Department of Employment, Economic Development and Innovation

INTEGRATED MANAGEMENT OF PHYTOPHTHORA ROOT ROT OF PAPAYA IN THE WET TROPICS OF

FAR NORTH QUEENSLAND, AUSTRALIA

2© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

•Location:•Mossman-Tully, (50%) of total production. •(200 ha - 8,400 tonne of fruit)

•Av. plantation size - 2 ha.

•Limitations: cyclones, pests and diseases - Phytophthora root & fruit rot, foliar diseases.

‘Wet Tropics’ papaya growing area

3© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

• high rainfall (3600 mm)

• frequent high intensity downpours

• ~ 75% occurs December–April

Rainfall in the papaya growing area of the wet tropical coast

0100200300400500600700800

Jan Feb Mar April May Jun Jul Sep Oct Nov Dec

4© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Phytophthora diseases of papaya in Australia

Phytophthora fruit rot Basal trunk rot

Phytophthora root rot

5© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

The Pathogen (Phytophthora palmivora)

General Biology

Distinguishing Features

Papillate, ellipsoid to ovoid, deciduous sporangia with short pedicels

Globose to subglobose chlamydospores or resting structures

obvious papilla

ellipsoid sporangia

chlamydospore

short pedicel

Parasitic on over 1000 plant species, including major food crops, forest trees, sub-tropical and tropical fruits, berries and ornamentals

6© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Research into the integrated management of Phytophthora root rot of papaya in north Queensland

1) Use of mounds and surface mulches

2) Field and glasshouse evaluation of metalaxyl-M and potassium phosphonate

3) Screening for Phytophthora resistance

7© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Use of mounds and surface mulches

Mound/organic mulch

Flat/organic mulch

Mound/plastic mulch

Flat/plastic mulch

8© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

0

10

20

30

40

50

60

70

Mounds Flat ground

% p

lant

s with

roo

t rot

a

b

0

10

20

30

40

50

60

Plastic Bare ground Organic mulch

% p

lant

s with

roo

t rot

a

bb

Mounds

• best survival

• highest yield

• best tree vigour

Overall effects of mounds and mulches at harvest

Mulches

Plastic - best survival

- highest yield

- best tree vigour

**Bars followed by the same letter are not significantly different

9© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

0 10 20 30 40 50 60 70 80 90

Flat/bare soil

Flat/organic mulch

Flat/plastic mulch

Mound/bare soil

Mound/organic mulch

Mound/plastic mulch

Percentage papaya at harvest with root rot when grown on mounds or flat ground, with or without organic and plastic

mulches

% plants with root rot

a

a

a

a

b

b

**Bars followed by the same letter are not significantly different

10© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

1

2

3

4

5

6

7R

oot r

ot se

veri

ty

1.25 0.625 0.312 Infested control

Root rot severity assessed on a 1-7 scale of increasing disease severity

Glasshouse study of the effect of metalaxyl-M on root rot severity in papaya

In field:

Metalaxyl-M as Ridomil Gold®

at 1 kg/100 m of row

a a

b

c

**Bars with the same letter are not significantly different

g a.i./m2

11© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Untreated Metalaxyl-M

Metalaxyl-M (Ridomil Gold®)

12© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Untreated

Metalaxyl-M

13© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Plant age x rates of phosphonate (AgriFos 600®)Plant age (weeks) Rates of potassium phosphonate (g a.i./L)

0 3 6 128 7.0 c 7.0 c 7.0 c 7.0 c12 7.0 c 7.0 c 6.8 c 7.0 c

16 5.2 b 5.4 b 3.0 a 2.2 a

Root rot severity assessed on a 1-7 scale of increasing disease severity

14© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

0

20

40

60

80

100

% p

lant

surv

ival

Treatments

Effect of metalaxyl-M and phosphonate alone and in combination on the survival of papaya at harvest

Metalaxyl-M+phosphonate Phosphonate

Metalaxyl-M Untreated

a

abb

c

15© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Screening for Phytophthora resistance - susceptibility of 62 papaya cultivars and breeding lines

01020

3040

5060

7080

90100

Paris*NT RedSubang 6Paris*Sunrise (RB1)Subang*SunriseSaipan RedLine 1BNT Red

* The other 55 cultivars fell between Saipan Red and NT Red

% m

orta

lity

LSD = 5%

16© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

South Johnstone RS trial post Cyclone Larry

Phosphonate treated plot

Untreated plot

17© The State of Queensland, Department of Employment, Economic Development and Innovation, 2010

Phytophthora root rot – current integrated control method

Land preparationHealthy seedlings Dry season transplanting

Pre & post plant chemical applications

Single row mounds