|Persea americana subsp. var. americana||Avocado|
Growth Habit: The avocado is a dense, evergreen tree, shedding many leaves in early spring. It is fast growing and can with age reach 80 feet, although usually less, and generally branches to form a broad tree. Some cultivars are columnar, others selected for nearly prostrate form. One cultivar makes a good espalier. Growth is in frequent flushes during warm weather in southern regions with only one long flush per year in cooler areas. Injury to branches causes a secretion of dulcitol, a white, powdery sugar, at scars. Roots are coarse and greedy and will raise pavement with age. Grafted plants normally produce fruit within one to two years compared to 8 - 20 years for seedlings.
Foliage: Avocado leaves are alternate, glossy, elliptic and dark green with paler veins. They normally remain on the tree for 2 to 3 years. The leaves of West Indian varieties are scentless, while Guatemalan types are rarely anise-scented and have medicinal use. The leaves of Mexican types have a pronounced anise scent when crushed. The leaves are high in oils and slow to compost and may collect in mounds beneath trees.
Flowers: Avocado flowers appear in January - March before the first seasonal growth, in terminal panicles of 200 - 300 small yellow-green blooms. Each panicle will produce only one to three fruits. The flowers are perfect, but are either receptive to pollen in the morning and shed pollen the following afternoon (type A), or are receptive to pollen in the afternoon, and shed pollen the following morning (type B). About 5% of flowers are defective in form and sterile. Production is best with cross-pollination between types A and B. The flowers attract bees and hoverflies and pollination usually good except during cool weather. Off-season blooms may appear during the year and often set fruit. Some cultivars bloom and set fruit in alternate years.
Fruits: West Indian type avocados produce enormous, smooth round, glossy green fruits that are low in oil and weigh up to 2 pounds. Guatemalan types produce medium ovoid or pear-shaped, pebbled green fruits that turn blackish-green when ripe. The fruit of Mexican varieties are small (6 - 10 ounces) with paper-thin skins that turn glossy green or black when ripe. The flesh of avocados is deep green near the skin, becoming yellowish nearer the single large, inedible ovoid seed. The flesh is hard when harvested but softens to a buttery texture. Wind-caused abrasion can scar the skin, forming cracks which extend into the flesh. "Cukes" are seedless, pickle-shaped fruits. Off-season fruit should not be harvested with the main crop, but left on the tree to mature. Seeds may sprout within an avocado when it is over-mature, causing internal molds and breakdown. High in monosaturates, the oil content of avocados is second only to olives among fruits, and sometimes greater. Clinical feeding studies in humans have shown that avocado oil can reduce blood cholesterol.
Adaptation: Avocados do well in the mild-winter areas of California, Florida and Hawaii. Some hardier varieties can be grown in the cooler parts of northern and inland California and along the Gulf Coast. The northern limits in California is approximately Cape Mendocino and Red Bluff. Avocados do best some distance from ocean influence but are not adapted to the desert interior. West Indian varieties thrive in humid, tropical climates and freeze at or near 32° F. Guatemalan types are native to cool, high-altitude tropics and are hardy 30 - 26° F. Mexican types are native to dry subtropical plateaus and thrive in a Mediterranean climate. They are hardy 24 - 19° F. Avocados need some protection from high winds which may break the branches. There are dwarf forms of avocados suitable for growing in containers. Avocados have been grown in California (Santa Barbara) since 1871.
Location: Avocados will grow in shade and between buildings, but are productive only in full sun. The roots are highly competitive and will choke out nearby plants. The shade under the trees is too dense to garden under, and the constant litter can be annoying. In cooler areas plant the tree where it will receive sun during the winter. Give the tree plenty of room--up to 20 feet. The avocado is not suitable for hedgerow, but two or three trees can be planted in a single large hole to save garden space and enhance pollination. At the beach or in windy inland canyons, provide a windbreak of some sort. Once established the avocado is a fairly tough tree. Indoor trees need low night temperatures to induce bloom. Container plants should be moved outdoors with care. Whitewashing the trunk or branches will prevent sunburn.
Soil: Avocado trees like loose, decomposed granite or sandy loam best. They will not survive in locations with poor drainage. The trees grow well on hillsides and should never be planted in stream beds. They are tolerant of acid or alkaline soil. In containers use a planting mix combined with topsoil. Plastic containers should be avoided. It is also useful to plant the tub with annual flowers to reduce excess soil moisture and temperature. Container plants should be leached often to reduce salts.
