Symptoms of boron deficiency include yellowing or bronzing of leaves, followed by reddish discolouration along the leaflet margins and undersides of the youngest fully developed leaves. Eventually the upper leaf surface also turns red or reddish yellow. The lower leaves remain green. Plant tops become bunched due to shortened internodes and the growing point may die. Severe boron deficiency prevents plants from flowering or setting seed.
Symptoms are more severe under dry conditions.
Alfalfa which winterkills the first season is an indication of boron deficiency. Alfalfa will generally show deficiency symptoms if a soil test indicates levels below 0.75 ppm boron or if tissue tests of the top 7.5 cm of alfalfa measure below 20 ppm boron. Boron may be applied in custom blends or as a broadcast application of Borate 40 or Borate 68. Boron is best applied to new or established alfalfa fields in early fall. Boron should never be applied when seeding alfalfa with a cereal nurse crop, because cereals are susceptible to injury when boron is in close contact with the germinating seed.