Winetech Technical Yearbook 2022

NOVEMBER

SAWING BACK OF GRAPEVINES FOR RETRAINING

BY HENNIE VISSER

WHICH VINEYARDS CAN BE CONSIDERED FOR SAWING BACK AND RETRAINING? There are a few scenarios where grapevines can be sawn back for renewal. The most common reason would be in older vineyards where Eutypa dieback is widely observed. In this first scenario poor growth would thus present with lots of dead arms and/or bearers that could be renewed with great success. The second scenario is when vineyards are mothballed during extreme droughts by sawing back the vines. In this way the vineyard will require much less water and won’t bear grapes in the following season. As soon as water is available again, the vines can be retrellised and the vineyard can thus be saved. The third scenario refers to vines that are sometimes sawn back in order to raise the cordon for various reasons, for example in blocks that regularly suffer frost damage. VINEYARDS THAT WON’T BENEFIT FROM SAWING BACK AND RETRAINING The decision to saw back and renew a vineyard requires thoughtful consideration. In certain cases, the inputs required for renewal are not justified by the likely outcome. One such example is vineyards that display weak growth due to poor long-term practices, like incorrect and poor soil preparation and/or inferior planting holes. In these cases, the vineyard will

not show much improvement after renewal. Then there are also examples where vineyards have been infected with viral diseases, like leafroll or fanleaf virus. Renewal will likewise not lead to improvement in such cases, as producers cannot eliminate the virus by sawing back. HOW AND WHEN ARE VINES SAWED BACK? Vineyards are sawed back in winter during the normal pruning period. Saw the trunk at an angle to prevent water accumulating on the sawing wound. Paint the wound with a wound sealant within 24 hours after sawing back. Preferably use a wound sealant containing Trichoderma. Vines should be sawn back at least 10 cm below the position on the trunk where the most recent trunk pathogen symptoms are visible, but above the graft union. In the other cases as mentioned above, the trunks can be sawed back at any position. Note that sawed back vines will bud approximately two weeks later than normal. RETRAINING OF SAWED BACK VINES Green shoot development is performed as normal. The vine will grow very vigorously due to the well-developed root system and ample reserves in relation to the amount of buds that will bud. Ensure that sufficient labour is regularly available to perform timely actions for green shoot development. The big risk with

PHOTO 1. One year after sawing back. The correct method for sawing back and retraining is illustrated here. The shoot that was used to form the new trunk, is in the correct position. Vine development is correct and was done on time. Vine growth was very poor (30 - 50 cm shoot length) due to dieback with lots of dead arms and spurs. Note the vigorous growth after sawing back.

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WINETECH TECHNICAL YEARBOOK 2022