Insect Vectored Bacterial Diseases Why is Greening so Difficult?

1. Insect Vectored Bacterial DiseasesWhy is Greening so Difficult? Michael S. Irey

2. What’s the big deal about insect vectored diseases? • Many Insects • Many Pathogens • Many Diseases • Many Mechanisms

3. Aphids Thrips Mites Leaf hoppers Plant hoppers Tree hoppers Whiteflies Mealybugs Psyllids Flies Honey bees Beetles Leaf beetles Bark beetles Curculios Ants Vectors

4. 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 Pathogens

5. 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

6. Barley Yellow Dwarf Viral (BYDV) Most economically important virus in cereals Control – vector control on a regional basis Cereal aphids Persistent circulative Diseases

7. Pierces disease (grapes) Bacterial Limiting in Florida Control – vector control on a regional basis Glassy Winged Sharpshooter Persistent Diseases

8. Fire Blight Bacterial Control – IPM (pruning, insect control, resistance, etc.) Bees Surface Examples

9. Leprosis/Mite Citrus Tristeza Virus/Aphid Examples - Citrus

10. Citrus Stubborn/Leafhoppers CVC/Leafhoppers Examples - Citrus

11. Huanglongbing

12. 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 • 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

13. Vectors • Diaphorina citri– Asian citrus psyllid; discovered in FL, June 1998 • Trioza erytreae – African citrus psyllid;NOT found in Western Hemisphere

14. 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

15. 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

16. In the Presence of HLBPsyllids Must be Controlled!

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

18. Solid Plantings of Young Trees

19. Solid Plantings of Young Trees

20. Solid Plantings of Young Trees

21. Successful Psyllid Management The success of your psyllid control program is dependent on your neighbors!!!

22. 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

23. 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

24. 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 SPRAY PROGRAM

25. 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

26. 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

27. Disease Free Nursery Trees • Cost of nursery trees = $8.00 • Trees removed = 265,585 265,585 X $8/tree = $2,124,680

28. 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

29. 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

30. Latency and Asymptomatic Trees

31. Why is greening so difficult? • Opinions not to be mistaken as fact

32. 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

33. 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

34. 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

35. Questions?