampetia equestris (Fabricius), 39

Lantana, host for: Luden spider mite, 7; greenhouse
whitefly, 20

Laphygma exigua Hiibner, 36

Latania aphid, 19

Latania scale, 29

Lauryl thiocyanate, 58; for cyclamen mite, 10

Lead arsenate, 48; for: leaf blotch miners, 33; saw-
flies, 41

Leaf blotch miners, 32; control of, 33; species: azalea
leaf miner, 33

Leaf -curl plum aphid, 19

Leaf miners, 40; control of, 41; species: chrysanthe-
mum, 40; serpentine, 40; burdock, 41

Leaf rollers, 34; control of, 35; species: orange tor-
trix, 35; carnation, 35; apple skinworm, 35; cycla-
men, 35; oblique-banded, 35

Leaf tiers, 33; control of, 34; species: greenhouse
(celery), 34

Least bulb fly, 40

Lepidosaphes beckii (Newman), 30

Lepidosaphes machili (Maskell), 30

Lepidosaphes mackiana McKenzie, 30

Lepidosaphes noxia McKenzie, 30

Lepidosaphes tokionis (Kuwana), 30

Lesser bulb fly, 39

Lesser snow scale, 30

Lily aphid, 17

Lily, host for: thrips, 15; tulip bulb aphid, 19

Lily mottle virus, transmitted by aphids, 16

Lily thrips, 15

Lime-sulfur, 60; for: false spider mites, 8; cyclamen
mite, 10

Liothrips vaneeckei Priesner, 1 5

Liquefied-gas aerosols, 64

Liriomyza subpusilla (Frost), 40

Listroderes obliquus Klug, 37

Long-tailed mealybug, 22

Long- winged thrips, 15

Loopers, 32; control of, 32; species: omnivorous, 32

Louse mites, 10; control of, 10; species: grass mites,
10

Luden spider mite, 7

M

Mackie scale, 30

Macrosiphoniella, see Macrosiphum
Macrosiphum pelargonii (Kaltenbach), 18
Macrosiphum pisi (Kaltenbach), 18
Macrosiphum rosae (Linnaeus), 18
Macrosiphum sanborni (Gillette), 18
Macrosiphum solanifolii (Ashmead), 17
Maranta, host for: palm spider mite, 7
Marguerite, host for: chrysanthemum leaf miner, 40

Mealybugs, 21; control of, 23, 46; species: citrus,

21; Mexican, 22; grape, 22; long-tailed, 22;

ground, 22; citrophilus, 23; palm, 23; striped, 23;

amaryllis, 23
Mercuric chloride, 54; for: bulb flies, 40
Merodon, see Lampetia
Metaldehyde, 54; for: slugs and snails, 44
Methoxychlor, 52
Methyl bromide, 55; for: thread-footed mites, 10;

fungus mites, 11; bulb flies, 40
Mexican mealybug, 22
Mexican red scale, 29

Microcephalothrips abdominalis (Crawford), 15
Micromyzus violae (Pergande), 18
Milax gagates (Miiller), 44
Millipedes, 42; control of, 43; species: greenhouse,

43; common, 43; bulb, 43
Mining scale, 30

Mosaic, disease transmitted by aphids, 16
Moulton flower thrips, 15
Myzaphis rosarum Walker, 18
Myzus circumftexus (Buckton), 17
Myzus convolvuli (Kaltenbach), see Myzus solani

(Kaltenbach)
Myzus ornatus Laing, 17
Myzus persicae (Sulzer), 17
Myzus solani (Kaltenbach), 17

N

Naphthalene, 56

Narcissus bulb fly, 39

Narcissus, host for: bulb scale mite, 10; bulb fly, 39

Nasturtium, host for: bean or dock aphid, 17

Nematodes, 45; control of, 45; species: root-knot,
foliar, bulb and stem, 45

Nephthytis, host for: striped mealybug, 23

Nicotine, 58; for: springtails, 12; aphids, 19; white-
flies, 20; leaf blotch miners, 33

