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Pollination Aware Avocado
Case Study 4
Avocado (Persea americana Mill.) is an evergreen subtropical
fruit tree native to Central America and Mexico where it was
domesticated and cultivated in ancient times (Alcaraz and
Hormaza 2009). Total world avocado production reached more
than 3.3 million tonnes in 2007, with Mexico, Indonesia, the
USA, Colombia, Brazil, Chile, the Dominican Republic and Peru
accounting for more than 70% of production (Alcaraz and Hormaza
2009). Mexico is, however, the world leader in avocado
growing, producing some one million tonnes and accounting for
30% of world production (Alcaraz and Hormaza 2009).
Yield of avocados is dependent upon successful floral initiation,
floral development, pollination and fruit set (Whiley 2000;
Sedgley 1987). Problems with any one of these processes may
have a detrimental effect on fruit production and therefore it
is important for the grower to understand the physiological
and reproductive processes so that the management of the crop
includes provision for optimising yield.
Avocados have been recorded growing in Australia as early
as the mid-eighteenth century (Whiley 2000). However, the
modern-day industry dates from 1928 with the first importation
of named varieties from California (Whiley 2000). Production
has since spread to all mainland states where the crop is grown
from latitudes 17?S to 34?S (Whiley 2000). There are approximately1,200
growers within Australia which produce a total of
46,000 tonnes of avocados each year, worth approximately $120
million at farm gate level and $420 million at retail level (Whiley
2000).
Avocado production in Australia covers a wide geographic
distribution (Figure 1). Key growing areas include north, central
and southeast Queensland, Northern and Central New South
Wales, the Sunraysia or Tristate area (South Australia, Victoria
and south-western New South Wales) and Western Australia.
Australia?s environmental diversity, combined with selected
varieties, gives fruit supply to markets on a year-round basis.
Production peaks from June to November with lighter supplies
during the summer months (Table 1).
Introduction
Table 1 Avocado production 2005/06
(ABS 2008)
Orchard fruit
? Avocados
? production
(tonnes)
Orchard fruit
? Avocados
? total trees (ha)
NSW 5,844 1,122
QLD 22,165 3,523
SA 1,614 396
VIC 1,879 332
WA 2,950 1,019
Total 34,452 6,392
This case study is the primary source of information on potential pollination services for the industry. It is based on data provided by
industry, the ABS and other relevant sources. Therefore, information in this case study on potential hive requirements may differ to
the tables in the Pollination Aware report (RIRDC Pub. No. 10/081) which are based on ABS (2008) Agricultural Commodities Small Area
Data, Australia 2005-06.
Avocado production in Australia
72
NSW 5,844 1,122
QLD 22,165 3,523
SA 1,614 396
VIC 1,879 332
WA 2,950 1,019
Total 34,452 6,391
F igure 1 Avocado produc tion regions within Aus tralia (AB S 2008)
Pollination in avocados
The evidence is clear that avocados must be insect pollinated, and that production is best when
varieties are interplanted (McGregor 1976; Ish-Am and Eisikowitch 1993). The observations that pollination within a cultivar is accomplished during the overlapping phase of its pistillate
(female) and staminate (male) flowering, during which bees collecting nectar and pollen move among neighboring staminate and pistillate flowers (Ish-Am and Eisikowitch 1993).
Each flower opens twice, the first functionally as a female flower with a white receptive stigma; the flower closes and the following day the flower reopens functionally as a male flower with stigmas no longer receptive and dehisced anthers (Sedgley 1987; Alcaraz and Hormaza 2009). different avocado cultivars are classified in two groups (A or B) based upon their flowering
behaviour. In the type A cultivars, the female organs are receptive to pollen in the morning, pollen is released in the afternoon. With type B varieties, the pollen is released in the morning, the female organs are receptive in the afternoon.
A general problem of commercial avocado fruit production is the excessive flower and fruit
abscission; thus, final fruit set can vary significantly (Sedgley 1987) and a yield of 300 fruits can be considered as a good production (Whiley 2000). Under optimum conditions, floral Pollination Aware
Case Study 4
The evidence is clear that avocados must be insect pollinated,
and that production is best when varieties are interplanted (Mc-
Gregor 1976; Ish-Am and Eisikowitch 1993). The observations
suggest that pollination within a cultivar is accomplished during
the overlapping phase of its pistillate (female) and staminate
(male) flowering, during which bees collecting nectar and pollen
move freely among neighboring staminate and pistillate flowers
(Ish-Am and Eisikowitch 1993).
