Sugar Apple or Sweetsop (Annona squamosa) is a species of Annona native to the tropical Americas, India and Pakistan. Its exact native range is unknown due to extensive cultivation, but thought to be in the Caribbean; the species was described from Jamaica.
Sugar Apple is a semi-evergreen shrub or small tree reaching (20–26 ft tall. The leaves are alternate, simple, oblong-lanceolate, 5–17 cm long and 2–5 centimeters broad. The flowers are produced in clusters of 3-4, each flower 1.5–3 cm across, with three large petals and three minute ones, yellow-green spotted purple at the base. The fruit is usually round, slightly pine cone-like with a scaly or lumpy skin. There are variations in shape and size. The fruit flesh is sweet, white to light yellow, and resembles and tastes like custard. The edible portion coats the seeds generously; a bit like the gooey portion of a tomato seed. Sugar-apple has a very distinct, sweet-smelling fragrance. The seeds are scattered through the fruit flesh; the seed coats are blackish-brown, 12–18 mm long, and hard and shiny. Sugar-apple fruit is high in calories and is a good source of iron.
There are also new varieties being developed in Taiwan. There is a pineapple sugar-apple, which is similar in sweetness but has a very different taste. Like the name suggests, it tastes like pineapple. The arrangement of seeds is in spaced rows, with the fruit’s flesh filling most of the fruit and making grooves for the seeds, instead of the flesh only occurring around the seeds.
In the Philippines, it is popularly known as “Atis”. The fruit is commonly eaten by the Philippine Fruit Bat (Kabag or Kabog) which then spreads the seeds from island to island. There is also a company that produces Sugar apple wine here in the country.
Production of Sugar Apple or Atis
Climate
The sugar apple tree requires a tropical or near-tropical climate. It does not succeed in California because of the cool winters though in Israel it has survived several degrees below freezing. Generally, it does best in dry areas and it has high drought tolerance. However, in Ceylon it flourishes in the wet as well as the dry zones from sea level to 3,500 ft (1,066 m) elevation. During the blooming season, drought interferes with pollination and it is, therefore, concluded that the sugar apple should have high atmospheric humidity but no rain when flowering. In severe droughts, the tree sheds its leaves and the fruit rind hardens and will split with the advent of rain.
Soil
The sugar apple is not particular as to soil and has performed well on sand, oolitic limestone and heavy loam with good drainage. Water-logging is intolerable. The tree is shallow-rooted and doesn’t need deep soil. Irrigation water containing over 300 ppm chlorine has done the tree no harm.
Propagation
Sugar apple seeds have a relatively long life, having kept well for 3 to 4 years. They germinate better a week after removal from the fruit than when perfectly fresh. Germination may take 30 days or more but can be hastened by soaking for 3 days or by scarifying. The percentage of germination is said to be better in unsoaked seeds. While the tree is generally grown from seed, vegetative propagation is practiced where the crop is important and early fruiting is a distinct advantage.
Seedlings may be budded or grafted when one-year old. In India, selected clones grafted on A. reticulata seedlings have flowered within 4 months and fruited in 8 months after planting out, compared with 2 to 4 years in seedlings. The grafted trees are vigorous, the fruits less seedy and more uniform in size. A. senegalensis is employed as a rootstock in Egypt. A. glabra is suitable but less hardy. The sugar apple itself ranks next after A. reticulata as a rootstock. In India, budding is best done in January, March and June. Results are poor if done in July, August, November or December unless the scions are defoliated and debudded in advance and cut only after the petioles have dehisced. Side-grafting can be done only from December to May, requires much skill and the rate of success has not exceeded 58.33%. Shield-budding gives 75% success and is the only commercially feasible method.
Inarching is 100% successful. Cuttings, layers, airlayers have a low rate of success, and trees grown by these techniques have shallow root systems and cannot endure drought as well as seedlings do.
