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Cornell University

Library

OF THE

Rew Work State College of Agriculture

Ag. §6al- MITA

Sror

Cambridge Farm Institute Series

GeneraL Epitrors: T. B. Woop, M.A.
FE. J. Russet, D.Sc.

FUNGOID AND _ INSECT
PESTS OF THE FARM

CAMBRIDGE UNIVERSITY PRESS
Cc. F. CLAY, Manacrr
DLondor: FETTER LANE, E.C.
Hvinburgh: 100 PRINCES STREET

flew Bork: G. P. PUTNAM’S SONS
Bombay, Calentta and Madras: MACMILLAN AND Co., Lap.
Goronta: J. M. DENT AND SONS, Lp.
Tokpo: THE MARUZEN-KABUSHIKI-KAISHA

All rights reserved

FUNGOID AND INSECT
PESTS OF THE FARM

BY

F. R. PETHERBRIDGE, M.A.

BIOLOGICAL ADVISER, SCHOOL OF AGRICULTURE, CAMBRIDGE

Cambridge :
at the University Press
16
wae

PREFACE

HIS book has been written for those who wish
to acquire some practical knowledge of farm
and garden pests. It does not aim at dealing with
all the numerous diseases which affect crops but
rather at giving an accurate account of some of the
commoner forms. It is hoped that a working know-
ledge of these pests will be of great commercial value
to farmers and market gardeners, and also that by
their own observations they will be enabled to co-
operate with those who are engaged in studying
plant diseases in finding the most economical means
of preventing the increasing annual losses due to these
pests.

Direct cures of some of the diseases are unknown;
but even in these cases an accurate knowledge of the
enemy will enable us to carry out remedial measures
which will prevent big losses.

Figs. 29, 316, 32, 34a, 36a, 37, 48, 49, and 50
are taken from Curtis’s Farm Insects. Figs. 11, 14,
23, and 24 from Diseases of Cultivated Plants and Trees

vi Preface

by Massee (Duckworth & Co.), and Figs. 46 and 21
from Percival’s Agricultural Botany (Duckworth & Co.).

My thanks are due to Prof. Biffen and the editors
for suggestions and criticisms and to the above-
mentioned authors and publishers for kind permission
to reproduce certain illustrations.

F. RB. P.
ScHoot or AGRICULTURE,

CAMBRIDGE.
March, 1916.

VIII.

XIII.

CONTENTS

PART I

IntRopDUCTION TO FuNGI : .

Potato DisEAsE AND ALLIED DISEASES .

FIncer anp Tok, aND Wart DISEASE
MitpEws

Er@ot anD CLovER SICKNESS

Rusts

Smuts

PART II

IntRopuction To INSECTS
BUTTERFLIES AND Morus
BEETLES

FLIEs

APHIDES AND SAWFLIES.

ExLworms

INDEX .

103
127
158
165
172

PART [

CHAPTER I
INTRODUCTION TO FUNGI

It is well known that the yields of the common
farm crops show enormous variations which may be
due to a number of causes, e.g. kind of soil, variety
of seed, management and climate. Often, however,
very different yields may be obtained when the above
conditions are almost identical, and in these cases it
is usual to attribute the loss of crop to a ‘“‘disease.”’
Diseases of plants then may be looked upon as causes
which prevent normal growth.

It is usual to classify plant diseases into two groups:

(1) Those caused by unsuitable surroundings, such
as unfavourable conditions of soil, or of weather.

(2) Those caused by living agencies.

It is this second group, the diseases caused by
fungi and insects, with which we are here concerned.

The two groups are not however strictly separable,
for we often find plants weakened by some condition
of their surroundings marked out for attack by a
living agency.

The mangolds at the Rothamsted Experimental
Station often suffer from leaf spot caused by a fungus
known as Uromyces betae, but not all the plots are

P.F. 1

2 Introduction to Fungi [CH.

equally susceptible to the disease. The plots which
have received the largest quantities of nitrogenous
manures but no potash suffer most. Except for the
manuring all the plots are under similar conditions.
Variations in food supply therefore seem to be important
in that they cause varying susceptibility to disease.
The fungi belong to the lowest group of the plant
kingdom and, as we shall see later on, cause a large
number of plant diseases. They differ from ordinary
green plants in that they do not contain any of the
green colouring matter so characteristic of the latter.
Itis this substance, known to botanists as “chlorophyll,”
which enables green plants to take from the air certain
food materials that they are unable to obtain from the
soluble substances in the soil. A fungus is unable
to live in this way on the constituents of air and soil,
but requires its food to be manufactured for it, and so
it takes advantage of the food materials made by
other plants. Some live on the decaying remains of
plants and animals, e.g. toadstools live on leaf mould
and also on manure heaps; others can only take their
food from living plants, or in a few cases from animals.
Those living on dead materials are known as Saprophytes
and those on living plants as Parasites. There is no
definite boundary line between these two classes:
some members are capable of living as parasites at
one period of their life and as saprophytes at other
periods when the living food supply is not at hand.
Among cultivated plants are forms which differ very
considerably in appearance and this naturally is found
in other groups of plants. It is difficult to see any
resemblance between the mushroom which we eat and
the smut that blackens corn, or the yeast used by

1] Introduction to Fungi 3

brewers, or the mould that grows on jam or decaying
fruit, and yet all these belong to the group of fungi.
The best method of studying fungi is to grow them.
The following experiment shows an easy way of doing
this: allow a piece of bread to stand exposed to the
air for a few hours. Then moisten it, and place it
on a piece of damp blotting paper under a glass or bell

Fig. 1. Mucor growing: on bread.

jarina warmroom. Ina few days the surface becomes
covered with white tufts having a velvety appearance.
Under the microscope these appear as a number of
white interlacing threads which are part of a fungus
plant and collectively known as its mycelium. If one
of these mycelial threads known as a hypha is carefully
examined it is seen to consist of a tube-like structure

1—2

4 Introduction to Fungi [CH.

containing a somewhat granular substance which is
the living portion or protoplasm of the fungus. Some
of the tubes have no dividing walls but others are
divided by cross walls into compartments called cells,

Fig. 2. Spore bearing cases of Mucor. (Magnified.)

the length of which varies with the fungus under
observation. Further examination of the tufts on the
bread shows that all the threads do not belong to the
same fungus. Some of them carry tiny balls, at first
white and later on turning black, each being borne on

1] Introduction to Fungi 5

a long stalk (see Fig. 2). This fungus is known as a
Mucor. Other threads give rise to a greyish powder,
which under the microscope is seen to consist of
numerous egg-shaped bodies like bunches of grapes.
These are the seeds or, as they are usually termed, the
spores of the fungus known as a Botrytis (see Fig. 3).
We may also find a fungus bearing light-blue spores

Fig. 3. Spores of Botrytis borne like bunches of grapes and some
of the spores germinating. (Magnified.)

borne in chains at the ends of branches which join to
form a single stalk. This fungus is a Penicillium (see
Fig. 4).

Spores of any of these fungi placed under suitable
conditions give rise to the same kind of fungus plant
or mycelium as that on which they were borne. The
following is a means of studying the growth of spores.
Take a Ward’s Tube (see Fig. 5) and fix the base of the
chamber to a glass slide by means of paraffin wax;
put in a small quantity of water. Take some of the
spores of the Botrytis fungus on a brush and put them

Fig. 4. Spores of Penicillium as seen under the microscope.

Fig. 4.6. (a) Erect hyphae bearing conidia (c) in chains. (b) Detached
conidia. (s) Germinating conidia. (¢) Germ tube. (h) Mycelium.
(Magnified.) (After Percival.)

CH. I] Introduction to Fungi 7

into a small drop of water on a coverslip large enough
to cover the top of the chamber; smear the top with
vaseline and place on it the inverted coverslip. The
spores are now in a hanging drop in a moist chamber
and can be watched under the microscope. After
about 12 to 24 hours the oval spores send out small
projections which continue to grow; later on cross
walls are formed (see Fig. 3).

In water growth ceases as soon as the food in the
spore is used up. If, however, a food solution is used
for a hanging drop instead of the water, the tube
continues to grow, branches and gives rise to the

Fig. 5. A Ward’s tube. A, paraffin wax; B, vaseline; C, the
hanging drop.

same kind of mycelium as that on which the spore
was borne.

A method now in common use for the study of
fungi consists in making cultures of them in such
substances as plant extracts, meat extracts, gelatin,
or agar-agar (prepared from sea-weed) or a mixture of
some of these. The medium is freed from living
organisms by means of heat and then infected with
fungus spores or pieces of mycelium. Saprophytes and
many parasites grow and form spores; some parasites,
however, such as rusts, will not grow in this way. The
experiment is usually carried out in tubes stopped with
cotton wool or in Petri dishes (see Fig. 6).

8 Introduction to Fungi [CH.

In neither case can foreign organisms enter the
culture. It is thus possible to grow a fungus free
from all other organisms. If at first the culture 1s
not pure a few spores of the required fungus may be
transferred to a sterile medium and a pure culture so
obtained. The mushroom fungus resembles those
already examined in consisting of a mycelium and a
part which bears the spores. The spawn contains a

Fig. 6. Colonies of a fungus growing on gelatin in « Petri dish

dense growth of hyphae which take up food from
decaying matter and then produce the fructification
known as a mushroom.

If some of the white strands (i.e. mycelium) from
mushroom spawn are placed in decaying manure or
rich soil containing much organic matter, and kept
moist and at a suitable temperature, mushrooms will
be formed. If however the soil contains very little

1] Introduction to Fungi 9

organic matter, no mushrooms will form. This is
because the mushroom does not live like a green plant,
but requires organic matter for its food.

Remove the stalk of a ripe mushroom and place
it with the coloured part downwards on a piece of white
paper and leave it for some time. Then tap it gently
and lift it; on the paper will be found a print similar
to the gills or coloured part of the mushroom which is
found to consist of coloured spores (see Fig. 7). These
are borne in pairs on some of the cells on the sides of
the gills. The mushroom is the spore-bearing part of
the fungus and it can be produced from these spores
as well as from spawn. Toadstools similarly bear
spores.

So far we have been growing the fungi on dead
materials and dealing only with saprophytes. Para-
sitic fungi can be obtained by growing plants under
suitable conditions for fungus attacks. Sow cress
seed in a pot of soil, keep the soil very wet and in a
fairly warm atmosphere. The young seedlings soon
wilt and die. Examination of the surface of the soil
shows a ramifying growth of mycelium, some of which
has entered the plant. Here, then, we have a case of
a fungus capable of injuring a plant and therefore a
parasite, but it is also capable of living on the soil as
a saprophyte. There are many others besides this one
capable of living either as saprophytes or parasites.
Some however can live only as saprophytes, e.g.
Penicillium, and others only as parasites, e.g. rusts.

In a previous experiment we simply moistened a
piece of bread, and on leaving it found that fungi began
to grow. How did these get on the bread? The fol-
lowing experiment affords an answer. Take a piece

10

Introduction to Fungi

Fig. 7. Spore prints of common toadstools.

[CH.

1] Introduction to Fungi 11

of bread as before and keep it for a short time in
boiling water. Now divide the bread into two parts
and place on separate pieces of glass which have also
been immersed in boiling water. Cover one piece,
while still hot, with a small bell-jar—call this A. Allow
the other piece (B) to cool and to remain uncovered for
two or three hours, and then cover it also with a bell-jar.
After a few days a whitish fungus appears on B, but
‘not on A. Now the only difference in treatment of
these two pieces of bread is that B has been exposed to
the air for a short time while A has not. As A has no
fungus growing on it we may conclude that the fungus
has not been produced by the bread. The only
other source from which it could have come is the air.
Fungus spores which we have already examined are
very light and can readily float about in the air. The
moist bread offers suitable conditions for the germi-
nation of any which may find their way to it; the
hyphae take up food from the bread and produce a
mycelium which gives rise to similar spores some of
which in turn may fall on the bread and germinate as
before.

Considerable use is made of the knowledge that
fungus spores float about free in the air, but can be
killed by heat. In jam making the jam is heated and
any fungus present is killed. The jam is then tied
down whilst still hot and any spores that reach the
surface before tying down are killed, consequently
there is no growth of mould on the surface. If however
the pots are allowed to cool before being tied down, any
fungus spores that reach the surface after the tempera-
ture has fallen too low to kill them grow and produce
a mycelium which is commonly known as “mould.”

12 Introduction to Fungi [CH.

In tinning fruit the tin and its contents are heated
and sealed up whilst still hot; hence foreign organisms,
such as fungi, are prevented from growing on them.
Use is also made of the fact that fungi will not grow
in certain substances known as “preservatives”; e.g.
boric acid is added to cream to prevent the growth
of organisms which would turn it sour.

These fungi are saprophytes, but a large number of
parasites which cause plant diseases also spread them-
selves by means of spores floating in the air. Spores
are produced in very large numbers and only by chance
reach a substance on which they can feed as they have
no special guidance towards it. Some give rise to
several kinds of spores which were regarded as
separate forms until it was found that the spores of
one stage were capable of producing a mycelium
bearing the spores of another stage. Every fungus
is distinct from every other fungus: the spore of a
mildew never gives rise to anything but a mildew, nor
the spore of a rust to anything but a rust fungus, no
matter on what plant it is growing, just as an acorn
never gives rise to anything but an oak tree, or a
grain of wheat to anything but a wheat plant.

Fungus spores can be divided into two groups:

(1) Those formed directly from the mycelium,
usually by the cutting off of portions by transverse
walls. These are known as Conidia.

(2) Those formed as the result of fertilization, i.e.
the fusion of a male and female cell.

Up to the present we have only dealt with conidia;
these are usually produced under favourable conditions,
such as obtain in summer, and are often called “summer”
spores.

1] Introduction to Fungi 13

Those resulting from fertilization usually serve to
carry the fungus through bad conditions, such as winter.
They are known as “‘winter” or “resting” spores, and
some are capable of living for several years.

Many plants have other methods of reproduction
besides seed, e.g. potatoes are usually derived from
tubers in underground stems. Certain fungi have very
similar methods. Portions of the mycelium of the
potato disease fungus are capable of living in the potato
tuber and of producing a further growth of mycelium
and spores.

Mushroom spawn is capable of producing mushrooms
because it contains the mycelium of the fungus.

Parasitic fungi live in much the same way as those
which grow on bread. The plant which is being
attacked is known as the “host.” The mycelium
usually lives inside its host and absorbs the food
materials found there; it appears on the surface only
for the purpose of forming spores. The visible portions
of the fungus are the organs of reproduction and the
parts of the mycelium bearing them. In the case of
the true mildews, however, almost the whole of the
fungus is on the outside and the food is obtained by
suckers called ‘“‘ haustoria”’ penetrating into the plant.

Fungoid diseases are spread from one plant to
another chiefly by means of spores which may be
blown about in the air or carried by insects; some
spores can live for a long time in the soil and infect
plants sown there. In other cases the mycelium
itself is capable of infecting plants by growing through
the soil from one plant to another.

Enormous losses result from fungus attacks, but
the harm done by a particular fungus varies from year

14 Introduction to Fungi [CH.

to year. A fungus may become so abundant in certain
seasons as to cause considerable loss; such epidemics
are usually due either to very favourable conditions
for the fungus or to the introduction of a foreign
fungus. A cucumber grower estimated his loss from
a fungus disease as £1000 in one season. The potato
famine in Ireland in 1845 was the result of an enormous
reduction of the potato crop by the potato disease
fungus, and occurred in a season when conditions were
favourable to its growth.

The American gooseberry mildew as its name
implies came to us from America. It first appeared in
1900 and for a few years did comparatively little
damage, so that no means were taken to destroy it
and to prevent re-importation. It: has now spread
over all the gooseberry districts in England and causes
so much damage as to threaten the existence of those
varieties which are most liable to its attacks. If means
(however drastic) had been taken at first to destroy
all infected bushes and also to prevent re-importation,
this disease might never have established itself here.

Many countries adopt special precautions against
the introduction of diseases. In South Africa potatoes
are imported from this country only when accompanied
by a certificate from the Board of Agriculture that
they are free from certain diseases, that these diseases
are not present in the area in which they were grown,
and that they were packed in clean new packages.
On arrival in South Africa they are examined by experts
and are not admitted if found to be diseased. In this
way the black scab and other diseases of potatoes are
kept out of South Africa, thereby preventing consider-
able loss to the potato crop.

1] Introduction to Fungi 15

The various fungi behave very differently on
different plants and also in their manner of attack.
The mycelium of the potato disease fungus kills the
cells with which it comes in contact and then dies;
the living mycelium occurs only in and near the region
of living cells.

In rusts the mycelium lives together with the
protoplasm of the cells and both take their food from
the same source.

The mycelium of the smut fungi lives with the
young cells at the tips of the shoots without killing
them. When however it enters the grain all the cells
of the grain are used up and the mycelium produces
spores.

In the case of “finger and toe” in turnips, the
cells containing the fungus not only do not die but are
stimulated to increased growth with the result that
they are much larger than the surrounding cells which
contain no fungus.

Some fungi live on one kind of plant only and
are apparently incapable of living on others. Other
fungi live only on plants belonging to a certain natural
order. Others again live on a very large number of
plants belonging to different orders. Rotation of crops
is often very effective in keeping diseases in check,
since a fungus disease of one crop is often incapable of
attacking the following crop and may die out before a
suitable host crop is grown. But if suitable weed
hosts are present the disease may be carried on for an
indefinite period. In some cases the fungus may have
to travel a considerable distance before reaching a
suitable host.

Our present system of marketing in which empties

16 Introduction to Fungi [CH.

from one district are often sent to other districts is
very favourable to the spread of fungus diseases.

The fungus known as EHrysiphe graminis, which
causes mildew on cereals and grasses, really consists of
several different fungi resembling each other in structure
but differing in their behaviour towards plants.

Put some spores from a mildewed wheat plant on
to a healthy wheat plant under warm and moist
conditions—infection takes place. Now repeat the
experiment using a healthy barley plant, and no
infection of the barley results from the wheat mildew.
Similarly the mildew from barley will infect barley
plants but not wheat plants.

Take some spores from a mildewed wheat plant
and put them on a barley leaf which has been bruised,
the leaf now becomes infected with mildew.

The fungus causing potato disease attacks only
plants belonging to the same order as the potato.
The spores are blown about in the air and fall on a
number of other plants but no infection takes place.
It is not known why a fungus is capable of infecting
some plants and not others.

Some fungi are confined to definite portions of the
plant such as the root, the stem, or the leaf, whereas
others attack the whole plant. Some cannot enter
the healthy surface of a plant but can enter by means
of awound. The fungus Nectria ditissima, which causes
“apple canker,” is a wound parasite. Bad attacks of
canker often follow an attack of “woolly aphis,” which
causes wounds through which the fungus can enter.

In order to deal successfully with a disease it is
first necessary to find out its cause. If it proves to
be a fungus we must then learn all we can about its

1] Introduction to Fungi 17

life history, such as the times and methods of entering
the plant, the times and methods of reproduction and
the plants on which it is capable of living. From these
data we may be able to find weak spots at which we
can successfully get the upper hand or prevent it from
spreading to other plants. Without such knowledge
we may be attacking the fungus at the period when it
is least vulnerable.

CHAPTER II
POTATO DISEASE AND ALLIED DISEASES

Potato disease (Phytophthora infestans).

We must not gather from the name of this disease
that it is the only one from which the potato plant
suffers. Potatoes are subject to a number of diseases
but this one is so called because it is very widespread,
occurs in all parts of the world where potatoes are
grown, and because it does the greatest amount of
damage. It has other names such as potato mildew,
potato blight, late blight of potatoes, and dry rot of
potatoes. July is the month to look for signs of the
disease. The first indication of its presence is the
appearance of brown patches on the leaves. These
may appear on any part of the leaf, but are usually
found at the tips or edges (see Fig. 8). On the under
surface of these brown patches a pocket lens reveals—
near the healthy part of the leaf—a number of white
threads like those of the moulds on bread. Further

Pp. FB, 2

18 Potato Disease and Allied Diseases [CH.

examination under the microscope shows that the
white threads consist of a number of branched hyphae
carrying lemon-shaped bodies (Fig. 9A). This is the

Fig. 8. A potato leaf showing the patches which indicate the
presence of the potato disease fungus.

fruiting stage of the fungus which causes the potato
disease.

These small bodies are the spores or conidia of the
fungus. Each conidium is formed by the swelling of

11] Potato Disease and Allied Diseases 19

the end of the branch producing it; when the swelling
has reached a certain size a transverse wall divides it
from the rest of the branch. The branch then goes on
growing and so the conidium falls off or remains at the
side. The end of the branch then swells again and
produces another conidium. In this way a branch
may produce several conidia. We shall probably find
some at the tips and others at the sides of branches.
Those at the sides are the first formed, the lowest on
the branch being the oldest. The portion of the
mycelium bearing the conidia is known as the
conidiophore and is rather peculiar. The tube which
goes on growing after the conidium is produced is
wider than the portion below, and gives a knotted
appearance due to the variation in the bore of the
hyphal tube (Fig. 9A). The conidiophores reach the
exterior through the breathing pores of the leaf either
singly, or several through one pore. Together with
the spores they provide a means of recognizing the
fungus. The conidia may vary somewhat in size, the
average length being about jin. and the average
width being about ;4, in.

The conidia are very light and readily blown about,
and as the plants overlap and touch each other they
may easily fall or be washed by the rain from one plant
to another. It is difficult to watch the development
of these conidia after they have fallen on a potato
leaf, but the further development may be followed
by putting some of them in a hanging drop in a
suitable chamber (see p. 5). Here changes take place
similar to those which occur naturally when the
conidia fall on moist leaves. After a time a change
occurs in the contents of the conidium, there being a

2—2

[CH.

Potato Disease and Allied Diseases

20

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{Zuyeurmias osojoq ysn{ siodsooz wv ‘9 ‘fserodsooz ‘y puv wy ‘UIn{pluoo 8
woz Zutdvose serodsooz ‘gq ‘fumiprucs Aydure ue ‘9 ‘untpluoo wv ‘g SeIpruoo
dutieaq seroydoipruoo ‘fp —-(snSuny osvosrp oyeyod oy) summsafus vioysydopiyg °6 ‘SI

Ir] Potato Disease and Allied Diseases 21

suspicion of a division, but not a very marked one.
Then suddenly the whole of its contents come pouring
out through a small hole at the pointed end. The
whole process may take only about 10 seconds. The
contents do not pass out whole but in about ten separate
masses. Each mass is considerably larger than the
hole through which it emerges and consequently is
much constricted on passing out (see Fig. 9D). On
arriving outside the conidium these masses start
swimming about very rapidly. It is from this motile
power in which they resemble small animals that they
are called Zoospores. When one of them becomes
motionless the presence of two small threads is revealed
(Fig. 9# and F). By means of these the zoospore
moves; they lash the water and force it along. After
a time the zoospore ceases its movements and the threads
disappear ; it now loses its former shape and becomes
spherical (Fig. 9G). Later on a small protuberance is
formed ; this lengthens and forms a tube. The contents
of the zoospore pass into this tube which grows and
may give off branches (Fig. 9H, J and J). Eventually
growth stops and the young fungus dies of starvation.

All these changes take place when a conidium falls
on the surface of a moist potato leaf, but the hyphal
tube formed does not die of starvation; it enters the
leaf by means of a breathing pore or by dissolving
away the outer wall of the leaf. Growth now goes on
rapidly as the hypha has abundant food. A mycelium
forms which kills the leaf cells and changes them to
a brown colour causing the characteristic appearance
which first shows the presence of the disease. Both
young and old leaves may become infected in this

way.

