Agronomic principles in banana production

Bananas require moist and warm growing conditions.

Climatic zone

The major banana producing areas are situated in the tropics between the Equator and latitudes 20° north and south. However, the crop is also produced in warm/dry and cool subtropical regions up to 30° north and south of the equator.

Optimum growth occurs at temperatures of around 25-30°C. 22°C is the optimum temperature for flower initiation. High temperatures during flowering will reduce bunch size and at temperatures above 38°C there is a risk of sunburn to leaves and fruit - unless shades are erected or colored bunch covers are used. Exceptionally high temperatures of 40- 45°C just before or after flower emergence can result in 'Ripe Fruit Breakdown'.

This disorder results in fruit that ripens normally, but which has a very short shelf life of around two days before the pulp breaks down to a liquid, mushy consistency. In cooler producing climates – e.g. higher altitudes in the tropics - the ripening period is extended and levels of total soluble solids increase in the pulp, resulting in sweeter fruit.

Banana plant growth will stop at temperatures below 10°C resulting in bunch deformation. When cold winter temperatures restrict leaf and inflorescence emergence, ‘Choke Throat’ can occur. This deformation, results in bunches that are aligned horizontally rather than vertically or, in more severe cases, the bunch only just emerges, is severely stunted and the fingers are directly exposed to, and damaged by sunlight.

Similarly, very low night temperatures, during mid-winter coinciding with flower initiation within the pseudostem, can result in small malformed bunches, with fewer hands and variable, often twisted fingers. This is known as ‘November Dump’ in the southern hemisphere or ‘May Bunch’ in northern hemisphere countries. Even a few minutes of frost kills leaves. Irreversible plantation damage occurs at temperatures of -2°C.

Conditions of high sunlight provide maximum growth and quality fruit production. However, in tropical regions, good yields are still achieved in conditions with up to 50% shading or cloud cover during daylight hours.

Wind can tear leaves, reducing photosynthetic activity. Strong winds can destroy plantations – a problem exacerbated by the shallow-rooted nature of many crops. Thus, wind breaks and supports are used to help minimize crop damage. Hail can be a problem in subtropical regions, damaging leaves and downgrading fruit quality and storability.

Production units

In commercial plantations, one ‘mother plant’ and a ‘daughter sucker’ constitute a production unit, and most plantations have between 1500 and up to 3000 production units/ha.

Higher rates of planting are more appropriate in hot dry areas to boost yields as well as providing shade where heat stress is a problem. Long-term plantations of 4-5 years and more, suit less dense plantings. Larger plants, e.g. Williams, also suit wider spacings. However, disease pressure is reduced in less intensively planted crops. The plant produces underground rhizomes (corms), from which lateral buds produce suckers that develop into pseudostems upon which the fruit is produced.

Each pseudostem represents a different generation and the first crop produced on a corm is called the ‘plant crop’. Following plants are called ‘ratoon crops’. Flower (outlined) in pseudostem Inflorescence (flower) development begins in the pseudostem as early as the second month. By the fourth month inflorescence formation is completed. By this stage, the plant has established a set number of female flowers, which grow on to produce fruit. From the sixth to the ninth month, the inflorescence begins its journey up the middle of the pseudostem, emerging through the top of the plant around 3-4 weeks later.

Maturation starts with fruit filling and begins after the bract exposes the hand. It continues until harvest when fruits reach maximum size. Fruit fill normally takes between 3-4.5 months, in cooler climates it may take 6 months. For optimum yields, 10-12 fully functioning leaves are required at flowering (Figure 1). This can drop to 9 leaves per plant at bunch thinning, and depending on disease levels may drop to as few as 5 by harvest.

De-suckering is essential to maintaining high yields; suckers will drain nutrients from the mother plant reducing production of the selected ratoon. For this reason, suckers need to be removed before they reach 300mm in height. A typical harvest interval between mother and daughter plants in the tropics is 7 to 10 months.

Here 1.2 – 1.5 harvests per year are possible, depending upon plant genetics, nutrition, moisture, temperature, sunlight and health of the plant. The use of in-vitro plants has improved the harvest index to 2.2 in ideal growing conditions. Rate of development is strongly affected by the environment. Within the tropics, development is faster, while in the subtropics or at higher altitudes, banana production is slower.