Irrigation: Avocado trees may not need irrigation during the winter rainy season, but watch for prolonged mid-winter dry spells. Over irrigation can induce root which is the most common cause of avocado failure. To test to see if irrigation is necessary, dig a hole 9 inches deep and test the soil by squeezing. If it is moist (holds together), do not irrigate; if it crumbles in the hand, it may be watered. Watch soil moisture carefully at the end of the irrigating season. Never enter winter with wet soil. Avocados tolerate some salts, though they will show leaf tip burn and stunting of leaves. Deep irrigation will leach salt accumulation.
Fertilization: Commence feeding of young trees after one year of growth, using a balanced fertilizer, four times yearly. Older trees benefit from feeding with nitrogenous fertilizer applied in late winter and early summer. Yellowed leaves (chlorosis) indicate iron deficiency. This can usually be corrected by a chelated foliar spray of trace elements containing iron. Mature trees often also show a zinc deficiency.
Frost Protection: It is important to choose a cultivar that is hardy in your area. Mexican types are the best choice for colder regions. Plant above a slope for air drainage, or near the house for added protection. In youth, protect with rugs, towels and such spread overhead on a frame. For further protection heat with light bulbs and wrap the trunk with sponge foam. These measures also permit tender cultivars to become established in borderline locations; established trees are much hardier than young ones. The upper branches can also be top worked with hardy Mexican types, which will protect a more tender cultivar on lower branches, as well as serving as a pollinator. Harvest fruit before the frost season begins. Cold-damaged fruit turns black. Avocados are often in bloom at the time of frost and the flowers are killed, but the tree tends to rebloom. This is especially true of Mexican types.
Pruning: Columnar cultivars require pinching at early age to form a rounded tree. Others need no training. Current orchard practice avoids staking. The best results are obtained by fencing the tree with plastic mesh for the first two to three years. Container and dwarf trees will need constant staking. The skirts of avocado trees are sometimes trimmed to discourage rodents, otherwise the trees are usually never pruned. Branches exposed to sun by defoliation are extraordinarily susceptible to sunburn and will surely die. Such branches should always be whitewashed. It is better to avoid any pruning. Most cultivars are ill-adapted to espalier. They are too vigorous. Avocado fruit is self-thinning.
Harvest: The time of harvest depends upon the variety. Commercial standards requires fruit to reach 8% oil content before harvesting. Mexican types ripen in 6 - 8 months from bloom while Guatemalan types usually take 12 - 18 months. Fruits may continue enlarging on the tree even after maturity. Purple cultivars should be permitted to color fully before harvest. Guatemalan types can be stored firm, at 40 - 50° F. for up to six weeks. Mexican types discolor quickly and require immediate consumption.
Desired clonal rootstocks can be be propagated by a method known as the etiolation technique. The largest seed are planted in gallon cans and the seedlings are then grafted to a root rot tolerant clonal scion. When the stem of the graft reaches about 1/4 inch in diameter, the top is cut off leaving a whorl of buds just above the graft. A 4 inch band of black tar paper is formed into an extension of the can and filled with vermiculite and placed in a dark box with high temperature and humidity. When growth is some 3 - 4 inches above the vermiculite, the plant is removed into the light where the upper portion quickly assumes a green color. The tar paper collar is removed, the shoot is severed from the seed and then placed in flats where the cuttings are rooted in the conventional manner. Any seed may also be used for rootstock, but Mexican types make the strongest growth and are the most often used. Plant cleaned seeds as soon as they are ripe. The seedling plants are ready to bud the following year. Budding is done in January, when suitable buds are available. Larger stocks are worked by bark grafts in the spring. Scions are collected Dec - Jan after the buds are well-formed. Paint and cover the graft with a moistened plastic bag and place a vented paper bag over the whole.
Pests and diseases
Rats and squirrels will strip the fruit. Protect with tin trunk wraps. Leaf-rolling caterpillars (Tortrix and Amorbia) may destroy branch terminals. Avocado Brown Mite can be controlled by powdered sulfur. Six-spotted Mite is very harmful; even a small population can cause massive leaf shedding. A miticide may be required if natural predators are absent. Snails can be a problem in California.
