Under the microscope, new-generation nets show their secret

Braving the thunder, Hans Meiring has sat under nets during hailstorms to see its reaction to the pelting stones and its accumulating weight: he consults in the fruit and vegetable industries in the central Highveld, a high-altitude area at high risk of hail, battering the hard structures. Many years ago, agricultural engineering students from the University of Pretoria built a hail simulator in order to test the various nets available on the market because to the naked eye, all nets will appear hail-proof.

Thirty years have taught Meiring Strukture a few lessons: there are specific load-bearing tricks to hail-proof a net structure. The nets have to be woven, cables must be of the right thickness, and there can be no compromise on anchors, he says. Also, the yarn cannot be too thin.

"Woven net is dimensionally stable, and if it is teased correctly, the hail doesn't accumulate in pockets. Rather, the structure allows the hailstones to roll off and release the load from the structure," he explains.

Over the years it became clear that nets weren't only to protect against hail, but for many other things besides and today, many farmers erect nets to create favourable microclimates that are less costly and more labour-friendly than plastic tunnels.

© Meiring Strukture
Nanotechnological advancements make the difference
The range of nets recommended by Meiring include nets woven in South Africa by Standerton Mills, nets especially woven according to Meiring's specifications in China and finally those that make use of Spanish net technology.

The critical thing of which many farmers are not aware is additives to the yarn, and additives make a gigantic difference to the effectiveness and lifetime of the net, he says. Sulfur and copper sprays can influence the normal additives used to protect high-density polyethylene (HDPE) against ultraviolet radiation, so specific additives are used for extra protection against the South African sun. Sunburn is a major problem experienced by farmers in the Western Cape, and enquiries are streaming in from farmers who are looking to replace their current inadequate nets, sometimes expensively imported nets that cannot cope with local conditions.

Ultraviolet radiation breaks down the net's polyethylene fibers, but the Spanish technology employs nanoparticles of aluminium to absorb and refract much of the infrared radiation back into the atmosphere. "We realized that when you have the right additive in the net yarn, you can effectively manage sunburn without a negative impact. In the citrus industry, farmers have found that even under white nets, they're still getting sunburn. Since we started using the right additives to manage infrared rays, the fruit is cooler under the net than outside, and we've been seeing dramatically greater sun protection."

© Meiring Strukture
Sweet pepper farmers in Limpopo find their nets far preferable to the traditional plastic tunnels during the hot summer months.

Realizing a thirty percent reduction in irrigation needs in a covered orchard is no problem, and when less irrigation is required, it also translates into costs on electricity too.

"For me, the very worst thing is when the most attractive fruit gets damaged while it's hailing," he says. "You can't be spending thousands of Rands and then you still have fruit with marks that have to be downgraded from class one, or after a heavy hailstorm you're sitting with extensive damage. So, my advice to farmers is: let's do it a bit differently, a bit better. It's worth it for a long-term investment as this is."

© Meiring Strukture Hard lessons have been learned to perfect net structures

They also designed a clip so that nets can quickly be opened and bunched up ahead of a snow forecast (no nets can really protect against snow, he says).

The impact of nets on bees' pollination activities cannot be overestimated, he notes, and because bees navigate by polarized light, they can be completely thrown off kilter by the way light filters through some nets. Therefore, stonefruit and topfruit farmers will keep the orchards open until pollination has been completed and then cover up the orchards for the rest of the season.