WINETECH Technical Yearbook 2019

PHOTO 1. This young grapevine bears far too many grapes which will undoubtedly impact negatively on growth and yield in future.

PHOTO 2. The cordon wire, which cuts into the arm in this instance, has a restricting effect.

PHOTO 3. This Shiraz vineyard was known for premium quality, but the rapid distribution of leafroll by mealybug impacted so negatively on the bearing and quality that the block had to be uprooted within five years.

PHOTO 4. This young Cabernet Sauvignon grapevine is clearly infected with leafroll virus and has to be removed.

PHOTO 5. Typical symptoms of eutypa that may be dispersed via pruning shears. The protection of pruning wounds is of the utmost importance.

HANNO VAN SCHALKWYK: Vinpro, Paarl KEYWORDS: Grapevine lifetime, grapevine roots, balanced grapevines, leafroll virus, trunk diseases. AUGUST 2019 GRAPEVINE LIFETIME – PROTECTION OF A VALUABLE ASSET

prerequisite for survival. According to Archer and Saayman (2018) a buffered root system is the most important way to counter climate change which is accompanied by warmer and drier conditions. Grapevine roots should be properly managed to comply with the necessary nutrient, water and oxygen requirements. A healthy soil microbial environment is also essential and here the contribution of cover crops may be significant. Routine soil analyses are extremely important to accurately determine these requirements. Fertilisation often results in acidification of soil which also restricts roots. It may furthermore be necessary to counteract compaction of the soil periodically, but this should only be considered based on appropriate prior examinations. Cautionary measures are to be taken against soil pests and diseases, and a

GRAPEVINE ROOTS The first essential step for a longer grapevine lifetime is a well-distributed and buffered grapevine root system. The establishment process, from soil charting, planning and plant material selection to soil preparation and the actual planting of the grapevine should focus on this objective. All physical and chemical limitations should be removed in order to optimise root distribution and functioning. The management of brackish conditions, and specifically drainage of salts from the soil, will also extend a grapevine’s lifetime. What happens below the soil impacts directly on canopy growth and plant physiology, and therefore also the lifetime of the grapevine. Older grapevines are often encountered in areas where the formation of a deep root system (on soil types allowing for it) is a

The establishment of a vineyard block is a long-term investment which may amount to as much as R300 000 per hectare in the case of wine grapes. A longer productive lifetime may yield bigger profits in the course of time. Furthermore, it is known that grapevines in their prime are mostly

also better balanced, and may therefore offer superior wine quality. Relatively few grapevines were planted over the past decade and consequently vineyards have to become older to sustain production yields. Are we doing enough to protect this long- term asset?