Flowering without chemical induction
Mango flowers form from terminal buds of the most recent mature shoots. Most varieties flower once a year during winter or spring following a dormant period. Flower initiation is usually triggered by cool nights and dry conditions.
The most commonly grown mango variety in WA, Kensington Pride, is known to suffer from inconsistent flowering and irregular bearing, especially in climates with a short dormant period. The growth regulating chemical paclobutrazol used by conventional growers to promote flowering is not permitted under organic systems.
The following issues relate to flowering and irregular bearing and should be considered in organic production to minimise costs of these problems:
- Older trees tend to suffer less from irregular bearing than younger trees.
- Flowering can be reduced when tree carbohydrate reserves are diminished as a result of a heavy crop the previous year.
- Early pruning after harvest can improve uniformity of shoot growth and subsequent uniformity of flowering, especially after a heavy crop.
- Mangoes flower from the tips of branches. Pruning to give more terminal branches can lead to more flowers.
- Heavy pruning to reduce tree size can be detrimental to yield for several year.
- Adequate nutrition is important after harvest to ensure good growth and carbohydrate accumulation prior to flowering.
- Too much nitrogen can lead to excessive vegetative growth, often at the expense of flowering.
- Trees need a growth check or dormant period in winter to initiate flowering. Cooler weather and low soil moisture encourage dormancy.
- Withholding water from the tree (after the postharvest flush) for two to three months can help ensure trees enter a dormant phase and improve floral induction. Research in the dry tropics of Queensland showed water stress applied to trees, immediately following maturation of the first summer shoot flush, increased the percentage of terminals flowering (88% vs. 56%) and significantly increased fruit yield (235kg/tree vs. 195kg/tree).
- Late pruning can reduce flowering.
- Tip pruning prior to flowering has been shown to improve flowering in tropical areas. This technique involves lightly pruning trees back to mature wood just prior to flowering.
- Temperatures below 15ºC affect pollen viability. Later flowering in cooler climates can be manipulated by removing early flowers.
- Water stress during flowering can upset flower development and reduce fruit set.
- Wind and insects pollinate mangoes. Wasps, bees and large flies are the most efficient pollinators.
- Boron is important for pollination and fruit development and must be readily available from the soil or applied as a foliar spray prior to bud break.
- Any stress after flowering can increase the number of fruit dropped.
Other approaches to promote flowering and fruit production have been reported. CSIRO has demonstrated that flowering and fruit production of mangoes can be considerably enhanced by cutting a cincture around the tree trunk to induce stress by disrupting sap flow.