By MURIMI GITARI
At an avocado grower-supplier meeting held in Nairobi and hosted by DuduTech on 4 July 2019, Dr Steve Oosthuyse, an invited speaker and authority on avocado growing, gave the “low-down” on the latest methods of growing avocados.
Orchards, in terms of tree spacing, have moved from densities of 400 to 830 trees per ha. The permanent spacing of 6 x 2 m is now being successfully adopted in South Africa. Spacing can be even closer. In Mexico, the spacing of 4 x 2 m is in cases used on farms in arid regions in Jalisco state.
Trees are grown as hedge rows with a North –South orientation, and annual topping and balanced side (selective) pruning are carried out to keep the trees in the space allocated to them. As final trees size is “relatively small,” pruning operations to maintain size are easily carried out. The key management criterion is to ensure that the trees are never allowed to overcrowd, and the alleyway between canopies stays open. 30 MT of production annually, using this system, is easily attained. Yield per ha in traditional orchards is half or less of this tonnage.
Dr Steve considered the use of growth retardants in his talk, showing from his own research that Paclobutrazol applied when the trees are in flower reduces new shoot length (vigour) and increases fruit size, and as a result, yield. An increase in fruit number may occur. Results of Dr Steve’s research are in line with the results of previous research work carried out in the 90’s by others.
Nutritional practices were alluded to. Focus was placed on the control of Phytophthora root rot and the root environment ideally suiting avocado trees. Planting trees on ridges, and the incorporation phosphate as well as composted manure into the ridge prior to planting, were stated to be critical practices. Soil pH rectification to that of 6.5 to 6.8 is necessary, and was stated to be achievable in including lime or dolomitic lime in the ridges. Deep red Hutton soils are ideal for avocado growing, drainage being a key aspect to ensure health.
Dolomitic as opposed to calcitic lime inclusion was stated to be required if magnesium levels were low at the start. In developing and bearing orchards, the use of vegetative mulch was encouraged. Such mulching encourages surface root development, increases irrigation efficiency, and reduces variation in soil water content and temperature.
“Success in avocado growing depends on one’s knowledge of vigor control – i.e. maintaining a favourable reproductive-vegetative balance.” Dr Steve added that avocado trees are shallow rooted, most of its roots generally found within 40 cm below the soil surface. The root system stays in check in keeping canopy size in check. Overcrowding causes root expansion. Excess vigour at the expense of bearing occurs when the trees are pruned back to size. This is detrimental to productivity for a number of years even if proper pruning measures are adhered to. Excessive vigor leads to increased fruit drop, and is often associated with increased fruit physiological disorders incidence.
Dr Steve advised growers to carry out soil sampling and analysis prior to panting to enable professional phosphate and soil pH rectification. Phosphorus if often deficient in virgin soils.
Many other aspects were discussed, including the use of tensiometers to ensure ideal soil water content management, and to precisely manage a relative water stress for the purpose of timing and synchronizing inflorescence development.
Dr Steve gives intensive crop courses to growers. To date he has hosted 5 macadamia courses in South Africa. He has given avocado, mandarin, papaya, litchi or mango grower courses to growers in Brazil, Mexico, China, Pakistan, Egypt and many other countries during past years. All critical aspects are covered to ensure that growers make informed and efficient management decisions in managing their orchards.
Dr. Steve owns and manages the private research company, HortResearch SA, located on the outskirts of Tzaneen, in Limpopo, South Africa.
Dr Steve can be contacted by email (hortres@pixie.co.za or dsoh1@mweb.co.za), or in calling or WhatsApp-ing him on +27 79 886 2898.