Culture
In Egypt, sugar apple trees are spaced at 10 x 10 ft (3×3 m) in order to elevate atmospheric humidity and improve pollination. Palestinian growers were spacing at 16 x 16 ft (5×5 m) but changed to 16 x 10 ft (5×3 m) as more feasible. On light soils, they apply 132 to 176 lbs (60-80 kg) manure per tree annually and they recommend the addition of nitrogen. Commercial fertilizer containing 3% N, 10 % P and 10% K significantly increases flowering, fruit set and yield. Judicious pruning to improve shape and strength of tree must be done only in spring when the sap is rising, otherwise pruning may kill the tree. Irrigation during the dry season and once during ripening will increase fruit size.
Cropping and Yield
Seedlings 5 years old may yield 50 fruits per tree in late summer and fall. Older trees rarely exceed 100 fruits per tree unless hand-pollinated. With age, the fruits become smaller and it is considered best to replace the trees after 10 to 20 years. The fruits will not ripen but just turn black and dry if picked before the white, yellowish or red tint appears between the rind segments, the first signs of separation. If allowed to ripen on the tree, the fruit falls apart.
Keeping Quality
In India, mature fruits treated with 50-60 g carbide ripened in 2 days and thereafter remained in good condition only 2 days at room temperature, while those packed in straw ripened in 5-6 days and kept well for 4 days.
Storage trials in Malaya indicate that the ripening of sugar apples can be delayed by storage at temperatures between 59° and 68°F (15°-20°C) and 85-90% relative humidity, with low O2 and C2 H2. To speed ripening at the same temperature and relative humidity, levels of O2 and CO2 should be high. Storing at 39.2°F (4°C) for 5 days resulted in chilling injury.
In Egypt, of ‘Beni Mazar’ fruits, picked when full-grown, ll5 days from set, and held at room temperature, 86°,to ripened in 10 days. Of ‘Abd E1 Razik’ fruits, 140 days from set, 56% were ripe in 15 days. Therefore, ‘Abd E1 Razik’ is better adapted to Upper Egypt where the climate should promote normal ripening.
Pests and Diseases
In Florida and the Caribbean, a seed borer (chalcid fly), Bephratelloides cubensis, infests the seeds and an associated fungus mummifies the partly grown fruits on the tree. This has discouraged many from growing the sugar apple, though in the past it was a fairly common dooryard fruit tree. Similar damage is caused by B. maculicollis in Colombia, Venezuela and Surinam, by B. ruficollis in Panama, and B. paraguayensis in Paraguay. The soft scale, Philephedra sp., attacks leaves and twigs and deposits honeydew on which sooty mold develops. Ambrosia beetles lay eggs on young stems and the larvae induce dieback during the winter.
The mealybug is the main pest in Queensland, Australia, but is easily controlled. The green tree ant is a nuisance because of the nests it makes in the tree. Bird and animal predators force Indian growers to cover the tree with netting or pick the fruits prematurely and ripen them in straw.
A serious leaf blight in India is caused by the fungus Colletotrichum annonicola. In 1978 a new fruit rot of sugar apple was observed in India, beginning with discoloration at one end which turns brown or black in 4 or 5 days, and 2 or 3 days later the entire fruit starts to rot. Later, the fruit is covered with gray-black mycelium and spherical bodies. The isolated fungus was identified as the Colletotrichum state of Glomerella cingulata.
Food Uses
The ripe sugar apple is usually broken open and the flesh segments enjoyed while the hard seeds are separated in the mouth and spat out. It is so luscious that it is well worth the trouble. In Malaya, the flesh is pressed through a sieve to eliminate the seeds and is then added to ice cream or blended with milk to make a cool beverage. It is never cooked.
Landscape
Sugar apple trees in the home landscape are susceptible to trunk injury caused by lawn mowers and weed eaters. Maintain a grass-free area 2 to 5 or more feet away from the trunk of the tree. Never hit the tree trunk with lawn mowing equipment and never use a weed eater near the tree trunk. Mechanical damage to the trunk of the tree will weaken the tree and if severe enough, can cause dieback or kill the tree.
