Avocado (Persea americana Mill.) is considered one of the most nutritious fruits in the world. In the Philippines, however, it has not attained the popularity enjoyed by other fruits despite its early introduction in 1890. One reason for this is that it lacks that sweetness of such popular fruits as mango, banana and pineapple. To improve its taste to suit their palate, Filipinos eat avocado with sugar and milk. If Filipinos acquire the taste for the fruit, avocado can become a good market fruit and therefore source of income of small farmers in the countryside. Later, export market for fruit can be developed. Aside from the nutritional benefits that can be derived from the fruits, its various parts have several medicinal uses.
The Avocado tree is an evergreen tree that attains heights of 40 to 80 feet and has many branches. The leaves are elliptic or oval in shape and 3 to 10 inches long. Flowers are small, greenish, and perfect (has both male and female parts). The avocado fruit may be round, pear shaped, or oblong, and the skin of the fruit may vary in texture and color. The skin may be pliable to woody, smooth to rough, and green-yellow, reddish-purple, purple, or black in color.
The flesh of the fruit is greenish yellow to bright yellow when ripe and buttery in consistency, but inferior varieties may be fibrous. The avocado fruit has one large seed which makes up to 10 - 25% of the fruit weight. The fruit of different avocado varieties may vary in moisture and oil content, from less than 5% oil to more than 30% oil. Avocado fruits range from 0.25 lb to more than 3 lb in weight.
Family: Lauraceae
Scientific name: Persea americana Mill.
Origin: American Tropics
Pollination is usually done by honeybees and other insects. There are two avocado flowering types, A and B. Each flower opens twice, functionally female (pollen receptive) at the first opening and functionally male (pollen shedding) at the second opening. Type A opens first in the morning, closes at midday, and reopens in the afternoon of the following day. Type B opens first in the afternoon, closes in the evening, and reopens the following morning. The presence of both types of trees is important in orchards to improve production by adequate pollination.
VARIETIES
There are three distinct races of avocados: Mexican, Guatemalan and West Indian. Some important commercial cultivars are hybrids of the various races.
The Mexican race is the most cold tolerant, while the West Indian type is most adapted to warmer climates. Fruits of the Mexican race are generally small with thin, smooth skins, while those of the Guatemalan race have skins that are thick, hard, brittle and warty. The West Indian type has shiny skin that is thin to medium in thickness.
‘Haas’ is a black-skinned, ovate cultivar whose fruit weighs 5 to 12 oz. It descends primarily from the Guatemalan race. This cultivar accounts for about 75% of the production in California, the main producing U.S. state. ‘Haas’ is also important in Mexico, the world’s largest avocado producer, and in Chile, the main foreign supplier to the United States. In Mexico, ‘Haas’ is harvested all year but the main season is from October to May. In Hawaii, ‘Haas’ has not produced high quality fruits.
‘Sharwil’ is a Mexican and Guatemalan cross and represents more than 57% of the commercial acreage in Hawaii. Its green-skinned fruits weigh 8 to 20 oz and mature in winter and spring. ‘Greengold’ and ‘Murashige’ are other green-skinned cultivars recommended by CTAHR for commercial planting.
‘Haas’, with black skin when ripe, is the most widely consumed avocado cultivar on the US mainland. Avocado consumption declines during fall and winter when there are less-desirable cultivars in the market. According to the California Avocado Commission, California growers received the highest price for ‘Haas’ (average of 40 cents per lb from 1980-1989) when compared to ‘Fuerte’ (23 cents per lb) and other cultivars that have green skin when ripe (17 cents per lb).
‘Sharwil’ avocados have small seeds and greenish-yellow flesh with a rich, nutty flavor. In Hawaii, many consider ‘Sharwil’ to be superior to California cultivars and believe it should be marketed as a gourmet item. ‘Sharwil’ has green skin when ripe, which is a problem where consumers rely on black skin as a sign of ripeness. It is the only Hawaii avocado authorized for shipment to Alaska and the US mainland in compliance with USDA/Animal and Plant Health Inspection Service (APHIS) requirements. Avocados destined for these markets are required to be packed in a fruit fly-proof, APHIS-approved and -inspected packinghouse.
