Ecological Requirements are as follows:

Altitude: Avocados can grow from 0-2100m asl, but performs best between 1500 to 2100m asl.             

Soils: Avocado grows successfully on many types of soil provided they are deep, well aerated, free draining with good water holding capacity; The optimum pH is 5.5- 6.5. If the pH is above 6.5, Gypsum (CaSO4) may be used to lower it.

Waterlogged or saline soils are unsuitable because avocado plants have low tolerance to excessive soil moisture and high salinity. 

Rainfall: A well distributed annual rainfall of 1000 - 1500mm p.a is optimal for good production.

Temperature:  Temperatures between 16-24^oC are ideal for growing avocados. Above 33^oC fruits suffer heat and sunburn damage. Below 4^oc growth is impaired.

Prepare planting holes during the dry season, 1-2 months before the onset of rains.

Dig holes 60cm x 60cm x 60cm. Under dry conditions, the hole should be bigger (about 90 x 90 cm and 100 cm deep). Separate the top soil and the subsoil. Spacing may range from 6m x6m, 6m x 7m or 8mx 10m between trees depending on growth characteristic of the individual variety, the type of soil and climatic conditions. 

Selection of nursery site should be based on the following criteria:

• Nearness to quality water source
• Good drainage
• Security (Animals, thieves etc.)
• Accessibility to the road
• Availability of wind breaks (Casuarina, Grevillea etc.)

Nursery Establishment: Prepare a seedbed of width 1 m and a desirable length by removing soil from the seedbed to a depth of 30 cm. Refill the 30 cm depression with sand.

Seed Preparation: Select healthy, mature fruits from vigorous growing mother trees and extract the seeds. Treat the extracted seeds in hot water (not exceeding 50 ºC) for 30 minutes then coat or dip in a broad spectrum fungicide (e.g. Metalaxyl) to prevent infection with Phytophthora cinnamon.

Cultivars used as rootstocks are “Puebla” or “Local varieties”. Fuerte is not resistant to Phytophthora.

Sowing Seeds: Sow the extracted seeds either in nursery beds or directly into eco-bags, tins or pots of about 20 cm in diameter and 30 cm deep, with the flat basal end pointing downwards.

Transplanting: After germination, when approximately 20 cm high and having developed two pairs of leaves, the open seeded seedlings (in nursery beds) are uprooted and transplanted into containers. The potting media should have medium texture, sterilized if possible and with good drainage properties.

Grafting : The rootstocks is ready for grafting 6 months after transplanting into biodegradable containers (6 X 9 inches) or when seedlings reaches pencil thickness.

Wedged grafting method is the most successful. It should be done at the point where the root stock is soft. The rootstocks are grafted using dormant scions of desired variety matching the size of the stock. Wrap the grafting point thoroughly to exclude water from the union; 4 to 6 months later, the seedlings are ready for transplanting into the field and should be well healed and free from pests and diseases.

Varieties:

Hass

Is a vigorous grower and bears medium-sized, rounded, rough-skinned black fruits.

Hass variety

Is distinctive for its skin that turns from green to purplish-black when fruits are mature.

Is easy peeling with great taste.

Has outstanding shelf-life and shipping characteristics.

Matures in 8-9moths after flowering.

Fuerte

Is a hybrid of Guatemalan and Mexican races with thin-skinned, green, pebbled fruits of very good flavour. Skin remains green and smooth when fruits are mature.

Matures in 6-8 months after flowering.

Fuete variety

Fruit is pear-shaped with medium seed. Very productive.

Puebla

Spreading, dark green tree bearing deep purple, round fruits.

Skin of ripe fruit is black, thin and smooth. Fruit has a velvety flesh with nutty aroma and a rich butter taste.

Matures in 5-7 months after blossoming.

Used as rootstock. 

‘Pinkerton’

Pinkerton variety

Has long, pear-shaped fruit with small seed. Medium thick green skin that deepens in colour as it ripens; Excellent peeling; Creamy, pale green flesh.  

