The first sign is a white, netted chapping of the upper blade surface or a wilting of the tops, even when the plants are growing in moist soil or in aerated culture solution. Young leaves wilt the most, instead of the least, as they do in a true water shortage. In time, they collapse and fail to develop. Other symptoms are pronounced crinkling of the leaf blades and the darkening and cracking of the petioles. Also, the growing point dies, the crown darkens and becomes subject to "rot."

Boron deficiency appears to have a twofold effect: (1) the conducting tissue is damaged, causing wilting and occasionally the exudation of syrupy materials from the leaf blades and (2) the meristematic tissues of the growing point collapse and die. A further effect is on root growth, as fibrous roots fail to develop in solutions deficient in boron. This may be the primary cause of wilting of the tops. Cambium tissues of storage roots darken, cells collapse, growth stops, and the storage root becomes subject to decay.