Each flower opens twice, the first functionally as a female flower
with a white receptive stigma; then the flower closes and the following
day the flower reopens functionally as a male flower with
the stigmas no longer receptive and dehisced anthers (Sedgley
1987; Alcaraz and Hormaza 2009). The different avocado
cultivars are classified in two groups (A or B) based upon their
flowering behaviour. In the type A cultivars, the female organs
are receptive to pollen in the morning, while the pollen is
released in the afternoon. With type B varieties, the pollen is
released in the morning, while the female organs are receptive in
the afternoon.
A general problem of commercial avocado fruit production is
the excessive flower and fruit abscission; thus, final fruit set can
vary significantly (Sedgley 1987) and a yield of 300 fruits per
tree can be considered as a good production (Whiley 2000).
Under optimum conditions, floral behaviour is predictable. The
consensus of various research workers who have studied the
flowering and fruiting of the avocado is that only honey bees are
sufficiently abundant on the blossoms at all times to set satisfactory
crops of fruit (McGregor 1976).
When the flowers per bee ratio is low, the bees are required to
visit many flowers to obtain a load of food and their efficiency as
cross-pollinating agents is increased (McGregor 1976). Several
studies have shown increased fruit set and yields when using
managed honey bee colonies for pollination services.
Whilst the evidence strongly demonstrates that adequate
pollination will help ensure adequate fruit formation, which
in turn results in better outcomes for the grower, it has been
suggested that management to ensure good pollination often
may not be given sufficient attention, especially during the busy
spring season (Alcaraz and Hormaza 2009). Vithanage (1990)
demonstrated that honey bees had a positive influence on the
number fruits per tree (Table 2), while a hive density of three
hives/ hectare resulted in a significantly higher average fruit
weight (Table 3).
Figure 1 Avocado production regions
within Australia (ABS 2008)
Pollination in avocados
Table 2 Avocado yield with and without
honey bee foraging (Vithanage 1990)
Avocado Without
hives
With
hives
Statistical
significance
Mean fruit
weight
(kg/fruit)
0.270 0.238 ns
Mean no. of
fruits/ tree
227.2 788.2 P <0.05
Table 3 Average weight of avocados
(kg/fruit) with different hive densities
(Vithanage 1990)
Site 2 hives/
ha
3 hives/
ha
Statistical
significance
1 0.241 0.279 P <0.05
2 0.247 0.297 P <0.05
Page 2
Avocado
There are a number of factors within the orchard which have a
direct bearing on the pollination efficiency of honey bees:
Orchard layout
? Tree and blossom density: Depending on the value of land,
either intensive or extensive planting densities are used by
Australian growers. Intensive-planting densities rely on the
principle that close-planted trees will be thinned as they
begin to crowd so the mature orchard will have a reduced
number of trees compared with the initial number. Initial
tree numbers planted are about 300 per ha but once thinned
are reduced to about 170 per ha. Various spacing configurations
are used including 6 x 6 metres and 7 x 5 metres. The
advantage of intensive planted orchards is that greater cash
flow is generated in the early years of the orchard that more
than compensates for the extra costs of establishment. In
extensive-planted orchards, trees are planted in the position
they will occupy for the life of the orchard. One of the
most popular spacings in extensive-planted orchards is 9 x 7
metres which gives a tree population of around 150 trees/
hectare (Whiley 2000).
? Access: From a beekeeper?s point of view, all-weather truck
access is highly desirable. Limited access may lead to an
increased workload for the beekeeper, uneven placement
of hives and thus inefficient pollination. Ensuring the
beekeeper has good access will aid in placement of hives and
be mutually beneficial to the grower (increased pollination
efficiency) and the beekeeper (decreased labour effort).
Pollinisers
Vrecenar-Gadus and Ellstrand (1985) reported that out-crossing
rate and yield per tree were significantly higher in interplanted
versus pure groves of ?Hass? avocado. Planting or grafting other
varieties of avocado has been proven to be an essential step in the
strive towards better yields from avocado orchards (Vrecenar-
Gadus and Ellstrand 1985). The observations suggest that
pollination within a cultivar is accomplished during the overlapping
phase of its pistillate and staminate flowering, during which
bees collecting nectar and pollen move freely among neighboring
staminate and pistillate flowers (Ish-Am and Eisikowitch
1993). Pollination between cultivars of opposite flowering type
is carried out by bees moving between them throughout the
overlapping period of pistillate flowering of one cultivar and
staminate flowering of the other (Ish-Am and Eisikowitch 1993).