Nigra scale, 26

Nopoiulus minutus (Brandt), 43

Noxious scale, 30

Oblique-banded leaf roller, 35

Oils, 56; for: aphids, 19; mealybugs, 23; soft scales,

27; armored scales, 31; plume moths, 32
Oleander scale, 28
Omnivorous looper, 32
Onion thrips, 15
Orange tortrix, 35
Orchid, host for: two-spotted spider mite, 6; false

spider mites, 8; phalaenopsis mite, 8; yellow

orchid thrips, 15; California orchid thrips, 15;

English orchid thrips, 15; latania aphid, 19;

orchid soft scale, 26; cottony orchid scale, 27;

Boisduval scale, 29; cymbidium scale, 30; Mackie

scale, 30; noxious scale, 30; proteus scale, 30;

false parlatoria scale, 31; orchid weevil, 37; cat-

tleya weevil, 37; cattleyafly, 42; gray garden slug,

44; bush snail, 44
Orchid soft scale, 26
Orchid weevil, 37

Organic phosphates, 56; for: false spider mites, 8
Organic thiocyanates, 58
Ornate aphid, 17

Ornithogalum mosaic, transmitted by aphids, 16
Orthezia insignis Douglas, 24
Orthodichlorobenzene, 53
Orthomorpha gracilis Koch, 43
Oxalis, host for: oxalis spider mite, 7
Oxalis spider mite, 7
Oxychilus cellularis (Miiller), 44
Oxychilus drapernaldi (Beck), 44

Palm fiorinia scale, 31

Palm, host for: palm spider mite, 7; false spider
mites, 8; thrips, 15; latania aphid, 19; ground
mealybug, 22; palm mealybug, 23; elongate soft
scale, 26; Florida red scale, 28; latania scale, 29;
dictyospermum scale, 29; proteus scale, 30; false
parlatoria scale, 31; palm fiorinia scale, 31

Palm mealybug, 23

Palm spider mite, 7

Pansy flower breaking, transmitted by aphids, 16

Pantomorus godmani (Crotch), 36

Paradichlorobenzene, 53; for: bulb flies, 40

69

Parathion, 57; for: spider mites, 7; thread-footed
mites, 10; springtails, 12; thrips, 15; aphids, 19;
whiteflies, 20; mealybugs, 23; cottony-cushion
scale, 24; woolly-sac scales, 25; soft scales, 27;
armored scales, 31; leaf blotch miners, 33; leaf
rollers, 35; sawflies, 41; millipedes, 43; pillbugs
and sowbugs, 45

Paris green, 48

Parlatoria pergandei Comstock, 30

Parlatoria proteus (Curtis), 30

Parthenothrips dracaenae Heeger, 1 5

Pea aphid, 18

Pediculopsis gramineum Reuter, 10

Pelargonium, host for: greenhouse whitefly, 20;
Mexican mealybug, 22; tobacco budworm, 36

Pentalonia nigronervosa Coquerel, 18

Peperomia, host for: foliar nematode, 45

Pepper plant, host for: cyclamen mite, 10

Peridroma margaritosa (Haworth), 35

Periwinkle aphid, 18

Petroleum oils, 56

Phalaenopsis mite, 8

Phalaenopsis orchid, host for: phalaenopsis mite, 8

Phenacoccus gossypii (Townsend and Cockerell), 22

Philodendron, host to: thrips, 15; Mexican red scale,
29

Pillbugs, 44; control of, 44; species: greenhouse, 44

Phlyctaenia ferrugalis Hiibner, see Phlyctaenia rubi-
galis (Guenee)

