Agriculture for Beginners Part 15
[Ill.u.s.tration: FIG. 133. MOLDY PEACHES]
=Cotton Wilt.= Cotton wilt when it once establishes itself in the soil completely destroys the crop. The fungus remains in the soil, and no amount of spraying will kill it. The only known remedy is to cultivate a resistant variety of cotton or to rotate the crop.
[Ill.u.s.tration: FIG. 134. PEACH MUMMIES]
=Fruit Mold.= Fruit mold, or brown rot, often attacks the unripe fruit on the tree, and turns it soft and brown and finally fuzzy with a coat of mildew. Fig. 133 shows some peaches thus attacked. Often the fruits do not fall from the trees but shrivel up and become "mummies" (Fig.
134). This rot is one of the most serious diseases of plums and peaches.
It probably diminishes the value of the peach harvest from 50 to 75 per cent. Spraying according to the directions in the Appendix will kill the disease.
[Ill.u.s.tration: FIG. 135. HALF OF TREE SPRAYED TO PREVENT PEACH CURL Note the difference in foliage and fruit on the sprayed and unsprayed halves of the tree, and the difference in yield shown below]
CHAPTER VII
ORCHARD, GARDEN, AND FIELD INSECTS
SECTION x.x.xI. INSECTS IN GENERAL
The farmer who has fought "bugs" on crop after crop needs no argument to convince him that insects are serious enemies to agriculture. Yet even he may be surprised to learn that the damage done by them, as estimated by good authority, amounts to millions and millions of dollars yearly in the United States and Canada.
[Ill.u.s.tration: FIG. 136. ANTS]
Every one thinks he knows what an insect is. If, however, we are willing in this matter to make our notion agree with that of the people who have studied insects most and know them best, we must include among the true insects only such air-breathing animals as have six legs, no more, and have the body divided into three parts--head, thorax, and abdomen. These parts are clearly shown in Fig. 136, which represents the ant, a true insect. All insects do not show the divisions of the body so clearly as this figure shows them, but on careful examination you can usually make them out. The head bears one pair of feelers, and these in many insects serve also as organs of smell and sometimes of hearing. Less prominent feelers are to be found in the region of the mouth. These serve as organs of taste.
[Ill.u.s.tration: FIG. 137. PARTS OF AN INSECT]
[Ill.u.s.tration: FIG. 138. COMPOUND EYE OF DRAGON FLY]
The eyes of insects are especially noticeable. Close examination shows them to be made up of a thousand or more simple eyes. Such an eye is called a _compound eye_. An enlarged view of one of these is shown in Fig. 138.
Attached to the thorax are the legs and also the wings, if the insect has wings. The rear portion is the abdomen, and this, like the other parts, is composed of parts known as segments. The insect breathes through openings in the abdomen and thorax called _spiracles_ (see Fig.
137).
An examination of spiders, mites, and ticks shows eight legs; therefore these do not belong to the true insects, nor do the thousand-legged worms and their relatives.
[Ill.u.s.tration: FIG. 139. THE HOUSE FLY _a_, egg; _b_, larva, or maggot; _c_, pupa; _d_, adult male. (All enlarged)]
The chief cla.s.ses of insects are as follows: the flies, with two wings only; the bees, wasps, and ants, with four delicate wings; the beetles, with four wings--two hard, h.o.r.n.y ones covering the two more delicate ones. When the beetle is at rest its two hard wings meet in a straight line down the back. This peculiarity distinguishes it from the true bug, which has four wings. The two outer wings are partly h.o.r.n.y, and in folding lap over each other. b.u.t.terflies and moths are much alike in appearance but differ in habit. The b.u.t.terfly works by day and the moth by night. Note the k.n.o.b on the end of the b.u.t.terfly's feeler (Fig. 143).
The moth has no such k.n.o.b.
It is important to know how insects take their food, for by knowing this we are often able to destroy insect pests. Some are provided with mouth parts for chewing their food; others have a long tube with which they pierce plants or animals and, like the mosquito, suck their food from the inside. Insects of this latter cla.s.s cannot of course be harmed by poison on the surface of the leaves on which they feed.
[Ill.u.s.tration: FIG. 140. A TYPICAL BUG _a_, adult; _b_, side view of sucking mouth-part Both _a_ and _b_ are much enlarged]
[Ill.u.s.tration: Fig. 141. BEETLE _a_, larva; _b_, pupa; _c_, adult; _d_, burrow]
Many insects change their form from youth to old age so much that you can scarcely recognize them as the same creatures. First comes the egg.
The egg hatches into a worm-like animal known as a grub, maggot, or caterpillar, or, as scientists call it, a _larva_. This creature feeds and grows until finally it settles down and spins a home of silk, called a _coc.o.o.n_ (Fig. 145). If we open the coc.o.o.n we shall find that the animal is now covered with a hard outside skeleton, that it cannot move freely, and that it cannot eat at all. The animal in this state is known as the _pupa_ (Figs. 145 and 146). Sometimes, however, the pupa is not covered by a coc.o.o.n, sometimes it is soft, and sometimes it has some power of motion (Fig. 141). After a rest in the pupa stage the animal comes out a mature insect (Figs. 142 and 143).
From this you can see that it is especially important to know all you can about the life of injurious insects, since it is often easier to kill these pests at one stage of their life than at another. Often it is better to aim at destroying the seemingly harmless beetle or b.u.t.terfly than to try to destroy the larvae that hatch from its eggs, although, as you must remember, it is generally the larvae that do the most harm.