Density of bees
Vithanage (1990) found that a density of two hives per ha was
sufficient to improve the yield but three hives per ha significantly
increased the mean fruit weight of experimental trees. McGregor
(1976) concluded that a density of 2?10 strong bee hives
per hectare, depending on the amount of competing bloom,
placed in the orchard during flowering can significantly improve
fruit set. Furthermore it has been shown that honey bees
are more abundant within 100m of a 64-hive apiary site, and
more avocados were harvested within 60m compared to 300m
(McGregor 1976). Thus placement of hives is an important step
in pollination management for optimal production of avocados
(Vithanage 1990; McGregor 1976)
Thus, after careful study of the research by these scientists, one
must conclude that for commercial production of avocados
bees are essential, that honey bees are the primary pollinators,
and that two to three colonies per hectare should be used, the
colonies placed within or alongside the groves, and that steps
should be taken to insure protection of the bees and discouragement
of associated plants attractive to them (Vithanage 1990).
Pollination management for avocados in
Australia
Page 3
Pollination Aware
Case Study 4
Arrangement of hives
Hive placement within the orchard is a very important factor to
consider. The distance-from-hive-to-tree factor plays an important
role in obtaining optimal yields of fruit. South African
research indicates that honey bees will forage up to 300m along
rows of 4-year-old avocado trees and only 200m across rows
(Sedgley 1987). Again, this is important information for growers
setting up orchards or replacing some trees with pollinisers
to maximise yield. As the trees get older, anecdotal evidence
suggests that these distances will be reduced.
Other research work on distance found no significant differences
in yield when the distance to the hive was about 22m. That is
to say, placing hives not less than 22m apart would be heading
in the right direction for maximising the pollination service
growers pay for.
Timing
Unfortunately, our most common pollinator in horticulture, the
European honey bee is not highly attracted to avocado flowers,
thus timing is important when placing hives in the orchard. By
placing hives in the orchard when 5?10% of avocado flowers
are in bloom the honey bees are more likely to shown fidelity
towards avocado bloom and ensure efficient pollination (Vithanage
1990).
Preparation of bees
For a hive to be able to adequately pollinate fruit blossom, it
must be above certain strength in bee numbers. It is fundamentally
difficult to build a population of honey bees during
cool conditions, particularly if there are no naturally occurring
sources of pollen and nectar. Thus to have healthy bees early
in the season, August for avocado pollination, the preparation
and management of bees should be a major priority during the
autumn period. Having good bees in August may not be a major
concern for many beekeepers if their first expected honey flow
for the spring is not until October.
Attractiveness, nutritional value of
pollen and nectar
Honey bees visit both female- and male-stage avocado flowers.
Usually, they collect nectar from both flower stages and pollen
from the male stage. However, they sometimes collect pollen
only and will not visit the female flowers (Sedgley 1987). The
attractiveness of the avocado flower to honey bees is low, in
comparison to the flowers of numerous species that may be in
bloom simultaneously, such as various citrus species and species
of the mint, daisy and mustard families (Lamiaceae, Fabaceae
and Brassicaceae, respectively). In many cases, foraging honey
bees from hives that were placed in the orchard for pollination
purposes abandon the avocado flowers in favour of competing
bloom. It is quite evident, therefore, that the avocado flowers
are not as well adapted to supply the honey bees? needs, when
compared to the flowers of many other species (Sedgley 1987).
Availability of bees for pollination
Avocado blossom coincides with a number of nectar-producing
winter-flowering eucalypt species that have the potential to
provide alternative economic gains for the beekeeper in the form
of honey crops.
Feral bees
Orchardists relying on feral bees for part or all of their pollination
services should be similarly aware first, that feral colonies
are unlikely to be at full strength at the time that avocados
flower and, second, that even if they were, foraging by these
bees is unlikely to be sufficiently intense to achieve the level of
pollination required for optimal production, especially if there
are alternative floral resources available to the bees in the same
vicinity.
Risks
Pesticides: One of the biggest drawbacks of placing bees near any
agricultural crop is the possibility of colonies or field bees being
affected by pesticides. Pesticides should be kept to a minimum
while hives remain on the property. Most poisoning occurs
when pesticides are applied to flowering crops, pastures and
weeds.
Page 4
Avocado
It is strongly recommended that growers take the following
steps to prevent or reduce bee losses:
? follow the warnings on pesticide container labels
? select the least harmful insecticide for bees and spray late
in the afternoon or at night
? do not spray in conditions where spray might drift onto
adjacent fields supporting foraging bees
? dispose of waste chemical or used containers correctly
? always warn nearby beekeepers of your intention to spray
in time for steps to be taken to protect the bees; give at
least two days? notice
? always advise nearby farmers.