22 Potato Disease and Allied Diseases [cH.

Every potato grower knows that the disease is very
bad in some years which become known as potato
disease years and much less harmful in others. The
disease is bad when dull, muggy weather prevails in
July and August. Farmers formerly held the idea
that the dull weather caused it; indirectly it does, for
damp conditions are favourable to the growth and
spread of the fungus which produces the disease.
Potatoes grown in a shady place with a moist atmo-
sphere readily succumb to the disease, whereas others
in a dry sunny place may show no signs of it.
We are now in a position to understand why the
disease should be most marked in dull weather. The
conidia and zoospores by which it is distributed can only
germinate when a certain amount of water is present
and at certain temperatures. The optimum tempera-
ture has been found to be about 70°-74° F., and this is
about the temperature of dull weather in July.

If the weather is bright and hot the brown patches
formed on the leaves dry up and curl, and the disease
may not spread at all or only very slowly. If, however,
the weather is dull the brown patches rapidly spread
over the whole leaf. The formation of conidiophores
on the under surface accompanies the browning of the
tissues in its spread over the leaves. It is at this stage
that the casual observer usually notices the disease.
Brown patches also appear on the stem and in bad
attacks all the leaves are killed. A diseased field has
a very bare appearance, similar to that of a healthy
field when the leaves have died normally.

The tubers of diseased plants are marked in a
characteristic manner. They have sunken brownish
patches which at first do not extend very deep into

11] Potato Disease and Allied Diseases 23

the tuber. Later on however the browning may spread
throughout the tuber. These patches may show them-
selves soon after the leaves have become diseased,
especially on tubers near the surface. This stage of
the fungus has given it the name of “dry rot.”

Tubers which are apparently healthy have been
sown, and the plants from them grown under conditions
rendering external infection impossible, and still these
plants have become diseased. Careful examination of
a number of these apparently healthy tubers showed
them to contain portions of the mycelium of the potato
disease fungus. The disease then starts from the
tuber. When the tuber sprouts and produces shoots
the fungus mycelium also grows and makes its way
into the stems and leaves. We have seen how the
disease reaches the leaves and spreads from one plant
to another, but we have still to account for the in-
fection of the new tubers which carry the fungus on
to the following season.

We should expect to find that the fungus mycelium
grows down the stem and into the new tubers. The
evidence on this point is not very clear. It is supposed
that the new tubers are capable of being infected from
the conidia produced on the leaves. These conidia fall
on the damp earth and there produce zoospores which
are washed down to the tubers. The zoospores
germinate and penetrate the tuber, the mycelium
formed causing the brown patches so characteristic of
the disease. In favour of this hypothesis are the facts
(1) that the diseased patches appear as frequently at
the end of the tuber away from the stem as at the end
which is attached to the stem; (2) that the upper
surface is often more diseased than the lower; (3) that

24 Potato Disease and Allied Diseases [CH.

tubers near the surface are often more diseased; and
(4) that the browning of the tissues extends inwards.
It has been shown that zoospores will not pass through
a depth of 6 inches of sandy soil. An experiment was
made by covering potatoes with this depth of soil to
see if the tubers were thus prevented from becoming
diseased. Although a number of the tubers became
diseased the percentage was much less than in the
case of tubers covered with a lesser depth of soil. It is
important to know how the young tubers are infected,
because if it is entirely by means of the zoospores we
should hope to aim at preventing their infection by
trying to keep down the formation of conidia or to
prevent the zoospores from reaching the young tubers.
It is possible that the tubers are infected directly by
the growth of mycelium through the stem as well as
indirectly by means of the zoospores.

By killing the leaves of the potato plant the disease
stops their functions as feeding and breathing organs,
and as the plant is now capable of taking only very
little food from the air the growth of the tubers prac-
tically ceases. Having lessened the crop and reduced
the value of the tubers lifted the disease has by no
means finished its career. When slightly diseased
tubers are stored in clamps, the disease spreads,
especially when there is a sufficient supply of moisture
and a suitable temperature. Diseased tubers also
allow foreign organisms to enter thereby setting up the
well-known “wet rot.”

Take some diseased tubers, wash them, cut slices
across the diseased areas with a sterilized knife and
place them in a large sterilized Petri dish lined with
moistened filter papers.

11] Potato Disease and Allied Diseases 25

After a time white tufts will grow on the slices of
potato. Examine these and they will sometimes be
found to consist of the conidiophores of the potato
disease fungus, showing that the mycelium of that
fungus is present in the tubers. Sometimes the white
tufts are portions of saprophytes which have gained an
entry into the tuber, and when present these often make
it difficult to find the potato disease fungus.

Remedial Measures.

The life history of the fungus causing potato
disease provides us with a sound basis for deciding
what steps to take in order to minimize the amount
of damage done. Moisture is one of the conditions
favourable to the disease, and so, if possible, in choosing
a soil in which to plant potatoes preference should be
given to one that is well drained. Having chosen our
soil we must then exercise some care in choosing our
seed. The disease is carried on from one season to
another by means of mycelium in the tubers. Prac-
tically all the potatoes from badly diseased fields
contain this mycelium, although on many there may
be no outward sign of it: consequently we shall be
helping the disease if we plant them. Seed should be
chosen from fields with the smallest amount of disease.

In choosing between the different varieties the
grower has to consider the value of the crops produced.
Those susceptible to disease are usually the high
yielders and it is for the grower to decide which are
the more profitable on his particular soil. In good
potato years the amount of disease on the susceptible
varieties is usually small and even in bad years it is

26 Potato Disease and Allied Diseases [CH.

possible to prevent it to a certain extent, as we shall
see later.

It spreads in the field by means: of conidia which
form zoospores. If we can prevent the formation of
spores or their germination we shall put a check on
the spread of the disease. A large number of sub-
stances in the form of liquids and powders have been
put on potato plants with a view to checking the
damage done by this fungus, and some of them have
proved successful. An application of this kind to
check the spread of a fungus is known as a “fungicide.”
That which has proved the most valuable in the case
of potato disease is known as “Bordeaux mixture.”

Bordeaux mixture is made from copper sulphate
(blue stone), lime and water. Ordinary agricultural
blue stone must not be used as it does not contain
sufficient copper sulphate. The blue stone used must
contain 97-98 per cent. of copper sulphate. The lime
most suitable for this purpose is “fat” lime, or as it is
often called, ““white lime.” This is the kind used by
plasterers. It is important that the lime should be
freshly burnt and in lumps. Soft water makes a
better mixture than hard water.

For making 50 gallons of the mixture the following
are required :

A tub (of about 60 gallons capacity),

A tub (of about 30 gallons capacity),

A wooden pail,

6 Ibs. of copper sulphate,

4 lbs. of lime,

50 gallons of water.
Put 25 gallons of water into the large tub and weigh
out 6 lbs. of the copper sulphate (this should be in a

11] Potato Disease and Allied Diseases 27

powdered state). Tie the copper sulphate in a cotton
bag or a piece of sacking, and suspend it so that it
reaches just below the surface of the water in the tub.
Now carefully pick over the lime, throwing out any
pieces that are overburnt, and weigh out 4 Ibs. of it.
Put this into the wooden pail and slake it with about
a quart of water which should be added very slowly.
Covering the bucket with a piece of sacking helps the
lime to slake. When the lime has crumbled add about
another quart of water and work the lime into a stiff
paste; add more water and stir to make a creamy
liquid. Now put 20 gallons of water into the small
tub, pour the creamy liquid into it through a fine
sieve or a piece of coarse sacking, and add water until
the tub contains 25 gallons.

When the blue stone in the large tub has all dis-
solved slowly pour the lime solution into it, stir well
meanwhile and continue to do so for some time. If
the above operations have been carefully carried out
the mixture should consist of a light blue precipitate
suspended in a colourless solution. A granular pre-
cipitate which sinks quickly to the bottom shows the
mixture to be a poor one. It should remain floating
for some time. In some cases Bordeaux mixture
damages the potato plant. This is usually due to
some error in making and is caused by the presence
of free copper sulphate. It is a simple matter to test
the safety of the mixture. If a knife blade becomes
coated with copper when placed in the liquid, it is
unsafe and more lime solution should be added.

A better test is to add a few drops of the mixture
to a solution of potassium ferrocyanide on a piece of
white porcelain. If a brownish colour is produced

28 Potato Disease and Allied Diseases [ CH.

more lime solution must be added. If the above
directions are carefully followed the mixture will
usually be satisfactory.

The mixture is sprayed on the potato crop by means
of a pumping apparatus to which a special nozzle is
attached. For large areas a horse-drawn machine is
necessary. For small areas the potatoes can be
sprayed successfully by means of a “knapsack” sprayer
which is carried on the back.

The object of spraying the plant is not to cure
the disease but to prevent it from spreading by
covering all the parts liable to infection with a coating
of a substance which will prevent the spores from
germinating, or kill the delicate germ tube, and so
keep it from penetrating the plant. It is no easy
matter to cover the plant uniformly in the desired
manner. The best results are obtained by means of
a very fine spray, which on coming out of the nozzle
hangs about in the air for a short time like a mist.
Such a spray can only be obtained by means of suitable
nozzles of which there are several useful forms on the
market at the present time. A much finer spray is
formed when a high pressure is obtained.

Bordeaux mixture should be kept stirred while it is
being applied to the plant and this should be brought
about by an automatic stirrer inside the machine.
With a coarse spray the mixture easily runs off the
plants.

About 80-90 gallons are required to spray an acre.
The cost is about 6s. per acre, but varies with the
distance of carting the water. The time to spray is
just before the disease appears, i.e. the first and second
weeks in July. In a bad season it is advisable to spray

Ir] Potato Disease and Allied Diseases 29

early, and to repeat about three weeks later. Further
applications are desirable if the unfavourable conditions
continue. The result of spraying is usually a consider-
able increase per acre as the plants remain green longer
and consequently the tubers grow longer. This delays
the lifting which in some cases may be a disadvantage.
In dry seasons when the disease does little damage
spraying may not increase the yield, but as the
weather is so uncertain it is an insurance to the farmer
that he will benefit considerably if the disease does
appear. Early varieties are often dug before the
disease appears and the advantage of spraying is not
so marked with second earlies as with maincrop potatoes.

Burgundy mixture is often used for spraying
potatoes because although not so good as Bordeaux
mixture it is much easier to make. It consists of 6 lbs.
of copper sulphate and 8lbs. of pure washing soda
dissolved in 50 gallons of water.

The copper sulphate and the crushed soda are
dissolved separately and then stirred into the 50 gallons
of water.

Dry spraying consists in applying the fungicide in
the form of a powder and has been successful in
increasing the yield of potatoes in disease years. It
is not however as good as Bordeaux or Burgundy
mixture but it may be safer. Bordeaux mixture
requires a certain amount of care in making. In the
hands of an ordinary workman it may prove disastrous
and scorch the haulm. In cases where the men cannot
be relied on to make it properly it is better to use
Burgundy mixture; but with this also they may often
leave some of the soda undissolved, in which case it is
safer to use a dry spray.

30 Potato Disease and Allied Diseases (CH.

Bordeaux mixture, when properly made, gives a
larger yield than dry spraying, so that it is worth the
extra care. Dry spraying can only be applied when
the dew is on the leaves, which is a considerable draw-
back when large areas are grown.

The storage of potatoes requires considerable care.
Whenever possible they should be allowed to dry before
they are covered in the “pits” or “clamps.” The sound
tubers should be separated from the diseased tubers
preferably at the time of digging. If the potatoes are
wet and dirty so as to make this impossible a temporary
clamp should be made; later on the healthy potatoes
should be picked out and put into a permanent clamp
and the diseased potatoes may be fed to stock.

The site of the clamp should be as dry as possible.
It should be narrow and have steep sides in order to
let the moisture escape easily. It should be covered
with a good straight straw or similar material to keep
out the rain. It is a common practice to cover the
straw with a layer of earth. In the clamp the potatoes
heat and sweat so that moist warm conditions suitable
to the spread of the disease are obtained if it is not
properly ventilated. Other organisms also enter
bruised and diseased potatoes and set up the well-
known “wet rot.”

For the first few weeks the clamp should not be
covered with earth but later on this is necessary to
keep out sharp frosts. On covering with earth spaces
should be left at the top at frequent intervals which
are covered with straw only. The tubers should be ex-
amined from time to time to see if they are keeping well.
If the potatoes are wet and dirty on lifting it is advisable
to sprinkle them with some powder to prevent the

Ir] Potato Disease and Allied Diseases 31

rot from spreading in the clamps. Ground lime at the
rate of 1 cwt. to every ton of potatoes, or flowers of
sulphur at the rate of 2 lbs. to every ton of potatoes,
have proved very successful in preventing the spread
of winter rot.

<== oe

~~ Ca

Fig. 10. Tomato seedlings, one healthy and the other killed by
the damping off fungus Pythium de Baryanum.

Damping Off (Pythium de Baryanum).

In seed beds a number of seedlings are often found
lying prone on the ground, the stem of the plant being
rotten just at the ground level (see Fig. 10). This
state of affairs is known as damping off. There are
several fungi which cause young plants to damp off in
this way, one of the commonest being Pythium de

32 Potato Disease and Allied Diseases [cH.

Baryanum. This fungus is capable of living for a time
on the decaying matter in soils; on reaching a plant
its mycelium bores into the cells and soon kills them.
The stem is thus weakened at the ground level and
topples over. The non-septate! mycelium of the
fungus may be found between the cells of a diseased
seedling. After a time the tips of some of the hyphae
become round and swollen and are cut off by cross
walls. These round bodies are the conidia. Placed in
a hanging drop they give rise to zoospores, like those
of the potato disease fungus, which germinate and
produce a mycelium like that on which they were
borne. The area of the patches in which plants damp
off increases through the spread of these zoospores or
of the mycelium along the soil. Unlike the potato
disease, but like the majority of fungi, this fungus
produces as the result of fertilization another kind of
spore which is thick walled and capable of resisting
adverse conditions for some time. These are known
as winter spores, and as they remain in the soil through
the winter, seed beds which are attacked one season
are very liable to be attacked during the following
season unless the soil is treated and the spores killed.

Remedial Measures.

The conditions which favour the fungus are warmth,
moisture, and shade. If possible we must try and get
rid of these by avoiding shady spots for seed beds, and
also by using soil which allows water to pass through
freely.

1 In a non-septate mycelium the hyphae have no cross walls.

11] Potato Disease and Allied Diseases 33

In seed boxes the soil may be freed from this fungus
by heating it to 150° F. Mixing charcoal with the
upper layer of the seed bed reduces the disease. Take
two boxes of soil in which plants have damped off.
Heat one of them to a temperature of at least 150° F.
Sow each of the boxes very thickly with cress seed.
Keep the soil very wet and use water which has been
previously heated to 150° F. Keep the boxes in a
shady place. When the plants grow many of those in
the unheated box will damp off, whereas those in the
heated box will not. Now introduce some of the soil
and dying plants from the unheated box into the
heated box; the plants begin to damp off.

Onion mildew (Peronospora schleident).

This disease is usually present wherever onions are
grown. It is easily recognized by the yellowing of the
leaves and also by the ‘“‘necking” of the plant, i.e.
elongation of the stem between the leaves and the
bulbs. The leaves which are attacked soon collapse.
Like the potato disease it does most damage in dull
warm weather. On the leaves of a diseased plant a
dull violet-coloured growth forms. This is the fruiting
stage of the fungus and consists of tree-like conidiophores
bearing conidia on the tips of their branches. These
somewhat resemble those of the potato but each
conidiophore bears a larger number (see Fig. 11). In
water these conidia give rise to zoospores which are
capable of further infection. If damp weather con-
tinues the disease spreads rapidly. In dry weather,
however, it soon disappears.

This fungus also forms winter spores like those
of Pythium de Baryanum which serve to carry the

P. F. 3

34 Potato Disease and Allied Diseases [CH.

disease from one season to another. The fungus does not
attack the bulbs but prevents the leaves from carrying
on their normal functions of manufacturing food stuff
and so the bulbs are smaller.

Fig. 11. Conidiophore and conidia of Peronospora schleideni
which causes onion mildew. (Magnified.) (After Massee.)

Remedial Measures.

Well-drained land does not suffer so much as wet
land. Onions should not be planted on land which
had a diseased crop of onions in the previous season.

I] Potato Disease and Allicd Diseases 35

Spraying with Bordeaux mixture or with a 3 per
cent. solution of iron sulphate will help to check the
disease as by this means the spores are prevented from
sending their germ tubes into the plant.

CHAPTER III
FINGER AND TOE, AND WART DISEASE

Finger and Toe (Plasmodiophora brassicae).

This disease also goes by the name of ‘“‘anbury,”
“club root,” or “club.” It attacks all cultivated
plants of the cabbage order such as turnip, cabbage,
rape, kohl rabi, mustard, stocks and wallflowers, and
also the weeds, e.g. charlock, shepherd’s purse, and
hedge mustard. As far as we know it is confined
entirely to the Cruciferous order} to which these plants
belong. This disease is very widespread and has done
a considerable amount of damage, especially since the
practice of using acid manures became common and
the use of chalk and lime declined.

On taking up young cabbage plants from seed
beds for the purpose of transplanting, the roots are
sometimes found to be swollen and knotted. These
knots, which vary considerably in size and shape, may
occur on any part of the root system. If these plants
are put out into the field they do not grow normally ;
a few small leaves may be formed, but they soon

1 Order Cruciferae. It is exceedingly useful in this and several other

diseases to know the characteristics of this order, which are very simple
and can be found in any book on Systematic Botany.

—

36 Finger and Toe, and Wart Disease [CH.

i;
y
4

Fig. 12a. Swede turnips attacked by Finger and Toe.

Fig. 126. Charlock attacked by Finger and Toe.

1] Finger and Toe, and Wart Disease 37

become yellowish and the plant makes very little
growth. A diseased plant possesses, instead of the
normal development of fibrous root, a swollen nodular
mass. The fancied resemblance of this mass to fingers
and toes gives the disease its popular name. Exami-
nation of a thin section of one of these nodules mounted
in water shows large cells scattered amongst cells of

a, Spores. 6, Plasmodium.
Fig. 13. A section of a turnip root very highly magnified showing the
giant cells caused by Plasmodiophora brassicae. Some of the giant
cells contain “plasmodium” and other spores. (Magnified.)

ordinary size. The contents of the larger ones are
darker in colour and very different from those of an
ordinary normal root cell. The high power of the
microscope shows that the contents consist either of a
frothy granular mass or of a very large number of tiny
spheres (see Fig. 13). These are the spores of the
Finger and Toe fungus. They are very small and
measure only gj55 of an inch in diameter.

38 Finger and Toe, and Wart Disease [CH.

[N.B. Do not confuse these spores with the starch
grains of the cells. The latter are larger, irregular,
and not so numerous. |]

Some of these minute spores may be found floating
freely in the water in which the section is mounted.
Owing to their minute size their germination is difficult
to watch, except under a very high power of the
microscope. In a hanging drop the following changes
take place. A hole is formed on one side of the spore
through which the contents emerge as a minute body
which begins to move very slowly and in so doing
continually changes its shape. Each one is known as a
Myxamoeba, from its resemblance to a small animal
which moves very similarly, called Amoeba. It con-
sists of a naked mass of living substance known as
protoplasm. Attached to it is a hair-like process which
resembles those we saw on the zoospores of the potato
disease fungus.

In nature the spores formed in the large cells escape
into the soil by the rotting of the host plants. Here
they germinate and millions of myxamoebae are set
free. The interstices of the soil are very much larger
than these and so there is plenty of room for them to
move about. The amount of water they require to
move in is also small and there is sufficient in an
ordinary moist soil. In their wanderings through the
soil water some of them may chance to reach a rootlet
of a cabbage plant or a plant belonging to the order
Cruciferae. Of the large number of myxamoebae set
free only a very small percentage probably reach a
plant which they are capable of infecting. The others
of course die. We see now why such an enormous
number of spores are formed. If only a small number

II] Finger and Toe, and Wart Disease 39

were formed the chances of infecting plants would
be proportionately diminished and consequently the
existence of the fungus would be endangered. The
myxamoebae make their way into the plant through
the fine hairs near the tips of the rootlets.

The fungus causing Finger and Toe belongs to a
group which is very different from the majority of
fungi. It is not always classified as a fungus, but for
our purpose may be considered as such. If these spores
belonged to a fungus similar to those already studied, we
should expect them to give rise to a number of tube-like
hyphae known as a mycelium. In this case, however,
nothing of the kind takes place; when the myxamoeba
gets inside a root cell it begins to feed on the contents.
This particular cell seems to make a call on the food
supplies of the plant and gradually gets larger. The
myxamoeba continues to feed on the cell protoplasm
until eventually this is all used up. The large or giant
cell is thus filled by a naked mass of protoplasm
derived from the myxamoeba and which is now called a
“plasmodium.” This is the vegetative portion of
the Finger and Toe fungus, and so corresponds to the
mycelium of other fungi. As already mentioned it
appears as a frothy granular mass.

The plasmodium is able to pass from the giant cell,
which it has caused to be formed, into neighbouring
cells. Here it feeds on the protoplasm and these cells
gradually enlarge, and eventually become filled by it.
Examination of a section shows that the giant cells
touch each other and this is what we should expect
from the method of infection by creeping from cell to
cell. Now let us look at the case from the point of
view of the plant attacked.

40 Finger and Toe, and Wart Disease [cH.

The plant has to give up some of its food to the
development of the plasmodium, at the same time it
continues to grow and manufacture fresh food material.
As the plasmodium grows bigger it requires considerably
more food material and consequently the plant growth
is lessened until a time is reached when the plant
ceases to grow, or grows only very slowly, the whole
of the food manufactured by the leaves or brought
up by the roots going to the support of the plas-
modium.

The formation of giant cells causes the roots to
become swollen, and when a portion of the fungus
proceeds in a certain direction nodules are formed,
until eventually a state of affairs is reached as shown
in Fig. 12.

After a time the plasmodium becomes divided up
into a large number of small portions, each of which
becomes spherical and surrounds itself with a definite
cell wall. These spherical bodies are the spores.
When the host rots these spores are set free in the soil
ready to start on their destructive career, when the
favourable conditions of spring bring about their
germination. It is supposed that they can retain their
vitality for several years, which characteristic is
extremely favourable to the fungus in the ordinary
rotation of crops. This longevity of the spores, together
with the presence of certain cruciferous weeds which can
act as hosts of the fungus, enables it to continue its
existence when cruciferous plants are grown every
four or five years.

There are other diseases known as “club,” which
cause similar distortions to plants. One of these is
caused by a weevil which may be found inside the

m1] Finger and Toe, and Wart Disease 41

swollen parts (see p. 122). Another is caused by an
eelworm (see p. 170).

Finger and Toe may be distinguished from these
by the characteristic “giant” cells.

In addition to its dwarfing influence this fungus
causes turnips and swedes to rot quickly.

Remedial Measures.

No method is known by which this disease can be
cured once it has established itself in a crop. It is
possible however to carry out certain practices which
may considerably reduce the loss. The disease some-
times makes its appearance in cabbage seed beds, and
on pulling young cabbages to transplant they should
be rejected if attacked and others obtained for planting
in the field. Considerable harm may be done by trans-
planting infested cabbages, for a field may become
infected by putting in diseased plants. Special care is
needed to prevent the disease from spreading from field
to field, as it may be carried about in portions of
diseased roots or in soil containing the spores. This
disease is not carried through the air as are the spores
of the potato disease fungus. In ordinary practice
diseased crops would be folded with sheep or, the roots
carried to the homestead or pastures and fed there.

