Insect Vectored Bacterial Diseases Why is Greening so Difficult

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Insect Vectored Bacterial DiseasesWhy is
Greening so Difficult?

• Michael S. Irey

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Whats the big deal about insect vectored
diseases?

• Many Insects
• Many Pathogens
• Many Diseases
• Many Mechanisms

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Vectors

• Aphids
• Thrips
• Mites
• Leaf hoppers
• Plant hoppers
• Tree hoppers
• Whiteflies
• Mealybugs

• Psyllids
• Flies
• Honey bees
• Beetles
• Leaf beetles
• Bark beetles
• Curculios
• Ants

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Pathogens

• Viruses
• Rhabdoviruses
• Geminiviruses
• Marafiviruses
• Waikaviruses
• Closteroviruses
• Tenuiviruses
• Phytoreoviruses
• Luteoviruses
• Poleroviruses
• Tospoviruses
• Potyviruses
• .....Many more

• Fungi
• Phytoplasmas
• Spiroplasmas
• Bacteria
• Stewarts wilt of corn
• Fire blight of apple
• Xylella diseases
• Pierces disease
• Almond leaf scorch
• Plum leaf scald
• Phony peach
• Coffee leaf scorch
• CVC

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Mechanisms

• Foregut-borne (nonpersistent, semipersistent)
• very short retention time (24-48 hrs), lost at
  molt
• no latent period, retained in the foregut
• Circulative (persistent, non-propagative)
• retention time up to several weeks, not lost at
  molt
• latent period, retained in body (hemocoel,
  organs)
• Propagative (persistent, propagative)
• retention time up to life of insect, not lost at
  molt
• latent period of several days weeks
• retained in body (hemocoel, organs)
• Non-circulative
• No latent period, lost at molt, retained in
  foregut for life of the insect, doesnt circulate
  in body
• Surface

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Diseases

• Barley Yellow Dwarf
• Viral (BYDV)
• Most economically important virus in cereals
• Control vector control on a regional basis

• Cereal aphids
• Persistent circulative

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Diseases

• Pierces disease (grapes)
• Bacterial
• Limiting in Florida
• Control vector control on a regional basis

• Glassy Winged Sharpshooter
• Persistent

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Examples

• Fire Blight
• Bacterial
• Control IPM (pruning, insect control,
  resistance, etc.)

• Bees
• Surface

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Examples - Citrus

• Leprosis/Mite

• Citrus Tristeza Virus/Aphid

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Examples - Citrus

• Citrus Stubborn/Leafhoppers

• CVC/Leafhoppers

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Huanglongbing
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HLB - The Pathogen

• Candidatus Liberibacter asiaticus
• heat-tolerant, produces symptoms in either warm
  or cool climates
• Candidatus Liberibacter africanus (Africa)
• heat-sensitive, produces symptoms in cool
  climates (lt25C)
• Candidatus Liberibacter africanus subsp. capensis
  
• Candidatus Liberibacter americanus (Brazil 2004)
• New species
• Greening found in Florida
• August 2005
• Candidatus Liberibacter asiaticus

• Thought to be a bacterial disease caused by
  highly fastidious bacteria
• Have not been cultured
• Kochs postulates not fulfilled
• Member of the alpha-proteobacteria (gram -)
• Evidence
• Observed by light and EM microscopy in both plant
  and vector
• Sensitive to antibiotics
• Consistent association with the disease
• Graft and insect transmisson
• Can be separated from other disease causing
  organisms

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Vectors

• Diaphorina citri Asian citrus psyllid
  discovered in FL, June 1998
• Trioza erytreae African citrus psyllid NOT
  found in Western Hemisphere

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Diaphorina citri

• Adults are winged and typically sit at 45º angle
• Nymphs are flat and hard to see
• Psyllid feeding causes leaves to be curled and
  notched
• In the absence of greening, psyllids are
  considered a minor pest
• If pathogen is present, considered a major pest
  of citrus

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Diaphorina citri

• Adults may live in excess of 45 days
• Females may lay up to 800 eggs over lifetime
• Psyllids can acquire the disease after 30 min of
  feeding
• After an incubation period of 5-21days, the
  psyllid can transmit the disease by feeding
• Once infectious, the psyllids can transmit the
  disease for their entire life

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In the Presence of HLBPsyllids Must be
Controlled!
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Basic Control Strategies

• Inoculum management intensive survey and tree
  removal
• Control of the insect vector
• Use of disease-free planting material
• Regional approach

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Solid Plantings of Young Trees
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Solid Plantings of Young Trees
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Solid Plantings of Young Trees
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Successful Psyllid Management

• The success of your psyllid control program is
  dependent on your neighbors!!!

