THE fruit of the soursop tree has a spiny outer skin with a soft, heavily seed-laden pulped interior. Each fruit may grow over a foot in length and, when ripe, the soft pulp is used to make ice creams and sherbets.
In fact, this small, evergreen tree produces the largest fruit in the Annonaceae family. Reportedly, the fruit may weigh up to 15 pounds and is often a lopsided heart shape. The seeds and bark are toxic. Soursop is known by many different names, depending on its country of cultivation.
There are many different varieties of soursop trees in Guyana. There are three well known varieties: Blanca, Lizza and Marado. The National Agricultural Research and Extension institute (NAREI) is currently conducting studies to develop prescriptors to classify the lesser known varieties, based on various configurations such as taste and shape; and rectify the nutrient deficiencies observed in the fruit.
Usually, following the rainy season, fertiliser would be applied to the soil. However, it was observed that during prolonged rainy season there is proliferation of various pests and diseases. As such, it is recommended that fertilizer be applied to the soil prior to the rainy season. While this technique is likely to reduce the incidence of pests and diseases, other precautionary measures should be taken to eliminate certain pests such as the soursop wasp.
The soursop wasp is a pest that affects the healthy development of the soursop fruit. Adult females oviposit in the developing seeds of young fruit with a very long ovipositor. Over 75% of soursop fruits may be attached during a single growing season. Newly emerged female wasps prefer to oviposit in fruits that are 3-4cm in diameter and 2.5-5.0 mm long.
The wasp develops strictly in Annona seeds. Economic damage occurs when the adults chew their way out of the fruit, creating a 2mm diaphragm tunnel that provides entry for other insects and decay organisms. Female soursop wasps can reproduce without males. It produces approximately 4-5 generations per year.
The incidence of the soursop wasp is evident by two types of damage:
Seed damage by the developing larvae that can lead to the loss of seeds for propagation and valuable germ plasm.
Fruit damage by the adult wasp that emerges from the seed and tunnels an exit hole through the fruit. The main injury is the small exit hole made in the developing green fruit. The area around the hole forms a hardened callus that persists as a permanent injury through which other insects and pathogenic organisms enter, to cause further damage to the maturing or ripening fruit.
NAREI is currently conducting a pest-management trial at Parika, where the wasp is common. The institute recommends the following management techniques:
Good field sanitation is critical for wasp control, pick up any fallen and decaying soursop fruit and seeds and burn them. If you cannot burn in your area, place collected material in a strong, clear plastic bag and tie the mouth. Leave in the sun for about two weeks to cook before disposing or composting. This must be done on a regular basis to reduce the wasp population.
This can be achieved using either mesh bags or plastic bags. When bagging fruits, they should be approximately 2.5 – 5.0mm long. Before bagging, it is very important to ensure no aphids, whiteflies, mealybugs or scales are on the fruit. If either of these are present, they should be removed by hand using a small brush or washing with water. Alternatively, a mild insecticide, insecticidal soap or white oil can be used. When mesh bags are used, care should be taken that it hangs completely free, and is inspected and adjusted regularly to ensure the fruit does not touch the bag. When plastic bags are used, small holes should be pierced in the bags to allow for free drainage.