DO 'MANGO WINDS' CAUSE FRUIT DROP?
SCIENTIFIC NAME: Mangifera indica
FAMILY: Anacardiaceae
September is often the month of continual strong south-easterly winds referred to by mango growers as the 'Mango Winds' because they blow their prized newly-developing fruit off the trees.
Or do they?
To get a further insight into the problem of fruit drop, 18 six-year-old trees at Ayr Research Station were netted. Every week during the 1989/90 mango season, all dropped fruit was counted from flowering through to harvest.
Three cultivars were chosen in order to compare early, mid-season and late-maturing types (Kensington, R2E2 and Keitt).
During that period there were several days where the average windspeed was 18km/hr, with gust up to 30km/hr. However, high winds did not have any effect on the fruit drop pattern.
The number of fruit falling from all cultivars increased sharply to a peak three weeks after flowering, declining sharply during the following two weeks, and further tapered off in the succeeding weeks up to harvest.
(A set fruit is defined as having a diameter greater than 2mm).
Most of the dropped fruit was smaller than pea size (less than 10mm diameter).
In the weeks just prior to harvest, most Kensington fruit that fell were smaller than 30mm in diameter.
(All harvested fruit exceeded 80mm with an average weight 450g.)
Although better flowering gave better yields, trees that flowered poorly dropped a smaller proportion of their fruit.
For example a tree with 95% terminals flowering set 5599 fruit but retained only 58 (1.0%) while the tree with only 5% flowering, set 74 fruit and yielded 11 at harvest (14.9%).
A poor-flowering tree may be able to compensate by retaining a greater percentage of its set fruit, but there is still a limit to the fruit that can be borne on a single terminal.
Although there was no difference in fruit drop between cultivars, Kensington and Keitt had a better rate of fruiting (46% and 41% carried through to harvest) than the bigger-fruited R2E2 (only 14% carried fruit through to harvest).
So what causes fruit drop if it is not the Mango Winds? Other reasons could be:
Queensland Department of Primary Industries plant pathologist, Greg Johnson, found that although dropped fruit had a high incidence of stem-end fungus, healthy fruit also developed high levels of stem-end rot.
This shows that the fungus was not the cause of fruit drop. A nutrition study at Ayr showed that loose and fallen fruit had higher levels of 12 nutrient elements than tightly-held fruit.
For example, tightly-held fruit had 0.16% calcium while loose fruit had 0.26%, fallen fruit, 0.27%).
A possible explanation for the higher mineral level in loose and fallen fruit is that carbohydrates had been directed away from these fruit sometime earlier. This may be due to the tree setting more fruit than it could carry through to harvest.
These results appear to indicate that there is a maximum crop load that a tree is capable of carrying. Surplus fruit that cannot be carried through to harvest will be shed.
Normal September Mango Winds do not cause fruit drop, though such winds might blow down fruit that is pre-determined to drop.
However, cyclonic winds are a different story. In December 1990, Cyclone Joy proved that near-ripe mangoes offer little resistance to 120 km/hr winds.
Now that was a Mango Wind!
DATE: January 1992
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