Two fungi and one virus cause more damage than any pests. Dothiorella (Botryosphaeria ribis) canker infects the trunk, causing dead patches that spreads to maturing fruit, causing darkened, rancid smelling spots in the flesh. Flesh injury begins after harvest and is impossible to detect on outside. Mexican types are immune to trunk cankers but the fruit is not. The disease is rampant near the coast and has no economical control. Root Rot (Phytophthora cinnamomi) is a soil-borne fungus that infects many plants, including avocados. It is a major disease problem in California. Select disease-free, certified plants and avoid planting where avocados once grew or where soil drainage is poor. The disease is easily transported by equipment, tools and shoes from infected soils. Once a tree is infected (signs include yellowing and dropping leaves), there is little that can be done other than cut back on water. Sun Blotch is a viral disease that causes yellowed streaking of young stems, mottling and crinkling of new leaves and occasional deformation of the fruit. It also causes rectangular cracking and checking of the trunk, as if sunburned. It has no insect vector but is spread by use of infected scions, contaminated tools and roots grafted with adjacent trees. It is important to use virus-free propagating wood.
Other avocado cultivars include Bacon, Fuerte, Gwen, Pinkerton, Reed, Spinks and Zutano. The fruit of the cultivar Florida, grown mostly outside California, is larger and rounder, with a smooth, medium-green skin, and a less-fatty, firmer and fibrous flesh. These are occasionally marketed as low-calorie avocados.
- Anaheim - Origin Otto Keup, Anaheim, 1910. Guatemalan. Tree columnar, productive. Fruit very large, to 24 oz., elongated glossy green, seed small, oil 15%. Tenderest of cvs. for coast only. To 32° F. Season July.
- Bacon - Origin James Bacon, Buena Park, 1954. Hybrid. Tree broad, productive. Fruit small to medium, to 12 oz., round-ovoid, smooth green. Flesh only fair, almost colorless,seed cavity molds rapidly. Hardy for Bay Area, Central Valley. To 25° F. Season December.
- Creamhart - Origin Orton Englehart, Escondido,1969. Hybrid. Seedling of Reed. Tree open, upright, branching. Fruit medium, to 14 oz., skin green flesh extraordinarily pale,buttery, nearly fiberless. Not alternate bearing. To 30° F. Season April - July.
- Duke - Origin Bangor (Oroville), 1912. Tree vigorous, open, resists wind. Fruit small, 12 oz., elongated pyriform, waxy green, skin paper-thin. Flesh excellent, oil 21%. Seeds commonly used for rootstocks, resist root rot. Extraordinarily hardy, recovers quickly from freeze, to 22° F. Season October
- Fuerte - Origin Atlixco, Mexico, intro. Carl Schmidt, 1911. Hybrid. Tree open, spreading, tall. Fruit large to very large, 16 oz., elongated pyriform, skin dark green with numerous small raised pale spots, waxy bloom, skin thin. Flesh good, oil 18%, seed medium. Formerly standard cv. of California industry. Tends to bear in alternate years, unproductive near coast or in north. To 26° F. Season December.
- Ganter - Origin Albert Rideout, Whittier, 1905. Mexican. Tree tall, spreading, open. Fruit small, to 8 oz., long pyriform, skin paper-thin, pale waxy green. Flesh good, oil 18%. Oldest avocado cv. in California. Quite hardy, for Central Valley floor and far north. To 23° F. Season October.
- Gwen - Origin Riverside, Robert Whitsell, 1982, patented. Seedling of Hass. Tree dwarf, to 14 ft., low vigor. Fruit small, to 8 oz., a Hass look alike, elongated green, flesh good. Most productive of dwarf avocados, best dwarf for outdoor use, also for containers, greenhouse. Not hardy, to 30° F. Season February - October.
- Hass - Origin Rudolph Hass, La Habra Heights, 1926. Seedling of Lyon. Guatemalan. Tree rather open, not tall. Fruit medium, to 12 oz., pyriform, skin thick, pebbled, coppery purple. Flesh good, oil 19%, seed fairly small. Currently the standard of the industry. To 26° F. Season July.
- Jim - Origin John Reinecke, San Diego, 1939. Hybrid. Tree upright. Fruit small to medium, to 10 oz., olive green, with long neck, oil 12%. To 26° F. Season June.
