DOWNY MILDEW

Question 1

Also known as?

Answer 1

Donsskimmel

Question 2

Causative organism

Answer 2

Plasmopara viticola

Question 3

Important

Answer 3

• does not occur every season
• dependent on the rain pattern
• all Vitis vinifera species are suscpetible
• depending on rainfall: sporadic or epidemic

Question 4

LEAVES

Answer 4

first signs on the upper surface
-light yellow spots (oil spots)
turn red quickly in red juice cultivars
turn brown or reddish-brown and white downiness disappears
-humid conditions: white, downy fungal develop on the undersides = spore-producing organs of fungas and spores

Question 5

SHOOTS

Answer 5

• from 10cm lengths in favourable conditions
• become black
• dry out and die

Question 6

BUNCHES - age?

Answer 6

young bunches are very sensitive (before flowering)

- they may succumb without any signs on leaves of die fungus (crop loss)

Question 7

BUNCHES - berries at a later stage…

Answer 7

shrivel, become brown
purplish hues in berries (no shrivelling)
(not sour rotor sunburn)

but become less susceptible

Question 8

Germination of spores

Answer 8

require water after hibernating on dead plant material in the vineyard

Question 9

What will happen with no control

Answer 9

Fungal growth will continue in favourable conditions and leaves’ total surface become brown and desiccate

Question 10

How will Downey mildew look after harvest

Answer 10

Undersides of leaves will be covered in white fungal growth, without yellow oil spots on the upper surface

Question 11

Test between Oidium and Downey mildew

Answer 11

Wet plant material and keep it overnight in a moist plastic bag at mild temp (20-30).
Downey: vigorous fungal growth will be noticeable the next day
Oidium: no fungal growth