SECTION XXXII. 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.
Fig. 150. San Jose Scale | Fig. 151. Single San Jose Scale Magnified |
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 cocoon; f and g, moths;
h, magnified head of larva
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.
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 cocoon under a ridge in the bark. From the cocoon the moth comes ready to start a new generation. The last generation of the larvæ spends the winter in the cocoon.
Fig. 153. Spraying the Orchard brings Luscious Fruit
The picture in the corner at the top shows the right time to spray for codling moth
Treatment. Destroy orchard trash which may serve as a winter home. Scrape all loose bark from the tree. Spray the tree with arsenate of lead as soon as the flowers fall. A former method of fighting this pest was as follows: bands of burlap four inches wide tied around the tree furnished a hiding-place for larvæ that came from windfalls or crawled from wormy apples on the tree. The larvæ caught under the bands were killed every five or six days. We know now, however, that a thorough spraying just after the blossoms fall kills the worms and renders the bands unnecessary. Furthermore, spraying prevents wormy apples, while banding does not. Follow the first spraying by a second two weeks later.
It is best to use lime-sulphur mixture or the Bordeaux mixture with arsenate of lead for a spray. Thus one spraying serves against both fungi and insects.
Fig. 154. Plum Curculio
Larva, pupa, adult, and mark on the fruit.
(Enlarged)
Fig. 155. Leaf Galls of
Phylloxera On Clinton
Grape Leaf
The Plum Curculio. The plum curculio, sometimes called the plum weevil, is a little creature about one fifth of an inch long. In spite of its small size the curculio does, if neglected, great damage to our fruit crop. It injures peaches, plums, and cherries by stinging the fruit as soon as it is formed. The word "stinging" when applied to insects—- and this case is no exception—means piercing the object with the egg-layer (ovipositor) and depositing the egg. Some insects occasionally use the ovipositor merely for defense. The curculio has an especially interesting method of laying her egg. First she digs a hole, in which she places the egg and pushes it well down. Then with her snout she makes a crescent-shaped cut in the skin of the plum, around the egg. This mark is shown in Fig. 154. As this peculiar cut is followed by a flow of gum, you will always be able to recognize the work of the curculio. Having finished with one plum, this industrious worker makes her way to other plums until her eggs are all laid. The maggotlike larva soon hatches, burrows through the fruit, and causes it to drop before ripening. The larva then enters the ground to a depth of several inches. There it becomes a pupa, and later, as a mature beetle, emerges and winters in cracks and crevices.
Treatment. Burn orchard trash which may serve as winter quarters. Spraying with arsenate of lead, using two pounds of the mixture to fifty gallons of water, is the only successful treatment for the curculio. For plums and peaches, spray first when the fruit is free from the calyx caps, or dried flower-buds. Repeat the spraying two weeks later. For late peaches spray a third time two weeks after the second spraying. This poisonous spray will kill the beetles while they are feeding or cutting holes in which to lay their eggs.
Fig. 156. The Cankerworm
Fowls in the orchard do good by capturing the larvæ before they can burrow, while hogs will destroy the fallen fruit before the larvæ can escape.
The Grape Phylloxera. The grape phylloxera is a serious pest. You have no doubt seen its galls upon the grape leaf. These galls are caused by a small louse, the phylloxera. Each gall contains a female, which soon fills the gall with eggs. These hatch into more females, which emerge and form new galls, and so the phylloxera spreads (see Fig. 155).
Treatment. The Clinton grape is most liable to injury from this pest. Hence it is better to grow other more resistant kinds. Sometimes the lice attack the roots of the grape vines. In many sections where irrigation is practiced the grape rows are flooded when the lice are thickest. The water drowns the lice and does no harm to the vines.
The Cankerworm. The cankerworm is the larva of a moth. Because of its peculiar mode of crawling, by looping its body, it is often called the looping worm or measuring worm (Fig. 157, c). These worms are such greedy eaters that in a short time they can so cut the leaves of an orchard as to give it a scorched appearance. Such an attack practically destroys the crop and does lasting injury to the tree. The worms are green or brown and are striped lengthwise. If the tree is jarred, the worm has a peculiar habit of dropping toward the ground on a silken thread of its own making (Fig. 156).