‘Reed’

Reed variety

Round fruit with medium seed, medium to large fruits; Thick green skin with slight pebbling. Skin remains green when fruits are mature; Easy peeling; Creamy flesh with good taste.

Nabal

Bears fruits in alternate years. Its green fruits have a good flavour.

Matures in 8-9 months after flowering.

Other varieties:

Linda, Ettinger, Simmonds, Lyon, Tonnage, Zutano, Hardy, Teague etc.

Cultivars used as rootstocks are “Puebla” or “Local varieties”

Seed and Seedling acquisition: From HCDA /KEPHIS certified centres like JKUAT, etc. or nurseries spread in various locations.

Transplant the grafted trees as per the planting hole specifications made in the land preparation section above.

Mix topsoil with 2 buckets (20kg) of well rotten manure and basal fertilizer like TSP/DAP at 120-130g/hole.

Water the hole just before planting to ensure contact of the roots with moist soil then fill back the hole with soil, manure-fertilizer mixture.

Remove the polythene tube and hold the soil/ media around the roots. Maintain the position of the level of soil as it was in the polythene tube while planting carefully and firm the top soil mixture around the planted seedling. The subsoil may be used to make a basin around the tree. Water well and mulch after transplanting.

A windbreak may be appropriate under certain conditions, to protect the plant from leaning to one side and to help prevent leaf shading and fruit drop and bruising. 

Avocado nutrient requirements include N, P, K, Mg, Ca, Na, B, S, Zn, Mn, Fe, Cu, Al, Mo.

In the early years of crop development, avocadoes require high levels of nitrogen but after they begin to bear, the fertilizer should be higher in phosphate and potash.

At planting, mix one debe (20 kg) of well decomposed manure and 125 g of DAP with topsoil and return the soil to the dug hole to refill the hole.

Application of manure and fertilizer is desirable at the onset of each long and short rains. To determine the precise amount , the soil should be tested annually; otherwise the following table will serve as a guide;

During dry conditions, fertilizer application should be followed by increased application of irrigation water rates for one or two days until the soil-manure moisture is sufficient for the plant.

Deficiencies in one or more minor elements may occur in avocado orchards, seen usually as varying degree of leaf discoloration.

Symptoms of mineral deficiencies

Irrigation is essential where rainfall is not adequate, especially during early stages of growth and development. 

Irrigate grown up trees at 10-15 days interval from fruit set to maturity. Irrigation can also be applied to stimulate flowering after a distinct dry spell. 

Irrigation is not recommended for 2 – 3 months prior to flowering as it is likely to promote vegetative growth at the expense of flowering. There should be a marked season with dry weather for flowering and fruiting. 

Too much rain during flowering causes flower abortion resulting in significant reduction in production. Fungal diseases are also problematic in very wet weather.

Keep the orchard weed free in the early stages of growth. Once the seedlings have taken off well, break the hard pan formed when irrigating/ watering by shallowly digging at the base of the stem.

In mature trees, weed 2 m strip along the rows and cut grass in the rest of the field.

Intercropping:  Avocado orchards may be intercropped with other crops such as beans, peas, etc during the first 3-5 years to get Economic returns from the land before the trees start bearing.

Mulching is undertaken to conserve moisture, add organic matter to the soil and to smother weeds. The most common mulch for avocado is well-dried grass or dry leaves that is pest free. Sawdust should be avoided as it decomposes and ties up nitrogen.

Pruning

Initial pruning (Formative pruning) may be done to give the tree a good shape. It encourages lateral growth and multiple framework branching for ease of picking. Otherwise pruning should be limited to the removal of dead wood and parasitic plants.

• In order to reinforce this shaping of the tree, cut back shoots or pinch out the terminal buds of shoots growing straight up to keep the tree to a height of 5-8m. Remove all sucker growth originating from below the graft union.
• Remove all sucker and dead branches from main trunk branches.
• Prune the larger tree roots by cultivating to a depth of 50cm around the edge of the tree canopy.

The best time to prune is during the dormant season. The tree is very susceptible to sunburn, therefore pruning should be minimized. Excessive pruning of a young tree will delay the productive phase.

