New net solution to protect fruit from sunburn

Some growers in the Southern Cape are using nets that can easily be draped over tree rows to protect pome fruit against sunburn. Apart from their convenience and flexibility, the new nets cost a fraction of fixed net structures. Daan Brink of Two-a-Day and Ebbie Raubenheimer of Nulandis spoke to Glenneis Kriel about the technology, which was developed in Australia.

New net solution for sunburn
Drape Net is available in black or white, with black being the preferred option for green cultivars.
Photo: Supplied

Pome fruit producers in the Elgin, Grabouw, Vyeboom and Villiersdorp (EGVV) region lose thousands of rand annually to sunburn damage.

To reduce these losses, many farmers have started covering higher-value orchards with shade nets. However, the high cost of this is often not justified, especially for older orchards with only a few years of production left.

To help growers overcome this difficulty, crop protection company Nulandis imported Drape Net in September 2017. Unlike fixed nets, which require permanent structures, these patented nets are draped over trees like a blanket.

They are not left on the trees permanently, but used when necessary.

“We heard about Drape Net from members of [fruit and vegetable packing company]Two-a-Day, who saw the product in use during a trip to Australia almost five years ago,” says Ebbie Raubenheimer, regional manager of Nulandis.

Drape Net was developed 15 years ago by third-generation Australian fruit farmer Michael Cunial as a cost-effective solution to protect his orchards against hail. It has since also been found to reduce damage to fruit caused by sunburn, insects and birds.

In addition, it decreases cross-variety pollination between citrus trees, helping to increase the number of seedless fruit in seedless varieties and lower the pruning requirements of certain trees, depending on fruit variety and tree architecture.

Australian research also found savings of up to 30% in irrigation water demand during the months that trees were covered.

South African experience
Two-a-Day growers last year purchased 15ha worth of Drape Net to test the nets’ efficiency in apple and pear orchards. Raubenheimer foresees that this area will be expanded to about 86ha in the coming season across the EGVV region.

Daan Brink, a technical adviser at Two-a-Day, says the growers were happy with the results.

“When we do farm trials, I’m usually much more excited about the results than the farmers are, but this time it’s the other way round, which tells me the nets are making a huge difference.”
Orchards under the Drape Net trial produced more grade one fruit than controls, which

meant that less handling was required to sort fruit in the orchards. This not only saved time but resulted in fewer fruit injuries.

“Growers using the nets generally produced 20% to 30% more Class 1 apples in orchards protected by the nets than in control orchards. The number of fruit damaged due to sunburn was also 100% lower, at 9,3%, in comparison with the 19,8% of the control,” says Brink.

Some growers reported significantly less codling moth damage to their crop as a result of the physical barrier of the nets.

The nets also reduced evaporation, with less water needed for irrigation.

“According to international literature, water savings of up to 30% are possible when orchards are produced under nets. South African growers usually claim the same results, but Hortgro recently initiated trials to quantify savings scientifically.”

Raubenheimer warns, however, that water-saving presents its own risks.

“When using nets, growers have to alter their management practices to accommodate the new production conditions. In particular, they should prevent over-irrigation, as this can have the same impact as drought stress,” he says.

Cost comparison
“Since it doesn’t require expensive permanent structures, Drape Net works out at about a third of the cost of fixed nets,” says Brink.

The nets are available in 6m to 8m widths and come in a standard length of 100m.

“Farmers can sow nets together if they have orchard rows longer than 100m,” he adds.

Drape Net will pay for itself in one to five years, depending on the width; the variety, value and volume of the fruit produced; the number of trees per hectare; and the orchard topography.

Brink explains that it is more difficult to use the nets effectively in hilly and uneven orchards.

The average cost of Drape Net is between R100 000/ ha and R110 000/ ha for 8m-wide nets used in an orchard with a 4,5m row spacing. Brink calculates that the nets could pay for themselves within a year when used on high-yielding Granny Smith apple orchards and within three years when used on Packham’s Triumph pear trees.

With proper care, the nets should last 10 to 15 years.

Net colour and timing of placement

Drape Net is available in black or white, with black used for green varieties and white for coloured ones.

According to Brink, red and bicolour apple varieties require more light, as well as fluctuations in day and night temperatures for good colour development, making the white net a better option.

To protect fruit against sunburn, the nets in the EGVV region were placed on trees as soon as possible after hand thinning, towards the end of November.

“Timing is critical, as reduction in light during cell formation can result in premature weaning of young fruit, as well as bees not working as well as they should,” cautions Raubenheimer.

The ideal is to wait until the fruit is the size of a golf ball.

Raubenheimer also advises farmers to use a sun protection product such as Decco SunGard, which contains natural carnauba wax as its main ingredient, until the nets are placed over the trees. This should be sprayed onto the trees at least a day before a heatwave is expected.

Applying the nets
Two-a-Day last year imported a Drape Net Wizz applicator, which the growers shared, to place the nets in the orchards. Brink predicts that growers will use their own machines or rent them during the coming season.

Red End Engineering in the Southern Cape region has won the contract to manufacture the machines, which will be distributed by Nulandis.

The machine can apply netting on 5ha/day to 7ha/ day, depending on the efficiency of the labour team, tree size and terrain topography.

“Farmers prefer having their own machines, because they can cover the trees as soon as sunburn starts to become a threat,” says Brink.

The fruit should not be exposed to the sun during picking or transportation. Picking should be done under the nets, and growers who transport their fruit in open crates should cover the top layer.

According to Brink, picking under the net need not cause delays; it was found that on
most of the farms, the workers simply folded the bottom of the nets onto the top branches
as they picked the fruit.

“On some farms, the sides of the nets were placed on branches of trees in opposite rows, which  allowed workers to pick under much cooler conditions.”

Producers remove the nets mechanically as soon as possible after picking to allow the trees the full advantage of the sunshine required for the development of new fruit.

Raubenheimer says that over time these physiological processes become disturbed under fixed structures, requiring additional management interventions to prevent a drop in fruit production.

While wind will remain a concern for shade netting, Drape Net is more hardy than fixed structures as it provides less wind resistance.

“The nets ‘suck’ to the trees, so they don’t get blown away easily. Tears are easy to fix with
a sewing machine,” says Brink.

The nets should ideally be used only on trees older than five years, as the central leader
should be strong enough to keep the net upright. Drape Net Australia has overcome this disadvantage by patenting a system that uses bullhorns on trellis poles to accommodate younger trees.

Raubenheimer predicts that more farmers will use these nets as they seek ways to reduce the impact of climate change and improve their water-use efficiency.

Email Ebbie Raubenheimer at [email protected]