Bud is a botanical term referring to newly developing shoots which appears at the tip of a stem or in the leaf axil, the upper area where the leaf stem is joined to the branch. Buds are specialized to produce a flower or a shoot. Buds on trees may be protected by scales, modified leaves enclosing the delicate organ. The scales in turn may be covered with a gummy exudate which serves as a repellant to some insects and birds. In some tree species, the buds are naked, being protected by being excessively hairy.
When buds develop, the scales fall off leaving a scar on the growing stem. On a young tree branch, it is possible to determine the age of a young branch by observing the number of annual leaf scar series present.
Buds may develop incompletely and remain dormant for a time, in anticipation of spring or the start of the rainy season when environmental conditions are favorable to resume growth. In temperate areas with defined seasons, tree leaf and flower bud formation in spring is a notable event, as the bare trees present an unusual appearance with visible bud growth before leaf or flower development. In tropical semidesert areas, especially where the rainy season is irregular, the appearance of new buds on trees and shrubs is used by local people as an indicator that the annual rains are about to begin.
Buds contain stored energy in the form of nutrients and sugars for the growth of leaves or flowers and are therefore attractive animal food sources. In temperate zones, buds appear when other food sources are scarce.
Aphids can infest tree buds, their presence signaled by fuzz on bud tips. Fruit trees and garden vegetables are prone to aphid attacks. Powdery mildew is another insect pest attacking buds and in some areas is a particular problem of Crepe Myrtles (Lagerstroemia speciosa). Finches and cedar waxwing birds are known to eat buds, along with squirrels which eat confer and oak buds and deer eat those of red maple (Acer rubrum).
Excessive bud predation can be a serious problem, stunting tree growth. Pesticide insect control measures are known and ladybirds can be introduced to control aphid populations. Trees can be protected from animals by the application of retardants or netting.
The buds of a number of trees are also human food, such as those of red bud, birch and beech. A well-known example is the caper bush from which flower buds are harvested and pickled. Buds are most commonly consumed as salad ingredients. The dried flower buds of the clove tree are the source of that tropical spice.
Tree buds have a role in plant propagation as well. A dormant leaf bud can be excised from a tree and inserted into a slit in the bark of another tree and bound with tape. This is a common practice in fruits trees when growing a popular variety may have root disease problems. By grafting a bud onto a tree with healthy resistant roots the problem is resolved. However, the process must be repeated continuously.