Do hail nets improve the orchard microclimate?

Studies reveal that growing fruit under protective nets offers many benefits, including improved microclimate for better photosynthesis and reduced conditions that result in a vegetative response from plants.

Many growers around the world are now adopting these new orchard designs with protective nets and covers, or updating old ones. They believe these changes improve crop quality and yield.

In the 1960s, Valente entered the market at a time when fruit growers didn't cover their orchards.

Back then, protective systems were poorly designed, weather was predictable, and growers relied on advice from previous generations.

Fast forward to the 21st century and research is showing protective nets are the future.

The Kiwi Informa, published an article at the end of 2023, highlighting how hail nets offer multifunctional protection for crops against hail, thermal extremes, rain, insects, wind, and birds.

The article explains how nets can improve plant physiology; by controlling photosynthesis and growth and by by filtering sunlight, they can reduce excess light. This will in turn enhance the photosynthetic process to assist plants to grow better.

Research by Middleton and McWaters from 1996 to 2000 echoes this information.

This research explored the effect of hail nets on the microclimate and productivity of apple and pear orchards. These studies focused on analysing how nets influence temperature, humidity and light, and consequently, fruit growth and quality.

Growing fruit under nets provides a multitude of benefits and in many cases, a better microclimate for growing premium fruit. That’s why so many growers are jumping on board to design new and modern orchards under protective nets and covers or update their existing orchard design retrospectively.

But in the 1960s, when Valente first joined the market, the idea of covering an orchard was not a priority for fruit growers.

Back then, covers were not considered good practice but in the 1980s, protecting orchards started to trend in Europe and South America.

Initially, nets protected fruit from hail. But over time, the use of nets evolved to include protection from adverse weather, insects, sun, birds, bats and creating an ideal micro climate.

Rain covers are popular to protect cherries, peaches and small fruits from cracking and fungal diseases.

And increasingly, Valente customers report that such protective covers, can actually be multifunctional. In fact, nets are capable of performing several tasks and offering different types of protection.

An article published in the quarterly Kiwi Informa at the end of 2023, highlights how hail nets are becoming increasingly multifunctional, offering protection not only from hail but also from thermal extremes, rain, insects, wind and birds.

The nets, made of high-density polyethylene (HDPE), can of course have different meshes and textures depending on the specific function, but in any case the benefits brought to the crops on different sides are clear.

The article highlights that the use of these nets can also improve plant physiology, controlling photosynthesis and growth; by filtering sunlight, they can reduce excess light to enhance the photosynthetic process to assist plants to grow better.

This aspect of the research may be welcome news to some growers. Covers not only offer comprehensive protection as outlined above, but also provide a better microclimate for crops providing a myriad of benefits and ideal growing conditions.

Research by Middleton and McWaters from 1996 to 2000 echoes this information.

This research explored the effect of anti-hail nets on the microclimate and productivity of apple and pear orchards. These studies focused on analysing how nets influence various environmental parameters, such as temperature, humidity and light, and consequently, fruit growth and quality.

More specifically, the main parameters measured included air and soil temperature, relative humidity, light intensity and wind speed under the nets compared to uncovered areas.

The results, as anticipated, are enlightening.

They are presented in detail below:

1. Temperature:

   • Anti-hail nets helped to maintain a more stable temperature under the cover, reducing extreme fluctuations.

   • During summer months, the temperature under the nets was lower than in uncovered areas, helping to reduce thermal stress on the plants.

   • Conversely, during winter months (especially the colder ones), the temperature under the nets tended to be higher than in the open air, due in part to the protection from the wind.

2. Humidity:

   • The relative humidity under the nets was slightly higher than in the uncovered areas, promoting a more humid microclimate that was beneficial for these crops.

   • This increase in humidity helped reduce transpiration and water loss from the plants, improving water use efficiency and promoting root growth.

3. Light:

   • Anti-hail nets reduced direct light intensity, filtering sunlight and distributing it more evenly.

