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

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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

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An ounce of prevention is worth a pound of cure..
-- Ben Franklin, thinking like a plant virologist
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Plum Pox Virus
September 1999
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Electron Micrograph by Fred Gildow, PSU
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Eliminate Virus, Limit Host Availability

• 40 Prunus species and cultivars tested with PA
  isolates. Most could be infected with PPV.

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Search.
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and Destroy
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Samples Collected in Four-County Area
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U.S. Control ActionsCommercial 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
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With all this work going on, what progress have
we made?
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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?

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Imported nursery stocktrees, shrubs, garden
plants, roots and cuttings brought in from other
countries for sale to the U.S. consumeris one of
two chief pathways that bring invasive insects
and diseases into American forests. -- Nature
Conservancy Report, 2007
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USDA Regulated Plant Pest List

• 32 Agents
• 16 Bacteria
• 56 Fungi
• 99 Insects and
• Mites
• 2 Nematodes
• 95 Weeds
• 102 Viruses,
• Viroids, and
• Phytoplasmas

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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

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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

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RNRSV on Kalmia
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What is a Virus?

• Sub-microscopic parasite
• Can cause
• symptoms
• No chemical
• controls

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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

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

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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!
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Virus Control
PREVENTION
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CLEAN IN CLEAN WITHIN CLEAN OUT
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START WITH A CLEAN SITE

• Follow university site preparation guidelines.
• Test for nematodes
• Consider previous crops
• Check out the
• neighborhood

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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?

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SUSPECT ALL STOCK
All plants in the nursery or landscape
specimen plants, weeds, trial varieties
are equally good virus reservoirs.
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KEEP AN EYE OUT FOR ANYTHING UNUSUAL
Bring in experts to consider possible causes.
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Monitoring
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• 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.

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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.
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DONT INTRODUCE PROBLEMS

• Follow University recommendations for nematodes
  and weeds Keep weeds out!
• Separate crops as much as possible
• Dont 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
• Dont locate a dump pile for dead or unwanted
  plant material near your growing areas.

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Hosta Virus X
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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

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CLEAN IN CLEAN WITHIN CLEAN OUT
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Here for you

• PA Dept. of Agriculture
• PA Plant Pest Act
• Bureau of Plant Industry
• Field Staff
• Plant Protection Division

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Thank you!
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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)

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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