This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
When the leaves of currant bushes are nearly full grown, many of them bear blister-like elevations of a reddish color, beneath which will be found yellowish plant-lice, some winged and some wingless. The blisters are due to the attacks of these insects, and when, as is sometimes the case, they are very abundant, considerable injury is done to the bushes. Spraying forcibly with whale-oil soap, or kerosene emulsion will destroy large numbers of these plant-lice at each application; but the liquid must be copiously applied and driven well up beneath the foliage by means of an angled nozzle. Two or three applications at short intervals may be necessary.
Early in June a beautiful little bluish black fly-like moth, with three bright yellow bands around the body may be seen darting about, around, or at rest on the leaves of currant bushes of all kinds. This is one of the most troublesome enemies of these fruits. The moth lays an egg at a bud on the young wood, and the caterpillar, when hatched, eats its way into the cane and destroys the pith. It remains in the wood during the winter, and the moth emerges during the following summer. Close pruning is the best remedy. Burn the wood.
Red, black and white currants are in some places seriously attacked by the maggots of a small fly. These maggots come to full growth just as the berries are about to ripen, causing them to fall from the bushes, when the insects leave them and burrow into the ground to pupate. Attacked fruit is rendered useless by the presence of the maggots inside the berries; and frequently it is not until the fruit is cooked that the white maggots can be detected. Gooseberries are sometimes injured but far less frequently than black and red currants. The only treatment which has given any results is the laborious one of removing about 3 inches of the soil from beneath bushes which are known to have been infested, and replacing this with fresh soil. That which was removed must be treated in some way, so that the contained puparia may be destroyed. This may be done either by throwing it into a pond or by burying it deeply in the earth.
By far the best known of all the insects that injure currants and gooseberries, is the "currant worm." The black-spotted dark green false caterpillars of this insect may unfortunately be found in almost every plantation of currants or gooseberries, every year in almost all parts of America where these fruits are grown. The white eggs are laid in rows along the ribs of the leaf on the lower side, toward the end of May. From these the young larvae hatch and soon make their presence known by the small holes they eat through the leaves. Unless promptly destroyed, they will soon strip the bushes of their leaves, thus weakening them considerably so as to prevent the fruit from ripening the first year, and also reducing the quality of the crop of the following season. There are at least two broods in a season in most places; the first appears just as the leaves are attaining full growth, and the second just as the fruit is ripening. The perfect insect is a four-winged fly which may be seen flying about the bushes early in spring. The male is blackish, with yellow legs and of about the same size as a housefly, but with a more slender body. The female is larger and has the body as well as the legs yellow.
For the first brood a weak mixture of paris green, one ounce to ten gallons of water, may be sprayed over the bushes, or a dry mixture, one ounce to six pounds of flour, may be dusted over the foliage after a shower or when the leaves are damp with dew. For the second brood paris green must not be used, but white hellebore; or hellebore may be used for first brood, but it is necessary to kill quickly. This is dusted on as a dry powder, or a decoction, one ounce to two gallons of water, may be sprayed over the bushes. It is, of course, far better to treat the first brood thoroughly, to reduce the number of females which lay eggs for the second brood.
Several kinds of scale insects attack currants. These plants seem to be particularly susceptible to the attacks of the well-known oyster-shell scale of the apple, and the San Jose scale. In neglected plantations these injurious insects increase rapidly, and a great deal of injury results to the bushes. The remedies for scale insects are direct treatment for the destruction of the infesting insect, and preventive measures, such as the invigoration of the bush by special culture and pruning, to enable it to throw off or outgrow injury. Infested plantations should be cultivated and fertilized early in the season, and all unnecessary wood should be pruned out. As direct remedies, spraying the bushes at the time the young scale insects first appear in June with kerosene emulsion or whale-oil soap, or spraying in autumn before the hard weather of winter sets in with a simple whitewash made with one pound of lime in each gallon of water, give the best results. Two coats of the whitewash should be applied, the second one immediately after the first is dry. In putting on two thin coats of the wash instead of one thick one, far better results have been secured.
For the San Jose scale, the lime-and-sulfur wash is necessary, and must be repeated every year.
Fig. 1155. Currant cutting.
Fig. 1156. To illustrate the pruning of a currant bush. The old cane, a, is to be cut away. The straight new canes at left are to remain.
Diseases of the currant.
The currant is affected by very few diseases. The only ones that do much injury are the following:
The leaf-spot fungus affects black, red and white currants, causing the leaves to fall prematurely, and thus weakening the bushes. This disease is first noticed about midsummer, when small brownish spots appear on the leaves. These often become so numerous that they affect a large part of the foliage, soon causing the leaves to fall. As the disease often appears before the fruit is picked, it is difficult to control it if the bushes are not sprayed previously. By using the am-moniacal copper carbonate the bushes may be sprayed a week or two before it is expected, without discoloring the fruit, giving a second application, if necessary. As soon as the fruit is picked, the bushes should be thoroughly sprayed with bordeaux mixture. Experiments have shown that this disease can be controlled by spraying.
This disease, which may be mistaken for the leaf-spot, affects different parts of the bush, including the leaves, leafstalks, young branches, fruit and fruit-stalks. On the leaves it is made evident during the month of June by the small brown spots which are usually smaller than those made by the leaf-spot fungus. The lower leaves are affected first, and finally the upper ones. They turn yellow and gradually fall to the ground, and when the disease is bad the bushes are defoliated before their time. On the petioles or leaf-stalks, the disease causes slightly sunken spots. The fruit is affected with roundish black spots which are more easily seen when the fruit is green. On the young wood the diseased areas are light in color and are not so noticeable. The wood is not nearly so much injured by the disease as the leaves. The spores which spread this disease are formed in pustules, the majority of which are under the upper epidermis of the leaf. Where the spores are to appear, the surface of the leaf is raised and blackened in spots looking like small pimples. When the spores are ready to come out the skin breaks and they escape and re-infect other parts. When the foliage drops early on account of this disease the fruit is liable to be scalded by the sun.
The fruit may also wither before ripening properly, owing to lack of food or of moisture, as, the leaves having fallen, they are unable to keep up the necessary supply. The premature falling of the leaves prevents the buds from maturing properly, hence they are not in so good condition to bear fruit the next year. Spraying with bordeaux mixture is recommended as an aid in controlling this disease. It would be wise, when currant anthracnose is troublesome, to spray the bushes thoroughly before the leaves appear. A second spraying should be made when the leaves are unfolding, and successive sprayings at intervals of ten to fourteen days until the fruit is nearly full grown, and there is danger of its being discolored by the spray when ripe. Paris green should be added to the mixture when the first brood of the currant worm appears. A thorough spraying after the fruit is harvested is desirable.
Fig. 1157. Tree-form training of currant.
W. T. Macoun.