Fruit production part 10: Grape adventures

Grape farming in Zambia is not a new thing. In fact, it has been more than a decade since growers have started to produce grapes for the table grape industry. Some farmers have even ventured into wine-making or exporting grapes for juice making.

A favourite for many, this fruit’s juicy flesh quenches thirst and fills the tummy. Whether it is a snack, an ingredient in salad and desserts, or a refreshing drink, grapes and grape juice are enjoyed by many across the world. It offers many antioxidant properties and boosts immunity as well as keeping you hydrated. Grapes contain copper, vitamin B, C and K, as well as potassium, sodium, zinc, calcium, iron, and phosphorus.

The plump fruit belongs to the category of berries that grow on a deciduous woody vine from the Vitaceae family. A wide variety of types are available: more than just having the green, red, or black colours, there are also an array of varieties that impact the taste, size, and shape of the fruits. What is more important in these varieties are to know which grapes to use for table grape production, raisins, juice, or wine. Some are also hardier than others, withstanding high temperatures more than others.

Some of the varieties to consider when planting table grapes are:

Thompson Seedless: A popular green grape variety known for its sweet and seedless berries. It is widely used as a table grape and for making raisins.

Red Globe: One of the most popular red table grape varieties, known for its large size, crisp texture, and sweet taste.

Crimson Seedless: Red, seedless grapes with a sweet flavour. They are popular for fresh consumption and are resistant to cracking.

Flame Seedless: Red seedless grapes with a sweet and slightly tart flavour. They have an excellent shelf life and are popular in the fresh market.

If you aim to start grape production for wine or raisin making, you will need to consider other varieties. Investigating local varieties to plant is also an option.

The soil needs to have good drainage and be loose enough to ensure good root development. (Source: Juan Pablo Serrano Arenas on Pexels)

Soil and climatic requirements

To grow grapes, you need a climate that has moderate heat. Temperatures needs to range between 25 to 32 ° Celsius if the plants are going to thrive. They are, however, sensitive to frost. It is quite economical with water, and it is most successful when the annual rainfall varies from 635 to 890 mm. The plant grows best at elevations ranging from 200 to 250 meters. Grapes need plenty of sunlight, at least 7 to 8 hours of direct sunlight daily.

Winters need to be long and cold enough to ensure dormancy in the resting season.

The optimal soil condition has a soil acidity ranging from 6 to 6,5 pH. Grapes can be cultivated in a variety of soils including sandy loams, sandy clay loams, red sandy soils, shallow to medium black soils and red loams.

The soil must just be well-balanced between having good drainage and having good water-holding capacity to keep the plants hydrated. It is also important that the soil is without any hardpan layers.

To protect your crop from birds, you may want to consider agricultural netting. (source: Mathias Reding on Pexels)

Soil preparation

When preparing the soil, two things need to be considered: soil health and structure. You may loosen the soil with a pickaxe or with the use of a larger implement like a ripper. This ensures that the roots can spread wide and deep.

Grapes can tolerate less fertile soils and a variety of pH levels, but you may adjust these according to the results of a soil test.

Incorporating well-fermented compost or manure can enhance soil fertility and structure.

Planting

It takes at least a year for a vineyard to be established. One-year old seedlings will take an additional three years before it delivers a yield. You can plant the grape seedlings three to four weeks before spring starts.

Plant seedlings with precision, ensuring proper spacing, adequate depth, and firm soil contact around the roots. It is important to note that since grapes grow vines, you will need a trellis system to hold up the vines. Planting wooden poles to keep the trellis up means that you need to plan the row spacing before transferring the seedlings to the soil.

Plant the seedlings 0,24 to 0,28 metres apart in rows. Rows can be 0,3 metres apart. Ensure that you plant them at the same depth as the nursery pots. Prune the tops to encourage growth.

Fertiliser

For grapes, the soil does not need to be too fertile. In fact, if it is too fertile, the plant places use more energy to grow foliage than fruits. This is obviously not ideal. But the opposite can also be detrimental as it will cost you afortune in ensuring your crop gets the nutrients it needs. That is why frequent (about once every three years) soil testing is vital. Ask your agronomist about soil tests and how to use their results.

