1. Tools available to maintain productivity of HLB-infected mature citrus groves.
Gene Albrigo, Megan Dewdney, Reza Ehsani, Jim Graham, Evan Johnson, Michael Rogers, Arnold Schumann, Ariel Singerman, Lukasz Stelinski and Tripti Vashisth

2. Considerations for Maintaining Productivity
Psyllid Management
Tree Health
Retaining fruit on trees

3. Bad News First! Psyllid Management Tree Health
Retaining fruit on trees
Need to be aware of the problems with trying to control fruit drop
Give consideration to how much money spent on these efforts based on results from past studies

4. Retaining fruit on trees?
HLB Induced Preharvest Fruit Drop

5. Recent History of Preharvest Fruit Drop USDA-NASS Records % Fruit Drop
Fruit type
Early-mids
9-11 18 23 31
Late oranges 22 25
Grapefruit 27 26
Over 10 % increase last 3 years

6. 2014-15 harvest season Fruit drop – PGR tests
Can Plant Growth Regulators reduce fruit drop?
Which ones, if any, have an effect?
Albrigo

7. Summary of PGR Trials
Overall about 25 % of trials had a significant reduction in fruit drop due to a PGR application
More of the differences occurred in Hamlin trials than Valencia, but Hamlin also had higher % drop rates
No block characteristics were identified as a reason for a PGR working or not working
Albrigo

8. Summary
Over all Hamlin tests (pooled), GA plus 2, 4-D appeared to significantly reduce fruit drop about 5 %
This was about $100 of fruit value for 400 boxes/ acre yield
Still questionable if this is economically viable practice
Albrigo

9. Why was PFD so difficult to control?
Many trees in groves in various stages of decline
Trees affected by HLB often had multiple blooms
Which bloom should be targeted for fungicide application?
The one that will give the most fruit in the block
Rain events more than once a week during bloom
Heavy rainfall reduces residual effects of fungicides
Difficulty of applying fungicides every 10 days
Many demands for sprayers and large acreages
Dewdney

10. Fungicide efficacy No longer have long residual period fungicides
Benlate or Topsin-M
In bad PFD years, failures occurred even with these fungicides
Strobilurin fungicides not as efficacious or as long residual effect
Better with Ferbam but there is a very limited supply
Conducted trial with available fungicides including newer strobilurin mixtures
Still collecting fruit data
Dewdney

11. Canker-Related Fruit Drop
In areas with high canker incidence, use of copper sprays to manage canker can minimize canker-related fruit drop
Keep trees healthy

12. Things you can do now to help sustain productivity
Psyllid Management
Tree Health

13. Psyllid Management Keeping psyllids at low levels remains important
An aggressive psyllid control program is required!

14. Management varies widely
Organic
Intermittent Management
Abandoned (>57,000 ha in FL)
Conventional Management
6-12 sprays
2-3 sprays
No treatment
Stelinski

15. More psyllids found where management is intermittent
Insufficient Control!!!
Stelinski

16. How far can psyllids move on their own?
Psyllids are capable of 3 hours of continuous flight.
This translates to approximately four miles of continuous flight.
Stelinski

17. Coordinated sprays through the CHMA program provide the greatest reduction in ACP populations!
There is an economic benefit to participating in a CHMA – Presentation by Ariel Singerman later this morning!!!

18. Example Coordinated Spray Plan
Keys to success: Scheduled, fast and cheap!!!
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Pyrethroid
Organophosphate
Blue shading = Coordinated sprays; Using pyrethroid or OP
Green shading = Non-coordinated sprays; not using a pyrethroid or OP

19. Overall Tree Health
There are a number of approaches that can be used now to improve or maintain health of HLB-infected trees

20. Root Health

21. Soil pH and well water quality affect root health and HLB disease expression
Common condition: pH > 6.5 in wetted zone is associated with well water high in bicarbonate (>100 ppm) and > HLB expression (i.e. fruit drop)
Bicarbonate reduces root uptake of Ca, Mg, K, Fe (e.g. high Ca in soil/moderate levels in leaves)
Groves with bicarbonate stress are experiencing > deterioration in fibrous root density, lifespan and function in root uptake
Rootstock sensitivity: Swingle > Carrizo > Sour orange > Cleopatra
Graham

22. Acidification of the soil and/or water reduces root zone pH and promotes release of Ca and Mg for root uptake
Water conditioning
Lower soil bicarbonate, faster
not working during rainy season
Inject N-furic acid or sulfuric acid (40%) to reduce irrigation water to 100 ppm bicarbonates
Soil conditioning
High soil bicarbonate, slower, working all season long
300 lbs/treated acre of Tiger 90 sulfur lowered soil pH in 9 months
Valencia/Swingle - 10 yr old ____________________________
Sulfur pH Root density
(mg/cm3) No
Yes * *
____________________________
* Significant difference P < 0.05
Graham