   • This has led to reduced sunburn on the fruit and better utilisation of photosynthetic light, which is essential for plant growth

4. Productivity and Fruit Quality:

   • Anti-hail nets helped to improve fruit quality by reducing physical damage caused by hail and wind.

   • In addition, fruit harvested under the nets showed greater uniformity in terms of size and ripeness.

   • The overall yield of crops under nets increased, producing higher quality fruit.

Middleton and McWaters thus concluded that anti-hail nets offer significant benefits for apple and pear orchards by improving the microclimate, creating a more favourable environment for plant growth, and increasing productivity and fruit quality.

These were the conclusions of a study conducted more than 20 years ago. Today, many growers report the climate is more complicated, with mild winters and late frosts, concentrated and more intense rainfall, frequent hail events, excessive wind and insolation and an increase in alien pathogens.

A synthesis of the current climate change and the phytopathological situation that leads to only one consideration: growing fruit without orchard cover systems is a heightened risk.

Davide Neri, Professor of General Arboriculture and Arboreal Cultivation and Director of the Department of Agricultural, Food and Environmental Sciences at the Marche Politecnica University, shares this opinion.

"We talk about multifunctionality – with nets you protect the crop from hail, but you also create 15-20% shading; with lighter nets the value decreases, while with darker nets it increases," – Prof Neri said

"These levels of shading allow for excellent photosynthesis and make the phenomena of photo-inhibition and photo-oxidation, which are particularly harmful at very high temperatures, less dangerous."

The phenomena of photoinhibition and photooxidation are known as ‘heat stress’. They bring both direct damage, such as sunburn, and indirect damage, such as excessive leaf transpiration, that is, the loss of water in the form of vapour, sending the plant into water deficit.

Among other crops, the sweet cherry is certainly one of the species that benefits most from the application of multifunctional covers, due to the numerous biotic and abiotic factors affecting its production, mainly due to fruit cracking and damage by Drosophila suzukii.

Stefano Lugli, professor of stratigraphic and sedimentological geology at the Department of Chemical and Geological Sciences at the University of Modena and Reggio Emilia, firmly believes this, as witnessed by his speech at McFruit in 2021: ‘Until thirty years ago, no one imagined the need to cover cherries. But the situation has evolved: coverings in the cherry tree have changed over the years along with the evolution of plant systems. From the anti-rain models introduced around thirty years ago in traditional cherry orchards to protect cherries from cracking, covers have now become multifunctional, capable of protecting intensive specialised crops from numerous biotic and abiotic adversities: insects such as drosophila, fly and stink bug, birds, adverse weather events such as hail, rain and wind. All at once, protecting high quality and high income production. An aspect of high quality that I want to emphasise. The protection of the nets makes it possible to drastically reduce phytosanitary interventions, thus obtaining a product with a very low residue’.

For Valente, the company’s experience spans decades in the industry and countless completed installations all over the world also leads to the same conclusions.

Customers who have used the covers have always benefited from a successful harvest in terms of both quality and quantity.

Valente never stop experimenting and learning, in June we completed the covering work on about 2 hectares of figs of a late variety, maintaining an open field alongside the structure.

Together with the client company’s technicians, we set up a project for continuous monitoring and comparison between the 2 fields, to understand how the plant reacts under the net, taking into account water requirements, vegetative development, production, uniformity of size and resistance to the first rains.

The data are still being collected, but already after two months, the plants under the cover showed clear differences from the uncovered ones in terms of vegetative vigour and speed of growth.

In summary, both the experimental and field evidence seem to indicate quite clearly that multifunctional covers do indeed offer numerous advantages that go beyond mere hail protection, acting directly on improving the microclimate within the plant and promoting healthier and more productive growth of tree crops.

There are obviously different types of solutions, from traditional anti-hail systems to multifunctional systems equipped with anti-insect nets, single-wire or single-block and with different levels of automation, but all of them make a positive contribution that, while representing a significant initial investment, brings long-term benefits in terms of improving the quality and quantity of production that largely justify the costs.

This article was supplied by Valente