Roots of mature sugar apple trees spread beyond the drip-line of the tree canopy, and heavy fertilization of the lawn adjacent to sugar apple trees is not recommended because it may reduce fruiting and or fruit quality. The use of lawn sprinkler systems on a timer may result in over watering and cause sugar apple trees to decline. This is because too much water too often applied causes root rot.
Fertilizer Practices
During the first 2 to 3 years after planting, growing a strong, vigorous tree is the goal. It is recommended that any fruit that sets during the first year or so be removed so that the tree will grow vigorously. After the third year, the emphasis changes to cultural practices that enhance flowering, fruit set, and fruit development. These include reduced frequency of N-P2O5-K2O applications and close attention to irrigation from flowering to harvest during prolonged dry periods.
Fertilizer recommendations are based on experience and observation. Frequent applications of small amounts of nitrogen-containing fertilizer and watering during the growing season when there are prolonged dry periods is recommended. After the third year, trees will begin to bear fruit and the strategy is to reduce the number of applications of nitrogen-containing fertilizer. Minor element sprays to the foliage should contain magnesium, zinc, and manganese (some also contain boron, molybdenum and iron). Foliar sprays are most efficient from April to September.
Young trees should be fertilized with a complete fertilizer every six to eight weeks during the growing season. A complete fertilizer is a fertilizer containing a source of nitrogen (N), phosphate (P), and potassium (K) (many also contain a source of magnesium, Mg). By-convention fertilizer formulas are written as the percentage of nitrogen (N), phosphate (P2O5), and potassium oxide (K2O) (e.g., 6-8-9, 6% nitrogen, 8% phosphate and 9% potassium oxide). Acceptable mixtures include 6-6-6 or 8-3-9 or some similar material. Suitable fertilizer formulations for sugar apple include 2-8-8, 4-8-8, 6-6-6-3 or 8-3-9-5 or similar materials. Frequent applications at low rates will provide a more constant nutrient supply and reduce the potential for leaching of nutrients beyond the roots due to heavy rainfall.
Apply about 1/4 lb (100 g) per tree per application. The rate may gradually be increased as trees grow. For mature trees, increase the NPK rates from 1.5 to 4 lbs per tree per application as trees become older. Make 2 to 4 applications per year.
Applications of magnesium and micronutrients such as zinc and manganese may be made in ground applications to trees growing in sandy soil with a low-pH (4-7). However, foliar applications of zinc, manganese, and magnesium are more efficacious for trees growing in highly calcareous with a high-pH (7-8.5). Micronutrient applications should be made 2 to 4 times per year, generally during the growing season. Iron should be applied in a chelated formulation. For the calcareous, rocky soils, and for sandy soils with a high-pH, use a chelated iron specifically formulated for high-pH soils. For sandy soils with a low-pH, use either a chelated iron specifically formulated for low-pH, soils or iron sulfate, or similar materials. Iron should be mixed with water and applied as a soil drench under the tree canopy.
Compost and Mulch
Compost is composed of completely degraded (weathered) organic matter such as leaves, stems, wood chips, and other organic materials. Compost has a dark color, is friable, and usually has an earthy, pleasant odor. It is usually impossible to determine what the original plant material was. However, some compost, such as composted sewage sludge, may have a strong odor when first applied that dissipates with exposure to the weather. Compost has a high nutrient- and water-holding capacity and may be used as a very slow-release fertilizer material; although typically use of conventional fertilizer materials is recommended in conjunction with the compost. Compost may be used sparingly (in small amounts, 1-3 shovels full) as an addition to the native soil when planting landscape trees and added to the topsoil under the tree canopy.
In contrast, mulch is incompletely degraded organic matter such as straw, hay, wood chips, and bark chips. Generally, mulch does not have a strong odor and one can usually determine whether the mulch is made up of dead leaves, stems, wood chips, or wood bark. Mulch generally does not have a high nutrient-holding capacity because the microbes that degrade mulch into compost require most of the nutrients contained within the dead plant material. Mulch should never be added to the soil used to plant trees because the non-degraded plant material may be toxic to the tree roots. Instead, mulch is most useful when applied to the soil surface under the tree canopy. Mulching around trees reduces evaporation of soil moisture from the soil surface, thus reducing the need to water as often compared to bare soil. Mulch also has a moderating effect on the upper soil temperatures and eventually degrades into compost. Eventually mulch breaks down into compost, improving the soil structure and nutrient- and water-holding capacity. A thin layer of mulch 2 to 4 inches thick applied from the tree drip-line to within 6 inches of the trunk is recommended. Keep mulch away from the trunk of the tree to prevent the trunk area from becoming too moist, which can, lead to bark disease problems.