Many consumers have trouble identifying ripe ready-to-eat avocados, especially green-skinned cultivars. Stickers are now placed on ethylene gas-ripened avocados in retail outlets to help consumers select ripe fruits.
USES
Unlike many fruits that typically have a sweet or acidic taste, avocados have a smooth, buttery consistency and a rich flavor. A popular use is as a salad fruit. Avocados are also processed into guacamole and can be used in sandwich spreads. Avocado paste with flavor extracts and skim milk can also be used to make an ice cream.
Oil extracted from avocados can be used for cooking and preparation of salads, sauces and marinades. Avocado oil also can be used for skin care products such as sunscreen lotions, cleansing creams, and moisturizers, or for hair conditioners and makeup bases.
Avocados are often eaten with soy sauce or grated horseradish in Japan. In Europe, avocados are generally served as an appetizer with mayonnaise or salad dressing, or are filled with a seafood cocktail.
Avocados have 1.6 times as much potassium as bananas. A 3.5 oz serving has about 177 calories, contains no cholesterol, and has about 0.6 oz of fat, which is primarily the monounsaturated type. Nutrient values vary by cultivar.
PROPAGATION
Commercial avocado trees are propagated by grafting of budding scions of desirable cultivars onto seedling or grafted rootstocks. Avocados can be grown from seeds, but fruit quality and yield potential will be quite variable. Grafted or budded avocado trees usually produce fruits when three to five years old, while seedlings often require five to seven years.
To avoid contamination from Phytophthora root rot in the nursery when growing seedling rootstocks for grafting, (1) do not use seed from windfall fruits picked up from the ground, (2) propagate seedling rootstocks in sterilized, disease-free media, and (3) do not allow containers to contact soil.
SOIL TYPES and LOCATION
Avocado can be grown on a wide range of soil types, but requires good drainage as it does not withstand waterlogging. Annual rainfall of 50 inches that is well distributed over the year is adequate. Poor drainage and soil pH of less than 6.2 are favorable conditions for the development of Phytophthora root rot.
Areas with high winds are undesirable because avocado wood is brittle and flowers and fruits may be damaged. Areas along the shoreline are also undesirable because avocado trees are sensitive to sodium chloride (salt).
In Hawaii, Guatemalan and Mexican races and their hybrids can be grown up to elevations of approximately 2000 to 2500 feet. Pure Mexican varieties which are rarely grown in Hawaii can be grown up to the frost line. The West Indian variety produces better quality fruits when it is grown below 1000 feet.
CULTURAL PRACTICES
Trees should be spaced 25 to 35 feet apart, depending on the cultivar. In Kona, on the Big Island, avocados are often interplanted with coffee and macadamia nuts. But for the best management they should not remain interplanted with other fruit crops when mature. Organic mulches or herbicides are recommended for weed control. Cultivation for weed control should be avoided or should be done as shallow as possible to avoid damage to the avocado root system. Pruning is usually unnecessary except to shape young trees and remove dead branches.
FERTILIZATION
Specific nutrient requirements of avocado grown in Hawaii are not well known. Information on fertilization of avocado is based on avocado production elsewhere. For preplant applications, have the soil tested before planting and follow the recommendations. To make adjustments for soil pH and calcium (Ca) deficiencies before planting, soil from each distinct area of the orchard should be sampled. Soil type may be determined by the use of soil survey reports obtained from public libraries or the county USDA Soil Conservation Service offices. The University of Hawaii Cooperative Extension Service Circular No. 476, Soil Classification in Hawaii, may provide useful information on soil management.
The optimum soil pH for avocado is between 6.2 and 6.5. Lime (calcium carbonate) can be added to acidic soil to raise the pH to 6.5. Dolomite can be substituted for part of the lime requirement if magnesium (Mg) is deficient. Calcium nitrate or calcium sulfate (gypsum) may be used to provide calcium when soil pH is adequate. Also, adequate calcium may be provided by Phosphorus (P) applications when super phosphate (20% Ca) or triple superphosphate (14% Ca) is used. Lime, dolomite, and P fertilizers should be mixed with the soil thoroughly prior to planting to place the fertilizers at the root zone.
