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Washington State University

Pest Profiles

Whatcom County Horticultural Pest and Disease Board


The Whatcom County Horticultural Pest and Disease Board develops a list of pest priorities. These priorities outline the focus of the pest the board and represent the most economically damaging pest for the County’s horticultural crops at a given time. This web page provides the most up to date biological and integrated pest management (IPM) options for these pests based on the most recent science.

If you have an issue that needs attention, please use this form to give a description of the causal pest, the economic impact it is having, and any other specific information that can inform the Board. NOTE: Only signed grievances will be investigated.

Grievance Form (pdf)

Current Highlighted Pests:

Blueberry Scorch Virus


Pest Description

WSU Whatcom County IPM Pest Profile for Blueberry Scorch Virus:
Michigan State University Extension:



  • If a plant shows symptoms of scorch a confirmation lab test is needed. Contact the WHPDB for instruction on how to do this.
  • If the test is confirmed positive, the infected plants and roots should be removed immediately as well as six adjacent plants within the row.
  • Continue tissue sampling and plant tracking programs in the infected field to see if additional plants test positive.
  • Initiate intensive rouging of infected plants.
  • Implement rigorous aphid management programs for at least two years following virus management.
  • Yellow sticky cards will then be installed and monitored by the WCHPDB during that time period.


Further Management Guidelines
Pacific Northwest Pest Management Handbook:

Potato Virus Y (PVY)

Brochure and Potato Virus Y affected potato

Potato Virus Y Brochure (pdf)


Pest Description

WSU Mount Vernon Northwestern Washington Research and Extension Center:
Great photos for identification and management recommendation:



  • Reduce the level of initial PVY inoculum in the crop by following the below guidelines
  • If symptomatic plants are present contact the WCHPDB to confirm with a lab test.
  • Remove symptomatic plants immediately as well as six adjacent plants within the same row.
  • Implement rigorous aphid management program for the remainder of the growing season.
  • Yellow sticky cards will then be installed and monitored by the WCHPDB during that time period.


Further Management Guidelines

1) Plant only certified seed
Certified seed is harvested from potato fields that have been inspected and tested for several plant pathogens, including the “ordinary” and newer “tuber necrotic” strains of PVY.

Practice sanitation
All cutting and planting equipment should be disinfested before coming in contact with seed, as well as between seed lots. PVY can be mechanically transmitted from an infected plant to a healthy plant via plant sap on hands and tools. Several commercial disinfectants are available.

Destroy overwintering sources of PVY
Properly destroy cull piles according to established guidelines. Cull piles of tubers will produce sprouts. These sprouts can serve as a source of PVY, if the tuber carries the virus. Because they are cull piles, there is a greater chance, by definition, of the cull tubers to harbor PVY, other potato viruses, late blight, etc. Cull piles pose a very large risk to the potato farm and this risk is controllable.

Rogue volunteer potatoes early in the season
Roguing means the removal and destruction of unwanted potato plants, often growing as volunteer potatoes from the previous year’s crop. This practice eliminates infected plants from the field. In this way, the planted crop, derived from certified seed, will emerge from the ground without immediately being contacted by potential virus spread from volunteer plants already growing in the immediate area or within adjacent fields.

2) Use resistant cultivars
It is important to understand the classification of resistance, or the ways in which plants can resist disease—tolerance, resistance and immunity. Unfortunately, from the perspective of managing PVY, the level of resistance to PVY, ordinary and new strains, has not been fully characterized for many potato cultivars.

A tolerant cultivar is one that grows and yields well, despite being infected with PVY. Although tolerant cultivars may or may not show symptoms of virus infection, very often they support high levels (titer or concentration) of virus in leaves and tubers. Tolerant cultivars can make good sources of virus for spread to other cultivars, weeds, and other Solanaceous crops within a field and in adjacent fields. Avoid planting cultivars with poor symptom expression in close proximity to fields with susceptible cultivars.

