Avocado is a nutritious fruit. But awareness about it in Pakistan is not significant. Actually many people think that it does not grow in Pakistan. So here basic information about the production technology.
Soil and climate
Avocados cannot tolerate hot dry winds and frosts, typically grown in tropical or semitropical areas with rainfall in summer and humid, subtropical rainfall areas. Intolerant to saline conditions and optimum range of pH is from 5 to 7, are characteristics of this unique fruit. The climate zone of avocados is from true tropical to warmer parts of the temperate zone. Avocados can be grown on a wide range of soils, but they are extremely sensitive to poor drainage and cannot withstand water-logging. They are intolerant to saline conditions. Depending on the race and varieties, avocados can thrive and perform well in climatic conditions ranging from true tropical to warmer parts of the temperate zone.
Avocado is commonly propagated through seeds. The viability of seeds of avocado is quite short (2 to 3 weeks) but this can be improved by storing the seed in dry peat or sand at 50C. Removal of seed coat before sowing hastens germination. The seeds taken from mature fruits are sown directly in the nursery or in polyethylene bags. When 8-12 months old, the seedlings are ready for transplanting. The seedling trees took more time to start fruiting and the yield and fruit quality is highly variable. Due to cross-pollination, there is great variability in the seedlings produced from seeds, it is impossible to obtain genetically uniform plant as indicated for the formation of commercial orchards. These seedlings plants take long time to produce first crop and fruit quality in unreliable. Vegetative propagation of superior clones of avocado by budding or grafting is essential to avoid these problem. Experiments conducted with two method of grafting (veneer and cleft) and two methods of budding (T and patch).
California Long and Saloon Blue Avocado are the varieties that can grow in Pakistan.
Field preparation and Planting
The avocado plantation in a relatively new area required care in selection of the varieties. The varieties of both A and B groups should be selected and their flowering must overlap. The proportion of A and B group varieties can be 1:1 or 2:1. Avocado is planted out to a distance of 6 to 12 meters depending on the vigour of variety and its growth habit. For varieties having a spreading type of growth a wider spacing should be given. In areas prone to excess water, they should be planted on mounds as avocados cannot withstand waterlogging. A planting distance of 10 x 10 meters on hills slopes is preferred. When it is planted with coffee the plating distance varies from 6 meter to 12 meters. The pits of 1 cubic meter size are dug during April – May and filled with farmyard manure and top soil (1:1 ratio) before planting. Planting is done in June-July or sometimes in September.
Avocados need heavy manuring, and application of nitrogen has been found to be most essential. In general, young avocado trees should receive N, P2O5 and K2O in a proportion of 1:1:1 and older trees in the proportion of 2:1:2. At a pH of above 7, iron deficiency symptoms may appear, which may be corrected by applying iron chelate at the rate of 35 g/tree. Various micro-nutrients (Fe, Zn, B) have profound influences on tree growth, nutrient uptake and yield of avocado. Integrated nutrient management with inorganic fertilizer, supplemented by organic manuring, is advocated for avocado. Fertilizer may be applied in two split doses in March-April and September-October or just before and after the onset of the monsoon. Foliar application of zinc sulphate (0.5 per cent) and other micro nutrients may be undertaken in April-May or September –October. This micro nutrient may be applied as soil application along with other fertilizers.
Training and pruning
The plants need to be given light pruning in initial stages for developing an open centre canopy. After that pruning is rarely practiced. In upright varieties such as Pollock top is done to reduced the tree size while in spreading varieties .The dropping and ground touching branches need to be pruned for ease in cultural practices. Heavy pruning has been found to promote excessive vegetative growth, consequently reducing the yield.
Avocado is grown in those areas where rainfall is high and fairly distributed throughout the year. Therefore it is grown under rain fed conditions and irrigation is generally not given. Irrigation at intervals of three to four weeks during the dry months is beneficial. Sprinkler irrigation has been reported to improve the fruit size and oil percentage and advances harvesting time. To avoid moisture stress during winter season, mulching with dry grass/dry leaves is desirable. Flooding is undesirable as it promotes root rot incidence.
Intercultural and weed management.
Deep cultivation in avocado orchards should be avoided because of surface roots. Intercropping with legumes or shallow-rooted crops can be done in young orchards which can smoother weeds also. The monoculture plantation of avocado may be maintain with sod culture. The weed are major problems in high rainfall zones. The use of gramexone or Ghyphosate is recommended to control weeds. In coffee based plantation system, scruffling done for coffee is sufficient to control weed. Care should taken that the roots of avocado not disturbed during scruffling.
Pests and diseases
The Anthracnose root rot, leaf spot, Stem rot, The scab are the major diseases affecting avocado.
Anthracnose is becoming major problem but effecting the fruit yield and quality. It is caused by Colletotrichum gloeosprotioides. The symptoms are developed in the fruits either or after harvest initially the symptom is large light, brown circular, lesions which turns into dark brown or black colour of the sometime. Infection results in shedding of young fruits. Remaining fruits become deformed. The copper based fungicide copper oxide, copper trioxide may be used to control this disease in the initial stage. The orchards sanitation like burning of fallen leaves and fruitshelp to reduce inoculum. Post harvest treatment of urns to control the disease is also recommended inmany countries. Controlled atmospheric storage of fruits in 2% O2 at 7.2oC for 3-4 weeks helps to prevent the development of the fungus in storage.
