Frost damage to Date Palm

Date palm resists large temperature variations (-5 to 50°C) with a growth optimum between 32 and 38°C and a zero of vegetation of about 7°C. The vegetative activity will also decrease above 40°C and ceases around 45°C.

When temperature falls below 0°C, it causes serious metabolic disorders with some injury to date palm leaves characterised by a partial or total desiccation. Water of protoplasma freezes after coming out from the cells. During defrost, water invaded inter-cellular spaces and affected leaves turn brown and desiccated. The severity of damage is related to the intensity and duration of frost:

- At -6°C, leafl et ends become yellowish and dry up;

- At -12°C, leaves of external crown desiccate; and

- From -15°C, leaves of middle crown freeze and if low temperatures are suffi ciently prolonged, the central crown is reached and all foliage desiccates and the palm seems to be completely burned.

The relative stable temperature of terminal bud and trunk allows the date palm to resist frost in winter, and high temperature in summer. In fact, the terminal bud is protected by the fi brillium and the leaf bases; the internal temperatures of the trunk and terminal bud undergo less big variations than those of atmosphere; the difference is round 14°C less in summer and 12°C more in winter.

Frost injury to the date palm groves is not in direct loss of fruit on the palm but in freezing and loss of leaves so that the palm cannot support and mature the fruit crop the following year. Serious damage caused by frost was observed in plantations in Morocco (Guir, 1952; Tinghir, Tinjdad, 1965) and in USA (1873, 1940 and 1950) where temperatures of approximately -15°C occurred and frost caused a complete desiccation of leaves. In Morocco, palms were considered lost and the damage looked like a disaster to the local population. However, in spring, terminal buds started to grow although they were severely affected, and a good bloom was obtained (Djerbi, 1983).

The most practical and available protection for the date growers is to turn on the water and keep the date plantation wet when the temperature begins to get low enough (-5°C and below). A date plantation just irrigated or being irrigated when the temperature falls, has some heat stored, which gives protection.

By Hadi Laghari