in the high-rainfall areas of KZN are often low in available boron, and
deficiencies may be expected on such soils.
A deficiency is
characterised by an internal discolouration and cracking of the stem at the
base of the head. A roughness, almost a cork-like appearance, on the lower
surface of the mid-rib of the leaves, also occurs. Deficiency causes a browning
of cauliflower curds. Internal
cracking of the stem of broccoli, without any discolouration, is common when
the plants grow rapidly, especially at lower plant populations. This symptom
should not be confused with a boron deficiency, which causes an internal
well to foliar sprays of, for example, Solubor. Usually 3 kg will correct
such deficiencies. Where any bean crop is included in the rotation, rather
under- than overapply boron, because high rates of boron can be very toxic to
these crops (toxicity symptoms may be manifested in beans when soil boron
levels are above 5 ppm).