If the diseased roots are fed at the homestead
portions of the plants will become mixed with the dung.
The farmer must bear in mind that this dung will
spread the disease ; it should not be put on land which
is to grow a cruciferous crop in the next five or six years,
but used for such crops as mangolds, potatoes, carrots,
parsnips, beans, cereals, or grass, as these crops are not

42 Finger and Toe, and Wart Disease [CH.

attacked. In such cases the disease will remain in the
soil for four or five years, and if a cruciferous crop such
as turnip is grown it is liable to attack.

If it is necessary to use the dung for a cruciferous
crop the roots should be boiled before they are fed.
Diseased roots should not be put into the compost heap
if the compost is to be used for the cruciferous crops.
The disease very often appears on a small portion
of a field and by taking measures at this stage it is
easy to keep it in check. Sheep folded on such a field
spread it over the whole unless the diseased portion
happens to be the last portion folded. If such a patch
is found it should be isolated from the rest of the field
by means of hurdles, and the roots pulled and carted
and treated as infected material. Care must be taken
not to infect the whole field from the diseased portion,
which should be limed as shown below. The disease
may be spread by means of soil clinging to the feet of
sheep, horses or men, and also by cartwheels and
implements. Dirt should be scraped from these
before tliey are used on other fields. The spores of
Plasmodiophora brassicae are said to live for about
five years. Consequently the rotation should be so
arranged as to keep cruciferous crops, such as turnips,
cabbage, rape, koh] rabi, and mustard out for at least
six years. In the ordinary four course rotation turnips
may be replaced by mangolds, potatoes, parsnips, etc.,
by which means turnips will not be taken until eight
years after a diseased crop. Any crops other than
cruciferous ones may be grown. It is extremely im-
portant to keep the land free from the weeds of this
order for they carry on the disease from year to year.
Charlock is a great offender in this respect. By

111] Finger and Toe, and Wart Disease 43

growing immune crops the fungus cannot feed and so
eventually it is starved. It has been found that it
flourishes in sour or acid soils and not in soils con-
taining a sufficient supply of lime. It is practically
unknown on ordinary soils containing a high percentage
of lime. This provides us with the key for solving the
question as to why certain artificial manures favour
the disease. Experiments have shown that Finger and
Toe may become very bad on certain soils when acid
manures are used in large quantities. Such manures
as superphosphate and sulphate of ammonia use up
the free lime in the soil and tend to make it sour.
On soils liable to the disease through lack of lime
these manures should be given up in favour of
basic slag or bone meal and sodium nitrate, unless
large quantities of lime or chalk are also used. It has
also been shown that liming the soil keeps the disease
in check. As soon as a diseased crop is raised 2 tons
per acre of freshly slaked lime should be well spread
over the surface. It is essential that the lime should
be finely divided. If chalk is used about 4 tons per
acre should be put on but it is not so effective.
A similar dressing should be given about 18 months or
six months before the next cruciferous crop is put on the
soil. The object of putting on the lime is to get rid
of the conditions favouring the growth of the fungus
causing the disease. The lime also kills the spores
with which it comes into contact. White turnips
succumb more readily to this disease than swedes.
It is important that the soil used as seed beds for
cabbage should contain sufficient lime.

44 Finger and Toe, and Wart Disease [CH.

Wart Disease (Black Scab) of Potatoes (Synchytrium
endobiotica).

This disease, which also goes by the name of cauli-
flower disease, potato tumour, and canker, was intro-
duced from the continent about 20 years ago.

Its appearance varies with the virulence of the
attack. In slight attacks it may not be noticeable or
may appear as small blackish warts near the eyes. In
bad attacks large cauliflower-like outgrowths are formed
on the shoots arising from the tuber. These are at
first the same colour as the potato, but eventually
become almost black. The outgrowths always make
their appearance at the eyes, but later they may
spread over the tuber. They vary in size and at times
may be larger than the tuber on which they are borne.
By taking sections of the outgrowth many of the cells
may be seen to contain a number of roundish spore-like
bodies with thick walls. Some of these are said to
germinate directly but others do not germinate for
several years. On germination one of these spore-like
bodies produces a number of zoospores, each carrying
one flagellum. By means of these zoospores other
potato plants are infected. When a potato rots they
are liberated into the soil, and potatoes planted are
liable to infection. They are said to be capable of
living for five or six years. The disease also spreads
from slightly diseased tubers if they are planted the
following season. It does not attack other crops. It
is very local and prevails in certain districts in the
west and north of England, and in Scotland, especially

11] Finger and Toe, and Wart Discase 45

aN

Fig. 14. Outgrowths on the tubers and leaves of the potato plant
caused hy Synchytriwm endobictica. (After Massee.)

46 Finger and Toe, and Wart Disease [CH.

near large towns, where there are a number of market
gardens and allotments. Fortunately it is not known
in the eastern counties.

~

Fig. 15. Potato scab—the cause of which is not known.

Remedial Measures.

The best method of keeping this disease from the
potato crop is to exercise great care in obtaining
uninfected seed. It is advisable to get seed from
districts which are known not to be infected, or to have

111] Finger and Toe, and Wart Disease 47

been free from infection for the last six years. Some
of our well-known varieties such as Langworthy,
Golden Wonder, What’s Wanted, Peacemaker, and
Sutton’s Discovery, are immune from the disease.
All badly diseased tubers and other parts of the
plants should be destroyed. Slightly diseased tubers
may be fed, but they should be boiled beforehand,
as the spores pass through the animal unharmed, and
so infect the manure. This should not be put on
potato land.

All diseased fields should be isolated to prevent
infected soil from being carried about by the men,
horses or implements. If possible potatoes should be
kept from infected areas for six years. Land should be
dressed with good gas lime at the rate of 4-5 tons per
acre if a diseased crop is followed by potatoes. It
should be noted that this disease is scheduled under
the Destructive Insects and Pests Acts and all cases
must be reported to the Board of Agriculture and
Fisheries.

CHAPTER IV
MILDEWS

The term “mildew” is loosely used, and often
applied to a very large number of the smaller fungi,
both parasitic and saprophytic. It is now usual to
confine the term mildew to two families. The mem-
bers of the family to which the potato disease belongs
are known as Downy Mildews. The fungi we are

48 Mildews [CH.

considering in the present chapter are spoken of as
Powdery or True Mildews.

The true mildews comprise a large number of
different species. One of the commonest and also one
which will serve as an example of the group is the
well-known mildew of grasses and cereals, Hrysiphe
graminis, We shall have little difficulty in finding
specimens of this disease in cornfields during the

Si, i oe
tee a rl

Fig. 16. Wheat plant attacked by Erysiphe graminis.

spring, especially if the weather has been dull or wet.
In drier seasons it may be found in the shady and damp
parts of the field. The leaves of a mildewed plant are
covered with a white, a dirty white, or a pinkish
powdery substance. It was to this that the term
mildew was first applied, the leaves having the appear-
ance of being dusted with some kind of powder (see
Fig. 16).

Iv] Mildews 49

In the first stages of the disease the leaves are
covered with what looks like a dense spider’s web.
On examination this is found to consist of a network
of hyphae or mycelium ramifying on the surface of the
leaves and very similar to the mycelium obtained on
bread cultures. The hyphae are divided by cross
walls and so consist of long chains of cells. They
branch irregularly and cross each other to form the
dense network. Sections of the mildewed leaf show that
the mycelium is not present inside (a piece may be
dragged across the section on cutting and appear to
be running in the interior of the leaf). It lies very close
to the surface and is fixed to the leaf at certain spots;
sections show how this fixture is brought about. At
intervals along the mycelium short swollen tubes are
given off and penetrate the surface layer. These
swollen tubes are known as haustoria. This fungus
differs from those already studied in having its myce-
lium entirely outside the plant which it is attacking.
In the case of the other parasites the mycelium is
entirely inside the plant and the only portions visible
are the fructifications. This feature of having the
mycelium outside the plant is characteristic of the
“true mildews.” The haustoria which it sends into
the plant serve as a means of attachment and also of
absorbing the food supply. In favourable weather the
mycelium spreads rapidly over the whole leaf. After
a time a powdery substance is produced. This powder
consists of the conidia. The hyphae which produce
them differ from the ordinary mycelium in growing
out at right angles to the surface of the leaf instead of
parallel to it. These hyphae are divided up by cross
walls and the cells at the end of each become rounded

P.F. 4

50 Mildews [CH.

Fig. 17. Erysiphe graminis. A, conidiophores bearing conidia; B, a
spore case with appendages; C, a spore case which has burst
showing the asci and ascospores. (Magnified.)

Iv] Mildews 51

off as conidia (see Fig. 17). Each cell of the hypha
in its turn becomes the terminal one and forms a
conidium. The formation of these gives rise to the
powdery appearance. External conditions play a con-
siderable part in their formation. In muggy weather
they are produced in enormous numbers. Dampness
is also required for their germination. This is why the
disease is so prevalent under damp conditions. In
bright sunny weather fewer erect hyphae and conse-
quently fewer conidia are formed and conditions are
less favourable to their germination. The conidia are
oval in shape and collectively may be whitish grey or
pink. On germinating they send out tubes which, if
they happen to fall on the same kind of plant as the
one on which they were formed, immediately send
out haustoria into the host plant. The mycelium so
produced resembles the parent mycelium. In this
way the disease is spread rapidly from plant to
plant.

As the season advances the mycelium has a darker
appearance, and here and there among the hyphae a
number of dark bodies are formed. Under the micro-
scope these appear as a number of dark brown spherical
bodies attached to the mycelium on their under surface
(see Fig. 18). By separating them from the mycelium
they are seen to have a shiny appearance and polygonal
markings covering their surface (Fig. 17). They are the
“spore cases” of the fungus, and as they get older they
become darker in colour. When ripe their walls are
brittle. Put some on a slide under a coverslip and tap
it; the spore cases will burst open, revealing a number of
somewhat pear-shaped bodies which contain a varying
number of spores inside them. The latter are known

$0

52 Mildews [CH.

as ascospores and the pear-shaped body containing
them is known as an ascus. The wall of the spore case
is composed of a number of polygonal cells, whose walls
cause the polygonal markings on the outside. The
spore cases are formed at the points where the hyphae
touch one another, and each is the result of fertilization.

&:
.
é a

Fig. 18. Mycelium and spore cases of Erysiphe graminis. (Magnified.)

Attached to them are a number of “appendages.” In
the case of Hrysiphe graminis these are simple, un-
branched, short hyphae, but in other mildews they are
longer, often branched, and serve as a useful means
of distinguishing between the different mildews. The
number of asci in each case is also helpful in this way.
The ascospores do not germinate immediately but

Iv] Mildews 53

remain throughout the winter in their cases on the
dead leaves or in the soil.

They are protected from injury due to climatic
conditions by the walls of the spore case. In spring
the. cases burst and the asci are liberated. The walls
of these also split and the ascospores are set free, and
under suitable conditions germinate, sending out a
short tube capable of infecting growing host plants.
They germinate most readily at a temperature of about
50°F. The mycelium which they produce buds off
conidia during the spring and summer. The damage
done by this mildew to cereals in a wet season may
be considerable, arising not only from the food which
the plant gives to the fungus, but also from the
limiting of the work done by the leaves in manu-
facturing food from the air. The normal amount of
light is prevented from falling on the leaf by the
presence of the mycelium. The amount of air which
ordinarily enters the pores of the leaf is also reduced.
The diseased leaves become yellow, and die before
the normal ones, and hence their functions cease
earlier, with the result that the total yield is lower.

The fungus known as Erysiphe graminis com-
prises a number of different varieties; and each one
may be regarded as being distinct from the others,
although no difference has yet been found in their
structural appearance. The different varieties are
distinguished by the plants which they attack. One
variety attacks only wheat, another barley and
sometimes wheat to a very slight extent, another
attacks oats and a related grass. A cereal following
another cereal crop which has been badly attacked by
mildew will suffer no more than if it had followed a

54 Mildews [CH.

clean crop, as these varieties are so specialized that the
one attacking any particular cereal will not attack the
others.

Remedial Measures.

The whole of this fungus is on the outside of the
plant, and consequently we should expect to be able
to keep it in check by the use of a suitable fungicide.
In the case of cereals the difficulties of spraying are
so great that it is not usual to make application of
this kind. Damp shady places should be avoided if
possible as they provide conditions favourable to the
growth and spread of the fungus.

Hop and Strawberry Mildew (Sphaerotheca humult).

This mildew or mould as it is often called belongs to
the ‘true mildews,” and therefore grows on the outside
of its host. In wet seasons it has been known to do
a considerable amount of damage. The first symptoms
of the disease are small light-coloured spots on the
leaves. In damp weather the white mycelium of the
fungus soon appears and begins to spread rapidly. It
also spreads from plant to plant by means of conidia
very similar to those of Hrysiphe graminis. After a
time it becomes a greyish colour. In autumn the
resting stage or spore-cases are formed; these are of
a dark brown colour. The greatest amount of damage
is done when the mildew spreads to the cones. The
reddening of the cones by the spore-cases has given the
name of “red mould” to this stage.

The spore-cases are very similar externally to those
of Erysiphe graminis. Internally they are different as
they contain only a single spore-sac or ascus, as may

Iv] Mildews 55

be ascertained by squashing one under a coverslip.
This fungus also causes considerable damage to straw-
berries. This mildew also lives on several weeds, such
as dandelions, meadow-sweet, and wild geraniums, but it
has not yet been shown that hop plants can be infected
from these weeds.

Remedial Measures.

Its position on the outside of the plant offers easy
means of attacking this fungus. Sulphur in various
forms has proved very useful. There are several
fungicides used against this mildew:

(1) Flowers of sulphur,

(2) Liver of sulphur,

(3) Lime and sulphur,

(4) Bordeaux mixture.
It is important to spray the plant early, i.e. as soon
as or even before the mildew makes its appearance.
Later spraying depends on the weather. All badly
diseased plants should be burnt.

American gooseberry mildew, Sphaerotheca mors-
uvae, is a member of the same genus as the hop mildew.
It is scheduled under the Destructive Insects and Pests
Act, and all cases should be reported to the Board of
Agriculture and Fisheries.

Rose mildew (Sphaerotheca pannosa) which causes so
much trouble to rose growers is a suitable form on which
to try experiments. Watch some rose trees as soon as
the leaves are out for the appearance of mildew and
when it appears treat them in the following manner.

Leave Set I untreated for comparison with Sets IT
and III. Dust the trees of Set II with a coating of

56 Mildews [CH.

flowers of sulphur (the leaves should be damp when this
is done). Spray the trees of Set III with a solution
containing 1 oz. of liver of sulphur to 3 gallons of water.
Watch the trees carefully to see if the sulphur or liver
of sulphur has any bad effect on the leaves or buds, and
also to see if either of them prevents the mildew from
spreading.

CHAPTER V
ERGOT AND CLOVER SICKNESS

Ergot (Claviceps purpurea).

This disease is caused by the fungus Claviceps
purpurea. Its commonest hosts in this country are
rye, rye grass, couch, cocksfoot, and timothy, and it is
found occasionally on wheat and barley. Some of the
grasses, such as the bromes, are not subject to it. The
disease first shows itself at the time when the corn is
ripening or the grasses are dying off. It is often
abundant on the dried heads of roadside grasses. It
appears as long blackish bodies sticking out from the
ears (see Fig. 19). These are called Sclerotia or Ergots.
They are partly covered by the chaff and take the
place of the grain in the flower. The flowers of rye
are much larger than those of the grasses, and the
sclerotia produced in them are correspondingly larger.
In the case of rye the sclerotia are often more than
1 inch in length and about }-} inch in diameter. In
the case of grasses they may be }-3 inch long, and about
vz inch in diameter. The longer ones are usually
curved but the short ones are often straight. They
are hard and have a groove running along one side.

v] Ergot and Clover Sickness 57

In appearance they are not unlike small thin date
stones, but they are rather darker in colour. A cut
across one of them shows that only the outer layer is

Fig. 19. Cocksfoot and rye grass attacked by Claviceps purpurea.

dark in colour, the interior being whitish, resembling
very closely a cut grain of rye. Each sclerotium
consists of hyphae matted tightly together and running
in all directions, so that sections across it in any direction

58 Ergot and Clover Sickness [CH.

have the appearance of circular or oval cells, these
being the cut ends of the hyphae.

Sclerotia sown just under the surface of damp earth
or sand and kept in the open air begin to germinate in
the spring. Small lumps at first form on them and
eventually these take the form of short drum-sticks,
the thickened portions being carried above the ground
(see Fig. 20). On cutting sections these heads are
found to contain a number of flask-shaped cavities in
which are a number of club-shaped bodies known as
asci, which in turn carry eight needle-shaped spores
known as ascospores.

Fig. 20. A sclerotium of Claviceps purpurea which has germinated.

In the ordinary course of events some of the
sclerotia fall to the ground and others are harvested.
Germination of the sclerotia takes place in the spring
in the ground. Some of them fall to the ground
naturally and others are often sown with the seed.
The ascospores are produced about the same time as the
host plants flower. The spores are carried about by
various agencies and some of them reach the flowers
of the host plants. Here they germinate, putting out
germ tubes which penetrate the flowers at their base.
The mycelium formed from the germ tube grows
through the base of the flower and then spreads over
the surface covering the portion which normally

v] Ergot and Clover Sickness 59

forms the grain with a network of hyphae. The free
ends of these become swollen and conidia are formed at
these swollen ends. These are set free and others are
formed at the ends from which they have fallen. The
hyphae also secrete a sticky sugary substance in which
the conidia become embedded. This is known as the
honey dew stage because of the small drops of sticky
substance which are formed. This sugary substance
is very attractive to insects. They carry it about with
them and so transfer the conidia to other flowers.

b

Fig. 21. Claviceps purpurea. (2) Section of fructification showing
(n) the cavities containing asci; d, asci; a, ascospores ; b, germinating
ascospore. (Magnified.) (After Percival.)

A conidium which in this way reaches the flower of a
susceptible plant sends out a germ tube which penetrates
the base of the flower, a mycelium is formed similar
to that of the parent from which the conidium was
formed, and in its turn this very soon produces a crop
of conidia. A considerable number of flowers may
thus become infected from a single sclerotium. A large
number of spores are carried to flowers which they are
not capable of infecting and here they die. The fungus

60 Ergot and Clover Sickness [CH.

forms a large number of conidia so as to increase the
chances of reproducing itself.

After a time the mycelium at the base of the flower
grows to form a compact mass. This is composed of
hyphae woven together and running in all directions,
the outer layer of which becomes darkened. This
developing sclerotium pushes before it the portion of
the flower which forms the grain and also the remains
of the hyphae which bud off the conidia. It then
increases in length and sticks out from the ear providing
an easy means of recognizing the disease.

The sclerotia are formed in an entirely different
way from the smuts and bunt. In the case of these
the fungus spores are formed within the grain. In
the case of ergot the sclerotium is formed from the
mycelium below the grain and the portion which ordi-
narily forms the grain is pushed before it. The remains
of this portion may often be found at the top of the
sclerotium. The sclerotia are the resting stage of the
fungus and serve to carry it through the winter.

This fungus is divided up into several varieties, the
commonest of which attacks rye and several of our
grasses.

The damage done to grasses is very little, but it
may reduce the yield of rye considerably. This direct
amount of damage is negligible compared with the
harm it does when the sclerotia are eaten. They
contain several poisonous substances. Cattle feeding
on infested pastures during the winter often do badly
and become very thin. Sores are often formed on the
teats and mouth, the latter causing salivation. These
symptoms of the poisoning effect have led to its being
confused with the dreaded foot and mouth disease.

v] Ergot and Clover Sickness 61

The poisoned animals often become lame. In very
bad cases the extremities, such as the tail, hoofs, ears,
and teats, may dry up and fall off. Another effect of
feeding on ergot, which is very important from the
farmer’s point of view, is that it often causes abortion
in cows fed on infected pastures.

In Russia and countries where rye bread is eaten
this fungus brings about the above ailments in human
beings and a number of lives have been lost through it.

If the sclerotia are kept for some time they gradually
lose their poisonous properties.

Remedial Measures.

The sclerotia of this fungus are often present as
impurities in seeds. They are sometimes mistaken for
rats’ droppings, but by breaking them it is easy to dis-
tinguish between the two as the sclerotia are whitish
inside. All seeds should be carefully examined and
any ergot present should be screened or picked out.

This disease is not noticed in its earlier stages, as
it works hidden away under the chaff of the grasses
or rye. When noticeable the sclerotia are already
formed. In the case of infected pastures cattle should
be taken off immediately and the grasses which have
seeded should be cut, collected, and then burnt. After
this the pasture must be regarded as an “ergoted”’ one
and grasses should not be allowed to go past the
flowering stage. If they are cut just as the flowers
are forming the fungus is kept down considerably as
the sclerotia are prevented from forming. At the
same time those in the hedges must be cut at the
flowering’ stage.

62 Ergot and Clover Sickness [cH.

Meadow hay is perfectly safe for cattle as the ergot
does not form for some time after the stage at which
the grasses are cut. The grasses in the hedges and
roadsides should be cut and burnt in late autumn.

.

Fig. 22. A clover plant attacked by Sclerotinia trifoliorum; white
sclerotia are present at the top of the root. Later on these sclerotia
become black.

Clover Sickness.

The dying off of clover, known as “ clover sickness,”
is intimately associated with two organisms—one a
fungus known as Sclerotinia trifoliorum, the second
a small eelworm known as Tylenchus dipsaci (see
p. 166). The two are often found together attacking
the same plant. The disease is usually noticed first on
young clover in the autumn. Mild weather seems to be

v] Ergot and Clover Sickness 63

the most suitable for the fungus. It has been found on
red, crimson, white, alsike clovers, and on beans, lucerne,
sainfoin and black medick. It causes much more
damage to red clover than to the others. The shoots
of the attacked plants droop, the leaves turn brown
and usually become matted together in a rotting mass.
This state of affairs spreads from
plant to plant in suitable weather.
Small black irregular bodies, some-
thing like rats’ droppings, are found
on the stems or roots or on the
soil. These are the sclerotia or
resting stage of the fungus .They
consist of a dense mass of hyphae
(see Fig. 22). When kept in damp Fig, 85. Seleraiinte wi.
earth in the open air they even- Poliorimi& eolerctinm
tually send up small brownish which has germinated
saucer-like bodies on the ends of andproducedasaucer-
stalks of varying lengths (see Fig. 23). en acy ae
Near the upper surface are situated Massec:)

a number of asci, each of which

contains eight oval ascospores. In nature these asco-
spores germinate and produce a mycelium which enters
the clover plant, ramifies throughout the stem and
leaves, and kills them. After a time this mycelium
forms sclerotia.

Remedial Measures.

There is no evidence that the disease is ever carried
by the seed. If the disease occurs in small patches,
the plants on these patches should be dug up and burnt
to destroy the sclerotia and prevent the disease from
spreading. These patches may then be resown. The

64 Ergot and Clover Sickness [cH.

sclerotia are only capable of living for four or five years.
After an attack of the disease an interval longer than
this should therefore be allowed to elapse before clover
is sown again. Meantime the land should be kept
free from leguminous weeds.

CHAPTER VI
RUSTS

The group to which rusts belong, known as the
Uredineae, is very widely distributed, in fact some of
its members are present in all parts of the world where
plants are cultivated. The term “rust” in its popular
sense includes all diseases which cause a rusty appear-
ance of a green plant. From a farmer’s point of view
they are extremely important, as they bring about a
considerable loss in his cereal crop every year. They
are characterized by giving rise to several different kinds
of spores, some having as many as five different kinds.
Another peculiarity of certain members of the group
is that some of these spores may be borne on one host,
and other spores of the same fungus on an entirely
different host. There are a number of rusts which
attack our cereals, most of them belonging to the
genus Puccinia. The differences between them are
chiefly concerned with the number of kinds of spores,
their characteristics, and whether they are all or only
in part produced on the cereal host. A description of
two of the more important species will help to give
some idea as to what rusts are.

