Insect Vectored Bacterial DiseasesWhy is Greening so Difficult?

Michael S. Irey

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What’s 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, doesn’t 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

Huanglongbing

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• Candidatus Liberibacter asiaticus

• heat-tolerant, produces symptoms in either warm or cool climates

• Candidatus Liberibacter africanus (Africa)

• heat-sensitive, produces symptoms in cool climates (<25C)

• Candidatus Liberibacter africanus subsp. capensis

• Candidatus Liberibacter americanus (Brazil 2004)

• New species• Greening found in Florida

• August 2005• Candidatus Liberibacter

asiaticus

HLB - The Pathogen

• Thought to be a bacterial disease caused by highly fastidious bacteria

• Have not been cultured• Koch’s 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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• Diaphorina citri – Asian citrus psyllid; discovered in FL, June 1998

• Trioza erytreae – African citrus psyllid; NOT found in Western Hemisphere

Vectors

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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

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 TreesSolid Plantings of Young Trees

Tree SizeMonth Reset 2’ – 4’ 2’-4’ 4’-6’ 4’-6’

Jan Imidacloprid aldicarb imidacloprid aldicarb

Feb imidacloprid

Mar imidacloprid imidacloprid

Apr Imidacloprid imidacloprid

May imidacloprid imidacloprid Imidacloprid

Jun Imidacloprid

Jul imidacloprid

Aug Imidacloprid Imidacloprid Imidacloprid

Sep imidacloprid

Oct

Nov

Dec

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Solid Plantings of Young TreesSolid Plantings of Young Trees

Tree SizeMonth Reset 2’ – 4’ 2’-4’ 4’-6’ 4’-6’

Jan Imidacloprid aldicarb imidacloprid aldicarb

Feb imidacloprid

Mar Foliar imidacloprid imidacloprid Foliar

Apr Imidacloprid imidacloprid Foliar

May imidacloprid imidacloprid imidacloprid

Jun Imidacloprid Foliar

Jul imidacloprid Foliar Foliar Foliar

Aug Imidacloprid Imidacloprid imidacloprid Foliar

Sep imidacloprid Foliar

Oct Foliar Foliar Foliar Foliar

Nov Foliar

Dec Foliar Foliar Foliar Foliar

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Solid Plantings of Young TreesSolid Plantings of Young Trees

Tree SizeMonth Reset 2’ – 4’ 2’-4’ 4’-6’ 4’-6’

Jan Imidacloprid aldicarb imidacloprid aldicarb

Feb imidacloprid

Mar Foliar imidacloprid imidacloprid Foliar

Apr Imidacloprid imidacloprid Foliar

May imidacloprid imidacloprid imidacloprid

Jun Imidacloprid Foliar

Jul imidacloprid Foliar Foliar Foliar

Aug Imidacloprid Imidacloprid imidacloprid Foliar

Sep imidacloprid Foliar

Oct Foliar Foliar Foliar Foliar

Nov Foliar

Dec Foliar Foliar Foliar Foliar

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Successful Psyllid Management

Successful Psyllid Management

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

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

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Monitoring Psyllid PopulationsMonitoring 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

• 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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1=flagged as symptomaticSymptoms 1 2 3 4 5 6 7 8 9 10 11 12 13 14

3332 131 130 1 129 1 1 1 128 127 1 1 1 1 126 1 1 1 1 1 125 1 1 12423 1 1 1222120

1 2 3 4 5 6 7 8 9 10 11 12 13 14RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt RTPCR Sympt

33 - - - - - - - - + - - - - - + - - - - - - - - - - - + -32 - - - - - - - - - - + - - - - - - - - - + + - - - - - -31 - - - - - - - - - - + + - - - - - - Missing Missing - - - - - - + -30 - - - - - - - - + + + + + - + - - - - - - - - - - - - -29 - - - - - - - - + + - + - + + - + - + + - - - - - - - -28 - - - - - - - - + - + + - - Missing Missing - - - - - - + - - - - -27 - - - - - - - - - - + + + + + + - - - - - + - - + + - -26 - - - - Missing Missing + - + + + + + + + + + + - - - - - - + + - -25 - - - - + + - - Missing Missing + - + + + + - - - - - - - - - - - -24 + - - - - - - - - - - - + - + - - - - - - - - - - - - -23 - - + - + + - - + + - - - - - - - - - - - - - + - - + -22 - - - - - - - - - - - - + - - - + - - - - - - - - - + -21 - - - - - - - - - - + - Missing Missing Missing Missing - - - - - - - - - - - -20 - - Missing Missing - - - - - - - - - - - - - - - - - - - - - - - -

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 can’t 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?