Foliar feeding the growth of African cashew production

Dr Terry Mabbett speaks with Omex Agrifluids technical sales manager, Ben Odunlami and export sales manager, Oskar Winkler about the foliar application of their products to nut tree crops like cashew

Africa continues to achieve phenomenal growth in the production of cashew with recent rates reaching 7% per annum. The African cashew market was worth US$822.49mn in 2024 and is expected to reach US$984.91mn by 2029. The leading African producer is Cote d’Ivoire which now accounts for 40% of African production. Following on is Nigeria, Benin and Tanzania with Ghana, Guinea Bissau and Burkina Faso as other significant players. Africa as a whole produces 2.4 mn metric tonnes of cashew per annum and representing 60% of the global production.   

The Francophone country’s gross cashew production more than doubled from 460,000 metric tonnes in 2013 to 1.1 mn metric tonnes in 2021. During the same period shelled cashew nut production grew from 30,000 metric tonnes to 110,000 metric tonnes. In 2023, gross cashew production grew by a phenomenal 19% to reach 1.22 mn metric tonnes. 

"Foliar application of high quality soluble nutrient products is the way to feed the cashew tree," said Omex Agrifluids technical sales manager, Dr Ben Odunlami and export sales manager, Oskar Winkler. Omex Agrifluids is a research and development based company and a world leader in the design and manufacture of soluble nutrient products in both liquid and solid delivery systems and tailor-made for foliar application to a huge range of crops including tropical fruit and nut tree crops like cashew. This crop is virtually unique in this respect because it yields a commercially soft ‘pseudo-fruit’ called the cashew apple (which actually is the swollen receptacle); and the kidney-shaped and bean-like hard nut which as the true fruit is inserted into the cashew apple.

Seedlings in the nursery 

As with virtually all tropical tree crops, life for the cashew tree starts in the nursery as tiny seedling trees requiring rapid root establishment and fast foliar growth prior to transplanting into the field. Dr Mabbett asked Odunlami and Winkler what Omex has to offer cashew growers across Africa who want the fast, strong growth of seedling trees essential for successful establishment post-transplanting. “A pair of products called Omex Bio 20 and Omex 3X Emulsion”, said Odunlami and Winkler.

Ben Odunlami told African Farming how Omex Bio 20 is a highly concentrated liquid emulsion product providing growers with the full range of macronutrients, mesonutrients (magnesium) and micronutrients, with the latter in the chelated form, and with something special extra too. That is an organic extract derived from a specific marine alga (seaweed) and which delivers a biostimulation dimension to tree seedling growth and establishment. “Omex Bio 20 stimulates root growth and development and will mitigate the physiological stress experienced by young, tender seedlings whether from abiotic factors like temperature and moisture or biotic factors including pests and diseases,” Odunlami told African Farming.  

“But what about cashew growers in countries where Omex Bio 20 may not be available,” Dr Mabbett asked. “This is where Omex 3X Emulsion comes in as a sound and equivalent alternative”, said Winkler, highlighting that this fully water soluble fertiliser contains NPK macronutrients (nitrogen, phosphorous and potassium), magnesium and chelated trace elements (micronutrients). Recommendations are for foliar sprays to the young seedlings in the nursery and again when transplanted into the field. Omex Bio 20 is applied at 2.5 ml/l of water to seedlings in the nursery and transplanted seedlings. Omex 3X Emulsion is applied at 2.5 ml/l.

Juvenile plants in the field

Next plant growth and development stage to consider is juvenile plants having been transplanted into field and needing to be put on fast and robust vegetative growth. ”Omex Bio 20 or Omex 3X Emulsion is applied at 1 l/ha at monthly intervals for fast foliar growth and alongside Omex Zibo, one of Omex’s newest and most novel products, and specifically to deliver strong tree root systems through fast but disease resilient growth Ben and Oskar told African Farming. Omex Zibo is a highly concentrated liquid suspension product containing zinc (22.10% w/v) and twinned with boron (7.30% w/v).

“Zinc is pivotal in the formation and modulation of enzymes which are critical in the early stages of root and shoot development and is also important in the production of proteins from amino acids and therefore clearly important during periods of rapid plant tissue growth. Zinc also helps to maintain membrane permeability, thus enhancing stress tolerance,” said Odunlami. "Role of Boron is no less important and together with zinc is closely involved with the synthesis of cell wall material and the transport of sugars and therefore has crucially important tissue strengthening and growth consolidation roles,” said Winkler. Like Omex Bio 20, Zibo is applied as a foliar spray at monthly intervals and at a rate of 0.5 l/ha.

Mature plants

Cashew trees now mature and typically start to flower and bear fruit in the third or fourth year and reach maximum fruit yield by year 7, continuing to receive two spray applications of Omex Bio 20 or Omex 3X Emulsion one month apart and at an elevated rate of 3 l/ha, with the specific aim and purpose of providing complete, total nutrition with continued biostimulation to tree growth. 

Odunlami and Winkler said that high calcium products were critical at this flowering and fruiting stage. “Omex can offer cashew growers three products high in soluble calcium,” said Odunlami. Omex Calmax (22.50% CaO w/v); Omex Calmax Gold (24% CaO w/v) and Omex CalMaxB (22.50% CaO w/v plus 1.53% B w/v) and all sprayed twice at an interval of one month and at a rate of 2.0 l/ha. Key purpose of these Omex CalMax products is to strengthen cell walls, suppress disease and enhance the shelf life of harvested cashew.

Calcium plays a crucial and critical role in tissue strength as a component of calcium pectate which cements plant cells together. Last but not least is two more spray applications of Omex Zibo, four weeks apart and at a rate of 2.0 l/ha. The zinc and boron nutrients in Omex Zibo enhance flower fertility and minimise the abortion of flowers and newly-formed fruits.

Next is the fruit development stage with repeat applications of Omex CalMax, Omex CalMax Gold or Omex CalMaxB. Several (2 to 3) sprays are given one month apart and at a rate of 2 l/ha. This repeat application is to reinforce the cell wall strengthening, disease mitigation and shelf life improvement benefits of calcium. Also, one of two high potassium (K) products, Omex K41 (41.0% K2O w/v) or Omex Sequential 2 (40.0% K2O w/v) is applied at 2.0 l/ha to maximise the transport of soluble sugars to the fruit.

Cashew trees having started to flower and fruit in year 3 or 4 and having attained maximum production by year 7 must be kept in tip-top condition with regular applications of high maintenance Omex products. These are Omex Bio 20 or Omex 3X Emulsion at 2 l/ha once per month for total nutrition with the accompanying biostimulation of foliar growth and Omex Zynergy (Zn 4.72% w/v; Cu 2.66% w/v; SO3 9.10% w/v) with the express purpose of promoting and maintaining plant health.

“With this achieved, there is no reason why cashew growers cannot get between 30 and 50 years of good cropping,” Odunlami and Winkler told African Farming.