23. Valencia/Carrizo trees after 2
Valencia/Carrizo trees after 2.5 years of soil acidification in a grove with high bicarbonates – Hardee Co. 2015
Fruit crop 6/12/15
Graham

24. HLB root loss What we know Management considerations
30-50% root loss before leaf symptoms
70-80% loss as canopy thins
Root growth is stimulated in HLB-affected trees
Root loss from shortened lifespan
Increasing root growth is not likely to help
Root growth already stimulated by HLB
Need to encourage root longevity
Encourage optimal environment for roots
Minimize stress on roots from pests
Management depends on rootstock and site
Johnson

25. HLB reduces effectiveness of Phytophthora control – timing is essential
Johnson

26. Target applications of fungicides to onset of root flushes
Johnson

27. Manage root pest and pathogens after correcting water/soil stresses
Phytophthora, nematodes, weevils should be managed more aggressively to sustain root health – details in FCPMG
Phytophthora count >10-20 propagules/cm3 recommend rotation of fungicides:
Aliette/phosphite after spring shoot flush
Mefenoxam after spring-early summer rains begin
Aliette/phosphite after midsummer shoot flush
Mefenoxam after fall shoot flushes
Remember root flushes follow shoot flushes
Johnson

28. Balancing root : shoot ratios
HLB symptom expression on mature citrus tree canopies is preceded by considerable root decline
The unequal timing and severity of HLB symptom expression in the roots and canopies contributes to a major imbalance of root : shoot ratios
Roots sustain the canopies and the canopies sustain the roots, thus any major imbalance weakens the trees and may contribute to HLB symptoms like leaf and fruit drop
In response to HLB-induced root decline, a more favorable root : shoot ratio can be achieved by hedging and topping of mature tree canopies
Hedging and topping results in vigorous leaf flushes which must be protected from psyllid and leaf miner insects
Schumann

29. No Topping
8 feet

30. 8 feet
6 feet

31. 8 feet
6 feet

32. Severely Pruned
6 feet

33. Proper use of macro- and micro-nutrients
Nutrition is a practical, feasible tool to improve tree vigor and slow the decline of mature citrus trees affected by HLB
Proper nutrient use in the HLB era includes:
1) correction of critical HLB-induced deficiencies with foliar sprays to bypass the inadequate nutrient uptake capacity of HLB-impacted roots (N, K, Mg, Mn, Zn, B, Mo) – e.g. Rouse #7 spray
2) Provide a constant balanced nutrient supply DIRECTLY to the roots (frequent fertigation, controlled release fertilizers)
3) Maintain a soil chemical composition in the root zone that is most conducive for efficient constant uptake of nutrients (e.g. Ca availability is enhanced by neutralizing bicarbonates). Note that Ca, which is critically deficient in HLB-affected trees is not practically applied by foliar sprays and should be soil-applied
Schumann

34. Citrus Health Workshop (dates and times still tentative)
August 12, CREC
Half-day seminars on nutrition, root health, etc…
Discussion of knowledge gaps
Enlist assistance of growers in large-scale demonstration trials
…stay tuned for more details!

35. Heat tree until it reaches 130°F but not exceed 140°F
Thermal Therapy 1
TENTING
Using:
Solar heat
Target:
Heat tree until it reaches 130°F but not exceed 140°F 2
SUPPLEMENTARY HEAT
Using:
Dry heat
Steam
Methods
Ehsani

36. SUPPLEMENTARY HEAT
Systems using steam, recommended treatment at air temperature °F for 15 seconds to 2 minutes
On the right is a system using a surplus military truck as the system’s platform
Below is a system using a ‘goat’ truck as the system’s platform
A boiler, a water tank, and a generator are mounted onto the platform
Supplementary Heat
Ehsani

37. Summary Considerations for managing current fruit-bearing trees:
Unclear whether PGR’s and fungicides will reduce fruit drop due to HLB or PFD
Preventing canker fruit drop where a problem will help
Stay on an aggressive ACP control program (CHMAs)
Take care of the root system of tree
Manage soil/water pH
Proper timing of phytophthora control
Balance root : shoot ratios
Provide trees with proper nutrition
Thermal therapy may be used to prolong life of infected trees

38. Acknowledgements More Information?
Citrus Research & Development Foundation
More Information?
Gene Albrigo, Megan Dewdney, Reza Ehsani, Jim Graham, Evan Johnson, Michael Rogers, Arnold Schumann, Ariel Singerman, Lukasz Stelinski and Tripti Vashisth