CHAPTER VII[ToC]
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 José 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 José 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.