Handbook for Irrigation of Wine Grapes in South Africa

FIGURE 9.12. Straw mulches could prevent excessive heat losses during the night.

9.5

MANAGING VINEYARDS FOLLOWING COLD DAMAGE

The challenge is to decide what viticultural actions would be best to ensure a normal crop in the subsequent season. However, there are different opinions about this matter. This is probably due to different levels of damage, as well as cultivars responding differently to manipulations (Snyman, 2018). There are basically three strategies a grower can follow, namely (i) do nothing, (ii) remove all shoots to allow new growth and (iii) prune green, bearing shoots back to one bud. Following severe frost in October 2016 in the Breede River valley, a pilot study was carried out with Chardonnay to compare these strategies. At harvest in 2017, yields were (i) 2.24, (ii) 7.66 and (iii) 14.04 t/ha, respectively (Snyman, 2018). Furthermore, visual observations revealed that (i) doing nothing formed numerous fine shoots which resulted in a dense canopy, (ii) removing all shoots produced less, but bigger bunches formed on the new growth, compared to the single green bud strategy and (iii) leaving one bud spur produced more, but smaller bunches than total shoot removal. It must be noted that formal experiments which allow statistical validation will be difficult to carry out, since it is almost impossible to know when, where and how severe the cold damage will be. Consequently, funding of such research might also be complicated. However, repeating pilot studies such as the above-mentioned will probably begin to show consistent trends over time. Therefore, they should be continued where and when cold damage occurs in the future.

298 CHAPTER 9 – PREVENTING COLD DAMAGE IN VINEYARDS