Weather
Temperature and rainfall have a marked effect on honey bee
activity. Bee activity is very limited below temperatures of
13oC, with activity increasing up to around 19oC, above which
activity tends to remain at a relatively high level. Decreases
in both numbers of bees visiting blossoms and the distance
from the hive at which bees forage occur with a decrease in
temperature.
Alternatives
A recent development in honey bee pollination is the use of
?Bee Tubes? in place of full hives. These are essentially ?disposable?
mini-hives that are hung within the tree rows, they are
still experimental but are showing promising results and should
prove a cheaper option than full hives (Manning 2002).
Potential pollination service requirement
for avocados in Australia
Optimal use of managed pollination services in all avocado
orchards in Australia would require a service capacity as indicated
in Table 4 below.
Table 4 Potential pollination service requirement for avocados in
Australia
State Peak month Area (ha) Average hive
density (h/ha)*
Estimated number
of hives required
NSW September 1,122 3 3,366
QLD August 3,523 3 10,569
SA September 396 3 1,188
VIC September 332 3 996
WA September 1,019 3 3,057
Total 6,392 19,176
Notes: Area sourced from ABS (2008) Agricultural Commodities: Small
Area Data, Australia, 2005-06, flowering times and average hive density
from Vithanage (1990).
Page 5
Pollination Aware
Case Study 4
References
ALCARAZ, M.L. & HORMAZA, J.I. 2009. ?Selection of
potential pollinizers for ?Hass? avocado based on
flowering time and male-female overlapping?. Scientia
Horticulturae, 121: 267?271.
AUSTRALIAN BUREAU OF STATISTICS (ABS) 2008.
Agricultural Commodities: Small Area Data, Australia, 2005?06
(Reissue), ABS No 7125.0.
ISH-AM, G. & EISIKOWITCH, D. 1993. ?The behaviour of
honey bees visiting avocado flowers and their contribution
to its pollination?. Journal of Apicultural Research, 32:
175?186.
MANNING, R. 2002. ?The Beetube ? a new honey bee pollination
device in Western Australia?. Australian Journal of
Experimental Agriculture, 42: 643?647.
MCGREGOR, S.E. 1976. Insect pollination of cultivated crop plants.
USDA, Tucson, Arizona.
SEDGLEY, M. 1987. ?Flowering, pollination and fruit-set of
avocado?. South African Avocado Growers? Association
Yearbook, 10: 42?43.
VITHANAGE, H.I.N.V. 1990. ?The role of European honeybee
(Apis mellifera L.) in avocado pollination?. Journal of
Horticultural Science, 65: 81?86.
VRECENAR-GADUS, M. & ELLSTRAND, N.C. 1985. ?The effect
of planting design on out-crossing rate and yield in
the ?Hass? avocado?. Scientia Horticulturae, 27: 215?221.
WHILEY, A.W. 2000. ?Avocado Production in Australia?. In:
PAPADEMTRIOU, M.K. (ed.) Avocado Production in
Asia and the Pacific. Food and Agriculture Organization
of the United Nations, Regional Office for Asia and the
Pacific, Bangkok.
This case study was prepared as part of Pollination Aware ? The
Real Value of Pollination in Australia, by RC Keogh, APW
Robinson and IJ Mullins, which consolidates the available
information on pollination in Australia at a number of different
levels: commodity/industry; regional/state; and national.
Pollination Aware and the accompanying case studies provide
a base for more detailed decision making on the management
of pollination across a broad range of commodities.
The full report and 35 individual case studies are available at
www.rirdc.gov.au.
Page 6
Avocado
Notes
Page 7
This project is part of the Pollination Program ? a jointly
funded partnership with the Rural Industries Research
and Development Corporation (RIRDC), Horticulture
Australia Limited (HAL) and the Australian Government
Department of Agriculture, Fisheries and Forestry. The
Pollination Program is managed by RIRDC and aims to
secure the pollination of Australia?s horticultural and agricultural
crops into the future on a sustainable and profitable
basis. Research and development in this program
is conducted to raise awareness that will help protect
pollination in Australia.
RIRDC funds for the program are provided by the
Honeybee Research and Development Program, with
industry levies matched by funds provided by the Australian
Government. Funding from HAL for the program
is from the apple and pear, almond, avocado, cherry,
vegetable and summerfruit levies and voluntary contributions
from the dried prune and melon industries, with
matched funds from the Australian Government.
RIRDC Publication No 10/111
ISBN 978-1-74254-081-8
Topic: Avocado Farmer (Read 4844 times)