When avocado trees are transplanted into the field, a complete fertilizer containing nitrogen (N), phosphorus (P), and Potassium (K) should be mixed with the soil in the planting hole. Later fertilizer applications should be done by broadcasting fertilizer evenly over the root zone between about 1 foot from the trunk and 1 to 2 feet beyond the leaf drip line. Fertilizers may also be applied in solution by injection into drip irrigation waterlines, or in foliar sprays. Cultivation over the root zone to incorporate fertilizer should not be done because damage to the shallow roots may occur; mechanical damage to the roots may promote Phytophtora infestation. High levels of calcium in the soil, high levels of ammonium ions, and an increased amount soil organic matter help to combat Phytophtora.
Hawaii soils tend to be low in nitrogen and potassium. In addition, nitrogen and potassium are necessary to produce large high quality fruit. A 10-5-20 fertilizer is generally used after trees begin to bear fruit to provide the needed nitrogen and potassium. A 10-30-10 fertilizer is generally used during the early growth stages because phosphorus is needed in early stages to develop a strong root system. Zinc (Zn) is important to avocado and should be applied when zinc deficiency symptoms occur. Fertilizers should be used carefully because an excessive amount of fertilizer can cause root damage, leaf burn, defoliation and even death of the tree.
Leaves may be analyzed to determine any nutritional deficiencies. Leaf analysis is most reliable in mature orchards with trees over seven years old. Also, leaf analysis is often done in conjunction with soil analysis. Leaf samples should be healthy, full-sized, produced by the most recent growth flush, and taken from branches that are neither flushing nor fruiting. Six to eight leaves taken from each tree are combined to make one sample for each tree. Leaves may be taken from several branches if uniformity is maintained, and samples from uniform trees may be combined. Leaves should be gently wiped or rinsed (not soaked) in tap water to remove any soil or spray residues. Refrigerate leaves in plastic bags labeled with a permanent marker. The label should provide complete information on the sample source. Paper bags should be used if refrigeration is not available. The leaf samples should be transported to the laboratory as soon as possible.
HARVESTING
Avocados are harvested with hand-held poles and baskets. In flat areas in California, man-positioning machines are used to lift the pickers. Fruits are picked when mature but still hard. Determining when to harvest avocados can be difficult and may require experience. A slight change in skin color, loss of glossiness, or a brown seed coat is a sign of maturity. Pruning shears or special clippers should be used to harvest avocados. The pedicel should also remain attached to the fruit.
POSTHARVEST
The fruits are allowed to ripen off the tree. Softening of the fruit indicates ripeness. Determining ripeness of thick-skinned varieties may be difficult for the untrained. The fruit cannot be picked too early or the fruit will shrivel and fail to ripen. Fruits of some cultivars may be refrigerated for several days after ripening without damage.
DISEASES
- Dodder (Cuscuta sandwichiana)
- Avocado root rot (Phytophtora cinnamomi)
- Stem-end rot (Phomopsis sp., Dothiorella sp.)
- Fruit rot (Dothiorella sp.)
- Anthracnose (Colletotrichum gloeosporioides)
- Leaf tip-burn (various causes, not all disease related, including salt accumulation from over fertilizing)
- Algal leaf spot (Cephaleuros virescens)
- Scab (cause unknown; resistant varieties are available)
INSECTS
- Red-banded thrips (Selenothrips rubrocinctus)
- Armored scales (several species)
- Chinese rose beetle (Adoretus sinicus)
- Fruit fly (Ceratitis capitata and Bactrocera dorsalis)
- Mites
- Black twigborer (Xylosandrus compactus)
- Mealybug (Dysmicoccus neobrevipes, Nipaecoccus nipae)
- Plantbugs (Hyalopeplus pellucidus and other species)
source: extento.hawaii.edu, photo from daleysfruit.com.au
Related article: Cultivation of Avocados
For more information, contact:
Dept.of Agriculture
D.A. Compound, Elliptical Rd.,
Diliman,Quezon City
Tel. Nos. (632) 929-6065 to 67 / 920-3991 / 928-1134
Web: www.da.gov.ph
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