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NC State Extension

Phytophthora Baiting in Irrigation Water

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Detection of Phytophthora in Water Supplies

Commercial growers who suspect that Phytophthora spores may be present in the irrigation water supply for their greenhouse or nursery may test their water supply with the pear baiting method.

Please call ahead at 919-515-3619 before deploying pear baits, to discuss the timing of sample submission.

When submitting sample information in our online database, select “Ponds; Lakes; Impounded waters” as the host. Diagnostic fees apply. A set of 3 pears representing a single water source is considered as one sample.

Preparation of pear baits

  • Purchase pears directly from wholesalers such that the pears are coming directly out of cold storage. It is important that green, rock-hard pears be used.
  • Just before use, wash pears gently in warm, soapy, mild dish detergent to remove any fungicide residues. Rinse pears in clean water and blot dry with paper towels.

In ponds supplying a greenhouse or nursery

  • Supplies: Inner tube, (3/16″ or 1/4″) poly rope, and citrus-type mesh bag.
  • Place 5-7 pears in citrus bag. You won’t be submitting all of those (see below), but you need extras just in case.
  • Attach bag in center of inner tube with rope straps so that it is free to settle into the water.
  • If turtles are in the pond construct a cage of wire mesh hardware cloth to protect pears from being eaten.
  • Attach 100 ft. of poly rope on either side of inner tube. Place tube and bag in water at one corner of the pond, then have two people walk in opposite directions away from corner so that the tube is floating out in the pond.
  • Secure rope ends to stakes on bank so that tube will remain fairly stationary.
  • After 3 days, retrieve tubes.
  • Pack and ship pears as detailed below.

In the greenhouse

  • Clean, sanitize with bleach, and thoroughly rinse a large bucket or opaque storage bin.
  • Add about 5 gals of water to the bucket, combining water from two or three different points in the greenhouse where water is piped in. Water should be about 4-5 inches deep.
  • Float green, rock hard pears on water, about 3 pears/bin for 3 days.
  • After 3 days, remove pears from water.

Packing pears for shipment

  • For each water source/location, choose 3 pears at random to constitute the sample.
  • Place each pear in a sandwich-sized recloseable bag.
  • Put bagged pears from each location in a larger plastic bag and label accordingly.
  • Pack in a sturdy shipping container with plenty of padding to reduce bruising of fruit during shipment.
  • Call the PDIC at 919-515-3619 before shipping, so we can be sure to have the necessary supplies ready.
  • Ship on a Monday, Tuesday, or Wednesday for next-day delivery. See our shipping page for addresses.
pears suspended in a bucket of water using mesh lesions on pears after baiting period
Pears suspended in top of sample water just so fruit are covered. Pears after baiting period.