Puccimia graminis. The popular name of this

vi] Rusts 65

fungus is black or orange rust of wheat, and it appears
commonly in wheat fields in late spring or early summer.
The leaves of the wheat first of all lose their character-
istic green colour and become slightly yellowish.
Dark orange patches are then formed on them, and are
found between the veins of the leaf or on the stem.
This is the first spore stage that the fungus produces
on wheat and it is this which gives the popular name
of rust.

Examination with a lens shows that these patches
are composed of a number of minute bodies or spores
clustered together, and that they are partly covered at
the sides by the colourless skin or epidermis of the
wheat leaf. They are known as uredospores or summer
spores (see Fig. 24). On shaking the leaf some of them
fall out as a powder. They are ovoid in shape, the
coat or wall being of moderate thickness and covered
with a number of very short blunt spikes. Midway
between the apex and the point of attachment are
some thin places in the wall. A section through one
of the orange patches shows that each spore is borne
on a short stalk (see Fig. 24). The mycelium which
produces them does not extend throughout the whole
plant, but is confined to small areas near the spores.
It consists of a dense web of very fine hyphae growing
in the spaces between the cells. Small tubes or
haustoria grow into these cells for the purpose of
obtaining food. The hyphae have occasional transverse
walls. If the uredospores are placed in a hanging drop
under suitable conditions for germination they send out
tubes through the thin places in their walls (see Fig. 24).

One of these usually grows much longer than the
others and branches. An uredospore falling on a blade

P.F. 5

66 Rusts [CH.

Fig. 24. Puccinia graminis. (1) Uredospore stage on wheat; (2) uredo-
spore stage highly magnified; (8) uredospore stage very highly
magnified; (4) uredospore germinating; (5) teleutospore stage on
wheat; (6) teleutospores; (7) a teleutospore germinating; (8) aecidio-
spore stage on barberry leaf; (9) aecidium cup showing the chains
of aecidiospores; (10) two aecidium cups. (After Massee.)

vi] Rusts 67

of wheat germinates in the same way. When the germ
tube reaches a breathing pore it enters and so infects
the plant. The mycelium from an uredospore is said
to produce fresh uredospores in about 7-10 days.

These are continually produced throughout the
summer. In late summer we shall notice that the
appearance of the rust changes. The leaves look
darker and on closer examination this is seen to be
due to the production of dark brown or nearly black
spores together with the orange coloured ones. After
a time the latter disappear and the straw is now
marked with black lines, due to the long patches
which are placed one above the other in the soft tissue
between the veins. It is this stage that gives the name
of black rust to the fungus.

The black spores are not of the same kind as the
orange coloured ones and are not derived from them
by change of colour. They are known as teleutospores
or winter spores, and are produced from: the same
mycelium which gave rise to the uredospores. After
successive crops of the latter the fungus suddenly starts
to form teleutospores, and so we get the change from the
orange to the black colour. A teleutospore is almost
twice as long as an uredospore and is divided into two
almost equal cells by a thick partition across it. Its
walls are very thick and smooth (see Fig. 24). They
take much longer than the uredospores to germinate
and on doing so each of the two cells sends out a tube
from its upper part. This becomes divided into three
or four cells by cross partitions; from each of these a
short tube grows out and becomes swollen at the end,
and eventually cut off as a small spherical body,
known as a secondary spore (see Fig. 24).

5—2

68 Rusts [CH.

The fungus has now reached the stage when it
leaves the wheat plant and seeks a new host. Before
its life history was known it was held by farmers that
barberry hedges caused the wheat near them to become
rusted. This story aided de Bary in following out its
further development. He found that it was possible
to infect the barberry plant by means of the secondary
spores formed from the teleutospores. He also found
that the fungus produced on the barberry had a totally
different appearance from the rust of wheat which
produced it, but on infecting wheat with the spores
from the barberry it became rusted. Two kinds of
spores are produced on the barberry but only one of
them takes part in the reproduction of the fungus.
These are known as aecidiospores, and are borne in
a chain-like manner. A series of these chains is
enclosed in a kind of ball near the lower surface of the
barberry leaf. After a time the ball bursts and a
kind of cup is produced which can be seen with
the naked eye (see Fig. 24). The aecidiospores are
yellowish, spherical, and almost as large as the uredo-
spores. On germination they send out a simple tube
which is capable of infecting wheat. The aecidium
cups appear on the barberry in the early spring. This
is not a case of one fungus giving rise to another fungus
as the aecidiospores cannot infect other barberry
plants. The different spores are stages of the fungus
Puccinia graminis.

The damage done to the wheat plant consists in
reducing the yield, as some of the food which should
have gone to swell the grain is taken by the fungus, and
the amount of food manufactured is lessened by the
destruction of some of the chlorophyll in the leaves and

vi] Rusts 69

stem. In very bad attacks the grain may become
shrivelled.

In cases of attacks by some of the fungi which live
alternately on two hosts it is possible to reduce the
amount of damage by the removal of one of the host
plants. In the case of Puccinia graminis this plan does
not succeed. In Australia there are no barberry bushes
and no plant has been found on which the aecidium
stage occurs and yet this fungus survives and does
considerable damage. This is also true of certain
parts of England. In this case it is supposed that the
uredospores live until the next season’s crop is growing
and then infect it. It is possible that the mycoplasm
hypothesis put forward by Eriksson in which he states
“that the germ of the rust is present in the seed of the
host plant” may have some foundation, but it is not
usually accepted. This fungus has several different
varieties which all appear the same under the micro-
scope, but each will only infect certain host plants.
That usually found on oats will not attack wheat or
barley. That found on wheat, however, is occasionally
found on oats and barley.

From our point of view the Puccinia graminis
attacking our cereals may be divided into three different
varieties: (a) usually attacks wheat and occasionally
barley, oats and rye; (b) usually attacks barley, rye,
couch grass, and other grasses, but does not attack
wheat and oats; (c) usually attacks oats, tall oat
grass, and cocksfoot, but not wheat, barley or rye.

There are other varieties which attack grasses but
do not attack cereals.

70 Rusts. (cH.

Puccinia glumarum.

This species, known as yellow rust, is the commonest
form of rust found in this country. It may be readily
distinguished from Puccinia graminis by the uredospore
stage. In this case the uredo patches or sori are orange
yellow instead of dark orange coloured as in Puccinia
graminis and most of the other rusts. The sori are
smaller and are often united with their fellows, making
them appear as lines on the leaf and stem; they are
usually present in larger numbers. The uredospores
themselves are more rounded, but otherwise they are
very similar. The teleutospores are produced in smaller
sori, and the deep gaping wounds of Puccinia graminis
are never present. They are also much shorter and
appear more like black dots than lines.

No aecidiospore stage has been found and no
alternate host. The uredospores and teleutospores
germinate in a similar manner to those of Puccinia
graminis, and the uredospores probably carry on the
disease from one season to another. The yellow rust
of wheat cannot be distinguished from the yellow rust
of barley under the microscope, but by experimenting
it has been found that barley cannot be attacked by
yellow rust of wheat, neither can wheat be attacked
-by yellow rust of barley. From our point of view this
fungus may be divided up into a number of species
each of which has its particular host or hosts.

There are numerous other rusts besides the two
described, some of which possess all the spore stages
and others only one or some of the stages; the differ-
ences are very similar to those of the two species
described.

vi] Rusts 71

Remedial Measures.

All attempts to check rust by spraying and treat-
ment of seed have failed entirely. The cereal plants
do not lend themselves to spraying as the nature of their
leaves is not suitable for holding the spray, but rather
the contrary. It is chiefly with yellow rust of wheat,
as being the commonest, that work is being done to
help the farmer.

The susceptibility of wheat varies very largely
among the different varieties. Some are practically
immune, but these are either bad yielders or of poor
quality. Biffen has found it possible to cross a heavy
yielding variety susceptible to yellow rust with one that
is immune and to pick out from the offspring a variety
with the cropping power of the susceptible variety and
the immunity of the other.

Wheat immune to yellow rust may be susceptible
to other rusts.

On crossing a wheat which is susceptible to yellow
rust with a variety which is immune from that rust,
the whole of the plants derived from the seed produced
are readily infected. On sowing the seed from these
rusted plants it is found that although the majority
of the plants produced are infected, about one-quarter
of them are free from it. Of these a certain proportion
possess the high yielding property of the original
rusted parent together with the absence of liability to
rust.

On growing these wheats the plants produced are
all practically immune from the yellow rust. In this
way a wheat known as Little Joss was produced by
crossing Square Head’s Master with a wheat immune

72 Rusts (CH.

from yellow rust and known as Girka. Little Joss is
immune from rust and has a rather higher cropping
power than the high yielding parent Square Head’s
Master. This increase of yield in the Little Joss over
Square Head’s Master is probably accounted for by
the rust preventing the latter from yielding as high as
it would do if it were not rusted. Little Joss is immune
only to yellow rust.

It is to crossings of this kind that we look for
assistance in helping to prevent the rust fungi from
taking their yearly toll from our cereal crops.

Beet root Rust. The rust which attacks mangolds,
beetroot, and sugar beet does not belong to the same
genus as cereal rusts. It is known as Uromyces betae.
It also occurs on wild beet.

The three stages are found on the same plant and
it differs from Puccinia in that the teleutospores or
winter spores are single-celled.

In spring the yellow aecidium cups may be found
on the leaves. In summer the brown patches of
uredospores are present and in autumn these change
to a dark brown colour caused by the teleutospores.
This disease is most prevalent in crops manured with
too much nitrogen and not enough potash as is well
shown on the mangold field at the Rothamsted Experi-
mental Station. Diseased leaves should be collected
and destroyed.

Pea Rust is caused by Uromyces pisi. The aecidio-
spore stage occurs on a wild spurge.

Bean Rust is caused by Uromyces fabae.

vit] Smuts 73

CHAPTER VII
SMUTS

On walking through a cornfield just before the grain
is ripe here and there black ears, known as smuts
or Black Heads, may be noticed, as they are easily
seen by contrast with the colour around them. The
blackening of these ears is caused by various fungi and
it is from this black colour that they derive their
name “‘smuts.”” They may be found on barley, oats,
wheat, and also on a number of grasses. There are
many kinds, most of which belong to the genus Usitilago.
A host plant may have more than one species capable
of attacking it, but each smut has its own particular
host. Those attacking barley cannot infect the oat
plant, neither can those found on oats attack barley.

In place of the grain which is present in a healthy
plant, the blackened ears contain a dark brown powdery
mass (this powder is very dark and causes the ears to
look black). It consists of a large number of almost
spherical bodies, which are the spores of the fungus.
The development of these can be watched in a hanging
drop of water. After a time a small germ tube is
sent out. This does not grow very long but becomes
divided up into four cells by three cross walls.

From the upper portion of each of these cells a
process is given off, which eventually becomes divided
from the cell producing it. These are secondary
spores and in such places as manure heaps, where food
supply is abundant, they increase in number by
budding, but it is sufficient for our purpose to know
that the plants are infected by means of these.

74 Smuts [cH.

If grains of oats taken from a badly smutted field
are sown, some of the resulting plants will be smutted
and others quite clean. At the various stages of
growth very little difference is noticeable between the
plants which will produce healthy and those which
will give smutted grain until well on towards harvest.
The infected plants are said to be more robust and
usually taller. When the grains are beginning to
form some of the ears show a darker appearance, and
as they ripen become blacker until a stage is reached
when the ears seem to be making soot instead of
grain (see Fig. 25).

In looking for a suitable means of dealing with
the smuts it is very important to know how the
plant is first attacked. Barley, oats, and wheat show
differences in this respect.

When infection

Host. Fungus. Common name. takes place.
A. Barley Ustilago hordei | Covered smut of barley
( 5 avenae Loose smut of oats ...| At seedling
Oats . ,, levis or Covered smut of oats ... period.
kolleri :
B. Barley Ustilago nuda Loose smut of barley ... | At flowering
Wheat ; tritict Loose smut of wheat ... } period.

These fungi are very similar in structure and at
one time were considered to be the same. Experiments
have shown that under no circumstances can either
produce any of the others, thus indicating that they
are all distinct forms.

Loose smut can easily be distinguished from covered
smut as its spores come out of the grain and often
leave the stem of the ears bare, whereas in covered
smuts the spores remain in the grain on the ears.

vit] Smuts 75

In the case of the covered forms a large number
of the smutted ears are harvested with the sound ones.
On threshing the smutted grain is broken and the spores

+f

¥
¥

Fig. 25. Oat plants attacked by Ustilago avenae.

are spread to the sound grain. With loose smut of
oats the spores are blown about by the wind from the
time that grain is ripening until harvest. A number
of them settle on the chaff of the oat flower when it
opens, and on harvesting these get on the grain. In

76 Smuts [CH.

the case of group A the spores are sown with the
grain. Conditions which favour the germination of
the oats and barley apparently favour the germina-
tion of the spores. The secondary spores formed
from these produce germ tubes which make their way
into the shoots of the seedling plants. It has been
shown that the fungus can only obtain an entry into
the plant at a very young stage. When the leaves
have pushed their way through the leaf sheaths the
shoots become hardier and spores cannot enter.

On entering the plant the germ tube, or as it is
now called the mycelium, makes its way to the growing
point of the shoot. It takes its food from the cells of
the plant but does not kill them as in the case of the
potato disease; consequently there are no external
signs that the plant is being attacked. As the oat
grows in the spring the mycelium grows with it and
is to be found in the region of the growing point, but
not in the older parts of the plant. By maintaining
its position at the growing point it is able to pass out
into the new shoots as these are all formed there.
In this way all the flowering shoots of the attacked
plant are usually infected and practically all the
grains of an infected ear are smutted.

When the plant is supplying the grain liberally
with food stuff and so causing it to swell the mycelium
grows rapidly and a dense network is formed within
the grain. The spores are formed inside the tubes of
the mycelium and set free as a powder.

The loose smut'of wheat appears at the time of
flowering. The coverings which enclose it burst about
this time and the black spores are blown about by the
wind or washed to the ground by rain. Soon nothing

vit] Smuts 77

remains but the main stalk or rachis of the ear which
usually has a certain amount of smut adhering to it.
Some of the spores reach the stigmas of wheat flowers.
Here a germ tube is produced which grows through the
style much in the same way as the tube from a pollen
grain. Eventually the tube reaches the developing
seed. The grain so infected ripens normally and can
in no way be distinguished from a non-infected grain.
When these grains containing the smut mycelium are
sown the ears of the plants which they produce become
smutted and spores are blown about to infect fresh
plants. The mycelium maintains its position at the
growing point as described above. The loose smut
of barley has a similar life history. The weather
plays a big part in the prevalence of the loose smuts.

If at the time the spores are forming there is a lot
of rain the majority of them are washed to the ground,
with the result that fewer grains become infected and
less smut is produced in the following season.

Remedial Measures.

In the life history of the smuts we have seen that
they may be divided into two classes: (a) those which
infect at the seedling stage; (b) those which infect at
the flowering stage. The treatment will therefore be
different in the case of these two groups.

In both the disease is spread from smutted ears,
and consequently in choosing seed corn we shall do
well to obtain it, if possible, from fields which contain
no smut. This does not ensure our crop from attack
as the smut may have blown from neighbouring
fields, but seed from a clean field usually produces
considerably less smutted ears than that from a

78 Smuts [CH.

smutted field unless measures are taken to kill the
spores.

In the case of group A, which attacks the host at
the seedling stage, the spores are sown with the grain.
Lines of procedure consist in employing some method
which will kill the spore and not injure the grain.
Numerous experiments have been carried out with this
object in view, and from them the following methods
have been shown to give satisfactory results.

In Method 1 blue stone (copper sulphate) is used to
kill the spores. A clean wooden or concrete floor is
best for this treatment. A sack (i. 4 bushels) of
grain is emptied on this floor. The copper sulphate
solution is made by dissolving 1 Ib. of copper sulphate
in 1 gallon of soft water. The grain is then thoroughly
moistened by turning it over and watering it with this
solution. It should be turned several times and
allowed to stand for about 10 hours. It is then spread
in a thin layer until dry, when it is fit for sowing.

Another way of using copper sulphate is to dissolve
about 2 Ibs. of it in 10 gallons of water and pour the
grain into this, leaving it there for about 14 hours. The
copper sulphate is then run off, and the grain is spread
to dry. This method kills the smut spores, but it also
hinders the germination of the grain, especially of oats
and barley, and should not be used for them. The
loss is said to be lessened by watering with milk of
lime, or dusting with lime after treatment.

Any seed left over after sowing should not be
used for feeding purposes as the copper sulphate is
harmful.

In Method 2 commercial formaldehyde is used to
kill the spores. It contains nearly 40 per cent.

vit] Smuts 79

formaldehyde. One pint of it is mixed with 30 gallons
of water. The grain is then put into a sack or sieve
and placed in the solution and continually moved about
for 10 minutes. It is then spread to dry as rapidly as
possible. The same strength of formaldehyde is often
used to sprinkle on the grain in the same way as with
copper sulphate. This method does not injure the
germination so much as treatment with copper sulphate,
and may be used for oats and barley. Treated grain
if properly dried may be fed to fowls.

In Method 3 warm water is used to kill the smut
spores. Two tubs, several buckets, and a supply of
hot and cold water are required. It is essential that
an accurate thermometer be used. Hot and cold water
are put into the two tubs. The temperature of the
water in Tub 1 should be about 125° F., and in Tub 2
132° F. (not below 130° F. and not above 135°F.). The
grain is placed in a fine wicker or gauze basket or in a
sack and moved about in Tub 1 for 2 or 3 minutes. It
is transferred to Tub 2 and kept there for 5-8 minutes,
and then shot on a raised piece of canvas and sown as
quickly as possible or dried rapidly.

Hot water must be added to the tubs from time to
time to keep the temperature correct. Care must be
taken that it is not poured directly on the seed.

A temperature of 132° F. is sufficient to kill the
smut spores, but it does not injure the grain.

This method is very efficient and cheap, but it has
the disadvantage of requiring. a certain amount of
accuracy and care in keeping the temperature correct.
If the temperature is too high the grain will not ger-
minate, and if too low the smut spores are not killed.

After treatment with either of these methods the

80 Smuts [cH.

corn must be put into clean sacks or bins. Sacks may
be cleaned by boiling or the bins by washing with a
solution of formaldehyde. The grain must not be
allowed to freeze if it is at alldamp. If sown immedi-
ately after treatment a larger bulk will be required, as
it will be somewhat swollen.

Get 100 oat grains which have been grown in a
field almost free from smut; and also some smutted
ears of oats (either loose or covered smut). Shake up
80 of the grains with the smutted ears so that the
oats become covered with the smut spores. Treat the
infested grain as follows: (1) twenty with copper
sulphate as described in Method 1; (2) twenty with
formaldehyde as described in Method 2; (3) twenty
with hot water as described in Method 3.

Now sow the 100 grains in pots, making five sets
of twenty plants. Set (1) uninfested and untreated;
(2) infested and untreated; (3) infested and treated by
the copper sulphate method; (4) infested and treated
by the formaldehyde method; (5) infested and treated
by the hot water method.

The plants should be examined in all stages and
any differences, such as time of appearance above
ground and size of plants, should be noted.

We shall expect to find that Sets 1, 3, 4 and 5 are
free from smut and that all the ears of the plants in
Set 2 are covered with smut.

This experiment shows that oats can be infected
with smut from spores on the grain but that these
spores can be killed with little harm to the grain by
either of the three methods used.

Now take some wheat grains and cover them with
loose smut of wheat and sow them as before. These

vit] Smuts 81

grains grow perfectly free from smut as the loose smut
of wheat is incapable of infection at the seedling stage.

The public threshing machine is a great friend of
those smuts which infect at the seedling stage, as it
serves to spread them from one farm to another. When
smutted corn is threshed the next lot that goes into the
machine will be infected unless the thresher is cleaned.
If used it should be thoroughly cleaned beforehand.
The drill should also be thoroughly cleaned.

In the case of the group B the smut fungus is
already present in the harvested grain, having got in
at the flowering period. Dressing the grain as for
group A is not a prevention as the steeps cannot reach
the fungus. A modified hot water method has been
found which kills the fungus and at the same time does
little damage to the grain. This method consists of
soaking the seed for about 6 hours in cold water and
then putting it for 10 minutes in water at 130° F. The
soaking in cold water apparently affects the fungus in
such a way that the hot water kills it.

These two smuts are present in most of our wheat
and barley fields to a much greater extent than the
covered forms, as the latter are usually prevented by
one of the three methods given above.

Bunt or Stinking Smut.

Wheat is the only cereal which suffers from this
disease. The diseased plants are very similar to healthy
ones until the approach of harvest. On passing
through a wheat field, containing plants which are
bunted, by observing closely we shall be able to note
that in some of the ears the wheat grains are visible.
These bunted grains are swollen and cause the glumes

P. FE. 6

82 Smuts [CH.

or chaff to gape. Their appearance varies with the
different varieties of wheat. In most it is short,
swollen, and almost spherical. In some, however,
instead of shortening it becomes longer. The groove
is never so pronounced as in healthy grains and in
some cases is very shallow. The bunted ears are
usually darker as the grain is greyish or greyish black.

By rubbing an infected grain between our fingers,
we shall be provided with the means of recognizing this
disease on future occasions. It gives off a very dis-
agreeable odour—somewhat resembling stinking fish—
which clings to the fingers for some time.

It does not attack the chaff but only the interior
of the grain. The coat of the grain is not broken, and
inside are many dark-brown spores. There are two
species of bunt, Tilletia caries (see Fig. 26), which
has rough spores, and Tilletia levis, which has smooth
spores.

In many cases all the spores are rough, indicating
the presence of Tilletia caries, but in some cases the
smooth spores of Tilletia levis may be mixed with
them and in a few cases all the spores may be
smooth. As these two species behave in a similar
manner, we shall confine ourselves to the former.
The spores are almost spherical and their surface has
a rough, warty appearance. They are very small,
being about ;,4, of an inch in diameter. In the case
of this fungus the diseased grains are harvested with
the good ones and on threshing some of them are
crushed with the result that the spores get on the sound
grain. When this wheat is sown the spores germinate,
and eventually the young wheat plant is infected. The
brown spores yield a crop of secondary spores, and these

vir] Smuts 83

in their turn give rise to tertiary spores from which an
infection tube is produced. It is sufficient for our
purpose to know that the spores adhering to the wheat
grain germinate and eventually infect the young wheat
plant. They are said to retain their capacity for
germination for seven or eight years. When the young
plant is infected the mycelium grows as in the case of

os

Fig. 26. Spores of Qilletia caries as seen under a microscope.

Ustilago, without killing the cells of the host, and the
spores are formed within the mycelium. Usually all the
grains of the attacked plants are filled with spores. The
damage done by this pest is not only the loss of yield due
to the damaged grain for this is only small in proportion
to the total, but on grinding wheat which is infected the
flour has a dirty appearance and the peculiar odour of
6—2

84 Smuts (CH.

the fungus is very noticeable. It lowers the price of
the flour even if present only in small quantities, and
is sometimes sufficient to render it unsaleable. There
is no evidence of infected grain causing any damage
when fed to stock.

Remedial Measures.

The three methods given above for the treatment
of smuts are also effective in keeping down bunt, and
one of them should always be used. The precautions
given above should also be closely followed.

The experiment with smut of oats should be
repeated, using wheat grains for sowing and bunted
grains to infect the clean grains with the spores of the
bunt fungus.

PART Il

CHAPTER VIII
INTRODUCTION TO INSECTS

We have dealt with some of the plant diseases
caused by fungi and will now turn our attention to
those caused by members of the animal kingdom.
By far the greater number of these diseases are due to
the ravages of insects.

