An Ounce of Prevention: Controlling plant viruses in the nursery and landscape

1. An Ounce of Prevention: Controlling plant viruses in the nursery and landscape Dr. Ruth A. Welliver Plant Pathology Program Manager PA Dept of Agriculture Bureau of Plant Industry

2. An ounce of prevention is worth a pound of cure….. -- Ben Franklin, thinking like a plant virologist

3. Plum Pox Virus September 1999

4. Electron Micrograph by Fred Gildow, PSU

5. Eliminate Virus, Limit Host Availability 40 Prunus species and cultivars tested with PA isolates…. Most could be infected with PPV.

6. Search….

7. … and Destroy

8. Samples Collected in Four-County Area

10. U.S. Control Actions:Commercial Orchards • 18 Positive blocks 1999 • 40 Positive blocks 2000 • 12 Positive blocks, 58 Exposed blocks 2001 • 3 Positive, 10 Exposed blocks 2002 • 2 Positive, 6 Exposed blocks 2003 • 2 Positive, 11 exposed blocks in 2004 • 3 Positive, 15 Exposed blocks in 2005 • 1 Positive in 2006 TOTAL ~1,614 ACRES DESTROYED

11. With all this work going on, what progress have we made?

13. Origin of PPV in NA? • Known infection still in fairly small area geographically. • Neither Ontario nor Pennsylvania has uncovered the introduced source. • Have found no wild or non-Prunus hosts in the field. • If we do not know pathway of entry, how do we prevent re-introduction?

14. “Imported nursery stock—trees, shrubs, garden plants, roots and cuttings brought in from other countries for sale to the U.S. consumer—is one of two chief pathways that bring invasive insects and diseases into American forests.”-- Nature Conservancy Report, 2007

16. USDA Regulated Plant Pest List 32 Agents 16 Bacteria 56 Fungi 99 Insects and Mites 2 Nematodes 95 Weeds 102 Viruses, Viroids, and Phytoplasmas

17. Virus -- So what?!? FOR A PLANT PEST REGULATOR: • Some viruses are of limited geographic distribution and high economic damage potential, so are quarantine-significant • Some are wide-spread, but have significant damage potential, so are worthy of stop-sale to limit distribution • Some are quality pests • Some are apparently latent • With some, their damage potential is not known

18. Virus -- So what?!? FOR A GROWER: • Can kill plant …… sometimes • Can make ornamental plants unsightly • Can decrease plant vigor • Can delay rooting • Can slow growth or flowering • Even if not a problem in the plant you find it in, may be able to spread to other hosts

19. RNRSV on Kalmia

20. What is a Virus? • Sub-microscopic parasite • Can cause symptoms • No chemical controls

22. Plant Viruses • 800+ different virus species worldwide • Specific host ranges • Some broad, some narrow, not always well defined in ornamental hosts • Symptoms may vary from host to host • Specific ways of spreading • Insect vectors • Cultural practices • Control depends on proper identification

23. Viruses move to new plants via: • grafting, root grafting • pollen, to the mother plant or seed • nematodes • insects • mites • wounds • unknown routes

24. Viruses are eliminated from plants via: No practical way to eliminate virus once it is in a field setting - must destroy host tree to eliminate virus!

25. Virus Control: PREVENTION

26. CLEAN IN + CLEAN WITHIN CLEAN OUT

27. START WITH A CLEAN SITE • Follow university site preparation guidelines. • Test for nematodes • Consider previous crops • Check out the • neighborhood

28. ONLY PLANT CLEAN STOCK • Buy certified virus-free plant material whenever • possible. • Buy from a reputable nursery. • Ask questions! • Are the plants virus-tested? Virus-free? Tested for which viruses? What does virus-tested mean? • Can you visit? • What claims do they make, and how can they back them up? • Good management practices? • Will they send recent spray records?

30. SUSPECT ALL STOCK All plants in the nursery or landscape ~ specimen plants, weeds, trial varieties ~ are equally good virus reservoirs.

31. KEEP AN EYE OUT FOR ANYTHING UNUSUAL Bring in experts to consider possible causes….

33. Monitoring

34. Remove symptomatic plants as soon as they appear. • Prevent sucker re-growth. • Kill/remove as much root as possible (herbicide/fumigation). • Carefully monitor nearby trees / blocks over next 2-4 seasons.

35. If you must remove diseased plants: Prevent vector (and virus) movement…. Apply good cover spray of broad spectrum insecticide/miticide to plants before moving them. OR Remove plants while insects are dormant.

36. DON’T INTRODUCE PROBLEMS • Follow University recommendations for nematodes and weeds… Keep weeds out! • Separate crops as much as possible – • Don’t bring plants of unknown virus content near your clean stock. • Keep crops grown from seed separate from vegetatively-propagated ones • Isolate new material and inspect often • Beware hold-over or pet plants • Don’t locate a dump pile for dead or unwanted plant material near your growing areas.

37. Hosta Virus X

38. Pretend you are running a plant hospital • No unnecessary or unmonitored plants • Monitor and manage insects and weeds • Keep hoses, pots, hands, equipment clean • Be suspicious of odd-looking plants • Keep visitors at a minimum

39. CLEAN IN + CLEAN WITHIN CLEAN OUT

40. Here for you • PA Dept. of Agriculture • PA Plant Pest Act • Bureau of Plant Industry • Field Staff • Plant Protection Division

41. Thank you!

42. Current Regulatory System: • Importation: • Q37 restrictions • Some countries have USDA “pre-clearance” programs in certain crops • All other material must enter through the national quarantine center (testing takes 1-3 years) • U.S. Production: • Standard nursery licensing programs (based primarily on visual inspection) • Voluntary state virus certification programs (CA, OR, WA, NY…) • Nursery can submit material for testing or clean up ($750-$6000/vine, 1-3 years)

43. Plant Certification Programs available in Pennsylvania: • Mandatory nursery and nursery dealer certification – apparent freedom from plant pests • Voluntary programs • Fruit Trees • Geraniums • Impatiens (secondary propagator certification program) • Totally unregulated certification programs