Project title
Proof and quantification of grapevine leafroll disease vector dispersal and disease spread mechanisms

Project leader
Pietersen, G

Institution
Citrus Research International. Department of Microbiology and Plant Pathology

Team members
Pietersen, G
Krüger, K
Kotze, A
Schwerdfeiger, M

Project description
Various grapevine leafroll spread mechanisms occur simultaneously in vineyards. Infrequent or less easily identifiable mechanisms, for example wind dispersal, are masked by the more dominant or obvious mechanisms, for example secondary spread. As control strategies become increasingly better at controlling known spread mechanisms, these other 'hidden' dispersal mechanisms are likely to become more obvious and will require specific control interventions. It is therefore important to identify these and to quantify them in order to develop control strategies to them. The ultimate aim of the first aspect of the project is therefore to annually monitor the spatial progression of grapevine leafroll in vineyards in which control strategies to the known dispersal mechanisms are being applied. This must be done over the entire duration of this project. Based on this, the remaining dispersal mechanisms can be inferred and ultimately control strategies to them developed and assessed.

Grapevine leafroll spread mechanisms obtained in project WW 07-16 were inferred by the data rather than proven by just following spatio-temporal dynamics of case studies . These need to be proven and various aspects of the mechanisms quantified to fully implement efficient and effective control strategies. Firstly spread of the disease by scion material and rootstocks must be unequivocally demonstrated, the way that they are spatial distributed in new vineyards determined, and the potential latent phase of each of these sources determined within nurseries and new vineyards. Secondly, dispersal of mealybugs on man and implements must be demonstrated and strategies to counter this assessed. Thirdly the major means of secondary spread must be demonstrated (mealybug motility determined and differentiated from potential intra-row root union formation).

Presentation(s)
1. Pietersen, G. 2007. Progress report. Winetech Information Day. 2 May. Stellenbosch, South Africa.
2. Pietersen, G. 2007. Virus epidemiology. Winetech Virus Information Day. 4 May. Stellenbosch. South Africa.
3. Pietersen, G. 2008. Grapevine leafroll disease in South Africa. Talk presented to producers invited by New Zealand Wine. 6 March. Martinborough, New Zealand.
4. Pietersen, G. 2008. Current studies on leafroll controll in South Africa. Talk presented to producers invited by New Zealand Wine. 6 March, Martinborough, New Zealand.
5. Pietersen, G. 2008. Grapevine leafroll disease in South Africa. Talk presented to producers invited by New Zealand Wine. 7 March. Napier, New Zealand.
6. Pietersen, G. 2008. Current studies on leafroll controll in South Africa. Talk presented to producers invited by New Zealand Wine. 7 March. Napier, New Zealand.
7. Pietersen, G. 2008. Grapevine leafroll disease in South Africa. Talk presented to producers invited by New Zealand Wine. 10 March. Gisborne, New Zealand.
8. Pietersen, G. 2008. Current studies on leafroll controll in South Africa. Talk presented to producers invited by New Zealand Wine. 10 March. Gisborne, New Zealand.
9. Pietersen, G. 2008. Grapevine leafroll disease in South Africa. Talk presented to producers invited by New Zealand Wine. 12 March. Marlborough, New Zealand.
10. Pietersen, G. 2008. Current studies on leafroll controll in South Africa. Talk presented to producers invited by New Zealand Wine, 12 March. Marlborough, New Zealand.
11. Pietersen, G. 2008. Grapevine leafroll disease in South Africa. Talk presented to producers invited by New Zealand Wine. 13 March. Nelson, New Zealand.
12. Pietersen, G. 2008. Current studies on leafroll controll in South Africa. Talk presented to producers invited by New Zealand Wine. 13 March. Nelson, New Zealand.

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