Popularly most small animals such as flies, beetles,
butterflies and spiders are considered as insects.
Scientifically animals are classified into groups accord-
ing to their structural characteristics. The following

VIII] Introduction to Insects 85

characteristics distinguish insects from other animals:
the bodies of the adults are divided into three parts,
the front known as the Head, the middle as the Thorax,
and the hind portion as the Abdomen.

The head bears : (1) The eyes, which may be (a) simple
or (6) compound eyes, composed of what look like a
large number of hexagonal cells. (2) The antennae or
feelers, which vary considerably in different insects,
and may be simple pointed rods or may possess knob-
like or feathery endings. (3) The mouth, which is an
opening below or in front of the head around which are
grouped the jaws. These are fashioned according to
the functions which they are called upon to perform.
In biting insects they work horizontally and not up
and down as in the case of higher animals.

The thorax or middle portion of the body is divided
up into three rings or segments, each bearing a pair of
jointed legs. Both the second and third segments
usually bear a pair of wings, a marked feature of the
group. In flies however only the first pair are present
on the middle segment, the third bearing the remains
of the second pair which are used as balancing organs
(see Fig. 45). In some species, e.g. certain ants and
springtails, no wings are present, but other characters
resemble those of other members of the group. It is
therefore correct to classify them as insects.

The abdomen, usually the largest portion of the
body, is composed of a number of segments which
closely resemble one another. They have no append-
ages except in certain cases at the hind end of the body.

Unlike the higher animals insects have no internal
skeletons to support and protect their bodies, but the
outside is covered with a horny substance known as

86 Introduction to Insects [CH.

chitin, which serves the same purpose. Insects do
not breathe in the same way as the higher animals,
that is to say they have no lungs into which they draw
air through a special opening. They have, running
throughout their bodies, a number of air-tubes known
as tracheae, which give off numerous branches serving
the same functions as the lungs, their exterior openings,
at the sides of the segments, being known as spiracles.

Differences in such parts as wings, mouth parts,
antennae, legs, and eyes, etc., help us to distinguish
one insect from another.

The above characters also enable us to decide
whether the animals under observation are to be
classed as insects. Examination of a butterfly shows
that it possesses all the above characteristics and
therefore must be classified as an insect. If the animal
we are examining is a spider we find that its body is
not divided into three parts, that the adult form has
four pairs of legs and that it possesses neither wings
nor feelers. These and other characteristics have
caused spiders to be put into a different group.

An insect differs very considerably from most of
the higher animals in its structure and appearance at
the time of its birth as compared with its adult stage.
When a calf is born or a young chick hatched each is
very similar in appearance to its adult form, only very
much smaller. In the case of most insects this is not
so. On hatching from its egg it has few of the adult
characteristics. It passes through several changes
during its life, its appearance at one stage being very
different from that of the other stages. A description
of the life of a typical insect will help us to understand
these changes.

vill] Introduction to Insects 87

Most of us know the common large white butterfly
which flies about gardens and fields during the summer.
It is called the Large White Cabbage Butterfly, its
scientific name being Pieris brassicae (see Fig. 27).
If we watch this butterfly closely we shall see that it
sometimes settles on a cabbage or a turnip or some
allied plant and remains for a considerable time under-
neath one of the leaves. If we wait at some distance
until the butterfly flies away of its own accord and then
examine the leaf on which the butterfly has been, a
number of very small yellowish bodies arranged in a
cluster may be found. They are almost skittle-shaped
and marked by: longitudinal ridges (see Fig. 27a).

In about ten days these disappear and are replaced
by a number of small green worm-like creatures known
as caterpillars. The small yellow bodies are the eggs
of the butterfly, and were laid by the female. The
small green caterpillars hatch from the eggs, eat the
empty egg shells, and then begin to feed on the leaf,
leaving marks where they have been feeding. They
grow rapidly, but after a time growth ceases as
the hard chitinous skin only allows of a certain
expansion. At this stage the caterpillar fixes itself
on a small silken web and a new skin is formed under
the old one, the latter bursting and allowing the
caterpillar to crawl out. It again grows rapidly and
the new skin hardens. This process of casting the
skin is repeated four or five times and allows the
caterpillar to grow to a considerable size. When fully
grown it measures about 2 inches or more in length.
It is bluish green above and yellow below, having a
long yellow line along its back, and also one along
each side. These are broken by a number of black

88 Introduction to Insects {CH.

Fig. 27a. Eggs of Pieris brassicae.

Fig. 276. Caterpillar of Pieris Fig. 27¢c. Pupa of Pieris brassicae
brassicae. with butterfly emerging.

Fig. 27d. Pieris brassicae (female).

vir] Introduction to Insects 89

spots. The whole surface is covered with fine hairs.
The body consists of a distinct head and thirteen
segments. The head is of a dirty brown colour with
black spots. Each of the three following segments
bears a pair of jointed legs. The third, fourth, fifth
and sixth, and also the last of the abdominal segments
bear a pair of false legs each. These are simple protru-
sions from the lower surface of the body (see Fig. 27 b).
The stage after the egg—in this case the caterpillar—
is known as the larval stage and the young insects—
caterpillars—are known as larvae.

When fully grown the caterpillars usually leave the
cabbage and wander off to sheltered places where they
change into the next stage. Here the caterpillar
forms a silken web-like platform, fixes itself by its
tail head downwards, or horizontally, also placing a
silken thread round the middle of its body as additional
support. Its skin is then cast, and eventually a hard
body is formed incapable of movement except of its
tail. This is the Pupa or Chrysalis stage, and is very
different from the caterpillar (see Fig. 27c). It is about
an inch long, of a pale green colour, spotted with black,
and angular. The divisions into head, thorax and
abdomen can be roughly determined. After about a
fortnight the adult butterfly comes out. This stage is
known as the Imago stage. The adult—as is also the
case with other insects—does not grow, a small fly
never becomes a large one.

The front wings of the adult butterflies are white on
their upper surface with a black crescent-shaped patch
at the tip of each. The females may be distinguished
from the males by the presence of two black spots in
the middle and a small black patch at the hind edge

90 Introduction to Insects (CH.

of these wings. The under surface is white with a
yellow tip and in the case of the female it has two
black spots as on the upper surface (see Fig. 27d). The
hind wing is white on the upper surface with a small black
patch on the front edge. Underneath it is yellowish.
The colours of butterflies and moths are due to the
presence of numerous scales.

After pairing the female proceeds to lay her eggs
on a plant on which the caterpillars can feed. This
butterfly has at least two broods every summer, that
is to say the butterflies formed from the eggs laid in
early summer give rise to caterpillars in the same
summer. In favourable seasons three broods are formed.
While in the caterpillar stage this insect is liable to
attack from various enemies. Birds and wasps kill
a considerable number. I have seen a single wasp kill
five in half-an-hour. They are also attacked by a
small ichneumon wasp which by means of a piercing
organ lays its eggs in the body of the caterpillar. The
young larvae hatching from these eggs feed on the
inside of the caterpillar, thus causing its death, and
eventually come out and form little yellow bodies or
pupae (see Fig. 28). These bodies, which are falsely
known as caterpillars’ eggs, should not be destroyed for
they develop into wasps which lay eggs in other cater-
pillars and prevent them from forming butterflies.

In gardens the caterpillars can be prevented from
eating cabbages by searching for and destroying the
eggs in July and August. As the eggs are laid in
groups this is not very difficult. Any caterpillars
which hatch out may be destroyed at the same time.

Most insects are similar to the cabbage butterfly in
that they are derived from eggs. The old idea that

VII1] Introduction to Insects 91

insects may be derived from putrefying matter may
easily be shown to be wrong by keeping such material
as putrefying meat so that insects cannot get near it.
If however the meat is kept so that insects can reach it,

Fig. 28. A cabbage leaf bearing the cocoons of an ichneumon
wasp. (These cocoons are falsely called caterpillars’ eggs.)

they will lay their eggs there, and from these maggots
will be formed, and eventually flies.

The passage through these changes from the time
they are laid as eggs until they become winged forms
is known as the transformation or metamorphosis of
insects. Three different stages of metamorphosis are
found in all butterflies and moths and also in a large
number of other insects.

92 Introduction to Insects

[CH.

In flies the stage after the egg is usually known as

a Maggot.
example.

Those on fly-blown meat will serve as an
These eventually change into brown packet-

like bodies known as puparia, pupa-cases or cocoons,
and it is from these that the adult flies emerge.
In their first stage beetles are popularly known as

Grubs.

The wireworm is one of the best known. It

changes into a resting pupa stage from which the
adult beetle is formed.

We often find insects in one stage only at one
time so that it is important that we should be able to
recognize them in all stages.

The following key gives a rough means of dis-
tinguishing the three large groups:

Butterflies
and moths
A caterpillar pos-
sessing a distinct
head, 3 pairs of
jointed legs, 1-4
pairs of false legs on
abdomen, 1 pair of
false legs atthe hind
end of the body.
; The appendages
3 |and wings are en-
Bi cased. The tail is
” ringed and capable
of movement.
Two pairs of
wings covered with
scales are present.

Flies.

A maggot. No
legs. No distinct
head. Anterior end
narrow, possessing
a pair of dark jaws
(some ~ fly larvae
have distinct heads,
e.g. leather jackets).

Entirely enclosed
in a case or cocoon
(in the case of the
leather jacket it has
no case).

One pair of wings
is present. The
position of the
second pair is
marked by “bal-
ancers.””

Beetles.
A grub possessing
a distinct head, 3
pairs of jointed legs
or none. No false
legs.

Appendages and
wings free.

Two pairs of
wings are present:
those of the outer
pair are horny and
do not overlap.

N.B. The larvae of certain sawflies closely resemble caterpillars but
they possess more than four pairs of false legs on the abdomen.

vir] Introduction to Insects 93

In some insects such as aphides (green fly) and
cockroaches, the young on hatching resemble the adult
forms very closely—the difference being chiefly one of
size.

The first consideration in dealing with pests
attacking crops is to find out what insect is causing us
trouble. Our knowledge of the different stages should
help us considerably in at least finding out whether
it is being caused by a butterfly, a fly, or a beetle.

The time taken by an insect to go through its
different changes varies according to the species. In
the case of wireworms and chafer beetles several years
are required from the laying of an egg until the time
when the insect formed from this egg commences egg
laying. In some cases, such as the garden chafer, the
insects have one brood every year, in others, such as
the frit fly, several broods in the year, whilst green
flies may have new broods every week.

The length of life of any one stage varies according
to the species as does also the stage in which the
damage is done. Often the larval stage only is respon-
sible for this: in other cases it is done both in the larval
and the adult stage, and occasionally in the adult
stage only.

It is not necessary for the farmer to know what
kind of insect is attacking his crop provided that he
has sufficient knowledge to keep the pest under control.
In order to deal successfully with an insect disease it
is usually necessary for some one to study carefully the
characteristic features of that insect throughout the
whole of its life and very often throughout the life of
some of its descendants. Such knowledge often enables
us to attack the insect at a time when it is most

94 Introduction to Insects [CH.

vulnerable; otherwise treatment is haphazard and
may mean attacking the insect at a time when it
is most resistant, or sometimes attempting measures
which prove to be useless.

The object of studying the life history of an injurious
insect with a view of preventing damage is to find the
weak periods in its life. We want to know the time
and whereabouts of the insect when it is most easily
kept in check. Knowing this we can find only by
experiment the best means of controlling it. A know-
ledge of the cultivated plants and weeds on which the
insect can feed is useful as it enables us to starve the
insect or drive it away by keeping these plants from an
attacked field for a certain length of time.

The life history tells us where the various stages in
the insect’s life are passed, how long it lives in these
stages, and when the change from one to another
takes place. From this we can often decide when and
how to attack the insect in order to keep it under
control.

In the case of the winter moth whose caterpillars
eat the leaves of fruit trees the females have no wings,
and when they want to lay their eggs on the young
shoots they crawl up the trees. In England this takes
place from about the second week in October until
the middle of January. It was argued that if these
females could be prevented from crawling up the trees
the caterpillars would not be able to eat the leaves.
An experiment was tried of putting a band of a sticky
substance (as used on fly papers) round the tree trunks
and keeping them sticky during the time that the
female moths are active. It was found that when they
reach the bands they stick and are unable to go farther.

vit] Introduction to Insects 95

They often lay their eggs on the bands or sometimes
underneath them, but even if the caterpillars hatch
they cannot travel the long distance to the leaves
where they usually feed. From this experiment it was
decided that the damage done by these caterpillars
could be to a large degree prevented, and this method
of grease-banding trees is now largely used in com-
mercial fruit-growing. In seeking remedies for con-
trolling insect diseases we must always bear in mind
the question of expense. The farmer grows his crops
for profit, and if it costs more to control the insect than
the value of the damage done such measures are of no
use to him.

One very annoying factor in dealing with insects
is that they can sometimes travel considerable distances,
so that a farmer who keeps them down on his own farm
is often troubled by others coming from his neighbour’s.

Insects may be roughly divided into two classes:
(1) herbivorous, which feed on plants and cause dis-
eases; (2) carnivorous, which feed on other insects
and allied animals.

The members of the second group are extremely
useful as they keep down the numbers of those which
attack plants, e.g. large numbers of green fly are
devoured by the larvae of lady-birds.

In nature both kinds live side by side in such a
way that a sort of balance is set up so that no single
species increases rapidly in numbers. In planting
large areas with one particular crop man has upset
this balance by providing the insects which live on
this crop with an ideal feeding ground. Many herbiv-
orous species are capable of living only on certain
families or orders of plants. In nature this means

96 Introduction to Insects [CH.

that they often have to travel long distances in search
of food, which in many cases they may be unable to
find. In fields where we grow plants suitable for certain
insects these can get food without searching for it and
are thus enabled to increase rapidly. In this connection
it must be remembered that insectivorous birds are
useful in checking the increase.

Man has further upset the balance of nature by
introducing foreign insects capable of living on our
plants, e.g. the American woolly aphis. These are
often capable of enormous damage as the insects,
birds and animals which prey.on them in their native
country may not be present here. The introduction
of the enemies of imported pests has in some cases
proved extremely useful. Our present system of
marketing also helps the spread of diseases from one
part of the country to another.

Carnivorous species are capable only of keeping
the herbivorous form within certain limits, and as man
has favoured the increase of injurious insects he must,
if he wishes to prevent them doing a considerable
amount of damage, employ some means to reduce
their numbers. A single insect is not capable of doing
much damage, but it reproduces itself at an enormous
rate and gives rise to numbers which collectively can
often render crops almost useless. This rate of repro-
duction is necessary in nature because of the numerous
factors which lead to the death of so large a percentage
of the total number of eggs laid.

In endeavouring to keep injurious insects under
control it is better to aim at prevention rather than at
cure. Clean farming prevents a large number of insects
from living through the winter as the weeds on which

vir] Introduction to Insects 97

they would feed are destroyed. Dirty fields full of
weeds and rubbish are ideal wintering places as they
provide both food and shelter. The destruction of
grasses and other weeds in headlands, hedges and ditches
destroys many, and also gets rid of a favourite wintering
place for others. The time of carrying out the various
tillage operations affects the number of insects which
are destroyed by such operations. Suitable rota-
tions are very beneficial in keeping some pests in
check.

The date of sowing often decides whether the crop
will be good or poor. Thus the frit fly maggot is only
capable of entering young oat plants; early sown
crops may therefore escape the attack altogether,
whereas late sown crops may be rendered almost
useless. It is often possible to sow at such times that
the insect is capable of doing the least amount of
damage. Artificial manures are also useful in hastening
the plant through the stages when it is most readily
attacked.

Various substances known as insecticides have
proved useful in killing certain forms which attack the
shoots of plants. The kind to use depends on the way
in which the insect feeds. Some, such as caterpillars,
have biting mouths and feed by eating the leaves and
shoots. The insecticide used in these cases is a poison,
such as lead arsenate. This poison is sprayed on the
plant so that on eating the insects are killed. Others,
such as green flies, have sucking mouths and live by
penetrating the tissues and sucking the juices. If a
poison is applied on the surface of the plant it has no
effect on them as they do not eat the surface layers.
In this case an insecticide is used which kills the

PF. 7

98 Introduction to Insects [cH.

insects directly, usually by stopping the breathing
pores. A mixture consisting of soft soap and sub-
stances such as tobacco infusion or paraffin is often
used in such cases.

CHAPTER IX
BUTTERFLIES AND MOTHS

Surface Caterpillars.

There are a number of moths whose caterpillars
damage many crops by feeding on them below the
surface of the soil or at the soil level. This habit
gives them the name of Surface Caterpillars. There
are several different kinds, but the damage done by
them is very similar and the means of keeping them
under control are the same, so for our purpose we may
group them together.

The chief offenders are:

Agrotis segetum ... .... The turnip or dart moth.
Agrotis exclamationis ... The heart and dart moth.
Triphena pronuba _..._ The yellow underwing moth.

These do considerable damage to mangolds, turnips,
carrots, parsnips, cabbages, potatoes, wheat and grasses.
They attack most cultivated plants, but are partial
to certain species.

They live as caterpillars during the greater part of
the year. In the early summer they destroy young
mangolds and turnips by cutting through the roots just
below the surface of the soil before and after they have

Ix] Butterflies and Moths 99

been thinned. It is very noticeable after thinning as
gaps are made in the rows. The caterpillars may be
found by hunting in the soil near freshly damaged plants.
Later on in the season they attack the swollen roots of
turnips and mangolds by scooping out large holes. In
a similar manner potato tubers are attacked. The

Fig. 29. Caterpillar pupa and adults of a surface caterpillar moth.

nibbled roots and potatoes usually rot. Corn crops often
suffer from attacks on their roots in mild winters. The
grubs remain hidden under the surface or under leaves
during the day and come out to feed at night. The
moths giving rise to these usually fly at night and are
attracted by lamps or fires. Their hind wings are
lighter in colour than the front ones. The female has
7—2

100 Butterflies and Moths [CH.

a simple feeler, whereas that of the male is toothed.
They are usually to be found in June, July and August.
The eggs are laid on cultivated plants or weeds near
the surface of the ground. The caterpillars are of a
dull colour, either brown or greyish, and consequently
are hard to find. They are cylindrical and apparently
smooth, having, however, a few hairs which arise from
small black spots on the body. When fully grown they
are about an inch or more in length. They possess
three pairs of jointed legs, four pairs of false legs in
the middle of the body and a pair of false legs at the
hind end.

They usually live through the winter and continue
to feed on roots except in cases of hard frost. At the
end of the following spring they change into smooth
brown pupae. These may be found in small oval
spaces which the caterpillars make in the soil. The
moths come out about a month after the pupae are
formed.

Remedial Measures.

Our knowledge of the life history of this pest
should help us in finding the best: means of keeping it
under control. The pupae are formed in the soil
when a crop is growing and consequently are not
readily attacked except by the usual practice of hoeing.
As the moths themselves are attracted by light it was
thought that use might be made of trap lanterns.
This however did not prove a success and is rather
expensive as the period of hatching is long. We must
then turn our attention to the destruction of the cater-
pillars themselves.

They are difficult foes to combat owing to their

Ix] Butterflies and Moths 101

habit of living underground. In the case of drilled
crops such as turnips and mangolds, frequent hoeing
is found to be useful as some of the caterpillars are
destroyed and others exposed to birds. Starlings,
plovers, rooks, and gulls will eat them in large numbers.
Pigs will also eat them.

With turnips and mangolds sown on the flat
harrowing has sometimes proved effective.

In market gardens handpicking has been found to
be remunerative. The grubs are very difficult to find,
except after dusk. Each worker should carry a lantern
and a stout stick pointed at one end to search for cater-
pillars near the plants.

In the case of an attack on potatoes earthing up
as early as possible has proved effective. Weeds should
be kept down as eggs are often laid on them and also
because the young caterpillars feed on them until the
crop is ready.

Poisoned baits put along the rows have proved
advantageous. The bait consists of some green food
stuff, such as clover or lucerne, dipped into or sprayed
with a solution of Paris green (made by mixing 1 oz.
of Paris green with 3 gallons of water), or lead arsenate.
When the caterpillars eat this they are poisoned.

In fields of cabbages, mangolds, or turnips, where an
attack is feared, a small seed bed of cabbages will be
found useful as the blank spaces in the rows caused by
the caterpillars can be quickly filled by the cabbage
plants.

Toads will destroy enormous numbers and should
be preserved.

102 Butterflies and Moths [CH.

Other Caterpillars.

There are numerous other caterpillars (i.e. the larvae
of butterflies or moths) which cause damage to our
crops and especially to fruit trees. These may be
distinguished from other larvae by the key on p. 92.
Some of them are kept down by grease-banding the
trees which prevents the wingless females from reaching
the shoots. In other cases the trees are sprayed with
a poisonous substance such as lead arsenate, so that
when the caterpillars feed, they are poisoned. In
addition to the caterpillars of the large cabbage
butterfly we may find on cabbages those of the small
cabbage butterfly eating holes in the leaves, and also
the green or brown caterpillars of the cabbage moth
(Mamestra brassicae) which eat into the hearts of the
cabbages, leaving a lot of excrement behind them. As
the small cabbage butterfly lays its eggs singly it is
difficult to control.

The cabbage moth lays its eggs in groups and these
should be looked for and destroyed in July and early
August.

The small caterpillars of the diamond-back moth
(Plutella maculipennis) may check or even destroy
crops of turnips and swedes by feeding on their leaves.
In this case the plants should be immediately brushed
with large twigs attached to a scuffle.

x| Beetles 103

CHAPTER X
BEETLES

Wireworms.

The term “wireworm” is used as a popular way out
of the difficulty of giving a name to any small worm-like
animal, and it often includes such different forms as
leather jackets, millipedes, and centipedes. True
wireworms are the larvae of beetles known as click
beetles or spring-jacks. They attack all kinds of
crops with the exception of mustard and are usually
most abundant in permanent pasture, temporary leys,
or any covered ground which is not disturbed. They
do much damage to roots, corn crops, and peas,
especially to crops grown on newly broken pasture
land. They feed chiefly on or just above the roots of
plants. It is not the amount of food eaten which
makes them so destructive, but their habit of biting off
the plant above the roots.

On pulling up a cereal that is being attacked, the
wireworm may be found feeding on the stem a short
distance from its base. The damage is done only by
the wireworm or larval stage, but as it lives for three
to five years the amount of harm done by a single
individual is very considerable.

The eggs are said to be laid on or near the ground
in May and June. The young wireworms which hatch
out from these are very small and whitish. They
begin to feed immediately after hatching. Full grown

104 Beetles [CH.

wireworms vary in size according to the species of
beetle from which they are derived. Some may reach
a length of 1 inch and others only inch. The body is
cylindrical and divided up into segments. In the course
of their growth the skin is shed several times in the same
way as that of the caterpillar of the cabbage butterfly.
Their colour varies somewhat: after a moult they are
usually pale yellow, but later on they become a rich
golden yellow. The surface always has a shining
appearance, and the skin is very tough.

The head carries a pair of powerful jaws which
enable it to feed on all kinds of roots. Each of the
three segments behind the head possesses a pair of
jointed legs which readily distinguishes it from other
so-called wireworms (see Fig. 30). The last segment of
the body also has a downward projection which is used
in walking. When fully fed the wireworm goes deep
down into the earth and makes an egg-shaped space in
which it changes into a pupa. This change usually
takes place in spring and from the pupa the beetle
soon hatches out and makes its way to the surface.
The beetles may often be found on grass land or clover
leys during the summer. There are several species all of
a dull brown or greyish colour, rather long and narrow,
having short legs and serrated feelers (see Fig. 30(C).
When placed on their backs they spring into the air
with a clicking noise and fall on their feet. They are
enabled to do this by means of a projection on the
segment carrying the first pair of legs which fits into
a depression on that bearing the second pair. This
structure enables us to recognize the beetles fairly
easily. They also make a clicking noise if held
between the finger and thumb. The beetles are not

x] Beetles 105

often found as they usually hide during the day time.
The wireworms feed throughout the whole of their
lives on the roots of either cultivated or wild plants,
except in frosty weather, when they go deep down into
the soil. After a thaw they come up again and feed.

