Phytophthora is a major pathogen of macadamia trees that can cause trunk canker, tree decline, and tree death. It has over 120 species that infect over 3500 plant species. Phytophthora cinnamomi is the most widespread and devastating species infecting macadamia. It thrives in wet conditions and has a rapid life cycle. Management of Phytophthora in macadamia involves maintaining good root systems, soil health, monitoring for symptoms, and applying phosphite treatments when conditions favor the pathogen. A holistic approach integrating cultural, chemical, and resistant rootstocks is most effective for control.

1. C pP
Crop Protection
Phytophthora Management in Macadamia
6th International Macadamia Symposium,
Brisbane, Australia, 18 20 Sept.,
Brisbane Australia 18-20 Sept 2012
Dr. ’ F e m i A k i n s a n m i
University of Queensland, Brisbane
uqoakins@uq.edu.au
uqoakins@uq edu au
Working together with the
Queensland Government

2. ‘THE NUT RUSH Prospecting for Gold’

3. NEW
2012
1981
Macadamias prove a
M d i
guaranteed goldmine
for farmers

4. Prospecting for Gold

5. ‘THE NUT RUSH Prospecting for Gold’
Is Phytophthora a major clog in the wheel?

6. Phytophthora:
Phytophthora: Ecology & Description
There are about 120 Phytophthora species
They infect > 3500 p
y plant species
p
o Crops – Arable and tree crops
o Forest trees
o Mangroves
o Lifestyle horticulture – flowers, trees, etc.
• Able to cause large scale devastating diseases

7. Phytophthora in Macadamia
• Trunk canker

8. Phytophthora in Macadamia
• Tree decline

9. Phytophthora in Macadamia
• Tree death

10. Phytophthora: Lifecycle

11. Phytophthora: Ecology & Description
• Thrives in wet conditions
• Rapid formation of sporangia
• Abundant zoospore formation
• Rapid life cycle
• Many alternative hosts
y
• Infects multiple plant parts

12. Phytophthora in Macadamia
P.
P capsici : raceme, shoot and nut bli ht ,
i i h t d t blight
- Hawaii 1975, 1979
P. tropicalis : Macadamia quick decline (with sap bleeding, frass) -
- Hawaii
P. palmivora : raceme, new leaf flush and nut blight
- Hawaii 1975, 1979; Costa Rica – late 1960s
1975
P. cinnamomi : Stem canker, root rot, tree decline, dieback
- South Africa, Hawaii, Australia, Kenya

13. Phytophthora in Macadamia
Phytophthora cinnamomi
• Most widespread
• Most frequent
• g
Most devastating
• Multiple symptoms but similar impact on production

14. Phytophthora cinnamomi: Impact
• Over $300 million loss to Australian horticulture & agriculture
• $US30 million loss to the US avocado industry
• 60% macadamia yield loss in Kenya (Mbaka et sl. 2009)
sl
• 100s of macadamia trees died in SE Australia (Pegg,1981)
( gg, )

15. Phytophthora in Macadamia
1. Factors that i fl
1 F t th t influence di
disease severity in macadamia
it i d i
• Rootstock & root density (Good foundation)
• Soil fertility
• Environmental stress: drought, waterlogged
2.
2 Management of diseases caused by Phytophthora

16. Phytophthora in Macadamia
Good
G d root system provides a strong foundation
t t id t f d ti
Good soil Bad soil Ugly soil
U l il

17. Phytophthora in Macadamia
Good root system provides a strong foundation
Very poor Poor Good Very good

18. Good root system contributes to macadamia resilience to adverse conditions
2010
Courtesy: David & Liz Kirby

19. Good root system contributes to macadamia resilience to adverse conditions
2011
Courtesy: David & Liz Kirby

20. Good root system contributes to macadamia resilience to adverse conditions
2012
Courtesy: David & Liz Kirby

21. Phytophthora in Macadamia
Scion affects rootstock performance
5 y = 0.1384x + 0.0633
R 0 071
R² = 0.071
ating (0‐4)
4
severity ra
3
2
Tree canopy s
1
0
0 1 2 3 4 5
Trunk canker severity rating (0‐4)
T k k i i (0 4)

