BRUSSELS SPROUT
4.4 PHYSIOLOGICAL DISORDERS
Brussels sprouts show various non-parasitic disorders which cause tissues
to die off. In some
cases, these deviations have been shown to depend mainly on heritable
characters; whereas in
other cases external factors had a least marked effect.
Tip Burn of Brussels Sprouts
This problem can cause severe economic losses. Internal leaves turn brown,
especially on the
edges or tips. Inside sprouts, the centre tissues often breakdown. It is a
physiological disorder
which is associated with an inadequate supply of calcium to the young,
actively growing inner
leaves. High humidity, low soil moisture, high potassium, high nitrogen, or
low soil calcium all
influence calcium availability.
Internal Browning
In Brussels sprouts, the symptoms are a yellowing of the distal ends of the
leaves within the
sprout, generally on a line through the centre region of the sprout and
midway between its
growing point and exterior surface. From a practical aspect, internal
browning is especially
troublesome because it cannot usually be detected from external examination
of the sprouts, yet
quite a small number of affected sprouts may taint a large sample;
especially when they are
blanched for quick-freezing.
Factors which have contributed to internal browning have done so by
bringing about a temporary
localized calcium deficiency in the sprouts. Rapid growth, low soil
moisture and high relative
humidity, which inhibit transpiration, are commonly implicated. The actual
soil calcium levels
have very little influence unless they are extremely low.
Ensuring the soil moisture is close to field capacity can reduce the risk
of internal browning.
Excessive nitrogen fertilizer should be avoided. Foliar sprays of calcium
nitrate may prevent the
onset of internal browning if applied before the onset of adverse growing
conditions. \
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