Irrigation Practices (Watering)
Sugar apple trees are tolerant of drought conditions, however, fruit set and fruit size may be reduced and defoliation may occur due to drought stress. Mild to severe drought stress may reduce atemoya (a relative of sugar apple) fruit size by 10 to 50%. Therefore, periodic watering of sugar apple trees is recommended from flowering through fruit development to enhance fruit quality and production. Watering is important from flowering through the fall until harvest. Watering of young and mature trees should be reduced during the fall and cease once leaves have mostly dropped. Over watering during the fall and winter may lead to root rot and loss of tree vigor and health.
Water sugar apple trees that have been mulched for a slightly longer time to make sure enough water has been applied to wet the mulch and soil beneath the mulch.
Flowering Behavior, Pollination, and Fruit Set
Sugar apple trees produce flowers on -1 to 2-year-old wood and newly emerging shoots. Natural fruit set ranges from near zero to about 3% and fruit production may be severely limited by poor fruit set and fruit shape. This is due in part to the absence of their natural Nitidulid beetle pollinators in some areas and/or a lack of sufficient pollination during flowering. Misshapen fruit is caused by incomplete pollination.
Sugar apple have complete flowers, however, the male and female flower parts are functional at different times of the day (called protandry). Sugar apple flowers first open during the day and the female parts are receptive to pollen (female stage); early the next morning the flowers open wider and shed pollen (male stage). Subsequently, in the late afternoon and early evening, the male flowering stage occurs and the anthers release pollen.
Flowers of sugar apple in the female stage are characterized by only a slight opening of the petals and a glistening appearance to the stigmatic surfaces. Flowers in the male stage are characterized by flower petals being wide open, petals may easily fall when touched and stamens may have a brownish color. This arrangement of having male and female flower parts functional at different times during the day makes cross pollination among different flowers necessary.
The natural pollinators of sugar apple and atemoya are nitidulid beetles (Coleoptera: Nitidulidae); sometimes called sap beetles. Nitidulid beetles are commonly found feeding and breeding on decomposing fruits and vegetables and are attracted to the strong, sweet odor of annona flowers during bloom. They feed on the nectar and pollen of the annona flowers and effect pollination by transferring pollen from functional male flowers to other flowers in the female stage.
Flowers which open under conditions of high humidity and warm temperatures are more likely to set fruit than those flowers opening during low humidity and/or cool temperatures. This is because a dry atmosphere more rapidly desiccates the female flower parts than a humid atmosphere.
Hand pollination of sugar apple is possible and may be very effective in improving fruit set (up to about 50%) and fruit shape. In general, pollen is collected from stamens of flowers in the male stage, which may be late afternoon, early evening, and early morning. The collected flower may be placed on paper where the anthers (male flower parts) are allowed to dehisce (release pollen). The next morning the pollen may be mixed with talcum powder to improve handling and transferred to flowers in the female stage of development. Hand pollination is usually most successful in the early to mid-morning hours (sunrise to about 11:00 am) and is done by using a thin camel-hair paint brush (like the brush found in water color paint set) to transfer pollen through the slightly open flower petals of the female stage flowers to the stigmatic surfaces at the base of the flower.
Pruning
Periodic pruning of sugar apple trees can easily maintain trees at or below 8 to 12 ft (2.4-3.7 m) in height. Young nursery trees should be planted and left to grow during their first season so that they will establish quickly. However, during the early spring of the following year either trees should be cut back to force branching along the main trunk, or selective branches should be headed back and others cut out completely to encourage the formation of evenly spaced branches with wide branch to trunk crotch angles.