- Lula - Origin George Cellon, Miami, 1919. West Indian. Tree dense, broad, prolific. Fruit round, slightly pyriform, to 20 oz., slightly rough glossy green, oil 12%. Only West Indian type recommended for California, rather hardy, to 28° F. Season April.
- Lyon - Origin R. Lyon, Hollywood, 1908. Central American. Tree columnar, slow growing, difficult to propagate, often scion incompatible. Fruit commonly over 24 oz., dark glossy green, rough, pyriform, oil 21%. High quality. Tender, to 30° F. Season April.
- Mexicola - Origin Coolidge, Pasadena, 1910. Mexican. Tree tall and spreading, vigorous. Fruit small, 5 oz., round pyriform, skin paper-thin, purplish black, waxy bloom. Flesh highest quality, seed very large. Hardiest cv. known, seedlings useful as rootstocks in far north. Recovers rapidly from freeze. Defoliated at 20° F, trunk killed at 17° F. Season September.
- Mexicola Grande - Seedling selection of Mexicola. Mexican. Tree tall and spreading similar to Mexicola. Fruit 15% - 25% larger than Mexicola and somewhat rounder in shape with better seed/flesh ratio. Skin paper-thin, purple-black. High quality flesh with high oil content. Hardy to about 18° F.
- Murrieta Green - Origin Colima, Mexico, intro. by Juan Murrieta, 1910. Hybrid. Tree slow growing, easily trained. Fruit large, to 18 oz., oblate, green, resembling Fuerte. Flesh exceptional, oil 18%. Only cv. readily adaptable to espalier. For coast and intermediate. To 27° F. Season September.
- Nabal - Origin Antigua, Guatemala, intro. by F.W. Popenoe, 1917. Tree dense, columnar. Fruit handsome, large pyriform, to 17 oz., green, skin resembles Fuerte. Flesh exceptionally high quality, oil 16%. Young trees require pinching to force low branching. Tends to bear alternate years. To 27° F. Season July.
- Pinkerton - Origin John D. Pinkerton, Saticoy, 1972, patented. Guatemalan. Tree dense, productive. Fruit variable in size, 7 to 12 oz., skin thick, pebbled, green. To 30° F. Season November.
- Queen - Origin Antigua, Guatemala, intro. by E.E. Knight, 1914. Guatemalan. Tree broad. Fruit exceptionally large, to 24 oz., elongated, purple, flesh excellent, oil 13%. Fairly hardy for large cv., worth trying in Bay Area. To 26° F. Season August.
- Puebla - Origin Atlixco, Mexico, intro. by Carl Schmidt, 1911. Mexican. Tree broad, high branching. Fruit beautiful, medium to large, to 18 oz., ovoid, skin thin, lacquered maroon purple. Flesh excellent, oil 20%. Least hardy Mexican type, to 29° F. Season December.
- Reed - Origin James S. Reed, Carlsbad, 1948. Hybrid. Tree columnar. Fruit large, to 15 oz., round, skin thick, pebbled, green. Flesh good. To 30° F. Season August.
- Rincon - Origin Carlsbad, Sam Thompson, 1944. Hybrid. Tree small. Fruit small to medium, 10 oz., green, resembling Fuerte. Flesh good. For coast, Santa Barbara and Ventura. To 27° F. Season January.
- Ryan - Origin Albert Rideout, Whittier, 1927. Hybrid. Tree low, spreading. Fruit medium, to 14 oz., elongated, otherwise resembles Hass, skin thick, pebbled, purple. Flesh good, oil 25%. For Inland Empire, Bay Area. To 26° F Season August.
- Spinks - Origin E. Bradbury, Bradbury, 1911. Hybrid. Tree spreading. Fruit medium, to 15 oz., round with small neck, tangelo shaped. Lacquered, coppery purple, outstanding flavor, oil 16%. To 27° F. Season April.
- Topa Topa - Origin E.S. Thatcher, Ojai, 1912. Mexican. Tree columnar, vigorous. Fruit handsome, elongated pyriform, small to medium, 8 oz., smooth dark purple with white waxy bloom. Skin paper-thin. Flesh rather poor, oil 15%, seed elongated. Seedlings commonly used for rootstocks. Hardy, for far north. To 23° F.
