This document summarizes research on managing fruit diseases in avocados to improve quality. It finds that: 1) Rootstock selection, crop load management, and fungicide use can impact postharvest disease levels and fruit quality. 2) Lowering nitrogen and calcium levels in fruit reduces anthracnose disease. 3) Integrated control through nutrition, canopy management, fungicides and postharvest practices provides the most effective disease control.

1. Impacts of fruit disease management
on quality
Liz Dann, Lindy Coates,
Luke Smith, Ken Pegg,
Jan Dean, Tony Cooke
QPIF, Indooroopilly, QLD

2. Queensland Primary Industries and Fisheries
Topics covered
• Overview of anthracnose and stem-end rot
• Experimental results
• Rootstocks, including nutrition
• Crop load, including nutrition
• Integrated control
• Field fungicides, including strobilurin group
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

3. Queensland Primary Industries and Fisheries
Postharvest diseases
stem-end rot
anthracnose
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

4. Queensland Primary Industries and Fisheries
Anthracnose (Colletotrichum gloeosporioides)
Infection Symptoms
occurs in field develop
dormant
from fruit set to during fruit
harvest ripening
period
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

5. Queensland Primary Industries and Fisheries
Stem-end rot (many fungi)
• Botryosphaeria spp
• Lasiodiplodia theobromae
• Colletotrichum gloeosporioides
• Phomopsis perseae
• Thyronectria pseudotrichia
Stem-end rot (SER) fungi colonise the
stem tissue of avocado trees without
causing disease
Symptoms develop during fruit ripening
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

6. Queensland Primary Industries and Fisheries
Effect of rootstock on fruit quality & major nutrients
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

7. Queensland Primary Industries and Fisheries
Rootstock affects postharvest disease
• Fruit harvested from T. Whiley’s rootstock trials at
– Childers, QLD (‘Hass’ in 2008 and 2009)
– Walkamin, QLD (‘Shepard’ in 2009)
– Pemberton, WA (‘Hass’ in 2008)
– Hampton, QLD (‘Hass’ in 2007 and 2008)
• Ripened at 23° & 65% RH (Indooroopilly)
C
• Stored 5 weeks at 5.5° then ripened 20° (Maroochy)
C, C
• Assessed for postharvest disease
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

8. Queensland Primary Industries and Fisheries
Effect of rootstock on anthracnose, Hampton 2008
40
% anthracnose a
30 ab
20 bc
c
c c
10
0
3
s
k
d
no
7
-0
as
ic
ee
e
ta
lv
SR
uk
H
R
Zu
Ve
D
SH
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

9. Queensland Primary Industries and Fisheries
Effect of rootstock on fruit skin N:Ca ratio, Hampton 2008
50
Skin N:Ca
40
30
20
10
0
Velvick Reed SHSR- Zutano Duke 7 Hass
03 © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

10. Queensland Primary Industries and Fisheries
Effect of rootstock on leaf N:Ca ratio, Hampton 2009
4
Leaf N:Ca
a
ab ab
3 abc
bcd
cd
d
2
1
0
Velvick SHSR- A10 Reed Duke 7 Zutano Hass
03 © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

11. Queensland Primary Industries and Fisheries
Correlations between disease, yield & nutrient balance –
Hampton 2008
Variable 1 Variable 2 P r (correlation Relationship
coefficient)
Anthracnose Yield per tree 0.044 0.30 -
severity
Anthracnose Fruit skin N:Ca 0.011 0.39 +
severity
Stem-end rot Fruit skin N:Ca 0.013 0.38 +
severity
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

12. Queensland Primary Industries and Fisheries
Effect of rootstock on anthracnose, Pemberton 2008
20 % anthracnose
a
ab
bc
cd
d
d
0
A10 Reed Velvick Duke 7 Zutano Barr
Duke
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

13. Queensland Primary Industries and Fisheries
Effect of rootstock on fruit skin N:Ca ratio, Pemberton 2008
20
N:Ca
a
a
ab
ab
bc
c
0
Velvick A10 Zutano Duke 7 Barr Reed
Duke
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