Heavy pruning should only be carried out to reduce the size of the tree after 12 to 15 years of bearing.

(i)False Codling Moth

Caterpillar (left)   &   adult (right) of the False Coding Moth

Symptoms/Damage:

Female adults lay eggs mostly on fruit. Upon emerging from the egg, the young larva tunnels into the fruit and feed from inside with frass or excrement being produced at the entrance of larval tunnels.

Control

(i)Proper orchard sanitation in combination with natural enemies normally keeps this pest under control.

(ii)Remove infested fruits regularly (twice a week) and bury at least 50 cm or dump in a drum filled with water mixed with a little used oil. Leave the fruits in the drum for 1 week.

(iii)Use of pheromone traps.

(ii) Thrips

        Thrips                         Thrips Damage

Symptoms/Damage:

Affected parts become whitish or silvery and are usually covered with dark-coloured droppings. The infested plant tissues will turn brown and dry up, if the damage is too severe.

On fruit, feeding begins near the calyx, gradually producing a scar that can cover the whole fruit. Attacked fruits develop a leathery brown skin. Feeding is most common on young fruit with older fruit (with thicker skin) being less susceptible to attack.

Control:

• Conserve natural enemies that feed on thrips like the predatory lacewings and predatory bugs.
• Control measures are rarely needed.

(iii) Scales

Armoured Scales on leaf         Armoured Scales on fruit

Symptoms/Damage:

• Damage is caused by toxic saliva, sucking of plant sap and excretion of honeydew which lead to the development of sooty mould on leaves, branches and fruit.
• There occurs discoloration, malformation, leaf and fruit drop, and retarded growth.
• Severe infestation forms a continuous crust over the underside of leaves.

Control:

• Conserve natural enemies. Scales are usually kept under control by parasitic wasps, ladybird beetles and lacewings, provided no broadspectrum pesticides are used and no ants are present. Ants feed on honeydew and protect scales from natural enemies.
• Chemical control: Use recommended insecticide such as Malathion if pest infestation is high.

(iv)Fruit Flies

     Adult Fruit fly

Symptoms:

• Some fruit flies lay eggs under the skin of the fruit that is just beginning to ripen, but others attack young and old fruit. When the fruit reaches about the size of a golf ball a sting lesion appears as a slight puncture mark surrounded by a white exudate.
• As the fruit develops, the lesion becomes dry and turns into distinct star-shaped crack on the skin surface.

Control:

• Practise orchard sanitation.
• Practise monitoring.
• Trap flies using commercial pheromone traps.
• Remove infested fruits twice a week and destroy by burying 60cm deep.
• Use of natural enemies, especially parasitic wasps.

Spray with recommended insecticide eg Deltamethrin.

(v)Bugs

         Fruit bug

Symptoms/Damage:

Adults and nymphs feed on young and mature avocado fruit. Bug feeding causes necrotic bruise-like depressions. A hard lump develops, resulting in fruit spotting, and deformation.

Control

• Conserve natural enemies. Weaver ants in particular, are efficient predators of bugs.

(vi)Mites

Broad mite damage (here on passion fruit)

Symptoms/Damage:

Attack by spider mites produce circular necrotic spots covered by dense webbing. As mite population increases, feeding causes leaf drop.

Feeding by broad mites causes leaf distortion, discolouration, necrosis and deformation of tissues.

Control

• Conserve natural enemies to keep the pest under control.
• Wash leaves with water using high pressure hoses to reduce mite populations.

(i) Root Rot (Die Back)

Cause: Fungus (Phytophthora cinammomi), spread by infested planting material, soil and irrigation water.

Die back on avocado tree

The disease is prone in areas subject to flooding and in poorly drained soils.

Symptoms/Damage:

Leaves of infected trees are small, pale or yellow green, wilted and fall prematurely giving the tree sparse appearance.

In advance stages of the disease, branches die-back and fruit remains small; thus crop yield is drastically reduced.

Feeder roots get darkened, decayed and die; Infected trees eventually die prematurely.

Affected trees lose vitality, become sparsely foliated and do not produce a good crop.