- Whitsell - Origin Robert Whitsell, Riverside,1982, patented. Hybrid. Hass seedling. Tree dwarf, to 12 feet, low vigor. Fruit small, 6 oz., elongated Hass look alike. Flesh good. Bears in alternate years. For containers and greenhouse only, not hardy. To 30° F. February to October.
- Wurtz (syn. Littlecado) - Origin Roy Wurtz, Encinitas, 1935. Hybrid. Tree prostrate, difficult to train, low vigor. Fruit dark green, medium, to 10 oz. For containers and greenhouse. To 26° F. Season July.
- Zutano - Origin R.L. Ruitt, Fallbrook, 1926. Hybrid. Tree columnar. Fruit small to medium, to 10 oz. elongated smooth green, resembles Fuerte but inferior, has fibers. Hardy for Bay Area, Central Valley. To 25° F. Season November.
- Main article: Hass avocado
Standard Cyclopedia of Horticulture
|Standard Cyclopedia of Horticulture|
Avocado. (Persea gratissima, Gaertn.). Figs. 445, 446. One of the most highly valued of tropical fruits. It is commonly grown m Mexico, Central America, parts of South America, the West Indies, and Hawaii; to a limited extent in India, Madagascar, Reunion, Madeira, Samoa, Tahiti, Algeria, Queensland, and other tropical and subtropical countries. In Florida and California, its cultivation is conducted commercially. See Persea.
The avocado is considered by most authorities to be indigenous to Mexico, Central America, and South America to Peru and Brazil. From the Aztec ahuacatl has been derived the Spanish adaptation ahuacate or aguacate, the name in general use in Spanish-speaking countries. Avocado is an adaptation in use in the United States and other English-speaking countries. avocat in the French colonies. Alligator pear is a misleading corruption that should be dropped.
Seedling avocados grow to a height of 50 or 60 feet; when budded the tree is considerably dwarfed. The leaves are elliptical to oblong-lanceolate, varying from 4 to 8 inches in length, persistent, deep green, the new growth frequently wine-colored. The tree is worthy of a place in every dooryard for shade and ornament. The small, greenish flowers are produced in great abundance on loose axillary racemes.
The fruit is variable in form, color, and size, as well as in quality and minor characters. The form ranges from oblate or spherical to slender pyriform, including a great variety of shapes, one of the commonest being broad pyriform. The color may be light or dark green, purple, crimson, or maroon. The fruit varies from 1 to 6 inches in diameter, and in weight from a few ounces to three or four pounds. The skin is sometimes soft and pliable, and no thicker than that of an apple; in other forms it is coarsely granular, woody, and ⅛ inch thick,—in reality almost a shell. Inclosed by it is a mass of yellowish pulp, of the consistency of firm butter, and of delicious nutty flavor. The avocado is unlike most other cultivated fruits in the fact that it contains a large amount of vegetable oil, sometimes as much as 18 per cent; hence it can be considered more as a food than as a dessert. It is used in numerous ways, the commonest being as a salad, with the addition of salt, pepper and an acid. Sometimes it is cut in half, the seed removed, and the flesh eaten with a spoon, as muskmelons are eaten, salt or other condiment being added. The single, spherical or conical seed is frequently as large as a hen's egg. It is provided with two more or less distinct coats, which sometimes adhere to the seed, and in other instances to the flesh. In recent years the avocado has been given systematic attention in the United States, both in regard to cultivation and varieties. Previous to 1900, propagation was exclusively by seed, and as the species is variable when grown in this way, many trees produced inferior fruit and commercial cultivation on a sound and profitable basis was not possible. The choicest varieties are now propagated by budding and are grown on a large scale.
The diverse climatic conditions under which the avocado is found enable varieties to be obtained which are suited to regions with cool climates as well as those which are strictly tropical. In Mexico the fruit has been grown for centuries at altitudes of 6,000 or 7,000 feet, where severe frosts are experienced each winter; varieties from such regions, as opposed to those from hot and humid lowlands, are suitable for cultivation in those parts of California and Florida in which slight frosts are the usual winter occurrence. When mature, some types will stand temperatures as low as 20° F. without injury, if in proper condition at the time of the freeze; others will not withstand lower than 27° or 28° without serious damage.
