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Ministry of Agriculture, Food and Rural Affairs

Pear Psylla

Beginner

This pest affects:

Pear;

Scientific Name
Psylla pyricola

Identification
Eggs

  • Pear-shaped, 0.3-0.5mm long
  • Shiny white when laid, gradually turning yellow just before hatching
  • Short stalk attaches egg to bark and long, thread-like projection extends from narrow end

Nymphs

  • Smaller wingless nymphs are pale yellow with red eyes, flat and oval, and develop within a clear honeydew drop
  • Larger “hard shell” nymphs are darker with black areas interspersed with green or brown colouration, noticeable wing pads and are free-living

Adults

  • Resemble very small cicadas
  • 0.2-0.3mm in length, overwintering adults are larger
  • Reddish brown (overwintered generation) or tan to light brown (summer generations)
  • Wings held roof-like over abdomen, overwintering generation has dark spot on middle of inner wing margin

Damage

  • Secrete honeydew, cause russet blotches or streaks on skin of fruit
  • Sooty mould grows on honeydew giving fruit, leaves and bark a dark sooty appearance
  • Wilting or scorching on leaves due to toxic saliva injected during feeding
  • Heavy infestation can cause premature leaf drop, weaken fruit buds and reduce shoot growth
  • In extreme cases, trees can die from "psylla-shock", characterized by a blackening and burning of tree foliage caused by the buildup of a toxin injected into the plant as the psylla feed

Often Confused With
Psylla shock is similar to damage caused by mites, but typified by presence of copious amounts of honeydew on the pear leaves and fruit

Fire blight - cankers extend more than 5 cm into a spur; amber coloured bacterial ooze produced following rain; shepherd’s crook with dead leaves remaining attached

Period of Activity
Adults become active when temperatures reach 10°C. Mating and egg laying occur prior to bud break. There are two to three generations per year in Ontario. Third instar nymphs usually occur at petal fall, but in warm spring this event may take place at the "popcorn" stage of bud development.

Scouting Notes
There are currently no traps or pheromones to indicate the presence or activity of the pear psylla.

Collect fruit spurs weekly from late March through harvest to assess potential pest pressure. Record when first egg deposition occurs, as well as first egg hatch. A minimum of 25 fruit spurs and terminals per orchard (one spur per tree) will provide a good sample of stages present. Take at least ten spurs from the central areas of the tree and the remainder from the outside area of the tree.

As the foliage begins to develop, eggs are laid on the tender terminal leaves and petioles. Generally, eggs are concentrated at the base of the leaf along the midrib region. When foliage begins to appear, terminal shoots with 4 to 6 leaves should be collected. For records, psylla totals should be from the top 5 leaves of each shoot.

Summer populations can be monitored by sampling end terminals and "water sprouts" from the central portion of the tree. By mid-July the majority of leaves have hardened off and psylla activity is primarily limited to water sprouts and tender terminal growth.

By the end of June or early July populations frequently show a split age structure. Samples of shoots are critical at this time to determine the number of different stages present (eggs, young nymphs, hardshells). The presence of new honeydew and/or visual identification of nymphs/adults on the leaves/fruit are also important observations to accurately quantify pear psylla activity.  Remember, winged adults do not feed, only the nymphal stages feed directly on the plant tissues. 

Weekly samples provide the best means of effectively monitoring psylla development. For best results, sampling should be continued from late-April through to harvest.

Thresholds

Stage of crop development

Decision/threshold

Delayed dormant

Depends on previous history, adults present, egg laying started

Immediately at petal fall

3-5 active nymphs/spur and majority of eggs hatched

Emergency summer spray #1

3-5 active nymphs/sucker

Emergency summer spray #2

>5 active nymphs/sucker with low predator population; stickiness and fruit loss imminent

Advanced

This pest affects:

Pear;

Scientific Name
Psylla pyricola

Identification
Eggs

  • Pear-shaped, 0.3-0.5mm long
  • Shiny white when laid, gradually turning yellow just before hatching
  • Short stalk attaches egg to bark and long, thread-like projection extends from narrow end