B

Fig. 30. Click beetle or wireworm beetle. A, wireworm; B, pupa;
C, click beetle. (About twice natural size.)

Remedial Measures.

The first remedy which suggests itself is if possible
that of preventing the eggs being laid. This has proved
of little use to the farmer as it cannot be successfully
carried out on grass land and clover leys. In gardens a
number of beetles may be trapped by means of small
heaps of clover covered with boards or tiles. The
beetles which shelter in these traps may be collected
at intervals and destroyed. This should be done in
April and May before the eggs are laid as the beetle
itself does no damage and no advantage is gained if
they are trapped after laying their eggs. Wireworms

106 Beetles [CH.

are fond of carrots and potatoes and may be trapped
in these in market gardens and glass houses. Attempts
have been made to coat the seeds with various sub-
stances but they have failed to prevent attacks. In
attempting to reduce their numbers it must be
remembered that clean farming is extremely helpful as
large numbers are starved if the land is free from weeds
for any length of time. Clean fallowing will get rid of
considerable numbers. It must also be remembered
that the grasses in hedges and headlands provide food.
A crop of mustard will also starve a great many of them.

In breaking up grass land, leys, or any covered land
we must not forget that wireworms are usually present
and all crops except mustard are likely to be attacked.

Paring and burning has proved helpful, as also
applications of lime and gas lime, especially if the
grasses themselves are burned. These methods do not
kill the wireworm, but destroy their food. All these
methods aim at starving the wireworms. Applications
of various kinds are useful for a time, the wireworms
are not killed but simply go deep down into the soil
and come up again when the trouble is over. Appli-
cation of rape cake is thought by many to kill them.
It has been proved to benefit the crop to which it is
applied as wireworms are very fond of it and leave the
roots of plants in order to feed on it. In the following
season however we shall find that they are still present
in the soil ready to feed on any crop except mustard.
Rolling the land in order to consolidate it helps the
crop, as it prevents wireworms moving from one
plant to another as easily as in loose soil. Fora similar

reason driving sheep over the land when possible is
very useful.

x] Beetles 107

Ploughing in the fall of the year may kill some of
the pupae and may also turn up some wireworms for
birds. A number of birds, such as rooks, starlings,
plovers, pheasants and partridges, help to keep the
numbers down. The farmer only sees the damage that
these birds do; if he saw the food they ate he would
probably be led to think that the number of plants
they save in many cases outweighs considerably the
number which they destroy. Moles also eat wireworms.
Stimulating manures applied with the seed help plants
considerably against the attacks of wireworms.

Millipedes and centipedes, which are often confused
with wireworms, are not the larval stages of insects,
but adult animals closely related to insects. They are
readily distinguished by the enormous number of their
legs. It is important to know the difference between
centipedes and millipedes as the former help the
farmer by feeding on insects in various stages and also
on worms, snails and slugs. Centipedes should not be
destroyed. Millipedes are destructive and feed chiefly
on roots and other portions of plants which grow
underground, such as tubers and bulbs, and also on
strawberries. Centipedes have only one pair of legs on
each segment whereas millipedes have two pairs on
every segment, except the first four (see Fig. 31).

Millipedes may be trapped by means of a scooped
out mangold, or killed by means of poisoned bait.

Turnip Flea Beetles.

Every farmer knows that in a dry, dusty summer
his turnip crop is liable to be damaged. or even almost
entirely destroyed by what he calls the turnip fly or

108 Beetles [CH.

flea. If we succeed in catching one of these hopping
insects we shall find that it has two pairs of wings
and is therefore not a fly. The outer wings are
hard and protective, and from this we shall decide
that it is a beetle. The name turnip flea beetle is the
most appropriate as it tells us that the insect is a beetle

Fig. 31a. A centipede.

Fig. 316. Millipedes.

and also at the same time reminds us of its hopping
powers.

In spite of its small size this beetle is capable
of doing enormous damage on account of its numbers
and power of multiplying. Under favourable conditions
it is possible for six generations to hatch out in a
single season. It attacks the plant just at the time

x] Beetles 109

when it is most susceptible, viz. just as it pushes its
way through the ground. The adult beetles do the
most damage in this case. As soon as the young
plant appears they begin to feed on the seed leaves,
then on the heart of the plant, and so destroy it
entirely. In this way whole fields are eaten bare and
have to be resown.

The last brood of beetles formed in the autumn
hibernate through the winter in crevices or under
leaves. When the warm weather of spring begins,
usually at the end of May or beginning of June, they are
roused from their slumbers and are prepared to enjoy
themselves at the expense of any young turnip plants
which may be available.

After a time the beetle lays its eggs on the under
surface of the rough leaves of any turnip plants which
are not destroyed, or on the leaves of other plants of
the same order such as charlock and hedge mustard.
From the eggs small yellow larvae hatch and at once
commence to feed on the rough leaves by getting
inside them and eating the green portion between the
two skins. In this way colourless marks are found on
the leaves and by holding them up to the light the
young larvae can be seen in them. In about a week
they come out and bury themselves in the ground.
Here they change into pupae and from these the beetles
are formed in about a fortnight (see Fig. 32). These
then feed on the turnip leaves, especially of the younger
plants when the field has been resown. It is in hot dry
weather that the attack is worse, as this favours the
development and spread of the beetles. They do not
like wet weather and consequently less damage is done
in a wet spring. Curtis says they are attracted by

110 Beetles [CH.

the smell of the turnip crop and will fly from consider-
able distances against the wind. There are several
beetles included under the heading of turnip flea beetles
but they are similar in their mode of attack. They
are very small and measure only about ;4, inch in
length. Some are of a bluish black colour, the
commonest form having a broad yellow stripe down
each of its outer wings. Its antennae are one-half the
length of its body. By means of its very stout thighs,

Fig. 32. Flea beetle; egg, larva, pupa and adults of turnip flea
beetle. (Magnified.)

especially on the hindmost pair of legs, it is enabled to
jump long distances. The larva is yellowish with a
distinct head and a pair of legs on each of the first
three segments. The hind end of the body is turned
down to form a kind of foot.

In addition to turnips, other cruciferous crops, such
as swedes, cabbages, and rape, also suffer. Recently the
turnip flea beetle was found attacking young barley
plants. This was no doubt due to the absence of
cruciferous plants.

x] Beetles 111

Remedial Measures.

The eggs are laid on the under surface of the leaves
and do not lend themselves to treatment. As the
larvae feed inside the leaves we cannot hope to attack
the pest at this stage. It is chiefly against the adult
stage that attacks are aimed.

We have seen that the greatest amount of damage is
done when the turnips are young, consequently we must
aim at helping the plant in these stages and at the same
time make things as unpleasant as possible for the beetle.

Drought and frost retard the growth of the plant;
the former also favours the beetles and consequently
this state of affairs is bad for the turnip.

Clean farming plays a very important part in
reducing the numbers of this beetle as weeds, such as
charlock, serve to sustain it until the abundant supply
of food which the turnip crop supplies is ready. All
cruciferous weeds should be destroyed and the grasses
in hedges and ditches cut and burnt, as they provide
shelter for the beetle during the winter.

The method of cultivating the land is very important,
and operations which help the plant in its early stages
should be carried on. Cultivation should be done in
the autumn if possible as more moisture is retained in
the soil and a better tilth obtained. Seeds sown on a
fine tilth usually suffer less for this favours the growth
of the young plant and is unfavourable to the beetle,
as there are few suitable hiding places for it. Careful
rolling (if the land is suitable) after drilling the seed
breaks up the clods and disturbs the beetles. Miss
Ormerod says, “After a long experience I never saw
a failure of a braird of turnips on land which had been

112 Beetles {CH.

long and well prepared before the seed was sown.
Good seed and plenty of it, three pounds per acre,
drilled deeply from (say) two to three inches, ensures
a good start, even in the driest times.”

In addition to farmyard manure, artificial manures,
and especially superphosphate, have been shown to be
profitable when sown before or in the drill at a time when
they can help the young plant through the earlier stages.

Sowing mustard with the turnip crop has proved
beneficial in some seasons, but not in others. The
mustard comes up before the turnip and so is attacked
by the beetles. They prefer turnips and usually leave
the mustard as soon as the turnips are ready.

Rolling a piece of infected turnips early in the
morning while the dew is still on the plants is sometimes
practised with success. This process disturbs and
injures the beetle, and also makes the plants dusty,
in which condition they are not so readily eaten.
Driving sheep over turnips while the dew is still on is
also useful for similar reasons.

Many of the beetles can be caught on a wide frame-
work built on wheels with well-tarred boards upon it and
pushed over infested land. The boards are placed at
right angles to each other. The upright ones brush the
plant and disturb the beetles which are usually caught
on the board which projects forward. If the beetles are
very numerous they should be scraped off frequently
and the board kept sticky with tar. Cart grease can
be used instead of tar.

Dragging sacks which have been soaked in paraffin
so that they touch the plants has been tried in many
cases and proved beneficial.

Larks eat the beetles in considerable numbers.

x] Beetles 113

Chafers.

The so-called white grubs are the larvae of chafer
beetles. There are four kinds which are very destruc-
tive to plant life: (1) Melolontha vulgaris, the common
cockchafer or May bug; (2) Rhizotrogus solstitialis,
the summer chafer or midsummer dor; (3) Phyllopertha
horivola, the garden chafer or bracken clock ; (4) Cetonia
aurata, the green rose chafer.

These white grubs often do considerable damage
to the roots of plants, causing many to die and others
to look very sickly. Grass land is especially liable to
attack and whole patches at times die off from the
ravages of these grubs. This injury is sometimes
attributed to wireworms. Young trees, turnips, cab-
bages and other farm crops are also injured by attacks
on their roots. In addition to the damage caused by
the grubs, the beetles themselves feed on the leaves
of various trees. The adults are easy to distinguish
from one another. They are all characterized by
having feelers ending in flattened or leaf-like structures
folded one on top of the other.

The cockchafer is the largest and usually measures
more than an inch in length. The head and thorax
are black, the wing cases brown, each case having
five longitudinal smooth ridges. The whole body has
a mealy appearance. Five of the abdominal segments
have a white triangular marking on each side. The
end of the antenna is composed of six leaves in the
female and seven in the male (see Fig. 33a, 1).

The summer chafer measures about 2 inch in length,
is brownish in colour and covered with a quantity of
rather long hairs. The markings on the abdomen are

P.F. 8

114 Beetles [CH.

not so distinct as in the case of the cockchafer.
The end of the antenna has only three leaves (see

Fig. 334, 2).

Fig. 33a. (1) Melolontha vulgaris, the cockchafer; (2) Cetonia aurata,
the green rose chafer; (3) Rhizotrogus solstitialis, the summer
chafer; (4) Phyllopertha horticola, the garden chafer.

The garden chafer is not quite 4 inch in length.
Its head and thorax are of a metallic green colour,
and its wing cases brown (see Fig. 33a, 3).

x] Beetles 115

The green rose chafer has its thorax and wing
covers of a metallic green colour (Fig. 33 a, 4).

The grubs of these are not so easy to distinguish
and can best be identified by a microscopic examination
of one of the jaws!. The grub is of a whitish colour.
When at rest it lies on its side with its body curled in
the form of a semi-circle. It has a distinct head with
marked jaws and feelers. The three segments behind

5 6

Fig. 336. Melolontha vulgaris, the cockchafer; (5) the larva;
(6) the pupa; (1) the beetle.

the head have each a pair of jointed legs. The abdomen
is thick and fleshy, and swollen at the tail end which is
often darker in colour, the contents of the intestine
being visible through the body wall. The body is
wrinkled and each segment except the second, third,
and last bears a pair of spiracles. When fully grown
the grubs vary considerably in size.

The grubs of the cockchafer and the green rose
chafer measure from 1}-1} inches in length. They
1 See R.A.S.E., vit. 1897, p. 748.

8—2

116 Beetles [cu.

are easily distinguished by the red spots which the latter
possesses on each side of the segment behind the head.
When full grown those of the summer chafer measure
over an inch in length, whereas those of the garden
chafer only measure 3 inch.

The life histories of these beetles differ chiefly in
the length of time from one generation to the next.
The cockchafer takes four years to complete its life cycle
in this country, but in some countries it may take three
or five. The length of life of the summer chafer is
not known with certainty, but is thought to be either
one or two years. The garden chafer has a new genera-
tion every year. The green rose chafer has a new
brood every two or three years.

Cockchafers make their appearance in May and are
often abundant for five or six weeks. They remain
concealed during the day and fly about after dusk.
The leaves of oak trees are their favourite diet. The
female burrows into the earth to lay her eggs, pre-
ferably in loose soil or grass land, and lays about
ten eggs. The grubs hatch from these in about
six weeks. During the first summer they do very
little damage as decaying matter is their chief food.
In the following years they feed on plant roots. In
winter they escape the unfavourable conditions by
going deeper into the soil. After spending three years
in the grub stage they scoop out recesses deep down in
the soil and change into pupae. The beetles come up
in the following May. The cockchafer grubs are
responsible for most of the damage done to young
trees. Young oaks and conifers suffer considerably.

The life history of the summer chafer is very
similar, the beetles appearing after the cockchafers in

x] Beetles 117

June and July. The garden chafer also appears in
June and July, and flies about in bright sunshine.
These chafers sometimes feed on young apples.

The green rose chafer flies about during the day
and appears at the same time as the cockchafer. The
adults are especially harmful to the flowers of roses,
strawberries and turnips.

Remedial Measures.

These grubs feed chiefly on grass land and hence
are extremely difficult to eradicate. Surface applica-
tion seems to be of little value, as the grubs can descend
out of its reach. It is chiefly against the adult stage
that measures must be taken as they are then more
likely to succeed. On the continent co-operative
attacks are made against the adult chafers which
never travel far to lay their eggs; hence the districts
in which they are destroyed reap the benefit.

In this country the summer chafer and the garden
chafer seem to be the cause of most of the damage.
The cockchafer is very local, but may be abundant in
those districts in which it is found.

The importance of knowing the life history of these
chafers is evident if we are attacking them at the
adult stage. It takes four years for cockchafers to
produce another brood of cockchafers, so that having
noted when the beetles are numerous we know when to
expect the next brood. The date of appearance is also
important. We must be prepared to attack the cock-
chafer and the green rose chafer in May before they have
laid their eggs, as no advantage is gained by destroying
them afterwards, whereas the summer chafer and the
garden chafer do not appear until June. The small

118 Beetles [CH.

amount of damage which the cockchafer does during
the first year of its larval life often leads the farmer to
suppose that the grubs are not present whilst they may
be found in the young stage under healthy grass.

The cockchafer and green rose chafer fly at night,
and are very sluggish during the day time, when they
may be found on trees, usually isolated ones, in fields
and hedges. They rarely go into a wood except in
very rough weather. The beetles can be beaten from
trees and shrubs by means of long sticks, collected on
sheets and then destroyed. The best time for this
operation is in the morning; the trees must not be
shaken too much or the beetles will fly away. In this
way a single farmer in France has collected nearly a
ton of cockchafers. Pigs will readily eat them if they
are shaken on to the ground.

The summer chafer and the garden chafer must
be attacked in the early morning, in the evening, or
on very dull days, as they fly about in bright weather.
On arable land frequent hoeing has been found to be
useful and in gardens handpicking of the grubs is
profitable. Gas lime has been found to kill the grubs,
but it also kills the grass. In gardens the larvae may
be trapped by placing pieces of turf grass downwards
just under the soil.

When badly attacked grass land is ploughed up
pigs and chickens should be turned into the field as
they will destroy large quantities of the grubs. Rooks,
starlings, green plovers, gulls and moles devour a large
number of them, and the damage to grass land, which
is often attributed to rooks, is really due to the grub,
for which they are searching. The chafers themselves
are said to be eaten by owls and nightjars.

x] Beetles 119

Grain Weevil.

Considerable damage is often done to stored grain
by the larvae of two small beetles, Calandra granaria
and C. oryzae. They attack all kinds of grain, such as
barley, malt, wheat, maize, and oats, and are trouble-
some to cargoes of grain as well as in granaries and
breweries. The trouble begins in the spring and
summer. The beetle bores a small hole in the grain
by means of its snout or proboscis; into this hole it
proceeds to deposit an egg and then closes the hole with
saliva. One egg is deposited in each grain and in this
way a lot of grains are infected by a single beetle.
The larva which hatches from the egg feeds on the
grain, devouring all except the skin and the germ.
When it has eaten its fill it changes to a pupa and
shortly afterwards into the adult beetle. This then
eats its way through the husk, leaving a large hole
(see Fig. 34b). The time taken to complete the life
cycle depends largely on the temperature. Under
favourable conditions such as a close atmosphere this
may take only a month. It is difficult to detect any
damage that is being done by inspecting the grain,
as there is little difference between the injured and
the uninjured grain. If, however, a quantity of the
grain is placed in water the partly eaten grains float
on the surface.

The weevils cannot stand cold and on the approach
of winter usually migrate to cracks or shelters in the
floors and walls. In spring they return once more to
any corn which they may find. C. granaria is unable
to fly, but C. oryzae possesses flying wings.

120 Beetles [cH.

Fig. 340. Grain weevils. Calandra oryzae (on the left), Calandra
granaria (on the right). (Magnified.)

Fig. 346. Wheat damaged by grain weevils.

x] Beetles 121

The beetle is about } inch long and of a dark-
brown colour. As is the case with all weevils it has a
long snout or proboscis, carrying at its base a pair of
elbowed feelers (see Fig. 34a). The mouth is at the end
of the proboscis. The larva is a small white legless
grub with a wrinkled body, brownish horny head, and
distinct biting jaws. These beetles are very prolific,
and as only one larva is required to destroy each grain,
the introduction of a few weevils may mean a con-
siderable loss.

Remedial Measures.

As the beetle is averse to cold we can do some good
by keeping our barns well ventilated so as to keep
the temperature as low as possible. By leaving the
windows or door of the granary open on frosty nights.
the beetles are checked. They do not go very deep into
a heap so that storing in bulk will keep a considerable
quantity of grain free from the beetle.

If we find our grain attacked we have a fairly easy
method of killing the pest. This consists in fumigating
with carbon disulphide. In a closed bin it is a simple
matter and consists in putting the carbon disulphide
in saucers on top of the corn. About 1lb. to 100
bushels is sufficient (the amount depends on the space,
a small quantity of corn in a large bin will require
more than the above quantity). The bins should be
opened after about 24 hours.

If the grain is stored in a barn all holes should be
stopped up and the barn made as air-tight as possible.
Carbon disulphide is then put on the top of the grain
in saucers, 1 Ib. for every 1000 cubic feet of space.

If the heap is covered with canvas a smaller quantity

122 Beetles [CH. x

is sufficient and in a large barn this covering is often
necessary.

It must be remembered that carbon disulphide is
heavier than air and readily descends.

Treatment should begin at the bottom of a building
if several floors are being treated. After fumigation the
bin or granary should be opened for two or three hours
before entering the building as the fumes are poisonous.
No naked light should be taken into the treated building
as the fumes are highly inflammable. When empty the
walls of the granary should be whitewashed, a little
carbolic acid being added to the wash. All crevices in
the walls should be stopped up to prevent the beetles
from hibernating there.

Gall Weevil or Club (Ceutorrhyncus sulcicollis).

This pest may become very troublesome when it
has established itself in market gardens where cabbages
are grown annually. It attacks other members of the
same order such as turnips and swedes, and in these
cases indirect damage may be done, from the entrance
of organisms which cause the roots to rot. When
cabbages are attacked their growth is stunted, the
leaves become yellowish, and in many cases the plants
are killed. The presence of this pest may be recognized
by the swellings on the underground portion of the
stem in cabbages, and on the underground succulent
part of turnips (see Fig. 35). These swellings give the
name of “club” to the disease and sometimes lead to
its confusion with finger and toe, which is caused by
a fungus (see p. 35), or root knot, which is caused by
an eelworm (see p. 170). Itis readily distinguished from
these by examining the swellings of a diseased plant,

r
Fig. 35a. Cabbage plants attacked by the turnip gall weevil
(Ceutorrhynchus sulcicollis).

Fig. 356. Swede turnip attacked by the turnip gall weevil
(Ceutorrhynchus sulcicollis).

124 Beetles [CH.

which contains small curled yellowish legless grubs
measuring about } inch in length and possessing brown
jaws. These are the larvae of small blackish beetles
possessing the long snouts with elbowed feelers so
characteristic of weevils. These weevils lay their eggs
on or in the cabbage stalks or turnip roots and from
these eggs the young grubs hatch out.

By feeding on the plant these cause the food supply
to go to the places where they are feeding and hence
swellings are produced. After a time they eat their
way out of the swellings and go into the soil to pupate
in earth cases. Some of the grubs remain in the plant
through the winter, whereas others pass the winter as
pupae. In the following spring and summer the
weevils come out and eventually lay their eggs on
suitable plants.

Remedial Measures.

In ordinary farm practice where cruciferous crops
are grown every four years this weevil does little
damage as it has great difficulty in living from one
crop to the next when cruciferous weeds are kept down.
In market gardens these crops occur more frequently
and they become infested. The practice of putting the
cabbage stalks in a compost heap or ploughing them
under is favourable to the insect as the grubs go
into the soil, pupate and so give rise to weevils next
spring. The stalks containing the grubs should be
burnt. Care must be taken in planting to destroy all
young plants which have galls on them.

Gas lime in the autumn checks the weevil. Rooks
and partridges eat the grubs in the galls which they are
able to reach. Cruciferous weeds should be kept down.

x] Beetles 125

The grub of an allied weevil Ceutorrhyncus assimilis
feeds on turnip seeds while they are still in the pods.

Fig. 36a. Sitones weevils. Sitones lineatus (on the left), Sitones
crinitus (on the right). (Magnified.)

Fig. 366. Broad bean leaves attacked by Sitones weevils.

Pea Weevils (Sitones lineatus and Sitones crinitus).

These weevils attack peas, beans, and clover in a
very characteristic manner by eating semi-circular
patches out of the edges of the leaves (see Fig. 36 5).

126 Beetles [cH.

In this way whole leaves may be eaten. As the weevils
are not easily seen the damage is often attributed to
birds.

They may be found by carefully examining plants
that are attacked. On touching the plant they fall to
the ground and remain motionless. The eggs are laid
in the soil and the legless larvae feed on the roots of
peas, beans, and clover, and often bore channels along
the roots. In winter the weevils hibernate.

Remedial Measures.

These pests are difficult to keep in check. A fine
tilth is unfavourable to them as their hiding places
are destroyed. For clover and field peas, light rolling
followed by a good dressing of soot is said to be useful.
After an attack the land should be ploughed as deeply
as possible with a skim coulter.

The Pea and Bean Seed Beetles (Bruchus pisi and
Bruchus rufimanus).

