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

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an ounce of prevention controlling plant viruses in the nursery and landscape

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

an ounce of prevention is worth a pound of cure

An ounce of prevention is worth a pound of cure…..

-- Ben Franklin, thinking like a plant virologist

slide3

Plum Pox Virus

September 1999

eliminate virus limit host availability
Eliminate Virus, Limit Host Availability

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

u s control actions commercial orchards
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

origin of ppv in na
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?
slide14

“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

usda regulated plant pest list
USDA Regulated Plant Pest List

32 Agents

16 Bacteria

56 Fungi

99 Insects and

Mites

2 Nematodes

95 Weeds

102 Viruses,

Viroids, and

Phytoplasmas

virus so what
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
virus so what18
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
what is a virus
What is a Virus?
  • Sub-microscopic parasite
  • Can cause

symptoms

  • No chemical

controls

plant viruses
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
slide23

Viruses move to new plants via:

  • grafting, root grafting
  • pollen, to the mother plant or seed
  • nematodes
  • insects
  • mites
  • wounds
  • unknown routes
slide24

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!

slide25

Virus Control:

PREVENTION

slide27

START WITH A CLEAN SITE

  • Follow university site preparation guidelines.
  • Test for nematodes
  • Consider previous crops
  • Check out the
  • neighborhood
slide28

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?
slide30

SUSPECT ALL STOCK

All plants in the nursery or landscape ~ specimen

plants, weeds, trial varieties ~ are equally good

virus reservoirs.

slide31

KEEP AN EYE OUT FOR ANYTHING UNUSUAL

Bring in experts to consider possible causes….

slide34

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.
slide35

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.

slide36

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.
pretend you are running a plant hospital
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
here for you
Here for you
  • PA Dept. of Agriculture
    • PA Plant Pest Act
    • Bureau of Plant Industry
      • Field Staff
      • Plant Protection Division
current regulatory system
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)

plant certification programs available in pennsylvania
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