Diseases of Saskatoons

Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
 Saskatoon juniper rust | Entomosporium leaf and berry spot | Powdery mildew | Brown rot and mummy berry | Blackleaf and witches’ broom | Dieback and canker | Fireblight | Bacterial blast | Damping-off | Non-infectious disorders .
There are a number of disease that can reduce the yield of Saskatoons.

Saskatoon Juniper Rust
Gymnosporangium sp.

  • infected leaves and berries develop yellowish-orange spots often raised
  • later in season, spots may be covered with numerous spiny projections (like whiskers) which contain large numbers of spores
  • leaf can tolerate large quantities of spots, but one spot ruins the berry
  • on juniper there is a gall on branch

Leaf symptoms

Branch and fruit symptoms

Fruit symptoms

Conditions favoring disease
  • most of the rust diseases in Alberta are 2 host, meaning they move from one host to second, then return to first
  • when the weather is wet in spring jelly-like yellow-brown horns erupt from galls on juniper
  • spores are produced that blow to the saskatoon
  • heavy dew on the saskatoon enables the spores to infect the saskatoon
  • temps 10-24oC, with wet plant surfaces favor disease development
  • remove all junipers within a 2 km distance of orchard
  • junipers within a 1.5 km distance can cause a significant loss of fruit once every 5 years
Entomosporium Leaf and Berry Spot
Entomosporium mespili

  • leaves,small angular brown spots, often with a yellow halo or margin around spots
  • spots can grow in size and cause blight phase
  • leaf stem, petiole, berry stalks and fruit cluster can become infected causing defoliation and fruit loss
  • infected fruits have dark brown spots which are often paler or silvery in centre
  • berry spots tend to be darker brown than leaf spots, are round, may or may not have yellowish halo

Conditions favoring disease
  • high humidity and leaf succulence
  • grows rapidly at 20oC
  • disease explodes in wet and warm weather
  • disease can move up the plant, bouncing from leaf to leaf then attack the fruit
  • primary infection begins when spores are splashed onto the leaves
  • fungus overwinters on fallen leaves
  • water the ground, not foliage, allow for the foliage to dry
  • in young plantings, keep the bottom one third of plant clean of foliage
Powdery Mildew
Podosphaera clandestina

  • common on lower leaves or root sucker leaves
  • rare on the berries
  • found on one or both leaf surfaces, eventually the leaf discolors and dies
  • can cause stunting of stem and distortion of immature leaves if infection happens at that time
  • diseased parts may become chlorotic before premature death
Conditions favoring disease
  • warm, dry weather 15-27oC favors production and spread of spores
  • poor air circulation and shade
  • disease overwinters in leaf buds and on fallen infected leaves
  • collect and destroy infected leaves in the fall
Brown Rot and Mummy Berry
Monilinia amelanchieris

  • flowers turn prematurely brown
  • brown spots on fruit surfaces, and gray to light brown tufts on the rotted surface
  • fruit shrink and mummify
Conditions favoring disease
  • humid weather during flowering, with temps around 24oC
  • insect damage to flowers and fruit can increase the disease incidence
  • disease is spread by wind or splashing water
  • overwinters on the fallen mummified fruit
  • removal of fallen mummified berries, and leaves
  • cultivation to bury the fallen fruit and leaves
Blackleaf and Witches’ Broom
Apiosporina collinsii

  • non-lethal to saskatoon plant
  • fungus penetrates the shoot tips and stimulates many new shoots to develop
  • resulting in a broom with numerous short twigs that arise close together, often at a swelling or knot on the branch
  • only new wood is affected
  • suckers are very susceptible
  • shrub growth and berry production reduced
  • leaf edges roll downwards and underside becomes covered with grey felt
  • eventually leaves become coated with heavy covering of olive brown to black fungal mat
  • easily seen as dead leaves remain on the brooms during the winter
  • overwinters on dead leaves
  • infection is systemic and perennial

  • prune and destroy the infected shoots
Dieback and Canker
Sterenum purpureum, Nectria cinnabarina, Cytospora spp,

  • drying and shrivelling of buds and leaves in spring
  • leaves developing fall coloration earlier than normal
  • bark wrinkled or has vertical splits and folds, bark peeling off the branches
  • abrupt transition between dead and live bark
  • cut surfaces of infected shoots may be stained black
  • fungi can cause the eventual death of plant, as moves down into the root crown
  • cankers,sunken areas of cracked, broken bark
  • Cytospora canker has little, black pimple-like protrusions from the canker surface
  • Nectria canker has orange protrusions from the canker surface
  • Cytospora and Nectria are secondary colonizers, they move into damaged wood
  • silverleaf causes the leaves to become pale and silvery looking, may have a purple staining in the heartwood