Larvae grow very rapidly; therefore the food supply must be great to meet the needs of the insect.
[Ill.u.s.tration: FIG. 142. MOTH AND COc.o.o.n]
Some insects, the gra.s.shopper for example, do not completely change their form. Fig. 147 represents some young gra.s.shoppers, which very closely resemble their parents.
[Ill.u.s.tration: FIG. 143. b.u.t.tERFLY]
[Ill.u.s.tration: FIG. 144. STRUCTURE OF THE CATERPILLAR]
[Ill.u.s.tration: FIG. 145. MOTH PUPA IN COc.o.o.n]
Insects lay many eggs and reproduce with remarkable rapidity. Their number therefore makes them a foe to be much dreaded. The queen honeybee often lays as many as 4000 eggs in twenty-four hours. A single house fly lays between 100 and 150 eggs in one day. The mosquito lays eggs in quant.i.ties of from 200 to 400. The white ant often lays 80,000 in a day, and so continues for two years, probably laying no less than 40,000,000 eggs. In one summer the bluebottle fly could have 500,000,000 descendants if they all lived. The plant louse, at the end of the fifth brood, has laid in a single year enough eggs to produce 300,000,000 young. Of course every one knows that, owing to enemies and diseases (for the insects have enemies which prey on them just as they prey on plants) comparatively few of the insects hatched from these eggs live till they are grown.
[Ill.u.s.tration: FIG. 146. A b.u.t.tERFLY PUPA Note outline of the b.u.t.terfly]
The number of insects which are hurtful to crops, gardens, flowers, and forests seems to be increasing each season. Therefore farm boys and girls should learn to recognize these harmful insects and to know how they live and how they may be destroyed. Those who know the forms and habits of these enemies of plants and trees are far better prepared to fight them than are those who strike in the dark. Moreover such knowledge is always a source of interest and pleasure. If you begin to study insects, you will soon find your love for the study growing.
[Ill.u.s.tration: FIG. 147. THE GROWTH OF A GRa.s.sHOPPER]
=EXERCISE=
Collect coc.o.o.ns and pupae of insects and hatch them in a breeding-cage similar to the one ill.u.s.trated in Fig. 149. Make several cages of this kind. Collect larvae of several kinds; supply them with food from plants upon which you found them. Find out the time it takes them to change into another stage. Write a description of this process.
The plant louse could produce in its twelfth brood 10,000,000,000,000,000,000,000 offspring. Each louse is about one tenth of an inch long. If all should live and be arranged in single file, how many miles long would such a procession be?
[Ill.u.s.tration: FIG. 148. PLANT LICE]
[Ill.u.s.tration: FIG. 149. CAGE IN WHICH TO BREED INSECTS Flower-pot, lamp-chimney, and cloth]
SECTION x.x.xII. ORCHARD INSECTS
=The San Jose Scale.= The San Jose scale is one of the most dreaded enemies of fruit trees. It is in fact an outlaw in many states. It is an unlawful act to sell fruit trees affected by it. Fig. 150 shows a view of a branch nearly covered with this pest. Although this scale is a very minute animal, yet so rapidly does it multiply that it is very dangerous to the tree. Never allow new trees to be brought into your orchard until you feel certain that they are free from the San Jose scale. If, however, it should in any way gain access to your orchard, you can prevent its spreading by thorough spraying with what is known as the lime-sulphur mixture. This mixture has long been used on the Pacific coast as a remedy for various scale insects. When it was first tried in other parts of the United States the results were not satisfactory and its use was abandoned. However, later experiments with it have proved that the mixture is thoroughly effective in killing this scale and that it is perfectly harmless to the trees. Until the lime-sulphur mixture proved to be successful the San Jose scale was a most dreaded nursery and orchard foe. It was even thought necessary to destroy infected trees. The lime-sulphur mixture and some other sulphur washes not only kill the San Jose scale but are also useful in reducing fungous injury.
[Ill.u.s.tration: FIG. 150 SAN JOSE SCALE]
[Ill.u.s.tration: FIG. 151. SINGLE SAN JOSE SCALE Magnified]
There are several ways of making the lime-sulphur mixture. It is generally best to buy a prepared mixture from some trustworthy dealer.
If you find the scale on your trees, write to your state experiment station for directions for combating it.
[Ill.u.s.tration: FIG. 152. THE CODLING MOTH _a_, burrow of worm in apple; _b_, place where worm enters; _c_, place where worm leaves; _e_, the larva; _d_, the pupa; _i_, the coc.o.o.n; _f_ and _g_, moths; _h_, magnified head of larva]
=The Codling Moth.= The codling moth attacks the apple and often causes a loss of from twenty-five to seventy-five per cent of the crop. In the state of New York this insect is causing an annual loss of about three million dollars. The effect it has on the fruit is most clearly seen in Fig. 152. The moth lays its egg upon the young leaves just after the falling of the blossom. She flies on from apple to apple, depositing an egg each time until from fifty to seventy-five eggs are deposited. The larva, or "worm," soon hatches and eats its way into the apple. Many affected apples ripen too soon and drop as "windfalls." Others remain on the tree and become the common wormy apples so familiar to growers. The larva that emerges from the windfalls moves generally to a tree, crawls up the trunk, and spins its coc.o.o.n under a ridge in the bark. From the coc.o.o.n the moth comes ready to start a new generation. The last generation of the larvae spends the winter in the coc.o.o.n.