DEAD ARM DISEASES

Question 1

Also know as

Answer 1

Streepvlerk

Question 2

Causative organism

Answer 2

Phomopsis viticola

Question 3

When does it occur

Answer 3

start of and during spring
wet conditons
sporadic manner

Question 4

LEAVES

Answer 4

small black spots, with white to yellow circles (numerous cause a wrinkled & abnormal appearance)

leaves on basal internodes are the most severely affected

from 4th/5th internode leaves appear normal and cause misconception

Question 5

SHOOTS

Answer 5

first signs on basal internodes of young shoots

• dark brown lens-shaped spots
• expand to become longitudinal cracks, black discolouration and withering of tissue
• cracks are shallow and the extent to only the bark

Damp conditions: lesions are not visible and shoots are covered in dark brown to black tissue discolouration

Late season: favourable conditions severely affect shoots and they become dwarfed + die-back of buds and shoots

Question 6

BUNCHES

Answer 6

lesions occur on peduncles

spread to the rachis and other parts

young berries become black and shrivelled

Question 7

Where does dead arm disease occur

Answer 7

Western Cape cultivars are very susceptible

Question 8

Why not considered in the summer rainfall areas?

Answer 8

Spring is normally dry

Question 9

How does Dead arm disease spread/occur

Answer 9

Fruiting bodies are formed in the bark sections of affected one year old or older wood or on dead plant material lying on the ground.

This occurs during hibernation

Moisture (water in any form) cause spores to be released and these spores attached to the susceptible grapevine

Question 10

Conditions for successful germination

Answer 10

high relative humidity