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Beginner

This pest affects:

Scientific Name
Unknown virus.

Identification
Fruit

• Deep cone-shaped pits, extend 6 mm or deeper into the flesh
• At the base of each pit, cells have fused into a brown, stone-like mass without  extensive discoloration of the surrounding tissues
• Fruit may also have pits that are not typical:  not as deep, stone cells may be smaller or less fused and not as hard
• Stones are difficult to cut through with a knife
• Seriously affected fruits may be curved and malformed
• Bosc is most severely affected:  pits on Anjou and Bartlett are shallower, more scattered and fewer

Bark and limbs 

• On young Bosc trees, discrete scabby spots on bark and in some cases, chlorotic vein banding and mottling of leaves

Often Confused With
Plant bug injury, mechanical damage, boron deficiency, or cork spot –Pits caused by such factors are more superficial. The base of the pit is pithy or mealy with insect damage, Cork spot or boron deficiency - not hard as in stony pit. As well, puncture wounds are present in pits caused by insect damage. 

Period of Activity
Symptoms may first develop during early fruit set. On some less susceptible cultivars (like Bartlett & Anjou), pitting may not develop until late summer or early fall before harvest.  Symptoms on fruit vary from season to season as well as severity. Trees that show symptoms one year may have no pitted fruit the following year

Scouting Notes
Bosc tends to be the most severely infected cultivar.  Strains of the virus that cause characteristic pit symptoms in Bosc may not infect less susceptible strains similarly. Less susceptible strains may only display bark symptoms and reduced vigour. Generally, Bartlett is considered a symptomless carrier of the virus.

As fruit matures, look for dimpled or pitted appearance of fruit. Stony pit can be distinguished from other types of damage by the accumulation of stone cells at the base of the pit that are extremely difficult to cut. If an attempt is made to cut down through a pit, the stone is pressed deeper into the flesh instead of being cut apart.

Threshold
There are no threshold treatments for pear stony pit.

Photo credit: https://pnwhandbooks.org/plantdisease/host-disease/pear-pyrus-spp-stony-pit

Advanced

This pest affects:

Scientific Name
Unknown virus.

Identification
Fruit

• Deep cone-shaped pits, extend 6 mm or deeper into the flesh
• At the base of each pit, cells have fused into a brown, stone-like mass without  extensive discoloration of the surrounding tissues
• Fruit may also have pits that are not typical:  not as deep, stone cells may be smaller or less fused and not as hard
• Stones are difficult to cut through with a knife
• Seriously affected fruits may be curved and malformed
• Bosc is most severely affected:  pits on Anjou and Bartlett are shallower, more scattered and fewer

Bark and limbs 

• On young Bosc trees, discrete scabby spots on bark and in some cases, chlorotic vein banding and mottling of leaves 

Often Confused With
Plant bug injury, mechanical damage, boron deficiency, or cork spot –Pits caused by such factors are more superficial. The base of the pit is pithy or mealy with insect damage, Cork spot or boron deficiency - not hard as in stony pit. As well, puncture wounds are present in pits caused by insect damage. 

Biology
The causal agent of pear stony pit has not yet been isolated, but it can be transmitted by vegetative propagation, including grafting, budding or root cuttings. However, symptoms don’t appear for 2-3 years, until the tree has come into bearing.

As early as 3 weeks after petal fall, dark green spots form on the fruit. Cell growth immediately surrounding these areas becomes restricted while rapid development of healthy tissue results in pitted and deformed fruit as it matures. Pits often become necrotic and the fruit produces numerous sclerenchyma cells (grit cells) beneath or surrounding the pitted areas.

Bark symptoms appear only after several years of growth or not at all, depending on the varieties involved.

Period of Activity
Symptoms may first develop during early fruit set. On some less susceptible cultivars (like Bartlett & Anjou), pitting may not develop until late summer or early fall before harvest.  Symptoms on fruit vary from season to season as well as severity. Trees that show symptoms one year may have no pitted fruit the following year.

Scouting Notes
Bosc tends to be the most severely infected cultivar.   Strains of the virus that cause characteristic pit symptoms in Bosc may not infect less susceptible strains similarly. Less susceptible strains may only display bark symptoms and reduced vigour. Generally, Bartlett is considered a symptomless carrier of the virus.

As fruit matures, look for dimpled or pitted appearance of fruit. Stony pit can be distinguished from other types of damage by the accumulation of stone cells at the base of the pit that are extremely difficult to cut. If an attempt is made to cut down through a pit, the stone is pressed deeper into the flesh instead of being cut apart.

Threshold
There are no threshold treatments for pear stony pit.

Management Notes
Select virus-free trees for planting. 

Infected trees should be removed. However, removing all infected Bosc trees in some orchards could reduce Bartlett pear yields due to lack of sufficient pollination.

Some of the information included above excerpted from;

• http://extension.psu.edu/fruit-diseases/pear/stony-pit
• http://postharvest.tfrec.wsu.edu/marketdiseases/pearstony.html
• http://www.caf.wvu.edu/kearneysville/disease_descriptions/omstnypt.html

Photo credit: https://pnwhandbooks.org/plantdisease/host-disease/pear-pyrus-spp-stony-pit