4.3.1.4 Fungal Diseases

Question 1

What sort of pathogen is rose black spot caused by?

Answer 1

• caused by fungus Diplocarpon rosae
• serious rose disease

Question 2

Why does rose black spot make resistant roses difficult to breed?

Answer 2

• mutates rapidly, making resistant roses difficult to breed

Question 3

What are the symptoms of rose black spot disease?

Answer 3

• purple or black spots on leaves of rose plants which often turn yellow and drop early
• affects growth of plant as photosynthesis is reduced
• enlarging black patch on leaf
• drooping leaves
• small, black lesions on stems
• if plant is badly affected it can lose all its leaves

Question 4

How is rose black sport transmitted?

Answer 4

• by water - black spot fungus produces spores which are released under water conditions and are usually spread by rain splash
• by wind
• through direct or indirect contact - disease can be spread from plants to plant directly or via hands, clothing or tools

Question 5

What is the treatment for rose black spot disease?

Answer 5

treated using fungicides (tebuconazole with trifloxystrobin and triticonzale are labelled for rose black spot)

Question 6

How can the spread of rose black spot disease by prevented/controlled?

Answer 6

• collect and destroy fallen leaves in autumn, or bury under a layer of mulch
• prune out all stem lesions in spring before leaves appear