14. Queensland Primary Industries and Fisheries
Effect of rootstock on anthracnose, Childers 2009
80 % anthracnose a
ab
abc
abcd abcd
60 bcd
cd cd
d d cd
40
20
0
al
3
2
3
al
o
SH 10
S- k
10
e7
k
-0
-0
-0
an
c
S- lvic
ab
ab
A
-A
vi
uk
SR
SR
SR
ut
S-
N
el
-N
C
Ve
-D
-Z
SH
-V
H
C
C
S-
-S
C
C
S-
C
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

15. Queensland Primary Industries and Fisheries
Effect of rootstock on N:Ca ratio, Childers 2009
60
N:Ca
a
40
b
bc bc
bc bc bc bc
bc bc
c
20
0 al
3
2
-D 3
SH al
o
10
10
ck
7
k
-0
-0
-0
an
ic
ab
ab
e
A
-A
vi
SR
SR
SR
lv
uk
ut
S-
N
el
-N
C
Ve
S-
-Z
SH
-V
H
C
S-
-S
C
C
C
S-
S-
C
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

16. Queensland Primary Industries and Fisheries
Significant trends
• Rootstock affects fruit quality
– All locations
• yield ↓ as anthracnose severity ↑
– Childers and Hampton 2008
• anthracnose severity ↑ as N and/or N:Ca ↑
– All locations
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

17. Queensland Primary Industries and Fisheries
Effect of crop load on fruit quality
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

18. Queensland Primary Industries and Fisheries
Effect of crop load on anthracnose disease
100 A
% severity
% incidence B
80
N:Ca
60 a
40 y
b
z
20
0
high load low load high load low load
2007 2008
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

19. Queensland Primary Industries and Fisheries
Effect of crop load on stem-end rot disease
40
% severity
% incidence
20
a
b
0
high load low load high load low load
2007 2008
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

20. Queensland Primary Industries and Fisheries
Crop load affects quality
• ↓ anthracnose & ↓ N:Ca with ↑ crop load
• But, ↑ stem-end rot with ↑ crop load
– Stem-end rot more severe when trees are stressed
– Optimum irrigation and nutrition critical for control
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

21. Queensland Primary Industries and Fisheries
Using fungicides to improve fruit quality
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

22. Queensland Primary Industries and Fisheries
Assessment of new strobilurin products
• Initially a product screening trial (2008)
– pyraclostrobin – Group 11 (previously Group K)
– metiram – zinc based protectant fungicide
– boscalid – locally systemic f’cide with wide activity
– pyraclostrobin + boscalid
– pyraclostrobin + metiram
• Then as part of an anti-resistance program (2009)
– Pyraclostrobin ± metiram
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

23. Queensland Primary Industries and Fisheries
Product screening trial, Duranbah 2008 (cv. Reed)
% severity anthracnose % incidence anthracnose
60 a
50
ab
40
abc
abc
30
bc
20
c
10
0
untreated p'strobin boscalid p'strobin + p'strobin + Amistar
boscalid metiram
p’strobin = pyraclostrobin
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

24. Queensland Primary Industries and Fisheries
Anti-resistance trial, Glasshouse Mtns 2009 (cv. Hass)
% severity anthracnose % incidence anthracnose
120
100
a
80
ab
60 bc
bc bc
c
40 c
20
0
untreated copper Amistar + p'strob 20 p'strobin p'strobin p'strobin
copper + copper 20 + 40 + 40 +
metiram + copper metiram +
copper copper
p’strobin = pyraclostrobin
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

25. Queensland Primary Industries and Fisheries
Most effective and responsible use of fungicides
• Always follow label directions
• Protectants – no “short-cuts” in copper spray program
(every 28 days in fine weather, every 14 days if wet)
• Strobilurins – only Amistar® registered in avocado
– post-infection activity
– use with copper sprays in an anti-resistance strategy
– effective when applied close to harvest and after
extended periods of wet weather
• Postharvest – apply prochloraz within 24h after harvest
– use in conjunction with field spray program
– can’t be used on fruit destined for Europe
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

26. Queensland Primary Industries and Fisheries
Integrated control – the complete picture
Tree Strategic Careful Postharvest
husbandry fungicides harvest care
- nutrition (N, Ca) - protectants and - maturity %DM - cool chain
- canopy mgt post-infection - wet weather - pre-condition
- mulching - phosphorus acid - CA, ethylene
- root health - postharvest
- irrigation © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009

27. Queensland Primary Industries and Fisheries
Acknowledgements
Thank you to the many growers
and collaborators for supporting
our research!
© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009