Control:

• Use disease free seed
• Remove affected trees from the field.
• Treat seeds for planting with hot water bath at 48 to 50 ⁰C for 20 minutes, then rinse the seed immediately with clean, cold running water and allow to dry on a clean surface.
• Use tolerant/resistant rootstocks for grafting.
• Cultivate healthy portion of the orchard before cultivating diseased areas.

(ii)Anthracnose

Cause: fungus (Colletotrichum gloeosporioides). Infection takes place when fruit is still very young but the fungus stays dormant till the fruit ripens.

Anthracnose damage on avocado

Symptoms:  

Depressed spots on the fruit. The spots are manifested as a rot, which can penetrate deep into the flesh.

The spots may be covered with mass of slimy, salmon pink fungal spore mass in wet weather.

Control:

• Remove and destroy dead branches and twigs since they harbour the fungus.
• Remove fallen rotten fruits from the field.
• Apply copper based fungicides (g. Nordox or copper oxychloride) pre-flowering, at fruit formation, and after harvest. Repeat every 14 days.

(iii)  Cercospora Fruit Spot

Cause: fungus

Lesion on fruit caused by Cercospora

Symptoms: Lesions appear as small, light-yellow spots on fruits and leaves. They later become reddish-brown; hard and crack.

Mature fruits are resistant.

Control:

• Remove and destroy dead branches and twigs since they harbour the fungus.
• Remove fallen rotten fruits from the field.
• Apply copper based fungicides (g. Nordox or copper oxychloride) pre-flowering, at fruit formation, and after harvest. Repeat every 14 days.

(iv) Scab

Cause: fungus. The fungus readily infects young, succulent tissues of the leaves, twigs and fruits

Symptoms:

Lesions appear as small dark spots, slightly raised, oval to elongated. These coalesce, giving a corky appearance to the surface of the fruits, impairing the appearance but not the internal quality of the fruit.

Control:

• Remove and destroy dead branches and twigs since they harbour the fungus.
• Remove fallen rotten fruits from the field.

Apply copper based fungicides (e.g. Nordox or copper oxychloride) pre-flowering, at fruit formation, and after harvest. Repeat every 14 days. 

Maturity indices include; Change in colour from green to black or purple in dark varieties; Fruit stems turn yellow and the fruit skin may sometimes turn less shinny. The end of the green varieties may develop rust-like spot.

In most cases, it is not easy to tell when the fruits are ready for harvest, especially in the varieties where the colour of the fruit does not change with maturity. Mature fruits float on the surface when immersed into water.

Harvest a sample of fruits and keep them at a room temperature. If they soften within 10 days without shrivelling, then the fruits of that age are ready for harvesting.

Harvesting should be done early in the morning or late in the afternoon when it is cool. Harvest by clipping fruits from trees with secateurs leaving a short stem portion of about 0.5 cm on the fruit.

For fruits growing high on a tree, use ladders or a specially designed picking tool. Avoid inflicting damages to the skin as this allows decay diseases to enter the fruit.

Packaging

 Avocados in a packhouse            Avocados packed in a box for export

Pack the fruits in single layer in fibre board cartons, to avoid rubbing against each other that can shorten the shelf life of the fruits. The cartons should be well ventilated and should have a handle for handling.

Transportation and storage

Transport or store mango at 11^oC for green fruit and 8^oC for riper ones. Most varieties can store at temperatures between 10^oC and 13^oC with relative humidity of 85 to 90% for a storage period of between two to four months. Fruits should not rub against each other during transportation.

Storage and marketing:

Store the produce in a cool dry place. This will minimize internal chemical reaction that may accelerate early ripening before they reach the market. 

Fresh Quality Specifications for the Avocado market in Kenya

Processing

Generally, Avocado is served raw (ripe), though it can be processed into juices, shakes, ice creams, dips, pastes and purees.

Avocado oil is also famous as a cooking oil.

Avocado juice           Avocado pudding             Avocado oil

Avocado yields 250-300 kgs per tree per year (8-10 tonnes/acre. The yield increases as the tree continues to grow. A good yield is obtained from the sixth year onwards.