How to prevent tipburn in brassicas

Because tipburn is found in the inner layers of the head, it cannot be seen without slicing open the cabbage. In cauliflower and broccoli, tipburn shows up on the margins of the younger leaves.

Tipburn symptoms are caused by a breakdown of the plant tissue. These vary according to brassica type:

• In head forming cabbage the inner head layers are affected in an area that may range from a narrow zone along the margins of one or two leaves, to a more extensive area. 
• In chinese cabbage, the initial symptoms are often black spots at the leaf margins, which gradually expand onto the surrounding tissue and then become dark or black in color 

• In cauliflower, the tissue around the leaf margins gradually becomes dried in appearance and papery in texture. The young leaves are necrotic and deformed, and have to be removed from the curd during harvest which can cause quality problems in some markets.

Calcium and/or boron deficiency often results in tipburn

Tipburn is related to calcium and/or boron deficiency. This deficiency can be as a result of a shortage of supply, or induced by factors such as poor water management, imbalanced nutrition and restricted root growth. Air humidity has a strong impact on tipburn as both calcium and boron uptake and distribution inside the plant is affected by transpiration. Uptake of these nutrients is enhanced by low air humidity resulting in a high transpiration, but, the internal transport of calcium and B to the low transpiring tissues inside the head is promoted in a humid atmosphere.

Excess use of potassium (K) or ammonium can create imbalances that restrict the uptake of calcium and so exacerbate the problem.

Copper deficiency can also create tipburn symptoms

Yellowing along the leaf margins and tipburn and some die-back of leaves, can be a symptom of copper deficiency. It occurs generally in the youngest parts of the plant where new leaves become yellow-tipped (tip burn) and wilt. As the deficiency continues, leaves become completely pale yellow, and curled. Whip tailing can occur, where the leaf tip dies, rolls or twists and turns white.

In addition, too much forced growth through over-application of nitrogen - especially if this is out of balance with calcium and potassium availability - may create an inadequate supply of these elements and result in tipburn.