Fig. 157. The Spring Cankerworm
a, egg mass; b, egg, magnified;
c, larva; d, female moth; e, male moth
Fig. 158. Eggs of the
Fall Cankerworm
In early summer the larvæ burrow within the earth and pupate there; later they emerge as adults (Fig. 157, d and e). You observe the peculiar difference between the wingless female, d, and the winged male, e. It is the habit of this wingless female to crawl up the trunk of some near-by tree in order to deposit her eggs upon the twigs. These eggs (shown at a and b) hatch into the greedy larvæ that do so much damage to our orchards.
Nearly all the common birds feed freely upon the cankerworm, and benefit the orchard in so doing. The chickadee is perhaps the most useful. A recent writer is very positive that each chickadee will devour on an average thirty female cankerworm moths a day; and that if the average number of eggs laid by each female is one hundred and eighty-five, one chickadee would thus destroy in one day five thousand five hundred and fifty eggs, and, in the twenty-five days in which the cankerworm moths crawl up the tree, would rid the orchard of one hundred and thirty-eight thousand seven hundred and fifty. These birds also eat immense numbers of cankerworm eggs before they hatch into worms.
Treatment. The inability of the female to fly gives us an easy way to prevent the larval offspring from getting to the foliage of our trees, for we know that the only highway open to her or her larvæ leads up the trunk. We must obstruct this highway so that no crawling creature may pass. This is readily done by smoothing the bark and fitting close to it a band of paper, and making sure that it is tight enough to prevent anything from crawling underneath. Then smear over the paper something so sticky that any moth or larva that attempts to pass will be entangled. Printer's ink will do very well, or you can buy either dendrolene or tanglefoot.
Fig. 159. Apple-Tree Tent Caterpillar
a, eggs; b, cocoon; c, caterpillar
Fig. 160. The Twig
Girdler at its
Destructive Work
a, the girdler;
b, the egg-hole;
c, the groove cut by girdler;
e, the egg
Encourage the chickadee and all other birds, except the English sparrow, to stay in your orchard. This is easily done by feeding and protecting them in their times of need.
The Apple-Tree Tent Caterpillar. The apple-tree tent caterpillar is a larva so well known that you only need to be told how to guard against it. The mother of this caterpillar is a reddish moth. This insect passes the winter in the egg state securely fastened on the twigs as shown in Fig. 159, a.
Treatment. There are three principal methods, (1) Destroy the eggs. The egg masses are readily seen in winter and may easily be collected and burned by boys. The chickadee eats great quantities of these eggs. (2) With torches burn the nests at dusk when all the worms are within. You must be very careful in burning or you will harm the young branches with their tender bark. (3) Encourage the residence of birds. Urge your neighbors to make war on the larvæ, too, since the pest spreads rapidly from farm to farm. Regularly sprayed orchards are rarely troubled by this pest.
The Twig Girdler. The twig girdler lays her eggs in the twigs of pear, pecan, apple, and other trees. It is necessary that the larvæ develop in dead wood. This the mother provides by girdling the twig so deeply that it will die and fall to the ground.
Treatment. Since the larvæ spend the winter in the dead twigs, burn these twigs in autumn or early spring and thus destroy the pest.
The Peach-Tree Borer. In Fig. 161 you see the effect of the peach-tree borer's activity. These borers often girdle and thereby kill a tree. Fig. 162 shows the adult state of the insect. The eggs are laid on peach or plum trees near the ground. As soon as the larva emerges, it bores into the bark and remains there for months, passing through the pupa stage before it comes out to lay eggs for another generation.
Fig. 161. Borer Signs around Base of Peach Tree
Treatment. If there are only a few trees in the orchard, digging the worms out with a knife is the best way of destroying them. You can know of the borer's presence by the exuding gum often seen on the tree-trunk. If you pile earth around the roots early in the spring and remove it in the late fall, the winter freezing and thawing will kill many of the larvæ.
EXERCISE
How many apples per hundred do you find injured by the codling moth? Collect some cocoons from a pear or an apple tree in winter, place in a breeding-cage, and watch for the moths that come out. Do you ever see the woodpecker hunting for these same cocoons? Can you find cocoons that have been emptied by this bird? Estimate how many he considers a day's ration. How many apples does he thus save?
Fig. 162. Peach-Tree Borers, Male and Female
Female with broad yellow band across abdomen
Watch the curculio lay her eggs in the plums, peaches, or cherries. What per cent of fruit is thus injured? Estimate the damage. Let the school offer a prize for the greatest number of tent-caterpillar eggs. Watch such trees as the apple, the wild and the cultivated cherry, the oak, and many others.
Make a collection of insects injurious to orchard fruits, showing in each case the whole life history of the insect, that is, eggs, larva, pupa, and the mature insects.