Conditions favoring disease
  • drought, cold, frost, wind, mechanical injury from harvesting equipment, pruning wounds (especially heading back on larger diameter stems), rodent damage, poor soil drainage, late summer pruning and late fall injuries
  • canker fungi infect shoots through cracks caused by injury
  • remove all dead and dying stems and branches when observed, cutting back 30 cm (12 in) back from infection
  • sterilize pruning equipment between cuts if disease is present
  • harden plants properly for winter
  • good site selection, wind shelter
Erwinia amylovora

  • individual flowers or entire flower clusters
  • appear water-soaked, droop, shrivel and turn brown, some fall off but most remain on the
  • plant
  • disease moves back into the stems of flowers and spurs
  • often the first noticeable symptom is where young shoots die forming a shepards crook, and discolor
  • if this discoloration occurs on many of the shoots, the plant can look like it has been
  • scorched by fire,hence the name
  • if the bark of the infected area is cut away
  • with a knife, a brown discoloration is noticed
  • can girdle branches with cankers
  • lesions look water-soaked
  • cream to carmel colored bacterial ooz comes out in beads from the lenticels and wounds on recently infected parts in humid weather
  • diseased portions become sunken and wrinkled
  • often the only way to tell the difference between fireblight and bacterial blast is to get a lab to culture the diseased material
Conditions favoring disease
  • bacteria is present from overwintering cankers on diseased plant material
  • fireblight favored by warm temperatures (18-25oC) and light rains
  • prolonged host flowering due to wet cool springs
  • flowers, fruit, and succulent growth become infected
  • blight appears within 1-3 weeks of inoculation depending on the temperatures and moisture
  • hail storms that open up the bark, followed by warm and humid temperatures also favor inoculation
  • pruning wounds
  • pruning is the best method of control, sterilize the pruning equipment between cuts
  • disease can be delayed or halted by careful pruning
  • when pruning, go back into healthy wood 30-45 cm (12-18 inches)
Bacterial Blast
Pseudomonas syringae

  • blackening or browning of tissue
  • unlike fireblight disease is slow spreading
  • can also be confused with several other disorders like winter injury, cane borer, or some herbicides
  • very similar to fireblight symptoms
Conditions favoring disease
  • cool and moist weather
  • overwinters on the canes and buds
  • bacteria needs a place to enter, whether frost damage or mechanical damage
  • bacteria is systemic in the plant, and infection spreads as long as weather is cool and wet, once weather begins to warm up disease subsides until fall
  • pruning is the best method of control
  • harden plants for winter properly
Pythium, Rhizoctonia and other fungi

  • pre-emergent,seedlings and germinating seeds destroyed
  • post-emergent,rotting stems (near surface of media)
Conditions favoring disease
  • pre-emergent, cold, wet germinating media
  • post emergent, warm, humid conditions with overcrowding
  • pasturized media
Noninfectious disorders

Cold injury
  • related to prolonged periods of extreme cold temperatures in winter
  • also sudden temperature drops following a warm spell in winter
  • desiccation occurs when dry winds blow over the plant and dry it out, the roots when frozen can not replace the moisture that is being lost
  • death of entire plant
  • death of susceptible parts like new wood, leaf and flower buds
  • canker diseases often follow

Frost damage
  • killing frosts -2.2oC or lower
  • can kill any actively growing plant tissue
  • light browning of flowers and leaves
  • damaged parts fall off
  • flowers are susceptible to frost damage, could be restricted to internal parts of flower and and may not be noticeable except under magnification

Wind damage
  • strong winds can abuse plants
  • abrasion, tearing and desiccation
  • hard brown edges of leaves, torn leaf margins
  • new leaves and shoots are susceptible to wind damage

  • on cold sunny days during the winter, bark exposed to sun can warm up, sun goes down and the bark splits, due to expansion and contraction of the cells
  • in hot summer bark can discolor and bubble
  • this damage then gives the canker diseases an entry point
Prevention of these disorders
  • proper site selection
  • low levels of soil moisture and fertility in late summer and fall
  • windbreaks reduce the effects of strong, persistent winds
  • slight NE slope will help prevent sunscald and also can delay flowering
This document is maintained by Shelley Barkley.
This information published to the web on October 28, 2004.
Last Reviewed/Revised on October 15, 2008.