Cashew Nut: Origin, Distribution, and Ecology

Origin & Distribution

Cashew nut (Anacardium occidentale), locally known as Mkorosho or Mkanju in Swahili, originated in northern South America. The Portuguese introduced it to Mozambique, from where it spread across East Africa. In Kenya, cashew nuts are primarily grown in coastal regions, including Kwale, Kilifi, Tana River, and Lamu, with some cultivation in Taita Taveta and Tharaka Nithi.

Botanical Features

• Grows up to 12 meters tall with an irregular trunk.
• Leaves are elliptical, leathery, and spirally arranged.
• Flowers are small, initially green, turning reddish.
• The kidney-shaped nut grows beneath the edible cashew apple.
• Has a productive lifespan of about 45 years.

Uses

• Nut: Rich in protein (21.2%) and fat (46.9%), used as food.
• Shell oil: Used in medicine, waterproofing, and industrial products (varnishes, cement, inks).
• Cashew apple: High in Vitamin C, minerals, and sugar, consumed fresh or processed.
• Wood & shells: Used as fuel.

Ecological Requirements

• Temperature: Grows best in 24–28°C, tolerates up to 40°C.
• Rainfall: Requires 500–1200mm annually with 4–5 dry months for flowering.
• Altitude: Thrives at 0–1,000m, with an ideal 600m elevation.
• Soil: Prefers deep, well-drained, sandy soils (pH 4.5–6.5).
• Sensitivity: Does not tolerate frost, saline soils, or waterlogging.

Cashew Nut Varieties and Propagation

Recommended Varieties

Cashew nut varieties suitable for cultivation include A75/83, A100, A81, and A82, with varying yield potentials (Table 1). These varieties can be propagated through seeds or grafted seedlings.

Propagation Methods

1. Seed Propagation:
• Sow three seeds per hole.
• After two months, remove weaker seedlings, leaving only the strongest.
2. Grafting:
• Select healthy seeds and pre-germinate them in water (sinking seeds are viable).
• Transplant germinated seeds (2.5–3 cm radicals) into potting bags filled with a soil mixture (2:1 soil to farmyard manure + 150g DAP).
• Seedlings are grafted after developing two functional leaves (3–4 weeks post-transplanting).
• Graft scions from select mother plants onto the rootstock.

Planting Guidelines

• Best Time: At the onset of the rainy season (April–June in coastal regions).
• Land Preparation: Clear and plough the field before planting.
• Spacing: 12m x 12m (or 6m x 6m initially, thinning later).
• Hole Preparation: Dig 60cm x 60cm x 60cm holes 1–2 months before planting. Mix topsoil with farmyard manure and DAP.
• Transplanting: Place seedlings at the same soil depth as in the potting bag, avoiding graft union burial. Mulch and water after planting.
• Watering: Every 3–4 days until the plant establishes.
• Intercropping: Grow short-duration crops like papaya, maize, cassava, or vegetables to optimize land use.
• Weed Control: Keep the orchard weed-free for healthy growth.

Management of Young and Old Cashew Orchards

Young Orchard Management

1.Formative Pruning: Train grafted plants to grow upright (1.0-1.5m) within the first five years.

2.Sucker Removal: Remove rootstock suckers to prevent competition for nutrients. Desucker continuously in year one until the tree reaches 1m.

3.Fire Breaks: Establish fire breaks after planting, especially in the dry season.

4.Pest Control: Regularly inspect seedlings for pests and diseases and take preventive measures.

5.Shading & Irrigation: Provide shade, mulch, and irrigation during drought. Young trees benefit from irrigation, while mature trees need 1,800L of water every two weeks.

6.Fertilization: Use animal manure or compost. If unavailable, apply DAP, CAN, or potassium sulfate.

7.Wind Control: Maintain grass strips between rows to reduce erosion.

8.Pollination: Encourage pollinators, especially honey bees, to improve fruit set.

Old Orchard Management

1.Pruning: Remove dead, diseased, or intermingling branches, and those below 1m. Protect cuts with insecticidal paint.

2.Selective Thinning: Remove closely spaced, diseased, unproductive, or undesirable trees.

Rehabilitation Methods:

• Pollarding: Cut the canopy at 2.5-3.5m to improve management and yield.
• Coppicing: Cut old or low-yielding trees at 0.5-1m to promote new growth. Ensure a sloped cut to prevent water accumulation.
• Top-Working.Top-working involves grafting sprouts from coppiced trees. Select 3-4 pencil-thick sprouts per stem for grafting.

Pest and Disease Management

Cashew nuts are prone to pests like cashew nut bugs (Helopeltis anacardii), stem borers, thrips, mealybugs, weevils, caterpillars, and leaf miners. Key diseases include powdery mildew and anthracnose.

Common disease

• Powdery Mildew (Oidium anacardii): Affects leaves, shoots, and flowers, potentially reducing yield by 80%. Control methods include pruning, thinning, removing infected parts, and applying fungicides.
• Anthracnose (Colletotrichum gloeosporioides): Causes black spots on tender plant parts. Preventive measures include burning infected parts before the fruiting season and using copper-based fungicides.
• Dieback (Phomopsis anacardii): Leads to drying twigs, flowers, and leaves. Managing cashew nut bugs and coconut bugs helps reduce its occurrence.

Common Pests & Control

• Cashew Nut Bug: Feeds on young leaves, shoots, and nuts, multiplying in the rainy season. Control through regular monitoring and conserving natural predators.
• Bark Borer: Larvae bore into the trunk, causing water loss and tree death. Remove affected bark monthly and burn severely infested trees.
• Coreid Bug: Feeds on flowers and fruits, leading to fruit drop and damage. Control with synthetic pyrethroids and by conserving weaver ants.
• Mealybugs: Cover shoots, inflorescences, apples, and nuts with a white waxy coating, reducing yield. Manage using natural predators or insecticides mixed with white oil.

Harvesting & Post-Harvest Handling

Cashew trees bear fruit within 3-4 years when grown from seeds and 2 years if grafted. Yields range from 10-100 kg per tree annually, with one hectare producing 2,000-5,000 kg. Harvesting occurs from November to May, peaking between November and January.

For quality nuts:

1. Collect fallen fruits daily.
2. Separate nuts from apples and sun-dry them for 2 hours.
3. Grade nuts into Fair Average Quality (FAQ) (mature, dry, grey/pale brown, unspotted) and Under Grade (UG).

Cashew trees can produce for 40-50 years, with commercial harvesting lasting about 35 years.