APPLE SCAB,

Colonist, Volume XLVIII, Issue 11736, 19 September 1906, Page 3

APPLE SCAB,

ITS NATURE AND TREATMENT. (By J. 0. Blaokmore. ) ""The disease known as apple-scab ia caused by a parasitic summer stage of a saprophytic fungus, which has received the botanical |name Venturia inaequalis. The fungus possesses two stages, namely, a summer stage, adapted .to spread the disease during the growing season of the hosts, and a winter or permanent stage, adapted to carry the spores through the winter and then ensure the infection of the host again the following season. The scab in the apple is caused by the summer, or ccnidal, stage of the fungus, which is found in its perfect, stage in dead apple leaves. During spring the disease first appears on the apple leaves shortly after they unfold. First, infection comes from spores blown by the wind from the dead leaves of the previous season. The diseased spots on the leaves and fruit produce great numbers of spores, which spread the scab broadcast during the spring, summer, and early autumn. In a favorable season the flowers and young fruit and its stalks are attacked. The fungus grows in this manner throughout the summer and autunn. In late au tumn and winter the Venturia or perfect stage is produced in the dead apple leaves on the ground, from whence, as before stated, spores are liberated, and are blown by the wind from the dead leaves to the apple trees, and germinate on the unfolding leaves and blossom buds. Weather conditions play an important part, and in a great measure govern the abundance and deatructiyeness of the apple-scab fungus. During cold, damp seasons much injury results to both leaves and fruit. The effect of an attack in the leaves is to lessen the vigour and general health of the trees. The yield per tree is greatly lessened, and the value of the fruit harvested is much reduced compared with clean fruit! Besides, the .keeping value is considerably impaired. TREATMENT. The experience of many years has demonstrated that the loss from scab may be "almost entirely prevented — firstly, by endeavoring-to get rid, as far as possible, of the first source of infection, viz., the dead leaves, aa soon as possible after they drop from the trees, by cleaning up and burning, digging or ploughing in. In fact, when one knows ttie method of reproduction and spread of the fungus it suggests that it is well to bear in mind that the care given an orchard has as much to do with the suppression of apple-scab as sprat in p. Secondly, baviDg paid careful attention to the general condition of tbe orchard, timely spraying is indispensable. To be effective tbe proper time to begin spraying with tbe Bordeaux mixture is just when the blossom buds are bursting and beginning to show color, the object being to prevent the germinating tube of the fungus from penetrating the young leaves and calyx. A second spraying should be given immediately after the bloom has fallen. Should the

weather be moist, it might be advisable to make a further application of Bordeaux at intervals of about ten days. It should be applied as a tine mist, and caro should bo taken to cover every portion of the fruit, leaves, andbranches. If aty part of the trco is missed slight infection of the fiirgus may occur, from whence spores may bo disseminated through' out the soasqn, causing fresh infection ; or the f ungiis may remain latent until the conditions are favorable for growth during autmun, when it may burst into activity and cause late developments of the fungus of a serious nafiure in fruit previously quite'clean. When late infection occurs during damp autumn weather, in order to prevent its spread, immediately apply the washing soda Bordeaux 4-5-50 formula; it will stain the fruit less than the lime Bordeaux. For the spring spraying it is considered best to use a stronger mixture, the 6-7^-50 formula, which consists of 61b bluestone, 7iolb washing soda, SOgal water, or the lime Bordeaux may be substituted, if thought proper, for the eoda Bordeaux. In orchards where the trees have been carefully sprayed with lime-salt-sulphur wash late in the spring, before the buds have burst, experience demonstrates that the first spraying with Bordeaux recommended to be applied before the blossom-buds expaad may, as regards [ the apple, be omitted, but the f thorough application of the Bordeaux should not be neglected as soon as the petals fall. In order to make sure that the mixture is safe to use without injury to the foliage, it may be tested by dipping a piece of blue litmus paper in it — if the paper becomes red a further solution of washing soda or milk of liflie should be added, in small quantities at a time, until a fresh paper dipped in the mixture remains blue. For dissolving the materials for preparing Bordeaux, use separate half-barrel tubs, one for the bluestone solution and another for the milk of lime (or washing soda) solution, aod when combining from the dilution tubs be sure to pour in equal quantities of the two solutions simultaneously into a third barrel, and apply as soon as possible after it is prepared.