Nymphs

  • Smaller wingless nymphs are pale yellow with red eyes, flat and oval, and develop within a clear honeydew drop
  • Larger “hard shell” nymphs are darker with black areas interspersed with green or brown colouration, noticeable wing pads and are free-living

Adults

  • Resemble very small cicadas
  • 0.2-0.3mm in length, overwintering adults are larger
  • Reddish brown (overwintered generation) or tan to light brown (summer generations)
  • Wings held roof-like over abdomen, overwintering generation has dark spot on middle of inner wing margin

Damage

  • Secrete honeydew, cause russet blotches or streaks on skin of fruit
  • Sooty mould grows on honeydew giving fruit, leaves and bark a dark sooty appearance
  • Wilting or scorching on leaves due to toxic saliva injected during feeding
  • Heavy infestation can cause premature leaf drop, weaken fruit buds and reduce shoot growth
  • In extreme cases, trees can die from "psylla-shock", characterized by a blackening and burning of tree foliage caused by the buildup of a toxin injected into the plant as the psylla feed

Often Confused With
Psylla shock is similar to damage caused by mites, but typified by presence of copious amounts of honeydew on the pear leaves and fruit

Fire blight - cankers extend more than 5 cm into a spur; amber coloured bacterial ooze produced following rain; shepherd’s crook with dead leaves remaining attached

Biology

First Generation

Pear psylla overwinters as an adult in cracks of tree bark or under debris. On warm sunny days as temperatures reach 10°C, adults may be seen moving around on the bark. If temperatures remain about 10°C, mating and egg-laying may begin (as early as mid-March). Prior to bud break, psylla eggs are laid singly or in a line on rough areas of buds twigs and bark crevices. As buds develop and new shoots emerge, egg laying shifts to the margins of leaves and stems of shoots. The tiny eggs which can be detected with a 10-14x power hand lens hatch over a long period of time (i.e. 6 to 7 days at 21°C or 35 days at 5°C) resulting in the first generation.  The earliest laid eggs hatch as the foliage begins to expand.

A female psylla may lay 180 to 350 or more eggs over a 2 to 3 week period making timing of controls difficult.  Psylla nymphs feed by sucking sap from developing buds, leaves and shoots.  There are five developmental instars.  The first two instars are relatively immobile and produce small amounts of "honey dew" (the sap excretion of the nymph during feeding). The 3rd instar (as well as the 4th and 5th instar) nymphs are distinguished by the presence of wing pads. These nymphs are referred to as "hard shells" and often hide beneath the honey dew in leaf axils while feeding. This trait makes control with pesticides extremely difficult.

Complete development from egg to adult may vary from 3 to 7 weeks for the first generation but is highly dependent on temperature.

Second Generation

Second generation adults first appear in early to mid-June and may continue to live and develop throughout July into early August. Approximately 7 to 10 days after emerging, females begin laying eggs along the midrib of the lower surface of new leaves. Egg deposition (250-500 per female) may last 4 to 5 weeks. Eggs will hatch 7 to 14 days after deposition, potentially resulting in all developmental stages present at the same time. The lack of uniformity in development can make this generation the most difficult to control.

Third Generation

This is only a partial generation and generally populations are much lower than the previous two generations. Egg-laying is primarily on the new sucker growth at the centre of the tree or the young growing terminals. Egg-laying rates (200 to 400 per female) will be influenced by climate and temperature as psylla will not lay eggs on trees showing wilting or damage by extreme heat. Psylla may still be present in large numbers after harvest is complete. Eggs of the third generation may appear in early August or later depending upon weather conditions. Many nymphs hatching from these eggs will not survive the winter; however, those that reach adulthood are the ones that will overwinter.  It is difficult to separate second and third generations because of continuous egg laying and lack of uniformity in development.

Period of Activity
Adults become active when temperatures reach 10°C. Mating and egg laying occur prior to bud break. There are two to three generations per year in Ontario. Third instar nymphs usually occur at petal fall, but in warm spring this event may take place at the "popcorn" stage of bud development.

