According to Act 36 of 1947 olive producers may only use chemicals which are registered for use on olives in South Africa. Please refer to the latest list of registered chemicals which is available from SA Olive.
Olives, like other fruit trees, require the macronutrient elements such as nitrogen (N), potassium (K), phosphorous (P), calcium (Ca), magnesium (Mg) and sulphur (S). Trace elements, of which the most important are boron (B), zinc (Zn), iron (Fe), copper (Cu), manganese (Mn) and molybdenum (Mo), are only required in small quantities. The correct management of nitrogen is critical to maintaining the balance between growth and cropping.
Nitrogen is utilised throughout the growing season, and is to be applied monthly in spring and summer to young trees in the form of Ammonium Sulphate or “LAN”. It is recommended that nitrogen is applied regularly and in smaller doses to prevent excessive vegetative growth caused by single large applications.
Be especially careful of injudicious nitrogen applications in the summer months. Potassium (e.g. potassium sulphate) is applied in spring and autumn. Under local conditions replenishment of B and Zn are especially important in early spring.
Other elements are applied according to rates determined by means of leaf and soil analysis and adjusted according to expected crop, otherwise, imbalances can occur. Maintaining soil acidity at the right pH level (in the region of 6.5) is critical for facilitating the optimal uptake of other nutrients. Soil pH is determined during soil analysis (which should preferably be done on an annual basis) and rectified accordingly by lime application.
A young tree requires about 15 to 20 litres of water weekly during the first growing season. The irrigation required by a tree, i.e. the amount of water applied at a specific time and the frequency of irrigation, is influenced by the following factors: the age and size of the trees, the season and growth stage, the crop size (affecting crop factors), rainfall, temperature, relative humidity, and wind (affecting evaporation), soil texture, structure and depth (affecting soil water holding capacity, infiltration and percolation rate), and the type of irrigation system. Double line drippers or microsprinklers, where the system has been designed by experts, are used with success by olive growers locally. A range of apparatus is available today to help optimise irrigation scheduling
Weeds compete with the tree for available moisture, nutrients and oxygen in the soil. Weed competition is reduced by regular mowing or by spraying with herbicides. Although numerous herbicides are used on olives overseas, only glyphosate and fluazifop (both post-emergence) are currently registered for use on olives in South Africa.
Chemical weed killers have to be used with care since the long-term effects on tree performance and the environment have not been determined. In an organic farming system, a relatively thick mulch layer of high lignin material in the tree row helps suppress weed growth and stimulates beneficial fine root development.
During the first few years in the orchard, pruning is kept to a minimum. Only those branches which are in the way of others, or growing too near the soil surface are removed. There are different approaches to pruning and training olive trees. In a more extensive type of system, three to six main scaffold branches are selected to form a semi-open vase. All upright growth in the centre of the tree is removed to improve light interception throughout the tree, taking care not to expose the scaffolds to the risk of sunburn damage. In a more intensive system, a single leader tree is planted and this main leader is then staked and trained upright.
Lateral branching is encouraged over the entire length of the leader from a height of about 40 cm upwards, with stronger development at the base to form a conical shaped tree. Lateral branches should have a diameter of less than a third of that of the main leader and are kept at a flattish angle while all upright growth on the laterals is regularly removed.
Olive pests are, to a large degree, kept in check by their natural enemies in the Western Cape. Olives thus lend themselves here to be grown and marketed as organic products. Growers should be careful not to disturb this balance by injudicious pesticide use, and should, in addition, use other practices which can reduce pest infestation, such as correct pruning and minimising traffic dust.
The main pests which occur on olives in South Africa are:
- the yellow and black striped olive beetle, with its bright yellow larvae which eats and tunnels into leaves especially on young trees, destroying new growth.
- the olive lace bug or “tingid” which sucks out the sap of leaves, especially where growth is dense, and so causes tiny yellow dots on the leaves which later become completely chlorotic and die.
- the olive fly, which stings the fruit and lays its eggs which then hatch and destroy the fruit as the larvae burrow through the flesh.
Under dusty conditions, infestation by various scale insects can be damaging. Insects such as psylla only become serious pests when the ecological balance is disturbed through injudicious pesticide use. Effective control of most of these pests is available, but one should always strive to allow biological control to take place.
The main fungal diseases include:
- anthracnose (Colletotrichum), which causes fruit spoilage and cankers on shoots;
- peacock spot (Spiloceae) which causes sooty spots and yellowing of leaves, later resulting in leaf drop and death of shoots;
- various soilborne diseases (Phytophthora, Verticillium etc.) which cause damage to the roots and can lead to the death of trees
These diseases are controlled by integrated management practices.
Table olives are picked separately and carefully by hand and placed in picking bags or buckets, while oil olives may be stripped off the trees onto nets placed on the ground. Harvest date depends on the cultivar and the purpose for which the fruit is intended and normally stretches from February to July in the Western Cape.
Fruit which is intended for green processing is picked at the stage when they have turned from bright green to yellow-green and the first fruit show a light pink or purple blush. Only that fruit which is of the required size is harvested while the rest are left for later picking.
Those fruit intended for processing as ripe black table olives are picked when they have turned completely black, but before they become overripe and soften.
Oil olives are harvested when most of the fruit on the tree is ripe enough and then the entire tree is picked. The oil content rises initially with colouring and ripening, then remains relatively constant, but a delay in harvest will result in lowered oil quality.