The subject of races or types has not been given systematic attention outside of the United States, and no attempt at classification has been made, other than brief descriptions of types found in limited areas in Mexico and Central America. In California two very distinct types are grown, commonly referred to as the Mexican and the Guatemalan; the former (Persea drymifolia of some botanists) is ordinarily a small fruit, four to eight ounces in weight, oval or pyriform, and thin-skinned. It is one of the hardiest types in cultivation and very productive, as a rule. The Guatemalan type is characterized by its thick, woody skin, frequently rough or tuberculate on the exterior; the fruits are medium-sized. It is considered one of the best for commercial use, as it can be shipped without difficulty. The type grown in Florida is usually referred to as the West Indian-South American. It has a skin sometimes as thick as the Guatemalan, but of softer texture; some varieties are of large size and attractive appearance, but the type is rather susceptible to frost.
The avocado has been subjected to systematic cultivation for so brief a period that a large number of named varieties has not been established. In Florida the Trapp is the most widely planted and is, in fact, the standard commercial variety, Pollock occupying the place of next importance. Several others are grown to a limited extent, including Family, Rico, Blackman, and Wester. In California some of the most promising varieties are Taft, Lyon, Meserve and Murrieta; a number of others have been disseminated. Several named varieties have been established in Hawaii. For commercial cultivation, winter-fruiting varieties have been found to be the most valuable, since northern markets are almost destitute of fresh fruit during that season. It is desirable, however, to have a supply, for local consumption at least, during other seasons of the year. Fortunately varieties are obtainable which ripen at widely different times,—in California fruit is in the markets fully ten out of the twelve months, although the season in Florida, at the present time, is not so long. A variety running uniformly about a pound in weight appears to be the most desirable, and if the fruit is round or oval, it can be more advantageously packed and shipped than if pear-shaped or "bottle-necked." The skin should be sufficiently thick and tough to withstand shipment without undue care in packing, and the seed should be as small as possible. It is also important that the seed be tight in its cavity, for in the loose-seeded varieties, the flesh is often seriously damaged by the seed shaking around while the fruit is in transit. Flavor and quality must of course be up to the standard, there being a wide difference among the varieties in these respects.
Largo seedling trees of the small-fruited Mexican type sometimes produce as many as 2,000 or 3,000 fruits in a season, while a large-fruited variety may not produce more than a few dozen. Two or three hundred fruits may be considered a good crop for a tree of a medium-sized variety. In Florida, budded trees are planted in orchard form 20 feet apart; in California the distance is increased to 24 or 25 feet. Seedlings must be given more room,—30 feet at least. A well-drained, sandy loam is the soil best suited to the avocado, drainage being the most important requirement. For this reason it is best, where possible, to select a sloping piece of ground as a site for the orchard. Heavy soils, such as clay and adobe, will grow the tree successfully if the drainage is good.
Transplanting is best done in early spring, after danger of frost is over, but before the tree has started into new growth. In climates such as those of California and Florida, the tree is in a semi-dormant state after the cool weather of winter, and can be moved with little difficulty. A ball of soil should be taken with the roots, and the top pruned moderately. In light soils which cannot be balled, the trees should be transferred to pots or boxes and allowed to establish themselves, after which they may be set out in the orchard without disturbing the roots. When the budded trees have been grown in pots, the possibility of injuring the delicate roots is eliminated. The cultural requirements of the avocado are similar to those of the citrous fruits. In dry climates the trees must be irrigated regularly and frequently, particularly during the first two or three years. For bearing trees a fertilizer containing 3 per cent nitrogen, 5 per cent phosphoric acid, and 12 per cent potash has been recommended, the quantity required each season varying from three to ten pounds per tree, according to the character of the soil. This should be applied in several doses during the growing season. The growth of young trees is greatly encouraged by organic nitrogen. Leguminous cover-crops are very desirable, for the humus they will furnish as well as the nitrogen.
Often there is a tendency, especially in seedlings, to shoot upward and not spread out; this must be checked by heading back. All weak or unshapely growths should be trimmed out, and all wounds made when pruning should be covered with grafting wax or paint to prevent the entrance of any fungus into the wood. It is well to keep the trees headed low to prevent damage from winds as much as possible; this also brings the fruit within easy reach for picking.
In regions subject to severe frosts, the trees should be protected during the first two or three winters with a shelter of palm leaves, corn stalks, burlap, or some such material. Where irrigation is practised, it is well to harden the trees by withholding water in late fall.
