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 Drop USDA-NASS Records % Fruit Drop Fruit type 2009-2012 2012-13 2013-14 2014-15 Early-mids 9-11 18 23 31 Late oranges 22 25 Grapefruit 27 26 Over 10 % increase last 3 years

2014-15 harvest season Fruit 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 widely Organic Intermittent Management Abandoned (>57,000 ha in FL) Conventional Management 6-12 sprays 2-3 sprays No treatment Stelinski

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

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!!!

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

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 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 6.4 1.1 Yes 5.9* 1.4* ____________________________ * Significant difference P < 0.05 Graham

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

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

HLB reduces effectiveness of Phytophthora control – timing is essential Johnson

Target applications of fungicides to onset of root flushes Johnson

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 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 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

No Topping 8 feet

8 feet 6 feet

8 feet 6 feet

Severely Pruned 6 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!

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

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 Supplementary Heat Ehsani

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 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