Phlyctaenia rubigalis (Guenee), 34

Phytomyza atricornis Meigen, 40

Phytomyza chrysanthemi Kowartz, see Phytomyza
atricornis Meigen

Pinnaspis aspidistrae (Signoret), 29

Pinnaspis strachani (Cooley), 30

Pittosporum, host for: cottony-cushion scale, 24

Plant derivatives, 58

Plant lice, see Aphids

Platynota stultana Walsingham, 35

Platyptilia antirrhina Lange, 3 2

Platyptilia pica Walsingham, 32

Plume moths, 31; control of, 32; species: snapdragon,
32; geranium, 32

Podocarpus, host for: cottony camellia scale, 27

Poinsettia, host for: cottony-cushion scale, 24

Porcellio laevis Koch, 44

Potato aphid, 17

Prenolepis imparts californica Wheeler, 42

Privet mite, 8

Proteus scale (sansevieria scale), 30

Protopulvinaria pyriformis (Cockerell), 27

Pseudococcus adonidum (Linnaeus), 22

Pseudococcus bakeri Essig, see Pseudococcus mari-
timus (Ehrhorn)

Pseudococcus citri (Risso), 21

Pseudococcus gahani Green, 23

Pseudococcus longispinus (Targioni), see Pseudococ-
cus adonidum (Linnaeus)

Pseudococcus maritimus (Ehrhorn), 22

Pseudococcus nipae (Maskell), 23

Pseudococcus virgatus Cockerell, see Ferrisia virgatus
(Cockerell)

Pseudoparlatoria parlatorioides (Comstock), 31

Pulvinaria floccifera Westwood, 27

Pulvinaria hydrangeae Steinweden, 27

Pulvinaria phaiae Lull, 27

Pulvinaria psidii Maskell, 27

Purple scale, 30

Pyrethrum, 59; for plume moths, 32; leaf rollers, 35

Pyriform scale, 27

Red-spiders, see spider mites

Reticulitermes hesperus Banks, 13

Reticulitermes tibialis Banks, 1 3

Rhizoecus falcifer Kiinkel, 22

Rhizoecus terrestris (Newstead), see Rhizoecus fal-
cifer Kiinkel

Rhizoglyphus echinopus (Fumouze and Robin), 1 1

Rhizoglyphus hyacinthi Boisduval, see Rhizoglyphus
echinopus (F. and R.)

Rhododendron, host for: woolly azalea scale, 25

Rhopalosiphoninus latysiphon (Davidson), 18

Rhopalosiphum prunifoliae (Fitch), 19

Root-knot nematode, 45

Rose aphid, 18

Rose, host for: two-spotted spider mite, 6; termites,
12; western flower thrips, 15; potato aphid, 18;
rose aphid, 18; rose scale, 29; orange tortrix, 35;
Fuller rose weevil, 36; western rose stem sawfly,41

Rose scale, 29

Rotenone, 58; for: cyclamen mite, 10
Rubber plant, host for: thrips, 15; citrophilus mealy-
bug, 23; Florida red scale, 28
Rufous scale, 29

Sabadilla, 59

Sabulodes caber at a Guenee, 32

Saintpaulia (African violet), host for: cyclamen mite,
10; foliar nematode, 45

Saissetia hemisphaerica (Targioni), 26

Saissetia nigra (Nietner), 26

Saissetia oleae (Bernard), 26

Sansevieria, host for: lesser snow scale, 30; proteus
scale, 30

Sansevieria scale, 30

Sawflies, 41; control of, 41; species: western rose
stem, 41; violet, 41

Selenium compounds, 59

Schizotetranychus asparagi (Oudemans), 7

Scirtothrips longipennis (Bagnall), 15

Scutigerella immaculata (Newport), 43

Selenaspidus articulatus (Morgan), 29

Septanychus tumidus (Banks), 7

Serpentine leaf miner, 40

Slugs, 44; control of, 44; species: greenhouse, 44;
gray garden, 44

Small green rose aphid, 18

Smokes, 65

Snails, 44; control of, 44; species: European, 44;
bush, 44; cellar, 44; Drapernald, 44

Snapdragon, host for: snapdragon plume moth, 32;
garden centipede, 43

Snapdragon plume moth, 32

Sodium arsenite, 49

Sodium fluosilicate, 54

Sodium selenate, 59; for spider mites, 7

Soil treatment, 66; for: nematodes, 45

Soft brown scale, 25

Soft scales, 25; control of, 27; species: soft brown,
25; hemispherical, 25; elongate soft, 26; orchid
soft, 26; tessellated, 26; nigra, 26; black, 26; pyri-
form, 27; cottony camellia, 27; cottony hydrangea,
27; cottony orchid, 27; cottony guava, 27