In Florida the avocado is attacked by the wither-tip fungus (Colletotrichum gleosporioides), which can be controlled with bordeaux mixture. Two or three scale insects have been noted on trees in California, but up to the present time they are not of serious importance, with the exception of the black scale (Saissetia olex), which sometimes requires combative measures. The avocado mealy bug (Pseudococcus nipae) is troublesome in Hawaii.
For market purposes, the fruit should be graded according to size, color and form, and carefully packed; it is essential, if the fruit is to be shipped any distance, to select varieties having good carrying qualities. Light wooden crates are used for shipping, containing one layer of fruits, and provided with good ventilation. The fruits must be separately wrapped in pieces of strong paper, and packed closely together to prevent their shaking about and becoming bruised. If they arc to be shipped long distances, refrigeration is essential, experiments having shown that the temperature should be 40° to 45° F. Prolonged storage in temperature lower than 40° results in decomposition of the flesh.
Seedlings do not usually bear as early as budded trees, and on account of the variation which they arc likely to show in productiveness, as well as in form, size and quality of fruit, they are unsuitable for commercial cultivation. For the home grounds, on account of their ornamental value, they are worth planting; it is imperative, however, to select seeds from the most desirable fruits, of known quality and productiveness.
The avocado is budded on seedlings of the same species. For nursery purposes the seeds are usually planted singly in pots or in rows in the open ground. They may also be planted in flats, and potted off as soon as they have germinated; as the roots are delicate and easily injured, however, this is not a desirable method. A glasshouse is unnecessary, provided the seeds are planted during warm weather, but they are usually started under a lath or slat covering of some kind. Seeds will not retain their vitality very long, and should be planted as fresh as possible. Pots or boxes less than 4 inches in diameter should not be used. The soil should be light and porous, preferably rich in humus. Most avocado seeds are somewhat conical; they should be planted with the pointed end up, leaving the tip projecting above the surface of the soil. The pots should then be plunged in a frame, covered with straw or litter, and kept continually moist, but not soggy. Germination will take place in two or three weeks if conditions are favorable. If planted in the open ground, the seeds should be placed in rows 3 or 4 feet apart, and 14 inches apart in the row, covering them with an inch or two of soil. It is well to cover the ground with a mulch of straw to prevent evaporation as much as possible.
The avocado is a rapid grower, and young plants require frequent repotting. It is also a gross feeder, so that a rich soil should be used. The plants may be budded either in pots or in the open ground; if in the former, they must be given very careful attention so as to keep them growing vigorously, and should be in 6- or 8-inch pots. They may be budded when ⅜ inch in diameter, or even slightly less.
For avocados, shield budding, essentially the same as practised with the citrus fruits, is most successful and advantageous. The amateur may have some trouble in performing the work successfully, but after a little experience, few difficulties will be encountered. The season at which budding is most successful naturally depends somewhat upon the locality. In Florida, late autumn and winter budding is favored; in California, May and June seem to be the best, although good success is often obtained in the fall; in Hawaii winter and early spring are preferred. Probably the work can be done at any season when the bark will slip readily, but all seasons are not equally advantageous.
Selection of budwood is one of the most important matters, and one likely to give the novice most trouble. If the wood is too old or too far advanced, the buds are almost certain to drop, leaving a "blind" shield; this may happen even when good budwood is used, if the stock is not in vigorous condition. The ideal wood is of recent growth, but hardened up sufficiently so that it does not snap on bending, and having plump, well- developed buds.
It is essential that the buds be cut large,—not less than 1¼ inches in length, and thick enough so that a small quantity of wood will be taken. In budding large stocks, ¾ inch in diameter, 2 inches is not too long for the bud, provided the budstick is, as it always should be, not less than ⅜ inch in diameter. The budding- knife must be as keen as a razor, and kept in as nearly that condition as possible by frequent stropping or whetting the knife after cutting each thirty or forty buds. The incision in the stock may be made either in the form of a T or an inverted T, preferably the latter, which has the recommendation of the most successful avocado budders. In lifting the bark be careful not to injure the delicate tissues which lie under it, and push the bud in very gently. Tie it in firmly with waxed tape, leaving the eye exposed.
