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Growth Arrestment Phenomenon And Dying Back Disease In Vineyards In The Below Orange River Area

JH van der Westhuizen ¹, D Saayman ², F Knight ³, PA Myburgh ⁴, CG Volschenk ⁴, D Malan ⁵, J Burnett ⁶ & J Steenkamp ⁴
¹. VinPro (SA), Consultation Service, P O Box 50, Stellenbosch, 7600
². DISTELL, P O Box 184, Stellenbosch, 7600
³. Department of Economic Affairs, Agriculture and Tourism, Private Bag X1, Elsenburg, 7607
⁴. ARC Infruitec-Nietvoorbij, Private Bag X 5026, Stellenbosch, 7599
⁵. VinPro (SA), Consultation Service, P O Box 575, Keimoes, 8860
⁶. Blouputs Boerderye, P O Box 359, Kakamas, 8870
Photo right: Dricus van der Westhuizen
(The following is a synopsis of lectures on this specific topic presented by the above-mentioned persons at an information day in Upington organised by Dried Fruit Technical Services, Deciduous Fruit Producers Trust and Winetech. A complete set of lectures is available from ARC Infruitec-Nietvoorbij at R50 per volume.)
INTRODUCTION
The vine (Vitis vinifera) prefers long, warm and relatively dry summers, cold and wet winters, frost-free springs and low to moderately fertile soils. In areas that deviate from the norm, physiological abnormalities are therefore to be expected periodically (±3 out of every 10 years). For this reason the Growth Arrestment Phenomenon (GAP) has been known in the Orange River area since the beginning of vineyard establishment on the low-lying silty soils. It was first reported in 1955 and has occurred sporadically since then. Comprehensive investigations in the sixties showed that up to 80% of crop losses may occur as a result of GAP.
With GAP being linked to climate, its occurrence is sporadic and since the physiological status of the plant is involved, all vines are not necessarily affected to the same extent. This year (2000/2001) saw the most serious occurrence of dying back of young vines and GAP in the history of the Below Orange River.

Growth arrestment phenomenon in young vines
Similar phenomena can be observed in other parts of the world. In the United States of America (California) it is known as "Spring fever" and "Red cane", while in Australia it is called "Restricted Spring Growth".
SYMPTOMS
There is a strong link between GAP and the dying back of young vines, although symptoms of the two phenomena may differ. GAP is not considered a disease, since no pathogen has been linked to it. It can therefore be stated with some certainty that it is a physiological phenomenon related to the physiological condition of the vine, which in turn is influenced by the climate, soil and management practices. Symptoms may include some or combinations of the following:-

