Factors Influencing Fruit set of Hass Avocado In New ZealandJonathan Dixon, Roger Barber, Toni Elmsly, Elaine Dixon, Andrew Mandemaker, Henry Pak

Background

96/9797/9898/9999/0000/0101/0202/0303/0404/0505/0606/0707/080

5000

10000

15000

20000

25000

30000

Indu

stry

yie

ld (t

otal

tonn

es)

Harvest season

• Unexpectedly low yields in 2002 to 2005

• Strong alternate bearing pattern has developed

Background

Why?• The cause was assumed to be low temperatures where pollination is limited causing cukes and excessive fruit drop

• Marginal climate

– other countries are warmer

– Mean Annual Temperature: 15°C

Research Programme

• In the last 4 years we have investigated:

• relationship between temperature and yield

– flowering, bees, nectar, initial fruit set, phenology

• treatments to compensate for cool temperatures

– application of foliar boron

Results -Temperature

Pollination event:

For two consecutive days, maximum temperature > 17°C and night minimum > 11°C

0 5 10 15 20 25 30 350

10

20

30

40

50

Yiel

d (to

nnes

/ha)

Pollination events

Results – Foliar Boron

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

140

160

180

Ave

rage

num

ber o

f fru

it pe

r bra

nch

Boron concentration in the panicle (mg/kg dry weight)

Evaluation of Research Outcomes

• In New Zealand, avocado fruit set is not determined by one factor alone but is a complex of factors

• There is no single cause for fruit set failure

• The research programme focused on issues to do with the realization of fruit set at flowering not on understanding how the potential fruit set is established

New Direction• How is the potential fruit set determined?

• From cumulative influences in the two years before harvest.

• Based on a better understanding of tree phenology cycles from the initiation of flowering wood to flowering and fruit set in on and off years

• What are the influences setting up the flowering and fruit set?

Overview of Yields

0 5 10 15 20 25 30 35 40 45 50 55 600

5

10

15

20

25

30

35

40

45

50

55

60

Yields for orchards in the Western Bay of Plenty

Average yield

Sweet spot for consistent yields

Potential maximum yield

Number of data points = 442Number of orchards = 177

Average yield each year approx. 7 t/ha

Approx 75% of orchardsare underperforming

Yie

ld Y

ear 1

(t/h

a)

Yield Year 2 (t/ha)

Phenology in New ZealandEstablish a descriptive model using first principles based on phenology

Aug Oct Dec Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec

2005 2006 2007

Two years previous Previous year Current year

Spring WinterAutumnSpring

Har

vest

Leaf

dro

pLe

af h

ealth

Flow

erin

g

Flow

er in

itiat

ion

Flow

er b

ud b

reak

Shoo

t ini

tiatio

n?

Beyond Flowering

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

r2 = 0.962, p< 0.001

Cal

cula

ted

yiel

d (t/

ha)

Average yield (t/ha)

Model uses aspects of the weather in:

• September two years prior (shoot initiation?) • October one year prior (flowering)• July of current year (leaf drop)

Beyond Flowering

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

r2 = 0.962, p< 0.001

Predicted yield 2007

Cal

cula

ted

yiel

d (t/

ha)

Average yield (t/ha)

Model uses aspects of the weather in:

• September two years prior (shoot initiation?) • October one year prior (flowering)• July of current year (leaf drop)

Questions to Investigate

• It is likely there are factors outside of the main flowering period that set up the fruit set potential each year

• Do these factors influence the response to climatic conditions at the time of important phenological events?

• How can this knowledge be used to overcome alternate bearing?