Where the soil is absolutely poor, the trees should be manured every year ; but, otherwise, every second year will be sufficient. Of course, if the orchard has been established in rich alluvial bottoms, or fat loam, and the trees have a tendency to over-luxuriance. manuring is not only not wanted, but would be wasteful, and inimical to productiveness. In applying manure, if it be in fit condition, it is most profitable to dig it in just before the rainy season ; by doing this, the tree at once receives the full benefit of the dressing.
Mulching.—Mulcliing, especially while the trees are young, will be found a useful adjunct to the cultivation of the olive, as it is with other trees, in hot dry climates. Its effect is principally mechanical, in retaining moisture, and in keeping cool the surface of the soil about the roots of the tree. Long manure—grass, straw, or any such substance—will answer the purpose ; but it is as well to select something which will gradually decay, and, when dug in, will act as a fertilizer. Care should, however, be taken that the material selected be free from seeds, or it will involve additional labour with the hoe.
Pruning.—Judicious pruning is of great importance, as the olive has the character of only bearing in alternate years. The fruit is produced on the young shoots of the preceding year ; and, in pruning, the object to attain is to secure a regular distribution of wood of the previous year from the exile of the leaves. In poor soil, where the trees would have a struggle to produce both fruit, and young shoots for next year's harvest, pruning is especially necessary ; and it is probable that, in the genial climate of Australia, skilfully managed plantations ought to bear, with fair certainty, a regular annual crop. Some authorities consider that pruning once in 3 years is sufficient. By the old method of leaving the tree to attain its full growth, any considerable crop was not yielded for many years ; and hence the character of the olive for tardy productiveness. Under the present system, however, of cultivating comparatively dwarf trees, abundant crops are afforded in 3-4 years. A dear, straight stem, of 5-6 ft., should be kept. Not only is the growth thus made handsomer, but the tree is more vigorous and strong to resist wind, and the fruit is sufficiently remote from reflected beat, and consequent premature ripening.
Distance.—The distance apart for planting the trees must be determined partly by variety, and partly by soil and aspect. Under the old system, which was content with a biennial crop, and left the trees to grow much as they pleased, a distance of 30-40 ft. was necessary. But of late years, the propagation of new and highly productive varieties, and the adoption of a system of pruning the trees to such limits as will render the gathering of the fruit by hand comparatively easy, has enabled cultivators to bring their trees closer together, and thus to economize space, and consolidate their operations. Orchards are now planted at distances of 16-30 ft., according to variety, the
distance being further regulated by the quality of the soil.
While guarding against the false economy of overcrowding, the annexed table will show the number of trees which can be grown per acre at 16,20,30, and 40 ft. apart respectively, deducting a dray-road 12 ft. wide.
Excluding all consideration of the fractional spaces adjacent to the dray-road, and simply calculating how many times the area required for each tree is contained in the available areas of acres of each of the preceding forms, gives :— At whatever distance apart it is determined to plant the trees, the most effective method for securing a free circulation of air is what is known as " quincunx fashion," which has been explained under the cultivation of coffee (see Coffee, p. 693).
With careful attention, the olive will begin to repay the expense of culture in 4-5 years after planting, without taking into account what may meantime be got off the ground by inter cultivation.
Diseases and Enemies.—Many insects attack and live upon the olive. Perhaps the worst is the olive-fly (Dacus clew), which appears when the fruit is ripening, and is most numerous in years of abundance. It inhabits the pulp of the fruit, sometimes more than one in each, and is more trouble some according as the harvest is later. It is destroyed by ants, but no real remedy for it has been devised. Another pest is Tinea olsolla, which attacks the leaves, buds, and fruits by turn, and also causes excrescences on the branches. Psylla ole,ce is abundant at the flowering season, and attacks the leaves and the peduncles of the flowers ; it sucks the sap from near the flowers, causing them to be abortive, and attaches a cotton-like substance which increases the bleeding. No means are adopted to repel this parasite, and the growers in Italy look for the N.-W. wind to drive it away. Coccus olece does more damage by causing a serious loss of sap, than by what it actually consumes. No real remedy has been invented for it. Hylesinus oleiperda lives under the bark of the young branches, and even occurs on dead wood. Its ravages are curtailed by cutting and burning infected branches. Phloiotribus olece causes a manna-like exudation. Among vegetable parasites, are a mushroom, Dematium monophyllum, which causes branches and leaves to become black ; the remedies used are lime-water, coal-tar, and petroleum. Another fungus, Agaricus olearius, infests the stems of old trees.