Post harvest

26 October, 2006

There is a great sense of relief when the last grapes leave a vineyard – another season with all its excitements and anxieties is over, harvest is finished and the grower can relax a little.

Unfortunately, work in the vineyard doesn’t stop entirely. Grapevine root systems experience a flush of growth in autumn and favourable soil moisture levels will ensure this growth is maximised.

Mart Verstappen is Technical Manager for Corbans Viticulture, and he provides us with some interesting information concerning late season root growth in grapevines.

Late season root growth

Root growth occurs twice in the annual growing cycle of a grapevine. The first period occurs around flowering and the second growth cycle coincides with harvest in the autumn. There is an important correlation between root growth and the growth above the ground of shoots and leaves.

The growing period after harvest and until leaf fall is important for both root growth and nutrient uptake. The production of carbohydrates during this period is also important to fill grapevine starch reserves in shoots, cordon arms, cordons, trunk and roots. The longer the vine leaves can be kept in good condition for photosynthesis, the more carbohydrates will be produced for storage.

The availability of this stored energy is required for early growth in the following season, until sufficient leaf area has been established. Further to this, root growth during autumn demands carbohydrates. A more developed root system will lead to better uptake of water and nutrients.

Optimal use of the period after harvest for carbohydrate production and nutrient uptake will ensure grapevine productivity, particularly in the first years of vine establishment.

Young vine decline

Lack of carbohydrates has been implicated as a major factor in Young Vine Decline (YVD) and there is some suggestion that this lack is involved in other grapevine disorders. Most knowledge of these effects is still largely hypothetical, and they are currently being studied in detail.

Current research

The impact of factors such as climate and vineyard management reducing leaf carbohydrate production, leading to fewer reserves, is currently being studied. Any potential modifications to present vineyard practices must, first, be cost effective and, secondly, be practical. Slight adjustments to a harvester may decrease the level of leaf damage; continuation of an irrigation programme and continued disease control may pay off with healthier vines in the following season.

Post – harvest irrigation

During the post – harvest period, when temperatures are too low for shoot growth, a heavy irrigation is recommended to replenish some of the soil – water reservoir. Vines entering dormancy with a dry root zone tend to have poor bud break the following spring.

A reminder about soil testing

Last month we took an in-depth look at soil testing. Mart Verstappen reinforces the maxim:

Grape vines require an adequate supply of a wide variety of nutrients to grow well.

Soil testing measures the reservoirs of nutrients that are potentially available to plants, as well as the soil’s physical and chemical characteristics. Grapes are grown in a wide variety of soils, but it is mainly the sandy soils that show some nutritional problems due to the lack of ability to “hang on” to nutrients.

The most important aspect of soil testing is to ensure that samples ate taken from the depth the roots are located. This can vary due to soil structure, irrigation management and rootstock variety.

A comprehensive soil test is recommended and should always be analysed by a reputable agency that understands the physiology of the grape vine and its specific nutritional requirements. Of course, the grower’s grape quality requirements must also be considered.

Post – harvest applications of fertilisers by fertigation or broadcast application are becoming more common, especially where soils display low fertility and vines perform poorly – displaying low vigour and /or poor fruit set. Timing is very important here, as most benefits from fertiliser applications will be seen before complete leaf senescence (deterioration). Two to three weeks post – harvest is a general guideline. Fertigation may also be required if vines have carried a heavy crop or have been regularly frosted over several seasons.