WINETECH Technical Yearbook 2019

well-developed and healthy root system will once again be more resistant. BALANCED GRAPEVINES Balance in a vineyard is difficult to quantify and therefore it is not discussed often. Balance between growth and bearing is essential, however, to ensure that a grapevine remains productive in the long term. Due to financial constraints, producers are often inclined to encourage earlier production in grapevines and in the course of time it has been noticed that crop control at an early stage is no longer entirely discerning (Photo 1). Such young vineyard blocks are impaired, due to inadequate lignification processes and accumulation of reserves, inter alia; years later this will often impact negatively on growth, production and eventually lifetime. The accompanying stress also creates perfect conditions for trunk pathogens to attack the young grapevines at an accelerated tempo; early in the lifetime of such grapevines the symptoms are already visible. On the other hand grapevines may also grow too profusely with subsequent loss of good aeration. Infertility then sets in and bearers will also begin to die back due to excessive shadowing. A balanced grapevine can only be obtained provided grapevine development was properly done. This includes upright trunks,

uniform length and thickness of arms, and good bearer spacing. A mistake that is still commonly made is to wind the arms too tightly around the cordon wire. This practice leads to a constricting effect when the arms become thicker and results in the dieback of bearers, and even entire arms (Photo 2). LEAFROLL VIRUS The detrimental effect of leafroll virus is lethal to the grapevine’s ability to yield good crops of premium quality. Due to leafroll infection countless premium blocks have been relegated to the rosé category and shortly afterwards uprooted (Photo 3). South Af r i ca has a ver y good p l ant improvement and certification scheme which aims to eliminate leafroll virus, inter alia, from plant material. Unfortunately leafroll symptoms do occur in a new vineyard from time to time (Photo 4). It has been proven that the removal of such individual grapevines is highly effective in the fight against leafroll, but on many farms this practice is still neglected. A further persistent dilemma is the reinfection via mealybug from nearby and adjacent leafroll infected blocks to newly established vineyards. Excellent research has been conducted and control strategies and protocols are available on the Winetech website. Again some farms obtain very good results (often the result

of careful monitoring), but isn’t it high time that mealybug control be undertaken in a regional context? The successful control of fruit fly on a regional basis is a good example of collaboration to get rid of a problem. TRUNK DISEASES Trunk diseases such as Eutypa ( tandpyn – Photo 5) and Petri disease ( Black goo ), commonly encountered in vineyards, disperse in arms and cordons and cause the dieback of wood, and eventually the grapevine. The spores of these fungi are present throughout the year (with a peak during the winter months) and penetrate wounds made by pruning. Factors such as pruning when it rains, large pruning wounds and stress can accelerate infections. Young grapevines that bear too many grapes often show symptoms in subsequent years. Once again there are very good guidelines, South Africa being at the forefront of research in this field. However, too few producers effectively apply pruning wound protection (with Trichoderma for example) and the sterilisation of equipment (see informat ion on www.winetech. co. za/ research-databasis ). Saturated conditions due to excessive irrigation frequency on soil with a good water retention ability result in low oxygen levels in the soil and persistent wet soil conditions

create the ideal environment for fungal pathogens that attack roots and trunks. It is necessary to maintain wet and dry cycles in the soil to sustain a healthy root system. CONCLUSION The establishment of a vineyard requires a lot of time and money; being a long-term asset it has to be protected. The ideal is to have a vineyard block that is able to produce profitable high quality crops annually, for many years. The journey begins with the establishment, after thorough planning, of a balanced grapevine (certified plant material only) with a healthy and well-distributed root system. The choice of training method and trellis system should complement the growth so as to obtain a well-aerated canopy with the least possible input. The grapevine should be protected against pests and diseases, and not be exposed to excessive stress. The knowledge and control measures to achieve the above are known and readily available, but are sufficient steps being taken to do so? There are many examples of producers and farms who already implement these practices, and have older blocks that perform extremely well. On the whole, however, we have to admit that much more can be done to ensure a long and productive lifetime for the most important asset on a grapevine farm.

– For more information, contact Hanno van Schalkwyk at hanno@vinpro.co.za.