Blackleaf – Witches’ Broom

Apiosporina collinsii

Crops Affected: Saskatoon berries

Disease Cycle:

• Tends to be more prevalent in wild stands, in older or neglected orchards, or sporadically in managed orchards
• Does not tend to have much economic impact and is not typically considered to be lethal to plants
  • Reduces productivity of the orchard
• Fungal pathogen ooverwinters in infected tissues & debris
• Spores are released in spring
• Only new wood is affected (shoots & suckers)
• The crowns of young plants may be infected, destroying the tree
• Incidence of disease is typically linked to the presence of infected plant material (and the amount of infected material that is present)
  • Only new wood is susceptible to infection
  • 2^nd year and older wood is not affected

Symptoms:

• Infected leaf edges roll downward (scroll-like appearance)
• Underside of leaves is covered with a grey-brown felt-like growth
  • Leaves eventually become coated with heavy black mould and die
• Fruit on infected parts dries up or ripens prematurely
• Fungus penetrates shoot tips, stimulating the development of many new shoots (Witches’ Broom)
• Infected, dead leaves may remain on the branches during winter
  • Black “clumps” are easily visible in wild stands or orchards

Management:

• Remove & destroy all infected seedlings, transplants, & branches
• Prune infected branches 10 to 20 cm below infection site

Brown/black fuzzy growth on leaf undersides