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

Considerations for Maintaining Productivity

• Psyllid Management• Tree Health• Retaining fruit on trees

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

Retaining fruit on trees?• HLB Induced Preharvest Fruit Drop

Recent History of Preharvest Fruit DropUSDA-NASS Records

% Fruit DropFruit type 2009-2012 2012-13 2013-14 2014-15Early-mids 9-11 18 23 31Late oranges

9-11 22 31 25

Grapefruit 18 27 26

Over 10 % increase last 3 years

2014-15 harvest seasonFruit drop – PGR tests

Can Plant Growth Regulators reduce fruit drop?

Which ones, if any, have an effect?

Albrigo

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

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

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

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

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

Things you can do now to help sustain productivity

• Psyllid Management• Tree Health

Psyllid Management• Keeping psyllids at low levels remains

important• An aggressive psyllid control program

is required!

Management varies widelyOrganic

Intermittent ManagementAbandoned (>57,000 ha in FL)

Conventional Management

6-12 sprays

2-3 spraysNo treatment

Stelinski

More psyllids found where management is intermittent

Stelinski

Insufficient Control!!!

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

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!!!

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Pyrethroid

Organophosphate

Pyrethroid

Organophosphate

Pyrethroid

Organophosphate

Blue shading = Coordinated sprays; Using pyrethroid or OPGreen shading = Non-coordinated sprays; not using a pyrethroid or OP

Example Coordinated Spray Plan

Keys to success: Scheduled, fast and cheap!!!

Overall Tree Health

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

Root Health

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

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 long300 lbs/treated acre of Tiger 90 sulfur lowered soil pH in 9 monthsValencia/Swingle - 10 yr old ____________________________Sulfur pH Root density (mg/cm3)No 6.4 1.1Yes 5.9* 1.4* ____________________________* Significant difference P < 0.05

Graham

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

HLB root loss

What we know 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

Management considerations 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

HLB reduces effectiveness of Phytophthora control – timing is essential

Johnson

Target applications of fungicides to onset of root flushes

Johnson

• Phytophthora, nematodes, weevils should be managed more aggressively to sustain root health – details in FCPMG

• www.crec.ifas.ufl.edu/extension/pest/• 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

Manage root pest and pathogens after correcting water/soil stresses

Johnson

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

8 feetNo

Topping

6 feet8 feet

6 feet8 feet

Severely Pruned6 feet

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

Citrus Health Workshop(dates and times still tentative)

• August 12, 2015 @ 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!

TENTING

Ehsani

SUPPLEMENTARY HEAT

1

2

Using:• Solar heat Target:

Heat tree until it

reaches 130°F but not

exceed 140°F

Thermal Therapy

Using:• Dry heat• Steam

Methods

Supplementary Heat Ehsani

SUPPLEMENTARY HEAT Systems using steam, recommended treatment at air temperature 130-136°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

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

Acknowledgements• 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