22. Phytophthora in Macadamia
Effect on grafted tree @ 3 years after planting: H2 (Hinde) rootstock
3.5 Treated (control)
3.0 Untreated
2.5 40% reduction
Tree height (m)
)
2.0
1.5
15
h
60% reduction
60% d ti
1.0
0.5
05
0.0
842 816
Cultivar

23. Phytophthora in Macadamia
Soil health – Soil fertility
- Pc; + Fertilizer + Pc; + Fertilizer + Pc; - Fertilizer

24. Phytophthora in Macadamia
Management of Ph t hth
M t f Phytophthora di
diseases
Plant disease-free materials: good root structure
Monitor tree health: changes in tree performance symptoms etc
performance, symptoms, etc.
Manage soil health: adequate soil fertility, structure and biological
Apply treatment when disease conducive conditions prevail for extended
period
Treat affected trees appropriately

25. Phytophthora in Macadamia
y p
• Do not treat plants in the nursery with metalaxyl or phosphonates
• Disease Management options
– Chemical
• Metalaxyl –not effective in badly damaged trees; resistance
• Phosphoric acid products
– Cultural
– Resistant rootstocks
• Natural disease suppression (soil health)
• Holistic approach – combination of 2 or more cultural, rootstock,
chemical and biological tactics are most effective

26. Phytophthora in Macadamia
Management of Phytophthora: Chemical control
1.4
y = 0 22ln(x) + 1 01
0.22ln(x) 1.01
1.2 R² = 0.96
1.0
Mean disease severity rating
y = 1.14 - 0.29ln(x)
0.8 R² = 0.98
e
0.6
06
y = 1.21 - 0.43ln(x)
R² = 0.99
0.4
Potassium phosphonate
0.2 Metalaxyl-M
Untreated control
0.0
Year 1 Year 2 Year 3 Year 4
Assessment period

27. Phytophthora in Macadamia
Before & after Phosphite treatment
p

28. Phytophthora in Macadamia
Before & after Phosphite treatment
p

29. Phytophthora in Macadamia
Decision Guide for Application of Phosphite to Control Phytophthora in
Macadamia
Application strategy Severity level Description Application method
Scale
Healthy None 0 None
(Maintain good
good
management practices)
Maintenance Low ‐Medium 1 ‐ 2 Foliar
Curative High 3 ‐ 4 Trunk or Foliar
Restoration Very High 5 Trunk

30. Phytophthora in Macadamia
Management of Phytophthora: Cultural control
Drainage is the most critical factor
Inorganic nutrition e.g. Calcium
- Can be li d l h t (gypsum) – slow release of C ++
C b applied as sulphate ( ) l l f Ca
- Promotes resistance in roots
- Acts as a mild fungicide
- Improves soil drainage ~ aeration
O ga c amendments: oody u c (C:N at os 5 00 ),
Organic a e d e ts Woody mulch (C ratios 25-100:1),
composts, Chicken and green manure, cover crops
- P id a complex bi l i l suppression and promotes root growth
Provides l biological i d t t th

31. Phytophthora in Macadamia
Management of Phytophthora: Resistant rootstock
• Australian R t t k I
A t li Rootstock Improvement Program
tP
– Evaluate rootstocks originating from three different ecological
regions
– Evaluate both clonal and seedling rootstocks
– E l t M
Evaluate Macadamia species
d i i

32. Phytophthora in Macadamia
Conclusions
C l i
Holistic view of disease control is important
Know the ecology and biology of the pathogen – waterlogging,
drought
Know your crop – agronomy, p y
y p g y, physiology etc.
gy
Emphasis on sustainable management
Reduced reliance on chemicals

33. Other major diseases
Fruit & flower diseases
o Husk spot; Husk rot; Raceme blight; etc.
Emerging and new disease developments
o Tree diebark ~ Botryosphaeriaceae

34. Husk spot
Pseudocercospora macadamiae

35. Husk rot & Anthracnose
Phomopsis sp.; Colletotrichum gloeosporioides

36. Botryosphaeria tree dieback

37. Floret blight

38. Acknowledgements
Funding & Support Team members & Contributors
- Dr. Bruce Topp
- Associate Prof. Andre Drenth
- Dr Ken Pegg
Dr.
- Mr. Luke Smith
Working together with the
Queensland Government
PENCITON FARMS