INSECTS AND DISEASES AFFECTING THE APPLE
It is a common saying among farmers who have grown apples on their
farms for many years that there are many more pests to fight than
there used to be. How often we have heard a farmer tell of the perfect
apples that grew on a certain tree "when he was a boy," before people
had generally heard of codling moth, San Jose scale, apple scab, or
other troubles now only too common. "We never sprayed, but the apples
were fine," he says. Is this the usual glorification of the mythical
past or is it true? In all probability it is a little of both, but it
is undoubtedly true that insects and fungous diseases have increased
rapidly of late years.
REASONS FOR PEST INCREASE.--When there is an abundance of food and
conditions are otherwise favorable, any animal or plant will thrive
better than when the food supply is scarce and conditions unfavorable.
As long as apple trees were scattered and few in number there was not
the opportunity for the development of apple pests, but as soon as
they became numerous the prosperity of bugs and minute plant parasites
was wonderful to see. Another factor which has been at least partly
responsible for the great increase in our insect life is that man has
upset nature's balance by destroying so many birds, and, by
interfering with their natural surroundings, driven them away. Birds
are great destroyers of insects, and their presence in the orchard
should be encouraged in every possible way. Add to these facts the
marvelous fecundity of the insect tribe, and the increase is less
remarkable. Loss from these orchard pests has now run up into the
millions. It has been estimated that the loss in the United States
from wormy apples alone is over $11,000,000 annually. Thus has the
necessity for fighting these enemies of good fruit arisen.
In order successfully to combat an insect or a disease it is very
necessary to have a somewhat detailed knowledge of its life history
and to know its most vulnerable point of attack. It is impossible to
work most intelligently and effectively without this knowledge, which
should include the several stages of the insect or disease, the point
of attack, the time of making it, and when and with what it can be
most easily destroyed. The number of insects and diseases which affect
the apple is so great that it is simply out of the question to treat
them all in detail here. We have therefore selected nine insects and
three diseases as those pests of the apple which are most common and
whose effects are usually most serious. The essential facts in their
life histories and their vulnerable points will now be pointed out.
The method of study may be taken as applicable to any other pests
which it may be necessary to combat.
INSECT PESTS.--Of the many insects which affect either the tree or the
fruit of the apple, the nine selected probably inflict the most damage
and are the most difficult to control of all those in the Northeastern
States. According to their method of attack all insects may be divided
into two classes: biting and sucking. Biting insects are those which
actually eat parts of the tree, as the leaves or fruit. These are
combated by the use of stomach poisons as we shall see in the
following chapter. Sucking insects are those which do not eat the tree
or fruit directly, but by means of a tubelike proboscis suck the
juices or sap from the limbs, leaves or fruit. Of the biting insects
the five which we shall discuss are: (1) codling moth, (2) apple
maggot, (3) bud moth, (4) cigar case bearer, (5) curculio. The four
sucking insects discussed are: (6) San Jose scale, (7) oyster shell
scale, (8) blister mite, and (9) aphis or plant louse.
1. THE CODLING MOTH, the most insidious of all apple pests, is mainly
responsible for wormy apples. The adult is a night flying moth with a
wing expanse of from one-half to three-quarters of an inch. The moths
appear about the time the apple trees are in bloom. Each female is
supposed to lay about fifty eggs which are deposited on both the
leaves and fruit, but mostly on the calyx end of the young apples. The
eggs hatch in about a week and the young larvae or caterpillars begin
at once to gnaw their way into the core of the fruit. Three-fourths of
them enter the apple through its blow end.
After twenty to thirty days of eating in the apple, during which time
they become full grown and about three-quarters of an inch long, they
leave the apple, usually through its side. The full grown caterpillar
now secretes itself in the crevices in the bark of the tree or in
rubbish beneath the tree and spins a tough but slight silken cocoon in
which the pupal period is passed. This lasts about a fortnight, when
the process is sometimes repeated, so that in the Eastern States there
are often two broods each season.
The most vulnerable point in the career of this little animal is when
it is entering the fruit. If a fine poison spray covers the surface of
the fruit, and especially if it covers the calyx end of the apple
inside and out, when the young larvae begin to eat they will surely be
killed. It is estimated that birds destroy eighty-five per cent. of
the cocoons on the bark of trees.
2. APPLE MAGGOT.--It is fortunate that the apple maggot, often called
the railroad worm because of its winding tunnels all through the
fruit, is not as serious a pest as the codling moth for it is much
more difficult to control with a poison. A two-winged fly appears in
early summer and deposits her eggs in a puncture of the skin of the
apple. In a few days the eggs hatch and the maggots begin to burrow
indiscriminately through the fruit. The full grown larvae are a
greenish white in color and about a quarter of an inch long. From the
fruit this insect goes to the ground where the pupal stage is passed
in the soil. The next summer the fly again emerges and lays its eggs.
Spraying is not effective against this insect as the poison cannot be
placed where it will be eaten by the maggots. The best known remedy is
to destroy the fruit which drops to the ground and for this purpose
hogs in the orchard are very effective. The distribution of this
insect in the orchard is limited and it has shown a marked preference
for summer and autumn varieties.
3. THE BUD MOTH closely resembles the codling moth in form and size,
but differs from it in color and life history. The larvae, after
hibernating through the winter, appear as little brown caterpillars
about May first or as soon as the buds begin to open, and a week or
two later begin their work of destruction. They inflict great damage
on the young leaf and fruit buds by feeding on them. When full grown
the larvae, cinnamon brown in color with a shining black head, are
about one-half inch long. They then roll themselves up in a tube made
from a leaf or parts of leaves securely fastened together with silken
threads. In this cocoon pupation, which lasts about ten days, takes
place. Early in June the moths appear. There is but one brood in the
North. These insects can be successfully combated with a poison spray
applied early before the buds open.
4. THE CIGAR CASE BEARER winters in its case attached to a twig. When
the buds begin to open in the spring it moves to them, carrying its
case with it, and begins to feed on the young and tender buds. By the
time the leaves are well open, it has fed a good deal on the tender
buds and young leaves and is ready to make a new and larger case. This
it does by cutting a leaf to suit and then rolling it up in the form
of a cigar, whence its name. In this case the larvae continue feeding
about a month, causing much injury to the leaves, although this is not
as serious as the mutilation of the young buds in the spring, before
the tree is fully leafed out.
About the last of June pupation takes place and in about ten days the
moth emerges. The eggs are then layed along the midribs of the leaves
and hatch in about fifteen days. The newly hatched larvae become leaf
miners during August, and migrate to the branches again in the fall
where they pass the winter. These leaf and bud eating insects can be
destroyed by applying a poison to the buds before they open and again
later to the opening leaf and flower buds.
5. CURCULIO BEETLES pass the winter under leaves and grass. In the
spring they feed on the blossoms and the tender leaves. As soon as the
young fruits are formed the female deposits her eggs in a puncture
made just inside a short, crescent-shaped cut in the little apple. The
eggs soon hatch and the young grubs burrow into the fruit to the core
where they remain two or three weeks, or until full grown. The larvae
then bore their way out of the fruit and drop to the soil where they
pupate. The earliest of the beetles to emerge again feed on the fruit.
The principal damage from this pest comes from the feeding of the
beetles and the work of the larvae, although the latter is not as bad
in the apple as in the stone fruits. A poison on the young foliage as
soon as the beetles begin to feed is the best method of combating
curculio. Jarring the tree is not as practicable with the apple as it
is with the plum.
6. THE SAN JOSE SCALE, one of our worst apple tree pests, is a sucking
insect extracting the juices of the tree from the trunk, limbs or
branches, or even from the leaves and fruit when it is very abundant.
At first the growth is checked only, but as the insects develop their
work finally results in the death of the part, unless they are
destroyed. The insect winters in an immature condition on the bark
under a grayish, circular, somewhat convex scale about the size of a
pinhead. The young, of which a great many broods are produced, are
soft bodied but soon form a scale. In the early spring small
two-winged insects issue from these scales.
After mating the males die, but the females continue to grow and in
about a month begin the production of living young--minute, yellow,
oval creatures. These young settle on the bark and push their slender
beaks into the plant from which they begin to suck out the sap. In
about twelve days the insects molt and in eight to ten more they
change to pupae, and in from thirty-three to forty days are themselves
bearing young. A single female may give birth to four hundred young in
one season and there are several generations in a season. This great
prolificacy is what makes the scale so serious a pest.
In fighting it every scale must be destroyed or thousands more are
soon born. In order to be able to use a strong enough mixture of lime
and sulphur to destroy them by smothering or choking the spray must be
applied on the dormant wood in the spring or fall or both.
Thoroughness is most essential.
7. THE OYSTER SHELL SCALE, although it is essentially the same in its
habits and in its methods of sucking the sap from the tree is not as
bad a pest as the San Jose scale because it is less prolific, there
being but one brood a year. Still this scale often destroys a branch
and sometimes a whole tree. The "lice" winter as eggs under the scale
and hatch in late May or early June. After crawling about the bark for
two or three days, the young fix their beaks into it and remain
fastened there for life, sucking out the sap. By the end of the season
they have matured and secreted a scaly covering under which their eggs
for the next season's crop winter. A smothering spray like lime and
sulphur applied strong when the trees are dormant will practically
control this scale. But the young may be destroyed in summer by a
contact spray such as tobacco leaf extract or whale oil soap.
8. THE LEAF BLISTER MITE is a small, four-legged animal, so small as
hardly to be visible to the naked eye. It passes the winter in the
bud scales and as soon as these begin to open in the spring it passes
to the tender leaves which it punctures, producing light green or
reddish pimples according to the variety of apple. These later develop
into galls or blisters of a blackish or reddish brown color and
finally result in the destruction of the leaf. Trees are sometimes
practically defoliated by this pest, and this at a time when a good
foliage is most needed. Inside of the galls eggs are deposited and
when the young hatch they burrow in all directions. In October the
mites abandon the leaves to hibernate in the bud scales again. A
strong contact spray of lime sulphur when the trees are dormant
destroys the young mites while they are yet on the bud scales, which
is practically the only time when they are vulnerable.
9. APHIDES, or plant lice, are of seasonal importance. Although nearly
always present, it is only occasionally that they become so numerous
as seriously to damage mature apple trees. But they are more often
serious pests on young trees where they should be carefully watched.
Their presence is determined by the curled and distorted condition of
the terminal leaves on the under side of which the green or pinkish
lice will be found. Eggs deposited in autumn pass the winter in this
condition, hatching in the spring about the time of the beginning of
the growth of vegetation. From these winter eggs females are hatched
which bear living young, which may also bear living young and so on
for several generations until autumn, when eggs are again deposited
for the winter stage.
Fortunately weather conditions together with parasitic and predaceous
insects hold them more or less in check. Because of the difficulty of
getting at the underside of the curled leaves where these lice mostly
work they are extremely hard to control. Lime and sulphur when the
trees are dormant destroy as many of the eggs as it comes in contact
with. A tobacco extract is quite effective as a contact spray in the
growing season. The trees must be closely watched and if the lice
appear in any considerable number they must be promptly attended to or
serious damage is likely to result.
These are by no means all the insect pests which the fruit grower has
to combat, but they are usually the most important. Canker worm and
tent caterpillars often do great damage in unsprayed orchards, but
they are easily controlled by an application of a poison as soon as
they appear. The same is true of other caterpillars and leaf eating
worms. Apple tree borers are frequently serious, especially in young
orchards, where the trees should be regularly "grubbed" and the borers
dug out or killed with a piece of wire. They may be prevented to some
extent by painting the tree trunks with a heavy lime and sulphur or
some gas tar preparation.
DISEASES.--Although not as numerous as insects, the diseases which
attack the apple inflict great damage and are fully as difficult to
control. They are caused by bacteria and by fungi which may be
compared to weeds growing on or in the tree instead of the soil. If
either of these works within the plant, as is sometimes the case, it
must be attacked before it enters. It is very necessary to be thorough
in order to control these diseases. Weather conditions influence
nearly all of them materially. Of those which attack the apple tree or
fruit we have selected three as the most serious and the most
necessary for the grower to combat, namely, (1) apple scab, (2) New
York apple tree canker, and (3) fire blight. To these should be added
in the South and middle latitudes, sooty blotch and bitter rot.
Baldwin spot is also frequently serious in some seasons and
localities.
(1) THE APPLE SCAB, commonly known among growers as "the fungus," is
the most important of our common apple diseases and is most evident on
the fruit, although it attacks the leaves as well. In some seasons the
fruit is made almost unsalable. This disease lives through the winter
on old leaves. In the spring about blossoming time the spores are
scattered by the wind and other agencies, and reaching the tender
shoots germinate and enter the tissues of the plant. Their development
is greatly dependent on the weather. In a season in which there is
little fog or continued damp or humid weather, they may not develop at
all, but where these conditions are present they frequently become
very virulent.
Spraying will be governed by the weather conditions, but the mixture
must be applied very promptly as soon as it is evident that it is
likely to be necessary and must cover every part of the tree to be
effective. The object is to prevent the spores from germinating, the
spray being entirely a preventive and in no sense a cure. The disease
most frequently first manifests itself on the tender new growth and on
the blossoms. Two mixtures have been found to control it, namely,
Bordeaux and a weak solution of lime and sulphur. One or other of
these should be applied just before the blossoms open, just before
they fall, and when necessary two and nine weeks later.
(2) NEW YORK APPLE TREE CANKER is usually found mainly on the trunks
of old trees, but it also affects the smaller branches. Practically
every old or uncared for orchard has more or less of this canker, and
where it is not checked it eventually destroys the tree. This fungus
is the cause of most of the dead wood found in old orchards. The
surface of the canker is black and rough and covered with minute black
pimples. It lives over winter and spreads from one branch or tree to
another. As it most frequently enters a branch through wounds made in
pruning, these should be promptly painted over with a heavy lead and
oil paint. All diseased parts should be cut out and removed as soon as
observed. The value of spraying for this disease is not definitely
known, but it is seldom very troublesome in well sprayed and well
cared for orchards.
(3) BLIGHT appears on apple trees in three forms, as blossom blight,
as twig blight, and as blight cankers. It is a bacterial disease
which is distributed by flies, bees, birds, etc., and cannot be
controlled by spraying. The bacteria are carried over the winter in
cankers on the main limbs and bodies of the trees, oozing out in a
sticky mass in the spring. These cankers should be cut out with a
sharp knife cutting well into the healthy bark and then washing the
wound with corrosive sublimate, one part to one thousand of water.
Cutting out and destroying are also the chief remedies to be used when
the blight appears in the twigs and blossoms. It is not usually as
serious on apples as on pears. Some varieties, like Alexander, are
more subject to it than others.