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.