Brassicas, Tip Burn
Tipburn and internal browning are physiological disorders related to calcium uptake and transport. The inner leaves of heads of cabbage and Brussels sprouts are affected, often without external symptoms. Tipburn is caused by inadequate transport of calcium to rapidly growing tissues. Low levels of calcium at leaf margins result in tissue collapse. High nitrogen levels result in large outer leaves that accumulate calcium at the expense of young, expanding leaves. Environmental conditions that favor rapid growth also increase tipburn. Adequate soil moisture promotes rapid growth, while excess soil moisture reduces soil oxygen levels and reduces calcium uptake. Tipburn and internal browning are often associated with alternating dry and abundant moisture cycles and are more common where plants are grown on sandy soils.
Margin of leaves turn brown and later dessicate, becoming papery. Affected tissue may turn brown or black and is occasionally invaded by secondary, soft rot bacteria.
Cultural Controls & Prevention:
Avoid conditions that favor rapid growth such as excess nitrogen. Maintain optimum fertility with a phosphorous to potassium ratio of 1:1. Irrigation may be necessary to maintain even soil moisture. Additions of calcium to soil or as a foliar application do not alleviate the problem. Prompt harvesting of crops reduces this disorder. Cultivars differ in susceptibility.