Scouting Notes
There are currently no traps or pheromones to indicate the presence or activity of the pear psylla.

Collect fruit spurs weekly from late March through harvest to assess potential pest pressure. Record when first egg deposition occurs, as well as first egg hatch. A minimum of 25 fruit spurs and terminals per orchard (one spur per tree) will provide a good sample of stages present. Take at least ten spurs from the central areas of the tree and the remainder from the outside area of the tree.

As the foliage begins to develop, eggs are laid on the tender terminal leaves and petioles. Generally, eggs are concentrated at the base of the leaf along the midrib region. When foliage begins to appear, terminal shoots with 4 to 6 leaves should be collected. For records, psylla totals should be from the top 5 leaves of each shoot.

Summer populations can be monitored by sampling end terminals and "water sprouts" from the central portion of the tree. By mid-July the majority of leaves have hardened off and psylla activity is primarily limited to water sprouts and tender terminal growth.

By the end of June or early July populations frequently show a split age structure. Samples of shoots are critical at this time to determine the number of different stages present (eggs, young nymphs, hardshells). The presence of new honeydew and/or visual identification of nymphs/adults on the leaves/fruit are also important observations to accurately quantify pear psylla activity.  Remember, winged adults do not feed, only the nymphal stages feed directly on the plant tissues. 

Weekly samples provide the best means of effectively monitoring psylla development. For best results, sampling should be continued from late-April through to harvest.

Thresholds

Stage of crop development

Decision/threshold

Delayed dormant

Depends on previous history, adults present, egg laying started

Immediately at petal fall

3-5 active nymphs/spur and majority of eggs hatched

Emergency summer spray #1

3-5 active nymphs/sucker

Emergency summer spray #2

>5 active nymphs/sucker with low predator population; stickiness and fruit loss imminent

Management Notes
Do not over-fertilize.  Psylla populations flourish in soft lush vegetative growth. Excess nitrogen in the soil often results in excessive foliage development making the tree ideal for psylla. Good balanced fertilization programs will help control tree growth and limit the number of water sprouts/suckers produced.

Follow proper planting recommendations for the selected cultivar and rootstock.

Trees planted too closely (between trees and between rows) compete for soil nutrients and sunlight. This situation can result in excessive, willowy vegetative growth which can harbour a high psylla population. Also, the intertwining of branches from tree to tree will facilitate the migration of psylla throughout the orchard and making pesticide coverage extremely difficult.

Thin out windbreaks and orient tree rows to improve air drainage.  Adult psyllas are weak fliers, often moving only small distances. Dense wind breaks adjacent to pear blocks can create sheltered areas. This calm area will allow for wider dispersal of psylla adults and can make control difficult.

Ensure good spray coverage:  A large number of psylla control problems can be traced to inadequate spray coverage. This situation is usually indicated when the psylla population in the top central portion of the trees continue to thrive despite pesticide application(s). Calibration of equipment should be done on a regular basis (at least yearly) to ensure sufficient coverage is obtained. As the season progresses, or under high psylla populations, it may be necessary to increase the water volume used to penetrate and cover the expanding foliage and sucker growth.

Different pesticides registered for use on psylla have different use patterns. The appropriate selection depends on the pest population, stage of pest development and history of pesticide use at a particular site.Control of psylla requires monitoring to determine the stage of development of the population and the optimum timing for treatment. Best control of psylla is achieved when the majority of the population is in the first 3 instars.

Management with insecticides – Insecticides are used to control pear psylla in most commercial orchards. OMAFRA Publication 360, Fruit Crop Protection Guide:

Chapter 5 - Pear Calendar: Recommendations for pear psylla at Green tip, White bud, Petal fall, First cover, and Summer sprays.

Many predatory insects such as the mullein bug (campylomma), pirate bugs (anthocorids), lacewings, ladybird beetles, earwigs and some species of ants, feed upon pear psylla. Caution should be taken when determining a spray program to ensure the preservation of these beneficial insects.