It is well known that in order to cultivate any type of tree crop it is essential to operate in a protected environment and therefore, in the case of fruit trees, a support system including a good cover is mandatory.
We also know that depending on the desired result, covers are made of nets or coverings of different colours, fabricated with different techniques and with different levels of permeability.
One of the most important issues is undoubtedly the anti-rain system; the phenomenon of the rain, usually clearly positive, in some crops can cause irreparable damage. I am obviously referring to the problem of cherry cracking and to the bacterial canker of kiwifruit, also known as PSA.
Both crops have this common “enemy” of the rain, but the approaches to actively protect them with protective covers are different.
Let’s take a closer look at this.
In the case of the cherry trees, protection from water is needed during the period of veraison, in fact, when cherries are exposed to rain, they swell and split, becoming no longer usable.
The protection is therefore limited to a relatively short period (30-40 days max), and after harvesting the cover can be closed.
In this case the plant can be affected by the bacterium present in the air Pseudomonas syringae pv. Actinidiae, which can infect the plant up to its core thanks to the “entry doors” that are typically the junction of leaves and fruits, flowers and bark lesions caused by hailstones.
In all these situations, the main vehicle used by the bacterium to reach the heart of the plant is water.
Since these situations occur at different times during the annual life cycle of the plant, it is essential that the rain cover is always open to ensure adequate protection.
Analysing the two different issues described, we can see that the two crops need protection for different periods of time, so we have to design systems suitable to meet these different needs.
In the first case, protection is necessary for a short period of time, from April/May to June/July, and it is essential to have a rapid system of anchoring and releasing the waterproof sheet/net for a fast and effective management of the cover.
In the second case, however, it must be considered that the cover remains open throughout the year and therefore it is necessary to think about the loads that will stress the entire structure; wind, hail and rain are the main events to be prevented, but the customer must also be made aware of a possible “snow” risk that unfortunately is not considered in the design of the systems, because it would dramatically increase the costs of purchase and installation.
After these considerations, it is time to focus on the materials used for the production of the various covering systems.
Recently there has been particular interest in this field, due to the anti-rain nets that aim to replace the traditional waterproof plastic films used to protect the production of cherries and kiwis.
These materials are manufactured from woven monofilament in very tight meshes, with the dual ambition of not allowing water to pass through and at the same time offering little resistance to wind, so as not to stress the structure too much and to allow a better airflow to the plant.
Many customers ask for information about this, as they see in this new type of material a different and more effective solution compared to the classic plastic film cover, especially in terms of simplification of the system due to lower mechanical resistance requirements.
From the first experiences on the field, however, it is clear that these anti-rain nets do not guarantee impermeability but let water enter under the form of micro-drops, similar to fog. This phenomenon, which seems to be tolerated by cherry trees, is much less tolerated by kiwifruit (the red variety in particular), which can still be infected by PSA bacteria.
It is clear that this raises a big question about the opportunity to use this material for the protection of valuable kiwi plants.
Proceeding with the analysis, we must then consider the aforementioned assumed benefit of net permeability in relation to the wind factor.
Again, field-proven evidence shows that the benefit is more ideal than real.
On the one hand, the very narrow meshes of the net (we are generally speaking of a 10% permeability), do not prevent the passage of micro-drops, on the other hand they make it basically wind-proof, excluding the possibility of letting it pass and therefore raising another big issue concerning the stresses that the structure will undergo.
Therefore, the right questions are:
- What stresses does our system have to cope with?
- What dimensions does it need in order to work effectively and safely?
- Should we take into account the typical parameters of anti-hail covers (greater distance between posts, smaller post section, no internal anchorage, no blocking of the hoods to the posts), or the more strict parameters of anti-rain systems (smaller distance between posts, larger post section, mandatory internal anchorage, blocking of the hoods to the posts, greater distance of the anchorages from the perimeter posts, etc.)?
- How do I secure the anti-rain net to the system?
Questions that remain unanswered because no one tells us how this material MUST be used.
While still maintaining the interest in front of a new product that has important innovative features, we have to bear in mind to always take into account all the variables that influence the correct choice of a covering system.
Costs are also an important variable, and if we invest more money to build a system with an innovative cover, these higher costs must lead to a real and effective benefit.
On the other hand, simplifying the structure to lower costs on the grounds that the anti-rain net is more durable and just as effective as traditional covers would be a shameless and intentional lie.
Choices must be made together with qualified professionals, with the help of serious companies that guide you in the right evaluation of an expensive investment that must satisfy you in terms of performance and durability.
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