To maintain optimum fruit production, trees should be selectively pruned annually. In general, about one third of the previous year’s vegetative growth should be removed during early spring (February/March) as trees commence bud break. The goal is to maintain fruit production in the lower tree canopy, improve light penetration into the canopy, and limit tree size.
Insect Pests
- Annona Seed Borer (Braephratiloides cubense). The annona seed borer (ASB) is the most important insect pest of sugar apple in Florida. Female ASB lay their eggs in the young seeds of small fruits. The larva develops inside and the adult emerges, ruining the fruit in the process. ASB populations increase during the summer and peak during August-September. Symptoms of insect damage include small, black holes on the fruit surface, and brown to black decay of the fruit. Bagging individual fruit in small paper lunch bags will prevent the ASB from infesting fruit. Please contact your local County Agricultural Cooperative Extension Agent for further control information.
- Plumose Scale (Morganella longispina). Plumose scale attacks the shoots and stems of sugar apple and atemoya trees. Plumose scales are dark brown to grayish brown, circular, and often found infesting the crotch angle areas of stems and shoots. Damage from heavy infestation results in loss of tree vigor, leaf browning and drop, and stem and shoot dieback. Please contact your local County Agricultural Cooperative Extension Agent for control information.
- Philephedra Scale (Philephedra n.sp.). Philephedra scale attacks mature and immature leaves, leaf petioles, young stems, and fruit. Most commonly, these scales are found on the undersides of leaves. Damage from heavy infestation results in loss of tree vigor, leaf browning and drop, and stem dieback. Please contact your local County Agricultural Cooperative Extension Agent for control information.
- Mealy Bugs (Pseudococcus sp.). Mealy bugs are generally found at the stem-end of the fruit and the shady side of the fruit. Mealy bugs are small, white, scale insects with wispy protuberances along their surfaces. They exude a sticky, sugary substance, which becomes colonized by fungi, giving the fruit surface (and sometimes adjacent leaves) a sooty appearance. This is referred to as sooty mold. Please contact your local County Agricultural Cooperative Extension Agent for control information.
- Ambrosia Beetles (Xyleborus sp.). Ambrosia beetles occasionally attack limbs and the trunk of sugar apple trees. They bore into the bark and outer wood and inoculate the tree with a fungus they subsequently feed on. This boring causes the infested limb or tree to decline rapidly and die back. Please contact your local County Agricultural Cooperative Extension Agent for control information.
Diseases
- Dry Fruit Rot. Dry fruit rot or mummification of the fruit is caused by several fungi. Fruit appear purplish-black to black and may remain on the tree for some time. Usually fruit are colonized by these fungi after emergence of the adult annona seed borer from the fruit. Please contact your local County Agricultural Cooperative Extension Agent for control information.
- Fruit Rot. Fruit may be attacked by fungi which cause the fruit to rot before or after harvest. Fruit symptoms are very similar to dry fruit rot. Please contact your local County Agricultural Cooperative Extension Agent for control information.
Harvest and Postharvest Handling
Harvest of immature fruit should be avoided. Immature fruit will not ripen satisfactorily but will remain hard, turn brown, and slowly decay. As green type sugar apple fruit mature, fruit color changes from green to yellowish green, the area between protuberances swells and becomes yellowish, and the fruit becomes covered with a white or bluish bloom. As purplish-red colored sugar apples mature they take on a darker purple color and at maturity the color between protuberances becomes bright pink. Fruit should be picked at the mature stage and allowed to ripen (soften) at room temperature before being refrigerated. Ripe sugar apple may only be stored for 2 to 4 days.
Note:
- Use 6-6-6, 8-3-9, young tree, or slow-release fertilizer.
- Spray should contain zinc, manganese, boron, molybdenum and may also contain iron. Foliar sprays are most efficient from April to September.
- Iron chelate drenches will avoid iron deficiency, not the sprays. Apply from June to September.
Sources: Morton, J. 1987. Sugar Apple; Photos: jacobimages.com, www.riversendnursery.com