Phytophthora Root Rot
The most serious disease of avocado is the root rot caused by Phytophthora cinnamoni,leading to death of plant. The disease effects the roots and they became black and eventually die which effects the overall growth and yield of the plants. The disease situation is aggravated by ill drained and waterlogged conditions. Metalaxyl (Ridomil) mixed with soil before planting or applied as a soil drench controls root rot at least for four months after treatment. Soil drenching of Ridomil (1gai/10 lit) controls root rot.This disease may be minimized by using tolerant varieties , avoiding water logged areas for planting, soil solarization, use of metalaxyl, potassium phosphonate may be used.
Sphacelomaperseae Oval or irregular brown or purple spots on fruit with rough texture are formed. High humidity encourages scab growth and spread. Use of tolerant varieties and spray of copper containing fungicides helps to control the scab problem.
Mites, mealy bugs, scales are the important insect pests of avocado. Mites Three species of mites prey on avocado trees. The avocado brown mite lays eggs on the tree’s leaves, and in large numbers damages and destroys the plant’s foliage. The perseamite also harms avocado tree foliage, leading to fewer fruits, though the six-spotted mite typically only causes leaf discoloration. Predatory mites will keep the population of all three mites under control, as will avoiding the use of chemical pesticides that kill their natural enemies.
Mealy bugs (Planococcuscitri)
Mealy bugs are not major problem in avocado but use of insecticides kills the natural enemies of mealy bugs causing major problem. Mealy bugs are sexually dimorphic. Yellow eggs are produced in a loose colony of waxy filaments. About 50-100 or more than 100 eggs covered in an ovisac are deposited by female. Mealy bug breeds continuously on different hosts like citrus, Murraya koenigi, coffee in Coorg region. Mealy bug observed on fruits during September-October months. It was found both on the immature and ripened fruits. The mealy bugs produced large quantity of honey dew, which attracts other insects and these insect lay egg on the fruits and deteriorate the quality of fruits. Mealy bugs are tend to be serious pests in the presence of ants because the ants protect them from predators and parasites. These may be control by release of lady bird beetle, Cryptolaemus montrouzieri at 10 beetles/tree after fruit set. Spraying 150ml dimethoate + 250ml kerosene in 100 of water (or) 10g of carbaryl +10 ml kerosene in 10 l of water gives effective control of mealy bugs.
Thrips (Scirtothrips perseae)
Obvious feeding by Thrips scars on fruit. These scars begin as scabs or leathery patches and spread across fruit. The adult insect is orange-yellow in color with distinct brown bands and reaches 0.7 mm in length. Insect thrives in cooler temperatures and may undergo 6 or more generations per year. Addition of coarse organic mulch about 6 inches thick below trees may help to reduce survival of Thrips pupating in soil. Selective insecticide should be selected to control these insects so that minimum damage is done to populations of natural enemies.
Fruit fly (Bactrocera dorsalis, B. caryeaea)
Very less percentage of fruit fly infestation was noticed on rambutan. Fruit fly infests the ripened fruits. Its infestation is more in southern states. The female fruit fly lays eggs on the mature fruits with the help of its pointed ovipositor. After hatching the maggots feed on pulp of these fruits and the infested fruits starts rotting and fall down. As a result brown patch appears around the place of oviposition. The maggots come out of the affected fruit and pupate in the soil.
Pre-harvest IPM combined with sanitation (Collection and destruction of fallen/infested fruits) + Placing Methyl eugenol trap @ 4-6/acre + In severe infestation spraying of bait spray (Decamethrin (Decis) 2ml+ 100g of jaggery in 1 litre of water) is recommended. Avocado has high nutritional value and usefulness of it,s high quality fats in promoting health of heart and circular system is attracting lot of people to use it in their daily diet. The growing use of Avocado oils and fats in cosmetics is also a reason of increasing popularity of this fruit. Consumption of Avocado is limited to high elite group of large Metropolitan cities but with increasing awareness about the health concerns, the demand of avocado is increasing.
Fruit harvesting and yield
Avocado plants raised from seeds start bearing five to six years after planting while grated plants stars yielding in 3-4 years. Mature fruits of purple varieties change their colour from purple to maroon, whereas fruits of green varieties become greenish-yellow. Fruits are ready for harvest when the colour of seed coat within the fruit changes from yellowish white to dark brown. Mature fruits ripen six to ten days after harvesting. The fruits remain hard as long as they stay on the trees, softening only after harvest. The yield ranges from about 100 to 500 fruits per tree. Post-harvest handling, storage and marketing Avocados do not ripen on the tree, and fruits soften only after they are picked. Fruits need to be picked carefully. They should be harvested at the correct stage of maturity. Fruits of 250 to 300 grams in size are preferred. Hard, mature fruits are harvested and allowed to ripen during transport and distribution. Unripe avocados can be stored for up to four weeks at 5.5 to 8°C. Presently, there is no organized marketing system for avocado as the production is small and production areas are scattered.