These beetles are very closely allied to the weevils.
They have a short snout, but
their antennae are not elbowed
(see Fig. 37). The larvae re-
semble weevil larvae, being leg-
less and wrinkled. They feed
on the seeds of peas and beans,
eating some of the stored food
but without injuring the young
embryo. Fig. 37. Bruchus rufimanus,

The eggs are laid on the the bean seed beetle.
young pods in the flowering (Megamed
stage, and the larvae which hatch out make their way

x] Beetles 127

into the seeds. Each larva pupates in the seed
where it has fed and the beetles formed from these
also remain in the seed for some time. The seeds in
which the beetles occur have a small round pit in the
skin of rather different colour from the rest; no holes
are made until the beetles escape.

Remedial Measures.

The beetles may be destroyed by fumigating with
carbon disulphide as in the case of grain weevils (see
p. 121).

When seeds that have been attacked are sown they
take longer to germinate and under adverse conditions
may not produce healthy plants; under favourable
conditions however plants very similar to those from
healthy seed are produced, the only difference being
that they are delayed a few days in the young stage.

CHAPTER XI
FLIES

Frit Fly (Oscinus frit).

This pest has recently caused a considerable loss
to farmers in its attacks on the oat crop. In outward
appearance the affected oats closely resemble those
attacked by an eelworm known as Tylenchus (see
p. 168), and it is only by a careful examination that
the real culprit can be found. Occasionally both of
them occur in the same plant. In a badly infested

128 Flies [CH.

field very few ears of oats are formed as the shoots
which would normally bear the ears are killed.
Diseased oats tiller freely and each shoot attacked
becomes thickened at its base and remains stunted,
usually from 4 inches to 1 foot in height. An oat plant
in which all the shoots are attacked looks like a tuft
of very coarse grass (see Fig. 38). The young shoot is
yellowish or brownish and may be in a state of decay.
The older leaves may appear quite healthy or take on
a reddish appearance.

The fly attacks oats and occasionally barley, rye,
wheat and grasses. It is usually spring sown oats that
suffer, but winter oats are also occasionally attacked.
By far the greatest amount of damage is done to
late sown spring oats. Those sown early in March in
a good seed bed are practically free from the disease,
and it is only by a careful search that an infested
plant can be found. On the other hand those sown
late in April are sometimes so badly attacked that
less than 10 per cent. of the ordinary amount of
ears are formed.

If we carefully examine a diseased shoot about the
beginning of June we shall find a small maggot in the
middle of the plant. This is the larva of the frit fly,
and is about 4 inch long when full grown. It has a
somewhat transparent, shiny, fleshy appearance. Its
body is segmented and legless. The anterior end,
which is somewhat pointed, is easily recognized by a
pair of almost black jaws which are capable of being
protruded. Near the front end on each side is a
branched spiracle. The posterior end is blunt and
possesses two wart-like spiracles (see Fig. 39).

The maggot eats into the stem and in many cases

x1] Flies 129

130 Flies [cH,

may eat through it. The plant responds by forming
other shoots and so we get a tufted appearance.
Diseased shoots may be found together with healthy
ones on the same plant, especially in mild attacks.

Later in the season small brown cases are present
instead of the maggots. These are easier to find
because of their colour. These pupa cases of the fly
are slightly shorter than the maggots, cylindrical,
and of a reddish-brown colour. The two wart-like
spiracles are still present at the posterior end, and the
black jaws of the larvae can often be seen through the
case (see Fig. 39 B).

If we put some of them in a bottle, the mouth of
which is covered with muslin, the frit flies will hatch
out in July. This is precisely what happens in
nature, and at the end of July large numbers of these
flies may be found on the ears of oat plants. They are
very small and measure less than 4 inch in length.
They are black and shiny (see Fig. 39C).

The flies which are found in July lay their eggs in
the ears of young oats or barley, or on the young
shoots of grasses. The maggots which hatch out from
the ears of oats or barley live on the developing grain,
causing it to be gnawed and shrivelled. Pupa cases
may be found in infected ears just before harvest.
The maggots that hatch out on grasses feed on the
young shoots in the same manner as the maggots
already examined feed on the young oats. The third
brood of flies appear in August and September, many
of them after the grain has been harvested. They
have been found in swarms in granaries containing in-
fected grain. This brood lay their eggs on wild grasses
or winter corn, and the maggots which hatch from

x1]

Flies 131

ss

iffy,

sf ft

iy eh
aa

ptf
Hy ore
aa |
Me y foe
t ce ij

waa |
cA en i!
Py vd I
ps

rid es
4 yet it

byor Te
phy ji
Ce i te
Dn aN (ie
Fa eae q
Bhs
re af

Fig. 39. The frit fly (Oscinus frit). A, the larva; B, the pupa;
C, the fly. (Magnified.)

9—2

132 Flies [CH.

these feed on the shoots of their host and eventually
change into pupae. From the pupa cases next season’s
first brood of flies appear in April and May, ready to
lay their eggs on any young oat plants, or in their
absence other suitable hosts. The frit fly is capable of
attacking only young oats so that those which are put
in early and grow quickly through the early stages
have a good chance of escaping an attack. The frit
fly has three broods during each season and it is only
in the maggot stage that damage is done. The first
brood feed on the shoots of oats and sometimes on
related plants. The second brood feed on the grain of
oats and barley or on the shoots of grasses, and the third
brood feed on the shoots of winter corn or grasses.

By far the largest amount of damage is done by
the first brood. In some seasons the attack is much
worse than in others, this being largely due to the
weather conditions of the autumn and spring previous
to the attack.

Remedial Measures.

No means are known by which the attack can be
stopped when the crop shows itself to be attacked.
It is possible however to prevent future attacks to a
large extent. We have seen that the damage done by
this fly is chiefly to late sown oats, and consequently
our best means of prevention is to get them in as early
as possible. In 1912 a field of oats in Norfolk sown the
second week in April was ruined by frit fly, whereas a
neighbouring field sown the second week in March was
almost free from it. A careful search however revealed
the presence of a few specimens. This example will

XI] Flies 133

show the importance of putting oats in as early as
possible during March.

When oats are sown late they should be very
carefully watched for any signs of attack, and should
be helped as much as possible through the early stages
of growth by stimulating manures, such as sodium
nitrate.

In the case of a bad attack, when there is little hope
of the crop being a profitable one, it should be sheeped
off and the upper surface of the soil ploughed under as
deeply as possible by means of a skim coulter. By
these means the maggots and pupa cases are buried
and the flies are unable to hatch out. After this
ploughing there is still time for a crop of turnips
which somewhat reduces the loss occasioned by the
failure of the oats.

In cases where future crops, such as seeds or sainfoin,
are sown with the oats the most profitable method of
procedure is doubtful. If the whole crop is not
ploughed in, means must be taken to prevent damage
in the following season. Spring oats sown near such
an infected field should be put in as early as possible
and carefully watched for any signs of attack.

It is advisable to cut and burn all the grasses in
hedges and ditches and on the headlands where the
fly may live during the winter. Winter corn sown near
an infected field is also liable to be attacked.

The stubble from infected fields should be turned
completely under and the cavings from the threshed
oats, which will probably contain pupa cases, should be
burned.

We must continue to bear in mind that the fly is
always with us and ready to play its part, especially

134 Flies [CH.

after favourable ‘seasons, and that late sown oats are
always liable to be attacked.

Gout Fly (Chlorops taeniopus).

This fly attacks barley, wheat, rye, and certain
grasses. In this country the injury to the barley crop
is often very serious.

In a badly attacked plant the shoots are swollen
considerably suggesting the name “gout.” The ears
are usually unable to force their way through the
leaves which become spirally twisted at the top (see
Fig. 40). A groove is eaten out along the upper
part of the stem and the lower grains are usually
shrivelled. The plant itself is stunted and distorted.
On cutting open a diseased plant at the earliest stage
of an attack a small maggot may be found feeding on
the upper portion of the stem. This larva of the gout
fly is somewhat similar to the frit fly maggot, only
considerably larger. One maggot only is usually
present in each shoot. When fully grown it measures
from }-3, inch in length (see Fig. 41.4). It has a semi-
transparent, shining, fleshy appearance and is yellowish
in colour. It possesses no legs and is segmented.
The contents of the gut can be seen through the body
wall. At the pointed anterior end are a pair of small
black jaws, and at the posterior end a pair of spiracles
protrude. If we examine a diseased plant later in the
season we shall find that the maggots have changed
into pupa cases. The pupa case is slightly smaller and
of a brownish colour (see Fig. 41 B).

From these the flies hatch out in August and
September. They may be hatched out by keeping
puparia in a bottle covered with muslin. They are

x1] Flies 135

. CaN

Fig. 40. Barley plants attacked by the gout fly (Chlorops taeniopus).

136 Flies [CH.

about 3 inch in length and are of a yellow and black
colour. The thorax has three black longitudinal
markings on its back (see Fig. 41C). This fly has two
broods every year. The first brood appear in May and
lay their eggs on the sheathing leaves of the plants.
The maggot which hatches from one of these eggs
pierces its way until it reaches the stem. Here it
commences to feed on the lower portion of the ear, and
usually eats its way down the stem, making a groove
to the first joint. In the groove or in the leaves
surrounding the ear it changes into a pupa in July.
Flies hatch out from these in August and September
and lay their eggs on wild grasses or winter corn.
The maggots of this brood may be found on grasses in
November. They eventually give rise to the first
brood next season in May and June.

Remedial Measures.

Once this fly has established itself in our barley
plants we can do little to stop any loss. Barley on
poor soils suffers most, as on soils in good heart the ears
are often able to push their way through the leaves
even after they are attacked. If the attack is found
out in its early stages the application of a quick-acting
nitrogenous manure, such as sodium nitrate, may be
useful. It has been found that barley sown before
March 20th rarely suffers from attacks of this fly, but
that when sown in April it may suffer very considerably.
The best means of prevention then lies in getting the
barley in early so that the young plants are well
established before the flies hatch out. The land should
be kept as clean as possible so that the fly may be

XII] Flies 137

|

me (tas
= =

ee
at =
= =
. ES
a
~~
_=

ai ! Wi
i Wh

|

= ~3
=- xe
aa LS
oe a ae =

in

A B

Fig. 41. The gout fly (Chlorops taeniopus). A, the larva;
B, the pupa; C, the fly. (Magnified.)

138 Flies [CH.

prevented from living during the winter on such
grasses as couch.

An attack is often most noticeable near hedges and
ditches or strips of grass. This is probably because the
fly has been living there during the winter. Grasses
in hedges, ditches, and headlands should be cut and
burnt during the winter.

The straw from an infected crop should be stacked
as tightly as possible or used at once for litter; either
of these measures will prevent a large number of flies
from hatching.

A number of the puparia will be carried off in the
swollen heads when the crop is harvested ; on threshing
they may be found in the cavings and should be
destroyed. Winter corn sown near an infested field
should be put in rather late, so that the second brood
of flies may not be able to lay their eggs on this
crop.

When the attack is so bad that there is little hope
for the crop it is better to sheep off the barley.

The stubble should be turned under as deeply as
possible with a skim coulter soon after the crop is
harvested, by which means many of the puparia will
be buried.

Hessian Fly (Cecidomyia destructor).

This fly occasionally damages wheat, barley and
rye. It also lives on grasses, such as couch and
timothy.

Wheat suffers most from it and the effect is usually
noticed when in full ear. Plants here and there are
seen to have fallen down. This condition goes by the

x1] Flies 139

name of dog-leg, elbowing or “strailed corn.” On one
of these shoots may be found below the elbowing, just
above one of the lower nodes and underneath the leaf
sheath, one or more maggots or pupa cases, usually the
latter. The maggot is a small whitish, legless grub and
is easily recognized by a curious process just behind
the head, known as the breast bone. The pupa cases
found in the same position as the larvae are usually
known as flax seeds, which they somewhat resemble,
but they are considerably narrower. They are j—3, inch
in length and of a brownish colour. When the wheat
is cut some of the pupae are carried away in the straw
and others remain in the stubble. Some of them give
rise to flies in autumn which lay their eggs on such
grasses as couch and timothy. In America this brood
does enormous damage to autumn sown wheat, but in
this country it gives little trouble. Most of the pupae
hatch out in spring and the eggs are laid on the growing
wheat plants. The flies are gnat-like with bodies
about } inch in length and with long legs and feelers.
This pest is preyed on by a number of parasites, and
large numbers of these come out of the so-called flax
seeds.

Remedial Measures.

A stiff strawed wheat does not go down under an
attack nearly so much as a weaker strawed variety.
In one case where a crop was being attacked two kinds
of wheat had been sown in the same field, the weaker
strawed variety was badly laid but in the stiffer
strawed form it was difficult to find an elbowed stem.

An infected stubble should be deeply ploughed in
the autumn. Complete inversion of the soil by means

140 Flies [ CH.

of a skim coulter buries the pupae, and so prevents
them giving rise to flies in the following spring.
The screenings of infected wheat often contain flax
seeds which should be destroyed.
The grain of an infected crop should be carefully
examined if used for seed. Couch and timothy should
be kept down as much as possible.

Wheat Bulb Fly (Hylemyia coarctata).

This fly has been the cause of considerable loss to
wheat growers. It is said to be bad after a bare fallow
or a crop which only partially covers the land, but this
has not yet been proved.

The life history is not known with certainty, but
seems to be very similar to that of the frit fly. The
maggot is larger than that of the frit fly and reaches
nearly 4 of an inch in length. It may be found
during April feeding on the young shoot and thus
stunting the growth and preventing the formation of
ears.

No satisfactory preventive measures have been
discovered.

Cabbage Root Flies.

There are several flies whose maggots attack the
roots of cabbage and allied plants, but a description
of the cabbage root fly (Phorbia brassicae), which is the
commonest, will serve to show the method of attack
and how to deal with it. This fly attacks all cruciferous
crops, but the greatest damage is done to cabbages,
cauliflowers and turnips.

When a cabbage plant is attacked the outer leaves
turn yellow, the plant makes little growth and soon

x1] Flies 141

Fig. 42. A cabbage plant which has been attacked by the cabbage
root fly (Phorbia brassicae). The maggot is shown at the side.

142 Flies [cH.

withers. On pulling up one of these plants we find
that the main root is decaying and very few fibrous
roots are left; burrowing in the decaying root or at
the base of the stem are a number of fly maggots.

These are about 4 inch long when full grown, and
whitish in colour. The front end is pointed and carries
a pair of hook-like jaws. Behind the head are a pair
of much branched spiracles. The tail end is blunt and
carries a number. of projections which enable us to
recognize it (see Fig. 43.4). The eggs from which the
maggots hatch are laid just below the surface of the
soil, on or very close to the plants. On hatching they
begin to eat the outer layer of the root and reaching
the inside feed on the softer portions. They also make
it possible for other organisms to enter, thus hastening
the decay of the roots.

When fully grown the maggots change to brown
puparia (see Fig. 43 B) usually in the soil, but occasion-
ally in the roots. In about a fortnight or more the flies
come out of these pupae. They resemble the ordinary
house fly, but are considerably smaller. The first flies
usually appear towards the end of April. There are
two or three broods a year and the winter season is
usually passed as pupae in the soil, but also as adult
flies. From the pupae ichneumon wasps and small rove-
beetles may be hatched out; these are parasitic and
help to keep down the number of flies.

Remedial Measures.

In America these flies have been successfully kept
in check by preventing them from laying their eggs in
the soil near the cabbage roots. This is done by
means of tarred cards about 3 inches across. They

x1] Flies 143

Fig. 43. Phorbia brassicae. The cabbage root fly. A, the larva;
B, the pupa; C. the fly. (Magnified.)

144 Flies [CH.

are. stamped out by means of a special instrument.
Several thousands can be done in a day. They have
a slit to the centre where it is cut as shown in Fig. 44.
These are put round the stem

of the cabbages at the time of

transplanting. The cards must

be put on carefully as their

object is to prevent the fly

from reaching the soil near the

cabbage. They must be close

to the ground otherwise the fly

will crawl underneath. If the

eggs are laid outside the card

the larvae are unable to reach pea pa ble a ‘as
the plants. The plants should eee is . ae ae
be examined at the time of cabbage plants.
transplanting and any infested

with maggots should be burned.

When transplanting a little soot and lime dibbled
in with the plants helps to keep off the fly.

In cases of attack infected plants should be pulled
up and burned and the land dressed with gas lime
after the crop has been taken.

Cabbage and other cruciferous crops should not be
planted the year following an attack, and all cruciferous
weeds should be kept down.

In gardens, sand containing paraffin (at the rate of
% pint of paraffin to a bucket of sand) sprinkled round
the plant will keep off the fly for a time, and may prove
useful if done once a week until the plants have got
a good start.

The puparia remain in the soil or in the old stumps
and it is important that means should be taken to

x1] Flies 145

prevent them from hatching. All diseased stumps
should be burned and the soil should be turned under
as deeply as possible as soon as the crop is removed.
It is chiefly in gardens where cruciferous crops are
grown every year that this pest proves most destruc-
tive. When the crops are rotated the fly has great
difficulty in living from one crop to the next.

The carrot fly (Psila rosae) and the onion fly
(Phorbia cepetorum) have life histories very similar to
the cabbage fly.

The damage done by the former may be reduced by
keeping the carrots earthed up as tightly as possible.

In the case of the onion fly dusting with a mixture
of two parts of lime to one of soot is said to be useful.
All plants attacked together with the maggots should
be destroyed.

Leather Jackets (Tipula sp.).

Leather jackets are the grubs of the flies which are
commonly known as daddy longlegs or crane flies.
There are several different species which injure crops,
all very similar in appearance and in the damage
which they do.

It is the larvae or grubs which feed on nearly all our
crops and often do enormous damage to grass land and
roots. Clover leys and corn may also suffer consider-
ably. These grubs are of a dirty or smoky colour and
somewhat difficult to see in the soil. They vary from
4-1} inches in length, the longer ones being about
4 inch across, the others correspondingly thinner.
They are legless but possess a definite retractile head
with a pair of jaws. The tail end is thick and carries
six conical papillae. Their skin is tough and wrinkled,

P. F. 10

146 Flies [CH.

Cc

Fig. 45. Tipula sp. Daddy longlegs. A, the larva or leather
jacket; B, the pupa; C, the daddy longlegs fly.

xt] Flies 147

hence their name Leather Jackets. The pupa is about
the same size as the grub from which it is formed.
Its abdomen is covered with a number of spines. Its
head bears two horn-like projections (see Fig. 45 B).
When the adult fly is about to come out the pupa
moves to the surface so that its upper half is exposed.
The empty cases are often a nuisance on putting
greens.

The flies themselves are too well known to need
description. According to Curtis the eggs are laid
as the insects fly or when they are at rest amongst
the herbage and are propelled as from a pop-gun.
This takes place in damp or shady places, preferably
on grass land or on the grasses of ditches and hedges,
chiefly in late summer and autumn, but in some
species they may be laid in spring. The grubs live
for about eight months chiefly on various roots. They
may however feed above ground at night. In some
species there are two broods, the first brood of flies
appearing in the spring and the second in the autumn.
A large number of the grubs are often found after a wet
autumn.

Remedial Measures.

All wet land should be drained if possible and tufts
of rank grasses should be kept cut. The grasses of
hedges and ditches should also be cut and burnt.

Bush harrowing or rolling pastures when the flies
are seen in large numbers will kill some of them and
prevent others from laying eggs.

Pasture land and leys should be broken up early in
autumn if possible. A large number of substances
have been applied to grass land in order to try and kill

10—2

148 Flies [CH.

the grubs, but being very tenacious of life they are not
killed unless the application is so severe that the grass
is also killed. Heavy rolling early in the morning
when the grubs may be on the surface kills some of
them, and also consolidates the soil so that others
cannot move about so freely. This is particularly
useful when corn crops are attacked. They are eaten in

Fig. 46. Wasps eating daddy longlegs flies. These wasps
were destroyed in the nest.

large numbers by rooks, starlings, plovers, pheasants,
gulls, and moles, and to a smaller extent by thrushes
and blackbirds. Considerable numbers of adults may
often be found in wasp nests (see Fig. 46), and they are
also eaten by flycatchers, rooks, swallows, and spar-
rows. When a root crop is attacked frequent hoeing
is useful as many grubs are killed and others are turned
up and eaten by birds. The penning of sheep on the
land when the pupa cases begin to force their way up
to the surface has proved successful.

xI] Flies 149

Wheat Midge (Cecidomyia tritict).

This pest damages wheat by injuring the grain
and causing it to become very shrivelled. In an
ear that is attacked we shall find inside the chaff a
number of small yellowish or orange coloured legless
grubs about 4 inch long. These suck the juice of
the grain. Just before harvest some of the grubs go
down into the soil and pupate, forming orange coloured
pupae. Others remain in the ears and are harvested;
on threshing these may be found in the screenings.

The flies come out about June and lay their eggs
usually in the evening on the developing flowers.
The flies have yellowish bodies and very noticeable
black eyes.

Remedial Measures.

Deep ploughing has proved effective in checking
this pest, as the delicate fly is unable to make its way
through the soil. All infected screenings should be
burnt.

Warble Fly.

The well-known warbles on cattle are caused by the
maggots of flies known as Hypoderma lineata and
Hypoderma bovis. The affected cattle have lumps or
abscesses on their backs. Each of these lumps contains
the maggot of a warble fly.

The life history of the warble fly has not yet been
worked out in all its stages. It was formerly supposed
that the fly laid its eggs on or in the backs of cattle,
and that the maggot bored its way into the skin or was

150 Flies [CH. XI

hatched out in it. It has since been shown that the
eggs are not laid on the backs where the warbles are
found, but are laid on the hairs of the legs and sides
of the cattle. They are very difficult to find as they
are placed on the hairs close to the skin. The small
larvae which hatch out from the eggs have been seen
to bore into the skin when placed on it. The next
stage of the larva is found in the wall of the gullet and
from this it was for some time supposed that the eggs
or maggots were licked into the mouth. How the larvae
get from the egg into the gullet 1s not yet known.

From the wall of the gullet it is thought that the
larva bores its way through the tissues to the position
in which we find it under the skin of the back. The
eggs are laid during the summer, the actual date
varying according to the climate. Flies have been
seen as early as June and as late as the middle of
September.

The maggots live in the backs of the cattle until
May or June. The lumps containing them have holes
which ensure a sufficient supply of air.

When fully grown the maggot is about 1 inch long
and of a blackish-brown colour. It is segmented and
wrinkled. It has no legs but possesses a number of
very small hooks which are situated on transverse
ridges. The anterior end has a pair of fork-like jaws
and at the posterior end are a pair of dark brown
spiracles which touch each other (see Fig. 47).

They set up inflammation in the flesh and cause a
quantity of pus to be formed, on which they feed.
As we should expect from the presence of the spiracles
at the tail end, they live head downwards. When fully
grown the maggots make their way out of the lumps

B

Fig. 47. Hypoderma bovis. The warble fly. A, the larva or warble
taken from a bullock’s back; B, the warble fly. (The fly is only

half the length of the photograph.)

152 Flies [CH.

and fall to the ground, where they pupate and form
almost black pupa cases. This takes place in the early
part of the summer, and about a month later the flies
come out. They are very like small humble bees.
They fly about on hot days and produce a low humming
noise which terrifies the cattle and causes them to
rush about wildly. On tanning the hides of warbled
cattle the skins are found to have holes in them, each
hole being caused by a maggot. The surface of the
meat of infected cattle has jelly-like patches on it and
is known to butchers as “licked beef.” These parts
have to be cut away.

The presence of adult flies near cows may cause
injury as the cattle rush aimlessly about in their
endeavour to get away from them.

Remedial Measures.

It has been and is still the custom to smear the
backs of cattle with some nasty smelling preparation
just before the fly appears in summer; this is done
with the view of preventing the warble flies from
laying their eggs there. This method of treatment is
founded on a false account of the life history of the fly,
and such experiments as have been made tend to show
that smearing of the backs does little good as we should
expect, knowing that the eggs are laid on the legs and
shoulders. Cattle which have had their backs covered
with cloths from June until the end of September have
been found to have warbles on their backs in the
following spring.

