12. Replacing whole, highly leafroll infected vineyards with new healthy vineyards

Prof Gerhard Pietersen, University of Pretoria - 28 Apr 2016

(Scroll to bottom to download pdf version in English or Afrikaans)

It is not uncommon in South Africa that after 10 to 12 years vineyards are 100 % infected by leafroll, followed a few years later by unacceptable yield and grape quality losses. Such vineyards are therefore often replaced 15 to 18 years after planting, a significant financial cost.

Some circumstantial evidence has been obtained in South Africa, as well as in New Zealand, that grapevine leafroll-associated virus 3(GLRaV-3) may spread from an old, highly infected vineyard to the newly established vineyard via viruliferous (virus carrying) mealybugs which, 1) either survive in the soil on remnant GLRaV-3 infected roots from the old vineyard, or 2) on volunteer hosts of the old vineyard, growing within the new vineyard.

This mode of spread would be due to the carry-over of viruliferous mealybugs between the removal of the old vineyard and re-establishment of the new one at that site. They could have survived on some residual grapevine roots or on volunteer grapevines, not properly removed,
especially in the case of a short period between removal and replanting in the soil.

To control this mode of Leafroll spread a number of interventions are required, each reducing the chances of leafroll spread:

  • Mealybugs from the old vineyard, carrying the virus, must be eliminated or their numbers at least drastically reduced, prior to removal of the old vineyard. Do this by applying Imidacloprid (a systemic insecticide) to the entire old vineyard as early after harvest as possible in the season prior to removal of the vineyard.
  • All plant material from the old vineyard, carrying the virus, must be removed prior to planting the new vineyard. This requires the very thorough removal of old, infected grapevines and their roots. Pulling out the grapevine is best achieved when the soil is wet as fewer roots break off and stay behind. Earlier it was recommended that the old grapevines be killed with herbicide prior to removal, but experiments have shown that grapevines are not effectively killed (up to their roots) by these treatments.
  • Make use of a fallow period (a time in which no grapevines are planted on a site), to get rid of any volunteer hosts (grapevine material from the old vineyard) that may be sprouting.
  • Make use of the fallow period to also remove any residual root material remaining from the old vineyard.
  • The length of the fallow period is less important than the actual ability to remove this material in this time.
  • When establishing the new block, do so with certified planting material.
  • Treat the newly planted grapevines with a systemic insecticide, followed by annual rouging (to control the spread of leafroll through infected planting material).
  • Dig out and remove all volunteer rootstock and scion material coming up in the new vineyard. The rootstock material may not show symptoms but is likely to be infected with leafroll, having come from a highly infected old vineyard.
  • When planning on doing whole vineyard replacement of multiple vineyards over a defined period (for example when planning a replant across the whole wine estate), start by removing the vineyards upwind first and then successive vineyards bordering them.
  • Retain a running buffer zone between replanted new vineyards and the old infected vineyards.
  • The buffer zone, free of Vitis, is maintained to prevent infection from surrounding vineyards and should be a minimum of 10 meters (or three rows) but anything wider will reduce leafroll intrusion more effectively.
  • During the interim phases where highly leafroll infected vineyards and healthy replanted vineyards exist on the same estate, ensure that measures to avoid spread from surrounding vineyards and external sources is conducted.

 

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