Dying back of young vines occurs mostly in the first three to four years after planting.
Dying back of young vines occurs mostly late in winter between pruning (July) and budding (September). It occurs in a downward direction from the pruning wounds, sometimes as far down as the surface of the soil. At the time of budding new, strong shoots emerge below the dead wood.
Sometimes the stems of vines may burst open and die.
Long flattened internodiums.
Canes bud unevenly and have many dead and/or unbudded eyes. The bare cane sections appear white ("White shoot phenomenon").
In spring vineyards bud poorly or not at all, or will not grow any further after initial budding. Leaves appear blueish grey during the inert period.
Eyes that do bud have shortish internodiums and dark green shoots without active growth points.
Shiny spots occur on the leaves.
Curled leaves, yellowing of leaf edges and/or upward curling of edges.
Leaves are sometimes misshapen or rosette-like in form. Flower bunches are usually dark brown, necrotic or ringed, then dry out and fall off ("black bunch symptom").
Sometimes some of the bunches may recover partially, while the remaining bunches fall off.
Under certain conditions affected vines may grow even more vigorously than normal vines after the growth arrestment period, but will not bear any fruit.
FACTORS PLAYING A ROLE IN THE OCCURRENCE OF GAP
Based on research, investigations and numerous observations over the years, the following factors, or combinations thereof, have been found to play a role in the occurrence of GAP.
Winter rest physiology
To understand GAP, it is important to understand the growth and developmental cycle of a vine under normal conditions during dormancy (rest period). Dormancy begins with leaf ageing late in summer and autumn. In winter the vine rests, whereafter in the springtime, it buds, grows and bears fruit. For normal winter rest and budding in spring the accumulation of sufficient nitrogen (N) and carbohydrate reserves in the shoots, stem and roots, especially during the post-harvest period, is a prerequisite.
Environmental temperatures influence not only the formation, but also the movement of biochemical substances in the vine. At high temperatures the movement of nutrients is mostly upward towards the growth points, while at low temperatures it is mostly downwards towards the stems and roots. During the post-harvest period, when the vine begins to accumulate reserves, this concept plays a very important role. High night temperatures during the post-harvest period accelerates respiration and consequently the carbohydrate reserves are also reduced. The second post-harvest root growth peak also consumes reserves, but it is still uncertain to what extent this influences possible GAP vines.
During the rest phase important carbohydrate transformations occur in the wood. With the inception of the winter chill, the starch is transformed to sugars. At the end of winter when it begins to get warmer, the opposite happens. The sugar concentration in the tissue is therefore high during the coldest part of the year so as to protect cells against damage by freezing. In normal vines the carbohydrate transformation from starch to sugar occurs much earlier (June/July) compared to GAP vines where this occurs only during and/or after budding. In contrast with most other plants, the phloem of Vitis spp. remains functional for more than one season. If damaged in one way or another, for example by cold, the transport of nutrients and biochemical compounds in the vine is also harmed in the short term. Resistance to cold in canes is therefore directly dependent on the ripeness of the canes, in other words on the status of the reserves and on the carbohydrate transformation in vines.
Normal wood ripening begins in December/January, in other words long before winter rest starts, when the shoots begin to ripen and change colour from their base. In the Below Orange River area, active growth still occurs in this period due to high temperatures and rain. The active shoot growth is in direct competition with the accumulation of reserves in shoots, stems and roots.
The post-harvest synthesised starch is the first source of energy to be used by budding and new shoot growth in the spring. The first 4 to 6 weeks after budding, the vine only grows on reserves, until sufficient new leaves and roots have been formed to provide in the nutritional requirements of the vine. This usually occurs around flowering. During budding until approximately 4 weeks later, a vine uses ñ 50 % of its starch reserves. Under normal conditions the reserves stored in winter shoots are sufficient to provide in the vine's requirements with regard to budding, shoot and root growth for ñ 10 weeks.
Sudden cold and/or frost along the Orange River in April to May when the vines still have leaves, forces the vine into a sudden winter rest, with the result that a natural process of reserve accumulation does not take place, also damaging the unripe phloem in the process. It is thus clear that a detrimental interchange between active parts above the surface and passive root growth in spring results in a physiological abnormality known as GAP.
Climate
In Figure 1 the monthly average minimum air temperatures of Upington are compared to that of Stellenbosch and Vredendal, and also to overseas areas where similar phenomena occur (California and Australia). The big differences in temperature in Upington are clearly noticeable, as well as the tempo at which temperature decreases between summer and winter. Compared to other regions, the average decrease in temperature in Upington from March to May is at least twice as fast. Vineyards on the fertile silty soils along the Orange River are still growing actively in autumn, only to be suddenly de-leafed by the frost in the course of their active growth phase, thus causing serious damage to the accumulation of carbohydrate reserves.
The variation in climatic conditions, but especially the inception date of frost from year to year, is the most important single factor to determine whether or not GAP will occur in a specific year. High air temperatures in February, March and April will stimulate post-harvest shoot growth, especially if this goes hand in hand with sufficient water supply to the plant. Rain in this period is therefore an additional contributing factor.
Soil
Due to the low night temperatures, soil temperatures of finely textured, silty soils remain low for long periods in the spring (August/September), which may also delay root activity. It is a fact that the colder the immediate environment and soil, the bigger the danger of GAP. Producers from about Keimoes, higher up along the river at Grootdrink, Groblershoop and Douglas, experience much bigger problems on the low-lying so-called "inner soils" (that used to form part of the traditional irrigation scheme), than for example table grape producers on the "outer soils" from Kakamas and Augrabies.
It is a known fact that bare, compressed soil surface is a prerequisite for the limitation of cold or frost damage.
Plant nutrition
No shortage of nutritional elements is associated with GAP. The apparent K shortage associated with GAP is not the cause, but the result of excessive N-uptake from the silty soils. During the post-harvest period, nitrogen also stimulates the formation of new cells in the parts above the surface, instead of promoting reserve deposit. The problem is aggravated by accelerated uptake and mobilisation of nitrogen, as well as the delayed mobilisation of carbohydrate reserves, inter alia from the roots for new spring growth.
Irrigation
It is important for vineyard soils never to be too dry in winter or too wet in autumn. If soil is allowed to dry out too much in winter, the roots will be damaged or destroyed. This also limits the uptake of nutrients, mobilisation thereof and other biochemical compounds formed in the roots. During the period from harvest to budding, the soil in the root zone should be allowed to dry out to between -60 and -70 kPa. Monitoring of soil moisture in this period is therefore of the utmost importance.
Rootstocks
So far the rootstock 143B is known to control GAP to a certain extent, especially in the case of Sultanas. The characteristics that make 143B eminently suitable (especially from Riparia parent), are the induction of moderate growth, early dropping of leaves, early wood ripening and early ripening of grapes, while also offering proper resistance to cold.
Diseases
Diseases such as downy mildew and/or oidium which cause early de-leafing and promote active post-harvest regrowth, dramatically reduce the accumulation of reserves in the vine.
RECOMMENDATIONS
Producers in the Below Orange River area and the respective industries will have to come to terms with this kind of natural phenomenon which occurs periodically and may result in large losses. However, the following measures are proposed to reduce the risk and thus manage the problem better:

Limit the planting of vineyards in low-lying, cold N-rich silty soil.
Preferably use 143B rootstock on the low-lying silty soils.
Beware of overproduction which further exhausts reserves. Do not force young vines to bear too early. High yields per se do not control growth without damaging the vines permanently.
Ensure that soil is not too wet in autumn, nor too dry in winter.
Prevent excessive late summer (post-harvest) growth timeously. This can be done using the following management practices:
Prevent high N applications on silty soil (no N fertilising!)
Sow competing cover crops (permanent or Wimmera / Rye grass) on fertile "inner" soils.
Practice effective disease control against, for example, fungal diseases.
Apply strict topping actions into the ripe (brown) wood late in the season.
Apply frost control measures post-harvest and in spring by:
Taking precautions for cold air to drain away.
Flattening upright cover crops.
Keeping soil clean as well as wet or moist.
Installing alarm systems followed by overhead sprinkling, fans, smoke, etc.
Using protective "socks" over graft joints and stems of young vines.

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