The warble fly does not like shade and does not go
near cattle standing in water. It is very essential
that cattle should be provided with a necessary

XI] Flies 153

amount of shade so that they can take protection
from the fly.

The best method of keeping down this pest is to
examine cattle in the spring and to squeeze out the
warbles between the thumbs and destroy them. This
is a much more satisfactory method than putting some
kind of grease or ointment on the animals’ backs in
the spring in order to stop up the holes. No dressing
has yet been found which will kill the maggots without
injuring the skin.

The practice of squeezing out the maggots if carried
out systematically by farmers would considerably
reduce the number of flies, because, as far as we know,
the backs of cattle contain nearly all the warbles
during the winter, and if these were destroyed few flies
would remain to infect cattle the following year. Young
stock are more frequently warbled than older ones.

Horse Bot (Gastrophilus equi).

Damage is sometimes caused by the maggots or
bots of a fly known as Gastrophilus equi living in the
stomach of horses. When present in large numbers
the wall of the stomach may become ruptured with
fatal results. In small numbers little damage is
done.

The brown and grey fly lays its eggs on the hairs of
horses’ legs or in some position in which the horse can
reach them with its tongue. They are fixed very
tightly on the hairs so that the horse cannot lick them
off. One fly is said to lay over 500 eggs. In about four
or five days the larvae hatch out inside the eggs, where
they remain until warmed by the licking of a horse’s
tongue. They then come out of the egg and pass into

154 Flies [CH.

the horse’s mouth and thence into the stomach. They
do not necessarily get into the horse on which the eggs
are laid, as another horse may lick the eggs and swallow
the maggots. In the stomach the young larvae
attach themselves to the wall by means of a pair of
strong hook-like jaws. They are enabled to move
through the contents of the stomach by means of
transverse rows of curved spines pointing backward
situated at the juncture of the segments except at the
posterior end. The bots feed on the products of
inflammation which they set up. They may remain
fastened to the stomach wall for nearly a year when
they drop off and pass to the exterior in the faeces.
When fully grown they may reach about 1 inch in
length. They are somewhat pointed in front, but end
bluntly at the hind end which carries a large compound
spiracle. This can be closed by means of a pair of
fleshy lobes which prevent the bots from becoming
choked.

If they fall on suitable ground they burrow into it
to change into puparia. This usually takes place in
June and the flies come out a few weeks later. There
are several different species of bots in addition to the
one described above, one of which attaches itself to
the anus of the horse. Bots have also been found in
the brain and spinal cord.

Remedial Measures.

Like the warble fly this fly does not like shade and
hence plenty of shelter should be provided in the
fields. Well groomed horses rarely suffer from bots,
as the eggs are brushed off.

x] Flies 155

Horses should be watched for the eggs during the
months they are likely to be present, ie. from J uly to
October. The legs should be well brushed or washed
with warm water in order to hatch out the eggs. The

droppings of infected horses should also be watched for
the bots.

Sheep Nasal Fly (Oestrus ovis).

This grey fly may be seen in early summer flying
around sheep, especially in hot weather. The flies
settle on their noses from time to time in order to lay
their eggs or to deposit newly hatched larvae. The
sheep often try to keep them off by rubbing their
noses on the ground and may show uneasiness when
the flies are near them.

The maggots pass into the nasal cavities of the
sheep where they live for about 10 months on the
mucous discharge caused by their presence. Badly
infested sheep have a mucous discharge running from
their noses, and often sneeze violently. They also
rub their noses on the ground. They may frequently
shake their heads and hold them on one side. This
state of affairs is known as false gid, and is due to the
presence of the maggots in the nasal passages. It
must not be confounded with true gid, which is caused
by the cyst of a tapeworm.

When fully grown the maggots come out of the
nose or are forced out by the sneezing of the sheep.
They make their way just below the surface of the
ground and change into brown puparia. From these
the flies come out in June and July.

The condition of infected sheep is considerably
reduced and in severe cases they may die.

156 Flies [cu.

Remedial Measures.

The best method is to try and prevent the flies from
laying their eggs on the sheep’s nose by covering it with
a strong smelling substance such as tar.

A method has been suggested in which the sheep
smear themselves. They are supplied with a box of
salt to which they have access through holes, about
2 inches in diameter. These holes are then painted
over with tar and in this way when the sheep lick the
salt their noses become covered with the tar or prepara-
tion used. When known to be infested they should
be isolated about the middle of April so that the
maggots which are sneezed out may be destroyed.

A pasture which has become infested from sheep
containing the maggots should be kept free from
sheep during June and July.

Sheep Maggot.

The small maggots found on sheep are the larvae
of two green bottles, Lucilia sericata and Lucilia
caesar, and the larger ones are those of the blue bottle
(Calliphora erythrocephala). The smaller ones do the
most damage as they dig deeper into the flesh. Lambs
suffer more than older sheep, being attacked in the
parts around the tail, on the shoulders, and also on
the poll. Hot and damp weather seems to favour
the attack.

The affected sheep can usually be picked out by the
continual wagging of their tails. They also rub and
bite themselves to try and get rid of the irritation.

x1] Flies 157

The wool soon becomes discoloured and matted
together, in bad cases it falls out and large sores are
produced. The affected sheep lose condition very
rapidly. The flies lay their eggs from May until
October on the positions mentioned, and especially
where dirt has collected. Each fly is capable of laying
several hundred eggs.

The small legless maggots which hatch out feed
first on the surface and then in the sores formed. In
about a fortnight they fall to the ground and change
into puparia. In another fortnight or more the flies
hatch out. In this way several broods are produced
throughout the year.

Remedial Measures.

It is the shepherd’s business to watch the sheep
carefully so that those affected may be treated early.
The hindquarters should be kept as clean as possible
by docking and clipping the wool of the tail and the
regions around. The fly prefers putrid matter in which
to lay its eggs so that clean sheep may suffer less.
Clean sheep however are often: attacked.

Dipping sheep in some poisonous substance is
compulsory in this country between certain dates.
This order was brought in to reduce scab (caused by
a mite). It also kills maggots, keds, lice and ticks.
Sheep which have been dipped in this way may become
struck by maggot about a fortnight later. In bad cases
it may be necessary to dip for maggot once or twice.

A dip composed of sulphur, arsenic, soda, and soft
soap is useful for keeping off flies. Dressing the
affected parts with a mixture of equal parts of turpentine
and rape oil, or by means of paraffin mixed with water,

158 Flues [CH.

kills the maggots. Dusting sulphur on this serves to
keep the fly off for a short time.

A favourite spot for maggots is behind the horns
of rams. They may be kept off by means of olive oil
and pitch oil dusted over with sulphur.

CHAPTER XII
APHIDES AND SAWFLIES

There are a large number of different kinds of
Aphides, or, as they are usually called, Plant Lice, or
Green Fly or Blight, and in favourable circumstances,
such as a hot dry summer, they are present in enormous
numbers. They attack practically all cultivated plants
—usually the leaves and stems but sometimes also the
roots. They belong to the same group of insects as
bugs, and live in a similar way by sucking the
juices of plants after piercing them with their mouth
appendages, which are well suited for the purpose.
They differ considerably from the majority of insects
in their methods of reproduction. They have no
complete metamorphosis in which there is a resting
stage, and only in special cases do they lay eggs.

The life history of a typical aphis will help us to
understand them.

We will start with those found in spring. These
are without wings (see Fig. 48) and are all females.
Each one gives birth to a varying number of young.

XIt] Aphides and Savwflies 159

At this time of the year no eggs are laid. Instead
changes go on inside the mother who gives birth to
living young. These begin to feed on the juices of the
plants and in less than a week they may also give birth
to young. In this way a large number of broods are pro-
duced during a season, indeed one green fly is capable
of producing several millions in a very short time.

During the summer we find winged forms together
with the wingless ones (see Fig. 48).

The winged forms are also females, no males

Fig. 48. Wingless and winged Aphides. (Magnified.)

being produced at this time of the year. They also
give rise to living young and serve to spread the
aphides from one plant to another as one host plant
soon becomes overcrowded. It is only at the end of
the season that males are produced. They may be
either winged or wingless and are born together with
the females. Pairing takes place and the fertilized
females do not produce living young but lay eggs.
These do not hatch out at once but are capable of
resisting the cold weather of winter; in spring they
give rise to the wingless females who give birth to

160 Aphides and Sanwflies [CH.

living young as described above. In some cases the
females are capable of living through the winter.
Their life history may be shortly represented thus:

Wingless females

Several broods of wingless females ... Spring
Winged and wingless females and
Summer
Several broods of winged and wingless
females
Males and females a8 ue .. Autumn
1
Eggs si wi at ... Winter

The aphides have soft swollen bodies, the colour of
which varies in different species and may be yellow, green
or brown. The feelers are usually long, and the abdomen
carries a pair of short tubes on its upper surface pointing
backwards and slightly outwards. These are char-
acteristic of aphides and are called “honey tubes”
because of the sugary liquid they secrete. Aphides are
covered with a waxy bloom which causes water to run off
them. The winged forms have two pairs of membranous
wings of which the front pair is much larger than the
other pair and also considerably longer than the body
of the insect. The males are smaller than the females.
They all live by sucking the juices of plants and have
long probosces for piercing and sucking. They often
cause the leaves to curl in such a manner that the
insects themselves are hidden away inside the curled
leaf. They also excrete a sticky substance known as

XIT] Aphides and Sawflies 161

“honey dew,” which may be found on the leaves of
trees. It blocks up the stomata and sometimes
becomes so dirty, owing to the growth of a saprophytic
fungus, as to appear like a coating of soot.

If the aphides were not checked by some natural
means it is obvious from the rate at which they
reproduce that they would soon cover all the plants
on the earth. They have a large number of natural
enemies, and nature has given them this capacity for
reproduction in order to withstand these. After a bad

Fig. 49. Lady-birds. An egg (highly magnified), « larva, two
pupae and three beetles.

attack of aphis we often find a large number of lady-
birds on plants. These small beetles and their larvae
devour a large number of aphides. The larvae of the
lace-wing flies, also known as “niggers,” feed on
plant lice and may often be found with the skins of
their victims on their backs (see Fig. 50). They are
usually difficult to find when at rest.

The legless larvae of hover flies also eat a consider-
able number of green flies.

11
P.F

162 Aphides and Savwflies [CH.

On a plant attacked by aphis may be found among
the living forms a number of inflated skins of a whitish
colour looking like small balls. These are the dead
lice which have been killed by ichneumon wasps.
These little wasps lay their eggs in the bodies of the
lice and as the louse grows its parasite also grows and
kills it. From the inflated skins the ichneumon wasps
hatch out and continue their useful work of keeping
down the number of aphides by laying their eggs in
them.

Fig. 50. Lace-wing fly. Eggs. Two larvae, one with the skins of its
victims on its back and one adult.

Earwigs eat large numbers of green flies and also
their eggs.

Considerable damage is done by aphides in hot dry
weather. Rainy weather is unfavourable to their de-
velopment.

Remedial Measures.

It must be borne in mind that a certain number of
green flies are killed by other insects. The best means
of keeping down these pests is to spray with some
solution containing soft soap as a basis. The soft soap

xir] Aphides and Sawylies 163

makes the solution stick to the aphis and so stops up
the breathing pores.

MixtureI. Soft soap ... 5-10 lbs.
Water ... ..» 100 gallons.
Mixture II. Tobacco powder 30 lbs.
or Nicotine ... 5 ounces.
Soft soap ..._5 Ibs.
Water ... ... 100 gallons.

5 Ibs. of tobacco leaf may be substituted in this mixture
but it is much dearer.

This is the most effective mixture, but it is rather
expensive.

Mixture III. Quassia chips 10 Ibs.

Soft soap ... 5 Ibs.

Water ... ... 100 gallons.
The quassia chips are allowed to simmer for two hours
and then strained.

This spraying is in general use for fruit trees, hops,
and roses. It is important to spray early just after
the flies have hatched, as little good is done once the
leaves become curled.

In the case of the bean aphis the best method is
to “‘top” the beans as soon as the flies are noticed.
Spraying with soft soap has also been shown to be
profitable in bad seasons. This aphis also lives on
docks and thistles, and migrates from these plants to
the bean.

The hop aphis migrates to plums and damsons at
certain seasons and consequently when grown near they
should be sprayed as well as the hops.

The woolly aphis or American blight (Schizoneura
lanigera), which is found chiefly on the apple, lives

11—2

164 Aphides and Sauwflies [CH.

underground as well as on the shoots. In this case in
addition to spraying the trees it is necessary to inject
carbon disulphide into the soil in order to kill those on
the roots. If the root forms are not killed the tree
soon becomes infected by them. Painting the affected
parts with methylated spirit or paraffin or spraying
with paraffin emulsion has proved useful in keeping
down woolly aphis.

Carelessness among certain nurserymen in allowing
their young stock to become infected is responsible for
a large amount of damage done by this pest.

Various winter washes have proved effective in
reducing fruit aphides by preventing the eggs from
hatching.

Sawrflies.

Sawflies are not true flies as they possess two pairs
of wings. They belong to the same family as bees and
wasps.

Corn Sawfly (Cephus pygmaeus).

This pest rarely does much damage in this country.
It attacks wheat and oats.

The eggs are laid in the stems of young plants and
the larvae which hatch out feed on the soft substance
inside and eat their way through the knots. About
harvest time the maggots are fully grown and they
make their way to the bottom of the stem where they
eat a ring almost round it. The attacked plants may
be picked out as the shoots die and the dead ears are
easily seen among the ripening corn.

Unlike the larvae of most sawflies the maggots seem
to be legless: as their legs are too small’ to be-seen.

XII] Aphides and Sawylies 165

The maggots are small, curled, wrinkled grubs with a
definite head. They pupate in the stem just below. the
cut, and here they remain until the following May, when
they hatch into sawflies.

Remedial Measures.

As the pupae are present in the stubble after harvest,
means should be taken to destroy them. The stubble
should be burnt if possible: if not it should be harrowed
and the plant remains collected and burned.

The larvae of other sawflies may be found feeding
on fruit trees. They resemble small caterpillars, but
may be distinguished from them by the number of
their legs. In addition to three pairs of true legs they
possess more than five pairs of false legs, which is a
greater number than is found in any caterpillars of
moths and butterflies.

CHAPTER XIII

EELWORMS

Eelworms are not insects but true worms. Some
of them cause plant diseases and others are present in
a large number of diseased plants. They are unseg-
mented worm-like creatures, very small, and never
reach + inch in length, the majority being about
gy inch long. For our purpose we may classify them
as: parasitic forms; free-living forms.

The former cause plant diseases. The latter are
always present in decaying roots or stems, and are

166 Eelworms [CH. XIII

regarded as living saprophytically on decaying matter,
but it is possible that they hasten the destruction of
the plant. Parasites may readily be distinguished
from free-living forms, by the possession of a retractile
spine-like process at the head end which is used for
penetrating plants (see Fig. 51(C).

The parasitic forms are comparatively much thinner.
They are very sluggish in their movements as compared
with most free-living forms. Many of the latter have
long tails which help them to move quickly.

Tulip-rooted Oats.

Tulip root in oats is due to two causes, one of
which, frit fly, has already been studied. The other
cause is due to an eelworm known as T'ylenchus dipsaci
(formerly devastatrix). Sometimes both are found in
the same plant. The two diseases are very similar in
appearance (cf. Figs. 38 and 52). On examining diseased
plants containing frit fly we usually find (not in the
earliest stage) in addition to the frit fly a number of
free-living eelworms. If the tulip root is due to
Tylenchus we shall find a considerable number of
Tylenchus together with a number of free-living forms.
We are now in a position to distinguish T'ylenchus from
the free-living forms (see Fig. 51). In looking for
eelworms we simply tease a small portion of the stem
in water on a slide and examine it under the microscope.

A Tylenchus very similar to J. dipsaci in appear-
ance is one of the causes of “clover sickness” and
is held by many authorities to be the same as that
which attacks oats: nevertheless healthy crops of oats
have been grown after clover attacked by the eelworm
Tylenchus sp.

Fig. 51 A and B, free-living eelworms; C, « parasitic eelworm;
D, the swollen female of Heterodera radicicola. (Magnified.)

Eelworms [CH.

168

‘OIystzojoereyo AJA OI SUIO}S poystMy oy,

sonsdap snyouahi., <q peyoesye squed yo 2a “Sr

XI] Eelworms 169

Remedial Measures.

Deep ploughing or ploughing with a skim coulter is
recommended for this disease. Such crops as red
clover and oats, which are very liable, should not be
taken for some time on land containing their respective
eelworms. When possible the refuse of diseased crops
should be destroyed.

Fig. 53. Ear cockles of wheat caused by Tylenchus scandens. The
dark grains somewhat resemble bunted grains.

Ear Cockles in Wheat.

Another disease caused by an eelworm is that
known as “purples” or “ear cockles” (Fig. 53).

170 Eelworms [CH.

The culprit in this case is known as Tylenchus
scandens.

In this disease the grains of wheat are affected.
They become rounded or irregular in shape and are of
a dark or purplish colour. If a portion of the inside
of a diseased grain is examined in a drop of water it is
found that the thread-like bodies composing the mass
begin to move about, and by their structure show them-
selves to be parasitic eelworms. The eelworms are
said to crawl up on the outside of young plants and
enter the developing flowers.

Remedial Measures.

The grains containing the eelworms are very light
and float to the surface when wheat is steeped and are
easily skimmed off.

Root Knot.

The eelworm which produces knots on the roots of
a large number of plants is known as Heterodera radi-
cicola. It may also be found at the base of the main
stem which is below the ground (see Fig. 54).

This eelworm is peculiar in that the female after
being fertilized swells and becomes almost spherical
(see Fig. 51 D)

Inside the knots formed by this eelworm are small
white balls which when examined under the microscope
show themselves to be eelworms. The males are very like
T'ylenchus. These eelworms flourish best on sandy soils.

Remedial Measures.

In fields this disease can be reduced by means of
gas lime. In greenhouses it may be kept down by
watering heavily or by partial sterilization.

XIII] Eelworms 171

A B

Fig. 54. A, a healthy tomato root; B, a tomato root attacked
by Hetercdera radicicola.

The beet eelworm (Heterodera schachtii) does not
form knots in the same way, but the female is outside
the plants, only its head being inside.

INDEX

Abdomen 85
Acid manures 43
Aecidiospores 68
Agar-agar 7
Agrotis 98
American gooseberry mildew 14,
55
Amoeba 38
Anbury 35-43
Antennae 85
Aphides 158
Ascospore 52, 59
Ascus 52, 59

Barberry 68
Barley ergot 61

frit fly on 127

gout fly on 134

Hessian fly on 138

mildew 47

rust 64

smut 73
Bean aphis 163

beetle 126

weevil 125
Beet rust 1, 72
Beetles 92, 103-127
Birds 90, 101, 118, 148
Black scab of potatoes 44-47
Blight 158

of potatoes 17
Blue stone 26-30, 78
Bordeaux mixture

55 :

Bordeaux mixture (dry) 29-30
Botrytis 5
Bots 149, 153
Bruchus 126
Bunt 81-84
Burgundy mixture 29
Butterflies 87-92, 102

26-30, 35,

Cabbage butterflies 85-91, 98
caterpillars 85-91, 98
club 35, 122
finger and toe 35
gall weevil 122
moth 98
root fly 140
root maggot 140

Calandra 119

Carbon disulphide 121, 127

Carrot fly 145

Caterpillars 87-92, 98

Caterpillars’ eggs 90

Cecidomyia destructor 138
tritici 149

Cells 4

Centipedes 107

Cetonia 113

Ceutorrhyncus 122

Chafers 113

Charlock 36

Chitin 86

Chlorops 134

Chrysalis 89

Claviceps 56-61

Click beetle 103

Clover sickness 62, 166

Club 35-43, 122-124, 170

Cocoon 92

Conidia 12

Conidiophore 19

Corn sawfly 164

Crane flies 145

Cultures 7

Daddy longlegs 145
Damping off 31-33
Diamond-back moth 102
Dry spraying 29-30

Ear cockles 169

Eelworms 165-171
Epidemic 14
Ergot 56-61
Erysiphe 47-54

Finger and toe 35-43
Flies 92, 127-158
Formaldehyde 78-79
Frit fly 127

Fungicides 26, 55, 78, 79

Gastrophilus 153
Gelatin 7

Gid 155

Gout fly 134
Grain weevil 119
Green fly 158
Gulls 101, 108

Haustoria 13
Hessian fly 138
Heterodera 170
Hop aphis 163
mildew 54-55
Horse bot 153
Hover fly 161
Hylemyia 140
Hypha 3
Hypoderma 149

Ichneumons 90, 162

Imago 89-92

Insecticides 97, 101, 121, 163

Insects, characteristics 85
useful 90, 161, 162

Lady-birds 161
Larks 112

Larvae 89-92
Leather jackets 145
Lime 26-31, 43
Lucilia 156

Maggot 92

Mamestra brassicae 102

Mangold rust 1, 72
surface caterpillar 98

May hug 113

Melolontha 113

Metamorphosis 91

Midge 149

Mildews 47-56

Index

Millipedes 107
Mole 107, 118, 148
Moths 92, 98-102
Mould 11
Mushroom 8, 13
Mycelium 3
Myxamoeba 38

Nectria 16
Niggers 161

Oats, eelworm in 166
frit fly 127
mildew 47
rust 64
smut 73
tulip-rooted 166

Oestrus 155

Onion fly 145
mildew 33-35

Oscinus 127

Owls 118

Parasite 2
Pea beetle 126
weevil 125
Penicillium 5, 6
Peronospora schleideni 33-35
Petri dish 7, 8
Pheasants 148
Phorbia 140
Phyllopertha 113
Phytophthora 17-31
Pieris 85-91
Pigs 101, 118
Plasmodiophora 35-43
Plasmodium 39
Plovers 101, 118, 148
Plutella 102
Potato, black scab of 44-47
canker 44-47
disease 17-31
dry rot 17-31
tumour 44, 47
wet rot of 24
Preservatives 12
Pupa 89, 92
cases 92
Puparia 92
Pythium 31-33

Rhizotrogus 113

173

174

Rooks 101, 118, 148
Root flies 140
knot 170
maggot 140
Rose chafer 113
mildew 55
Rotation of crops 15
Rusts 64-72

Saproph 2

Seotine OB, 164

Sclerotinia 62-64

Sclerotium 56

Sheep maggot 156
nasal fly 155

Sitones 125, 126

Smuts 73-84

Spiracles 86

Spore-cases 51

Spraying 26-30

Starlings 101, 118, 148

Sterilization 11, 12, 33

Suckers 13

Surface caterpillars 98

Synchytrium 44-47

Teleutospore 67

Thorax 85

Tilletia 81-84

Tipula 145-148

Toads 101

Trachea 86

Tulip-rooted oats 166

Turnip club 35, 122
finger and toe 35
flea beetle 107

Index

Turnip fly 107
gall weevil 122
moth 98
root maggot 140
surface caterpillars 98
Tylenchus 166, 169, 170

Uredineae 64

Uredospore 65
Uromyces 1, 72
Ustilago 73-81

Warbles 149
Ward’s Tube 57
Wart disease of potatoes 4447
Wasps 90, 148
Weevils 119
Wheat bulb fly 140
bunt 81
ear cockles 169
ergot 61
frit fly on 127
gout fly on 134
Hessian fly on 138
Little Joss 71, 72
midge 149
mildew 47
rust 64
smut 73
White grubs 113
Winter moth 94
Wireworm 103
Woolly aphis 163
Wound parasites 16

Zoospore 21

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