Coloured netting is picky with light

Photo selective netting gives fruit and vegetable growers something to smile about, says a provincial specialist in fruit crops.

“As far as I’m concerned, it’s a win, win, win,” Forrest Scharf of Saskatchewan Agriculture told the Saskatchewan Fruit Growers Association’s annual conference in Saskatoon Jan. 15-16.

The special netting helps control leaf size, stem length, plant height, rate of flowering, maturation and fruit size.

Scharf said it’s particularly useful in areas that are hot, dry and windy, such as Saskatchewan.

Israel has been developing the technology for 18 years.

“They have looked at trying to conserve moisture and use technologies that support orchard production in areas typically too dry to grow anything,” he said.

The protective netting is made of tightly woven plastic threads and held in place above crops using stakes.

Each section of netting canopy is six by 10 metres and comes in red, blue, yellow, pearl and grey. The colours have different photo selective filtration capacities.

“It has been designed so that it affects the wavelengths that come through in specific ways,” said Scharf.

“So depending on the colour, it has an influence on the light that has passed through.”

Red and yellow are known to enhance healthy growth.

“If you have a plant that is challenged to grow vertically, for example, under this netting they’ve found it to enhance vigour,” said Scharf.

“In Saskatchewan, haskap is one we would like to see grown under this kind of netting to see if it really encourages that rapid growth because it appears to grow somewhat slowly, or a limited amount and then stops in each season.”

The colour blue modifies the whole spectrum of light and absorbs a number of lights. It blocks some ultraviolet wavelengths (UVA+B+G transmittance) and allows other colours to pass through.

“Blue mainly causes dwarfing, so for example, apple trees that are vigorous growers may benefit from being under blue,” he said.

Pearl coloured netting scatters light, which may benefit apples by minimizing pruning. It limits growth, produces more branching and develops better canopy structure.

“Pearl is also supposed to increase fruit size and the dry matter content,” he said.

Grey is similar to pearl and increases branching.

Scharf said plants respond differently depending on their genetics.

“I know they’re (Israel) using nets for peppers, and it’s highly successful,” he said.

“It improves colour and quality of the fruit. That photo selective part improves the quality of the light, and the process that leads to nice colour is enhanced.”

Some of the colours provide shading, such as blue at 30 percent.

“The sunlight comes through, hits the net and below that you’ll get 30 percent less solar radiation than above,” said Scharf.

“You have less evaporation out of the soil, so you’re conserving your water resources better. When it’s less drying on the soil, it also modifies the soil lightly. There are micro-organisms that are probably better able to thrive in that more moderate environment.”

Shading also scatters the light underneath, which reduces the plant’s vertical growth and encourages more branching.

“Despite getting 30 percent less solar radiation, (plants) photosynthesize better and absorb carbon better and then that vigor is stronger with less light. The stomata on the leaves are more open under some of these colours. That means they are better able to incorporate CO2 so they can grow better.”

Photo selective netting also repulses certain insect species and can greatly reduce some populations.

“Red not so much, but yellow does due to the reflective light that comes off of it,” Scharf said.

“That 30 percent that is shaded out reflects and insects don’t like that reflected light so they avoid that area.”

The nets also achieve micro-climate control by moderating day-night temperature changes, diffusing strong winds and protecting against hail.

“It has very good elastic qualities. Even with heavy hail, it absorbs that and protects your plants from damage,” said Scharf.

“In Saskatchewan, normal protocol is you leave one apple every eight inches. People are leaving two because if you get hail, one protected the other and you still have a crop.”

Studies have also found disease control benefits.

“Part of this is due to the fact that some diseases are transmitted via rain splashing. The photo selective netting allows moisture to come through, but it doesn’t hit in the same way that it would if it was unprotected,” he said.

“The wind is also greatly reduced in the interior of the canopy. That means that there’s less rain splattering and moving disease spores from one plant to another. Yellow and pearl are also supposed to provide some disease resistance to fungal pathogens, like powdery mildew, for example.”

Scharf said the netting could also reduce damage from birds, particularly in saskatoon berries and haskap.

The product is not available in Canada, but Scharf sees advantages for Saskatchewan’s fruit and vegetable market.


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