Solenopsis xyloni maniosa Wheeler, 42

Sowbugs, 44; control of, 44; species: dooryard, 44

Spanish red scale, 29

Spider mites (red -spiders), 6; control of, 7; species:
asparagus, 7; Luden, 7; oxalis, 7; palm, 7; two-
spotted (common red-spider), 6

Spotted wilt, carried by thrips, 13

Sprays, 61

Springtails, 11; control of, 12; species: armed spring-
tail, 11

Stem wasps, 41; control of, 42; species: cattleyafly, 42

Stem nematode, 45

Stephanotis, host for: citrus mealybug, 21

Stock mosaic, transmitted by aphids, 16

Strelitzia, host for: apple-grain aphid, 19

Strawberry, host for: cyclamen mite, 10

Striped mealybug, 23

Sugar beet thrips, 15

Sulfur, 59; elemental, 59; lime-sulfur, 60; ammonium
polysulfide, 60; for: false spider mites, 8

Sweet pea, host for: pea aphid, 18

Taeniothrips simplex Morison, 1 5

Taeniothrips xanthius (Williams) 15

Tarsonemus laticeps Halbert, 10

Tarsonemus pallidus Banks, 9

Tartar emetic, 60; for thrips, 15

TDE, see DDD

Tenuipalpus bioculatus McGregor, see Brevipalpus

inornatus (Banks)
Tenuipalpus pacifxcus Baker, 8
Termites, 12; control of, 13; species: western, 13;

black-legged, 13
Tessellated scale, 26
Tetraethyl pyrophosphate, 56; for: spider mites, 7;

aphids, 19; whiteflies, 20
Tetramorium pacifjcum Mayr, 42
Tetrany china harti (Ewing), 7
Tetranychus bimaculatus Harvey, see Tetranychus

telarius Linnaeus
Tetranychus ludeni Zacher, 7
Tetranychus telarius (Linnaeus), 6

70

Thread -footed mites, 9; control of, 10; species: cy-
clamen mite, 9; broad mite, 10; bulb scale mite, 10

Thrips, 13; control of, 15; species: greenhouse, 15
western flower, 15; Moulton flower, 15; onion, 15
banded greenhouse, 15; dracaena, 15; chrysanthe
mum, 15; composite, 15; gladiolus, 15; lily, 15:
long-winged, 15; yellow orchid, 15; California
orchid, 15; English orchid, 15

Thrips nigropilosus (Uzel), 15

Thrips tabaci Lindeman, 15

Tobacco budworm, 36

Toxaphene, 60

Toxoptera aurantii (Fonscolombe), 18

Trialeurodes vapor ariorum (Westwood), 20

Trionymus peregrinus (Green), 23

Tulip bulb aphid, 19

Tulip, host for: lily aphid, 17; tulip leaf aphid, 18;
periwinkle aphid, 18; apple-grain aphid, 19

Tulip leaf aphid, 18

Two-spotted spider mite, 6

Violet, host for: violet aphid, 18
Violet sawfly, 41

Weevils, 36; control of, 37; species: Fuller rose, 36;

black vine, 36; vegetable, 37; orchid, 37; cat-

tleya, 37
Western flower thrips, 15
Western pavement ant, 42
Western rose stem sawfly, 4 1
Western termite, 13
West Indian red scale, 29
Whiteflies, 19; control of, 20; species: greenhouse,

20; iris, 20; fern, 20; azalea, 20; citrus, 20
Woolly azalea scale, 25
Woolly-sac scales, 25, control of, 25; species: woolly

azalea, 25; woolly cactus, 25
Woolly spine scale, 25

Variegated cutworm,
Vegetable oils, 56
Vegetable weevil, 37
Violet aphid, 18

Yellow orchid thrips,
Yellow scale, 29

Zonitoides arboreus Say, 44

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