Based on the soil test results, apply a balanced fertiliser (such as 10-10-10 N:P:K) during the growing season. Grapes need these macronutrients as well as micronutrients, such as copper, iron, and zinc.

If the vine growth is less than one metre in a year, additional nitrogen must be applied. A nitrogen deficiency will also show poor colour of the leaves (light green or yellowish). On the other hand, high nitrogen fertilisation promotes heavy vine production at the expense of fruit production. Applying phosphate is beneficial.

Ideally, fertiliser is applied two to four times a year, but you may also ask you agronomist for more information about this.

Irrigation

It is vital to have an irrigation system to supplement rainfall if consistent success in grape production is to be achieved. However, there are a few concerns with regard to minerals in water sources. Chlorides or boron in irrigation water may accumulate in grape leaves, and water that is high in sodium may reduce the water permeability of soil. This, in turn, reduces the yield.

Grapes’ watering needs change across the season according to the day length and growth stage. The younger plants need at least 20 litres of water per vine per week, dividing it into two to three applications. Mature vines require 100 to 300 litres of water per vine per week, divided into one to three applications. Soil moisture needs to be maintained in the critical growth stages of budburst, flowering period, fruit setting and berry ripening as water stress can severely affect the yield. Thankfully, farmers do not need to guess what the soil moisture is, they can use tensiometers to monitor soil moisture effectively.

There must be very little rain during the ripening period; too much rain can cause various grape diseases and the plump grapes may burst.

Most farmers find that it is best to use drip irrigation to manage water needs. Drip irrigation systems also has the added benefits of conserving water, minimising evaporation, and delivering precise amounts of moisture to the grapevines’ root zones.

Grapes require a trellis structure to help their vines grow over. (Source: Lukas on Pexels)

Pest and disease management

Most commonly, grapes are threatened by grape berry moth, whose larvae feed on grapes, and by birds. Keep an eye out for aphids, grape leafhoppers, and spider mites. Use neem oil or insecticidal soap for organic pest control.

You may also find out more about the insecticide that is best for your specific problem. To keep birds away, you may consider using netting.

Among the most common diseases are downy mildew, powdery mildew, and black rot.

Powdery mildew

All parts of the grape plant, namely leaves, blossoms, or fruit, can be affected by this disease. It leaves blemishes on the affected berries and results in deformation.

Symptoms of the disease are a powdery (ash-like) white substance on the leaves. To control this, apply a fungicide at bud break in vineyards where symptoms appeared the year before and follow the label instructions carefully.

Downy mildew

This disease is caused by light and continuous rain or heavy dew associated with high humidity. Low temperature also favours the development of the disease. The leaves, flowers, and fruits are attacked by the disease.

Signs that your vines are infected are light-yellow spots on the upper surface of the mature leaves corresponding with white spots on the lower side. The affected leaves turn brown and cannot support bunch development owing to reduced photosynthetic activity. To control the disease, start by pruning the affected sections. Destroy the removed parts immediately.

Bacterial leaf spot

The disease is more prevalent from February to March and in June and August when the temperature is 25 to 30 °C and humidity is 80% to 90%. Symptoms of infection first appear on young growing shoots, but it also affects leaves and berries. The leaves show minute water-soaked spots on the lower surface of the leaves along the main and lateral veins. The spots coalesce later to form larger patches and brown-black lesions on the berries, which become small and shrivelled. To control this disease, the easiest way is to collect and burn the infected plant parts as this will help minimise the spread of the disease.

Black rot

Black rot most often occurs in areas with a warm and moist climate that has extended periods of rain and cloudy weather. The disease attacks the leaves, stems, flowers, and berries. The new growth is attacked during the growing season.

The main symptoms are usually reddish-brown spots on the leaves and a black scab on the berries. The best control method is to collect and destroy any mummified berries left on the vines.