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Monitoring Psyllid Populations

• There no easy way to know when psyllid control is
  needed
• Development of thresholds for control is
  difficult since it only takes one psyllid to
  infect a tree
• Monitor new flush for building psyllid
  populations
• Keep psyllid populations as low as economically
  feasible

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SPRAY PROGRAM

• Dormant Spray-December/January Urea, Nutriphite,
  Danitol 2.4 EC
• Systemic Control- December/January Temik
• Post Bloom Spray- March/April Oil, Copper,
  Nutriphite, Potassium Nitrate, Nutritional,
  Dimethoate 4EC
• 1st Summer Oil- May/June Oil, Copper, Potassium
  Nitrate, Nutritional, Provado 1.6 F
• 2nd Summer Oil- July/August Oil, Copper,
  Nutriphite, Nutritional, Lorsban 4EC and miticide
  (if needed)
• 3rd Summer Oil- September/October Oil, Copper,
  Nutritional, Provado 1.6 F and miticide (if
  needed)
• Young Trees Only- March/April and August Admire
  trunk/soil drench applications

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SPRAY PROGRAM

• Pre - HLB
• Materials cost - 80.00/acre/year
• Application cost - 100.00/acre/year
• Post HLB
• Materials cost - 270.00/acre/year
• Application cost - 140.00/acre/year

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Cost of Psyllid Control Program

• Cost of application (differential)
• 40/ac X 16,579ac X 2 yrs 1,326,320
• Cost of chemicals (differential)
• 190/ac X 16,579ac X 2 yrs 6,300,020
• 7,626,340

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Citrus Nurseries

• Cost of producing nursery trees has increased
• New laws dictate how trees must be produced
• Some nurseries closed
• Most nurseries are smaller
• Producing less trees than in previous years
• Cost of a nursery tree has gone up from 4-5/tree
  to 7-9/tree

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Disease Free Nursery Trees

• Cost of nursery trees 8.00
• Trees removed 265,585
• 265,585 X 8/tree 2,124,680

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Direct Costs

• Scouting 3,390,406
• Tree removal 796,755
• Production lost 3,983,775
• Cost of chemical application 1,326,320
• Cost of additional chemicals 6,300,020
• Cost of resets 2,124,680
• 2 year cost (16,579 ac) 17,921,956
• Cost per acre per year 540.50

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Less Obvious Costs/Issues

• IPM will be a thing of the past if the current
  pesticide usage continues
• Snow scale
• Leaf miner
• Stewardship of pesticides
• Heavy dependence on Imidacloprid

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Latency and Asymptomatic Trees
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Why is greening so difficult?

• Opinions not to be mistaken as fact

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Why is greening so difficult?

• No disease resistance
• Regional control not practical in many instances
• Minor crop limited arsenal of chemicals
• Complete control of psyllid is hard to achieve
• Scouting is necessary and expensive
• Cost of control
• Stewardship of chemicals
• Year round presence of insects
• Insects long lived

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Why is greening so difficult?

• After acquisition, can transmit entire lifetime
  (circulative or propagative??)
• High populations
• Asymptomatic (but PCR positive trees) - source of
  inoculum
• Long latent period
• IPM not (may not be) practical other insects
  may become problems
• Cultural controls (i.e. pruning) not effective

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Why is greening so difficult?

• Young trees (citrus nurseries) must be protected
• Pathogen cant be cultured (or at least
  difficult) limits some aspects of the research
• Select agent status limits some aspects of
  research
• Lost Production
• Direct
• Time lost

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Questions?