Viral Diseases

Question 1

Describe fanleaf virus.

Answer 1

A group of diseases (also called fanleaf degeneration) that lead to:

• stunted early shoot growth
• distorted cane growth
• pale, malformed fan-shaped leaves

Question 2

One variety sucsceptible to fanleaf virus?

Answer 2

Cab Sauv

Question 3

How is the fanleaf virus spread?

Answer 3

• enormously by the move to grafted vines following phylloxera
• spread slowly by the dagger nematode

Question 4

Management options for fanleaf virus?

Answer 4

• no cure for the disease
• affected vines must be removed (costly)
• before vineyards are replanted, soil tests should be done to check for the presence of dagger nematodes and virus tested, clean plating material should be used

Question 5

Describe leafroll virus.

Answer 5

A group of viral diseases widely present around the world that slows down the growth of roots and shoots

• surviving fruit takes extra weeks to ripen (more acidity, less color and lower sugar levels)
• vine stores less carbohydrates
• does not kill vines
  -reduce yield, affects quality

Question 6

How is the leafroll virus spread?

Answer 6

• by grafting
• by mealing bugs, a key pest in South Africa, the Mediterranean, Argentina, and some parts of CA

Question 7

What are management options for leafroll virus?

Answer 7

• no cure
• remove unproductive vines and re-plant with virus-free stock
• nurseries can screen vines for viral infections
• mealy bugs favor humid environments and therefore open canopies help to reduce the pest
• encourage the mealy bug’s natural predators: ladybugs, lacewings, and others

Question 8

What is control by spraying difficult for leafroll virus?

Answer 8

• because of the mealy bug’s waxy coating