Do 'Mango Winds'
Cause Fruit Drop?
Article from Qld. Fruit and Veg
News 24th Oct.1991
Scientific
Name: Mangifera
indica
Family:
Anacardiacea
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:
• Water stress
• Disease
• Poor nutrition
• Low carbohydrate reserves
• Inadequate or ineffective pollination.
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!
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