In three to five weeks the bud will have united with the stock, and the wrap should be loosened; it should not be entirely removed until the bud has made a growth of 3 or 4 inches. Force the bud into growth by partly girdling the stock 3 or 4 inches above it, or by cutting off the stock about a foot above it. Lopping is difficult, as the wood is brittle and will frequently break off rather than be lopped. The stock must be gone over every week and all adventitious buds rubbed off. When the bud is 8 or 10 inches high, the stock may be trimmed off close above it, and the stump covered with paint or grafting-wax.
Both inarching and grafting are practised to a limited extent, the latter usually under glass. Neither of these methods is so desirable as budding. Cuttings can be grown if bottom heat is available but trees produced in this way do not seem to have the vigor of budded trees.
Large, unproductive or undesirable seedlings should be worked over to a good variety. This is not difficult to do by budding; grafting is also possible. Cut the tree back severely in spring, leaving only the stumps of the largest branches, 3 or 4 inches in diameter, and painting the cut ends with white lead. Numerous sprouts will soon make their appearance; all but three or four of these on each branch must be rubbed off, and when these have attained a diameter of % inch they can be budded in the same manner as seedlings. It is necessary to loosen the wraps oftener, however, as the sprouts naturally make a very rapid growth. Old trees worked over in this way will often produce fruit in two years.
|Standard Cyclopedia of Horticulture|
Persea gratissima-Gaertn.f. (P.americana, Mill.). Avocado. Alligator Pear. Ahuacate. Aguacate. Avocat. Avocato. Abacate. Fig. 2873; Figs. 445, 446, Vol. I. A large tree, commonly with broad crown up to 60 ft.: lvs. oblong-lanceolate or elliptic-lanceolate to oval or obovate, 4-10 in. long, 2^-6 in. broad, apex acute or shortly acuminate, sometimes almost blunt, the base acute to truncate, frequently rounded, surface glabrous above, usually somewhat glaucous with the venation prominent below; petiole 3/4-2 in. long, canaliculate above: fls. shortly pedicellate, in broad compact panicles at the ends of the young branchlets, about 3/8 in. across, greenish, the calyx-lobes oblong-lanceolate, acute, slightly concave, finely pubescent; fertile stamens 9, in 3 series, each stamen of the inner series bearing just above its base 2 oval flattened orange- colored glands; filaments slender, finely hairy, the anthers oblong-ovate, dehiscing by 4 valves hinged distally, the 2 outer series dehiscing extrorsely, the inner series with the 2 distal valves extrorse and the proximal pan- introrse; staminodes 3, flattened, orange- colored; ovary ovate-elliptic, the style slender, attenuate, finely pubescent: fr. a large fleshy drupe, commonly pyriform, ovate or spherical, 2-8 in. long, green, maroon or purple in color, the epicarp membranous te thick and woody; mesocarp soft, yellow, and buttery; seed 1, large, conical to oblate, inverted, exalbuminous, with 2 thin seed-coats often distinct, reticulated. Certainly indigenous in Mex. and Cent. Amer., extending perhaps to N. S. Amer.
The avocado is cultivated commercially in Florida and California, as well as in other parts of tropical America. See Avocado. Several distinct forms are known in cultivation, some of them having been considered botanical varieties by certain botanists. The horticultural varieties grown in the United States are generally grouped into three types, which may be distinguished as follows: Occasional forms will be found which are difficult to classify by the above key. Especially is this true of the Guatemalan type, of which there are several varieties in California with the skin no thicker than in some varieties of the West Indian type, and nearly as smooth. These can usually be distinguished, however, by the character of the seed and its coats. Solano and Blakeman may be mentioned as smooth-skinned examples of this class. Trees of the Guatemalan type usually have darker-colored foliage than those of the West Indian, and ripen their fruit from January to April, while the West Indian ripens from July to November. The Guatemalan type is considerably the hardier of the two. Both are greatly exceeded in hardiness by the Mexican type, which has been known to withstand temperatures of 18" to 20° without serious injury. Chappelow, Ganter, and Harman are varieties of this type well known in California, where they originated. This type is exceedingly common in northern Mexico; the Guatemalan type is found in southern Mexico (whence are derived many of the varieties cultivated in the United States), Guatemala,- and doubtless in other Central American states. The West Indian type is the commonest one in Florida, Cuba, and the West Indies in general, and on the eastern coast of South America. The well-known Florida varieties, Trapp and Pollock, are representatives of it. CH
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