The use of orchard coverings, which has now become standard practice for most modern forms of cultivation, actually has a rather recent history. In the 1960s, when our company appeared on the market with the production of pre-stressed reinforced concrete posts, the idea of covering the orchard was certainly not among the farmers‘ priorities, and this was due essentially to three reasons: lack of culture in terms of system design (products of low efficacy and few suppliers with poor specialisation), more stable climatic conditions with less frequent adverse events, and the habit of following guidelines established in the past (’covering’ was not synonymous with good agronomic practice).
As it is clear today, a lot has changed in just over 60 years.
The widespread use of nets to cover orchards started in the 1980s. Initially, nets were mainly used to protect fruit from hailstorms, especially in the northern and central regions of Italy such as Veneto, Piedmont and Emilia-Romagna, known for their fruit production and more prone to frequent hailstorms due to their climatic conditions.
Hail protection was soon joined by new demands. Over time, in fact, the use of nets evolved and today they are used for various purposes, from protection from adverse weather conditions to controlling the ideal vegetative development of crops. But let us proceed in order.
The use of nets on orchards to protect crops from insects, for example, is a practice that has become popular in recent years. In particular, the adoption of anti-insect nets has increased since the early 2000s, with a significant expansion in the last ten years. This method was introduced mainly to protect crops from key insects such as Drosophila suzukii and the Asian stink bug, reducing the need for chemical treatments.
Before that, anti-rain nets and sheets had become the norm to protect crops such as cherries, peaches and small fruits. These crops are in fact particularly exposed to the negative effects of rain, such as cracking on the fruit and fungal diseases.
Shading nets, on the other hand, are mainly used to protect crops susceptible to excessive heat, such as kiwis, peaches, and many other fruit trees when grown in particularly sun-exposed areas. These crops can benefit from shading to reduce heat stress and improve crop quality.
However, experience over the years has recently led to the realisation that such covers, in addition to fulfilling their specific functions, can actually be multifunctional, i.e. capable of performing several tasks and offering different types of protection.
An article published in the quarterly Kiwi Informa at the end of 2023, for example, 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 use of these nets can also improve plant physiology, controlling photosynthesis and growth; by filtering sunlight, they can reduce the excess light of wavelengths less efficient for the photosynthetic process, helping plants to grow better.
Despite these facts, however, there is still a large segment of farmers who prefer not to cover their orchards, claiming that they do not need to.
But the reality is that covers not only offer comprehensive protection as outlined above, but also provide a better microclimate for crops in so many aspects, conferring multiple benefits on crops and allowing them to develop and grow in the most ideal way.
In this regard, research conducted by Middleton and McWaters from 1996 to 2000 is enlightening.
This research explored the effect of anti-hail nets (certainly the most widespread today) 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:
- 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.
- Humidity:
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- 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.
- Light:
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- 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
- Productivity and Fruit Quality:
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- Anti-hail nets helped to improve fruit quality by reducing physical damage caused by hail.
- 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, the environmental situation has definitely evolved and become more complicated, presenting itself 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: doing fruit growing without orchard cover systems nowadays seems unconceivable.
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, certainly shares this opinion and in recent interviews he contributed his own academic testimony.
‘We talk about multifunctionality – he explains – 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,’ – Neri continues – ‘these levels of shading allow for excellent photosynthesis and make the phenomena of photoinhibition and photooxidation, 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.
Experimental studies carried out with different coloured meshes on apple and peach orchards, with a percentage of selective shading of approximately 15-30%, have recorded already in the first year a better elongation of the shoots, a greater size of the leaf surface, a stimulation on flower induction, flower quality and fruit set, i.e. the transition from flower to young fruit.
According to other experimental trials conducted by the Department of Agri-Food Sciences and Technologies of the University of Bologna using white and red nets on apple trees, controlling the temperature under the cover would lead to a decrease in water stress, surface damage and heat sunburn, thus improving fruit quality.
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’.
Our direct experience spanning many years in this sector and countless completed installations also leads to the same conclusions.
Customers who have used the covers have always benefited from a homogeneous and satisfactory harvest in terms of both quality and quantity.
And because we 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.