Oaks

OAK – Common name for Quercus, a genus of noble trees, sometimes evergreen, but generally deciduous, members of the Beech Family. They have inconspicuous flowers borne in catkins or spikes and oblong or roundish fruits called “acorns,” set in cup-like involucres. Beautiful in all their various forms, the oaks are usually wide-spreading with great trunks, often tall and majestic.

Oaks are valuable forest trees and most useful for ornamental purposes in street planting, in the park or on home grounds. Some of the low-growing species are excellent to plant on dry, rocky hillsides. The foliage, often beautifully cut, is always interesting, and in many species assumes brilliant autumn coloring. The evergreen species, with their holly-like leaves, grow only in the South States, California and Oregon, but almost all the deciduous species are hardy.

Many oaks grow in swamp ground but others, especially those of the Red Oak section, prefer drier soil. All are generally increased by seed sown as soon as gathered, but the varieties are grafted in the greenhouse on potted stock, preferably Quercus robur. Sometimes in the South the evergreen species are increased by layers or cuttings.

ENEMIES – Practically all specks of oak are subject to leaf blister, caused by a fungus that is common throughout the U. S. but more injurious in the S. Blisters appear on the leaves before they are full-grown, often causing them to curl. Control measures used for peach leaf curl should be successful : a bordeaux spray after the leaves fall and before the buds swell.

Four species of powdery mildew attack oak leaves, and, where necessary, control may be obtained by spraying with wettable sulphur. Anthracnose or scorch, caused by a fungus, and common also on the plane tree, may cause complete or partial defoliation of White Oaks. Spray three times with bordeaux mixture at 2-week intervals, beginning when leaves are half grown; also destroy fallen leaves. Several species of blister rust fungi have their alternate stage on oak leaves. One of them injures 2- and 3-needled pines and, if the pines are the more valuable in a locality, oaks should be removed to eliminate the menace from the pines.

The list of insects attacking oaks is a long one but few are of great importance. Scales are controlled by dormant spraying with a miscible oil. For protection against the many leaf-eating insects the foliage should be thoroughly sprayed with lead arsenate in the spring. In certain localities and years the canker worm will practically denude the trees. Caterpillars of the cecropia moth, the American silkworm, the luna moth and the gypsy, brown tail, and buck moths, and the forest tent caterpillar, as well as the orange striped oak worm, may all feed on the leaves. The California oak-moth is a destructive pest of live oaks on the Pacific Coast. A late summer as well as a spring spray may be needed to control the two broods. Leaf rollers that may attack oak are controlled by spraying the trees with lead arsenate before the leaves begin to curl, but there is no known way to control several conspicuous leaf miners.

Various deformities known as galls are extremely common and often conspicuous on oak twigs and leaves but no control measures have been devised.

Principal Species

Quercus alba (White Oak), to 100 ft., is one of the most characteristic and noble trees of the North States. It should be planted where it will have room to show its majestic proportions when full grown and the full beauty of its autumn coloring, a beautiful wine-red or purple. It grows best in rather moist soil, though it is most adaptable.

Quercus borealis (Northern Red Oak), to 80 ft., is a rapid-growing tree, forming a large round head; the foliage becomes dark red in fall.

Quercus rubra (Spanish Red Oak), to 80 ft., a handsome round-topped tree with spreading branches and foliage becoming dark red in the fall, is not quite hardy North.

Quercus coccinca (Scarlet Oak), to 80 ft., is excellent for a dry situation. The bright green foliage becomes brilliant scarlet in autumn.

Quercus palustris (Pin Oak), to 80 ft. or more, forms a symmetrical pyramidal head with long pendulous branches. The foliage is much cut and assumes a bright red in autumn. Because of its erect, symmetrical and rather rapid growth, it is much used for avenues and as a specimen tree on lawns.

Quercus imbricaria (Shingle Oak), to 60 ft., has in youth slender drooping branches, but becomes round-topped in age. The foliage is glossy, dark green above, downy beneath, and becomes russet-red in the fall.

Quercus velutina (Black Oak), to 100 ft. or more, with slender branches and an open head, is a rapid-growing tree with glossy foliage assuming dull red or dark orange autumn coloring.

Quercus montane (Chestnut Oak), to 70 ft. or more, has deeply ridged bark in age and turns dull orange in autumn. It grows well in dry ground. It should not be confused with Quercus prints (Basket Oak) which grows farther South.

Quercus robur (English Oak), to 80 ft., a stout wide-spreading tree, greatly valued for its historical associations. It has many horticultural varieties, among them var. atropurpurea with purple leaves; var. fastigiata of upright growth; var. pendula with drooping branches.