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Beginner

This pest affects:

Scientific Name
Blumeriella jappii

Identification
Leaves

• Symptoms usually first observed in tops of trees
• Small purple to brown spots, with definite borders, on upper leaf surface in early summer
• In July, the centres of the infected spots frequently fall out, giving a shot-hole appearance
• Eventually turn yellow and fall
• Often defoliates the tree by midsummer

Fruit

• When significant defoliation occurs before harvest, fruit can become soft and immature, have low soluble solids (sweetness)  and ripen unevenly

Overall tree health

• Two or more years with significant defoliation early in the season makes the tree more susceptible to winter injury due to reduced carbohydrate storage which may eventually kill it
• Return bloom may be reduced for at least 2 subsequent years

Often Confused With
Pesticide injury

Period of Activity
Ascospores may be discharged during and shortly after rainfall and cause primary infections from early bloom to about 6 weeks after petal fall.

New secondary infections can occur throughout the summer and fall due to the rapid increase and spread of the fungus during wet periods.

Scouting Notes
In early spring, while trees are still dormant, monitor the orchard floor for the presence of leaf litter which is the source of primary inoculum. After petal fall observe 50 leaves on each sample tree for the presence of spots four to six weeks. Spots may be only pinpoint in size. During wet, humid periods, examine the underside of leaves to determine if masses of whitish-pink conidia are beginning to form. Sometimes the first sign of infection may be on suckers close to the ground.

Threshold
The amount of lesions required causing leaf yellowing and drop is variable. Sweet cherries can tolerate quite a few lesions before leaf drop occurs, however, Montmorency sour cherries will drop with only a few lesions. At least two leaves are needed to effectively ripen each cherry on sour cherry trees.  Less than 50 percent defoliation by early September is considered acceptable control in sour cherry.

Advanced

This pest affects:

Scientific Name
Blumeriella jappii

Identification
Leaves

• Symptoms usually first observed in tops of trees
• Small purple to brown spots, with definite borders, on upper leaf surface in early summer
• In July, the centres of the infected spots frequently fall out, giving a shot-hole appearance
• Eventually turn yellow and fall
• Often defoliates the tree by midsummer

Fruit

• When significant defoliation occurs before harvest, fruit can become soft and immature, have low soluble solids (sweetness)  and ripen unevenly

Overall tree health

• Two or more years with significant defoliation early in the season makes the tree more susceptible to winter injury due to reduced carbohydrate storage which may eventually kill it
• Return bloom may be reduced for at least 2 subsequent years

Often Confused With
Pesticide injury

Biology
Leaf spot most seriously affects the foliage of sour and sweet cherries. Sour cherries, especially Montmorency variety, are generally more susceptible. In addition, various wild and cultivated Prunus hosts, can be affected by this disease, although a different species of the fungus affects plum.

The fungus overwinters on fallen leaves on the orchard floor and produces ascospores in apothecia in the spring. The primary infection period may last two to six weeks depending on conditions. Optimal ascospore development occurs between 6 to 16°C with ascospore discharge increasing with temperature between 8 to 30°C. Ascospore release occurs as tissue dries following the thorough wetting of mature asci. Germination occurs on the surface of the leaf and infection occurs through the leaf stomata. A wet period of only a few hours is sufficient for spore germination and infection when temperatures are favourable. Development of visible lesions occurs in 5 to 15 days.  Temperatures of 16-20ºC) are most favourable for disease development.

Leaves remain susceptible throughout the growing season. Following infection, acervuli develop on the underside of the infected leaf and produce a mass of light pink to white masses of conidia. Conidia are dispersed from leaf to leaf by wind or rain and the infection cycle can be repeated several times during a single season, depending on conditions.

Traditionally, cherry leaf spot is seen in the tops of trees and the fungus releases spores that move the infection “down” through the canopy.

Period of Activity
Ascospores may be discharged during and shortly after rainfall and cause primary infections from early bloom to about 6 weeks after petal fall.

New secondary infections can occur throughout the summer and fall due to the rapid increase and spread of the fungus during wet periods.

Scouting Notes
In early spring, while trees are still dormant, monitor the orchard floor for the presence of leaf litter which is the source of primary inoculum. After petal fall observe 50 leaves on each sample tree for the presence of spots four to six weeks. Spots may be only pinpoint in size. During wet, humid periods, examine the underside of leaves to determine if masses of whitish-pink conidia are beginning to form. Sometimes the first sign of infection may be on suckers close to the ground.

Threshold
The amount of lesions required causing leaf yellowing and drop is variable. Sweet cherries can tolerate quite a few lesions before leaf drop occurs, however, Montmorency sour cherries will drop with only a few lesions. At least two leaves are needed to effectively ripen each cherry on sour cherry trees.  Less than 50 percent defoliation by early September is considered acceptable control in sour cherry.

Management Notes
Pruning to allow for rapid drying of foliage and good spray penetration. 

Management with fungicides – Fungicides are used to control cherry leaf spot in commercial orchards.  See OMAFRA Publication 360, Guide to Fruit Production:

	Chapter 6 Sweet Cherries or Sweet Cherry Calendar only: Recommendations for Cherry leaf spot Post harvest.
	Chapter 6 Sour Cherries or Sour Cherry Calendar only: Recommendations for cherry leaf spot at Petal fall, Shuck split, First cover, Second cover, Third cover, Post harvest.