Resistant cultivars will often have reduced virus titer (the concentration of virus in the plant), will restrict movement (systemic spread) of virus in the plant, will develop a necrotic (cell death) response that walls off and kills the infected plant tissues, or will express a combination of these traits. All of these resistance mechanisms tend to reduce, slow, or limit the spread of virus within a field or to plants in adjacent fields. Resistant plants will have less severe to no disease symptoms.

Immune plants do not support virus infection. Keep in mind – PVY is a population of different strains, some which have emerged recently. Plant resistance or immunity may be defeated, or broken down, by mutations in the virus that give rise to the development of new strains or by the accidental introduction of such strains by interstate sales and transport.

3) Reduce on-farm spread of PVY by aphids
Chemicals to hinder or prevent aphid feeding
Insecticides can be used to prevent populations of potato-colonizing aphid species from increasing within a field and thereby limiting the plant-to-plant spread of virus. However, PVY is transmitted by many species of non-potato-colonizing aphids in a “non-persistent” manner and, because of this, insecticides are often considered an ineffective means of control.

Non-persistent transmission
PVY can be picked up within seconds by the aphid’s stylet (its syringe-like mouthparts) when probing a PVY-infected plant to find out if the plant is a suitable food source. Once inside the aphid’s stylet, PVY can be easily transmitted, within seconds, to another plant that the aphid probes. PVY does not remain in the aphid stylet for very long, a few hours at most.
Insecticides that interfere with non-persistent transmission include mineral oils, such as JMS Stylet Oil, or Aphoil. When applied to the leaf surface, these narrow-range distillate oils interfere with aphids’ interest and ability to puncture the leaf surface. Another promising approach incorporates the use of anti-feedant compounds or selective feeding blockers (e.g. Fulfill® or Beleaf®), timed when aphids are known to settle in potato fields. In turn it is critical to understand which aphid species are transmitting the virus and when they are moving into the field in order to time the use of these materials.

Field placement, management and design
Avoid planting seed potatoes downwind from commercial fields. Also, prevent late-season virus infection by top-killing seed potato fields early. This precludes the colonization of potatoes by late-season, migrating aphid populations which tend to move into potatoes. Incorporate the use of border crops surrounding high-valued seed lots to further limit the spread of PVY. Border crops will cleanse PVY from aphid sytlets before the aphids find the potatoes. This technique has proven effective in limiting PVY infection in seed potatoes. Borders consist of plants, or crop species, that cannot support infection of PVY. The non-host border is planted around small, early-generation seed lots, <0.2 ha field size, with fallow land around the outside of the border and no skips within the crop-plus-border area. The border buffers the potato seed lot from the in-flight of aphids, because the aphids usually land at the interface between fallow ground and green crop.

Eliminate volunteer potatoes and weed reservoirs of aphids and PVY.
Weeds and other crops that harbor PVY include members of the family Solanaceae, the nightshades, tomato, eggplant, peppers, petunia, etc. Control Solanaceous weeds such as eastern black and hairy nightshade. Do not plant seed potato fields near other Solanaceous crops. Eliminate volunteer potato plants from potato fields because they may be growing from tubers that are infected with PVY.

Potato Late Blight


Pest Description

Washington State University:
American Phytopathological Society:



Follow management guidelines as outlined below

  • If symptomatic plants are present contact the WCHPDB to confirm with a lab test.
  • If confirmed, remove infected plants and the next 100 feet surrounding of potatoes (if applicable).

Further Management Guidelines

Apple Maggot


Pest Description

WSU Tree Fruit Research and Extension Center:
WSU Extension – Protecting Backyard Apple Trees from Apple Maggot (for homewowners):
WSU Hortsense (for homewowners):
Pacific Northwest Pest Management Handbook:



Follow management guidelines as outlined below.

  • Monitor traps should be placed in trees that appear to be infested.
  • Traps will be installed and checked by the WCHPDB.
  • Control treatments should be applied for 21 days after apple maggot is caught on a trap.
  • Monitoring should continue for another 21 days until no apple maggot are captured.


Further Management Guidelines
PNW Handbook:
Protecting Backyard Apple Trees from Apple Maggot:
The Pros and Cons to Homeowners Planting Tree Fruit in their Backyards: