Cultivated plants can suffer the attacks of some pathologies, those who cultivate the vegetable garden will surely be confronted with the sickness of their crops. The causes of these diseases can be different: bacteria, fungi or viruses.
Among the diseases that affect plants those of viral origin much more difficult to control compared to fungal or bacterial ones, because there are no products allowed in organic farming to combat them. Consequently it is very important to implement all preventive strategies which allow us to minimize the arrival of viruses and the damage they can cause on vegetables.
In this article we will deepen the description of viruses, we will learn to recognize the typical symptoms on plants, and above all we will list the most effective preventive measures to avoid the onset of viroses. Finally, we list some examples of the most common viral diseases that can occur in the garden.
What are Viruses
Viruses are beings of extremely small size and in order to survive they are obliged to infect other living beings, including plant cells.
They depend in everything on the host cell, and once they enter this, they start their reproduction at the expense of the cell's energy. The new individuals can migrate to neighboring cells and start a new replicative cycle. In this way we have thethe spread of viruses throughout the plant, with an acceleration when the virus infects the lymphatic vessels. Then comes the time when the virus searches for a new host and consequently new plants become infected.
There are many different viruses, even the human body can be infected with these pathogens. For the avoidance of doubt, it should be noted that the viruses responsible for plant diseases do not infect humans. So we don't have to worry about being infected with viral garden diseases.
Symptoms of virosis and damage to plants
The symptoms of virosis are quite different, as the viruses that affect different plants can be many. The most typical signs are:
- yellowish leaves;
- foliar curling;
- dwarfism of the plant;
- deformations of various organs.
Preventing viral diseases
There are no remedies able to cure plants affected by virosis, even chemical treatments are not effective in most cases. So you need to know that an infected plant cannot be cured. For this reason, the only possibility to keep the garden healthy is to prevent this kind of pathology as much as possible. We can do it with proper cultivation, so let's find out what are the attentions to have for a really effective prevention.
Beware of carriers
Most viroses are transmitted by phytophagous insects, especially from those with pungent sucking mouthparts like aphids, which feed on vegetable juices. The fight against aphids, which in themselves cause direct damage to vegetables, fruit plants and ornamental species, is therefore very important. Fortunately, there are many methods with low environmental impact to keep them in check, such as spraying extracts of nettle, garlic and hot pepper, or Marseille soap for a safer defense.
The role of predatory insects, such as ladybugs, hoverflies and chrysopes, is to be taken into great consideration and is favored by avoiding treating the environment with non-selective insecticides.
Other insects potentially vectors of viral diseases are thrips and aleirodidae like Bemisia tabaci, the small whitefly found mainly in greenhouse crops. In these environments we can counteract it by means of chromotropic traps, otherwise it is useful to treat the affected plants with Azadirachtin (neem oil).
Viruses can be transmitted from one plant to another very easily through contaminated tools, such as shears and knives.
It is therefore good practice to disinfect them thoroughly every time they are used to eliminate parts or uproot diseased plants. When in doubt whether or not it is a viral disease, it is always good to be cautious and disinfect the blades anyway.
Pull out affected plants immediately
Given that plants with virosis tend to infect those that are still healthy, it is clear how important it is identify them as soon as possible and delete them, to allocate the remains to the collection of greenery.
Don't be afraid of losing a plant: if this means saving the rest of the crop from a virus it is a well-paid sacrifice.
In conclusion, the importance of keeping harmful insects under control, albeit with methods and means with low environmental impact, is clear, and always keeping plants under observation to see the first symptoms of adversity.
The most common viral diseases
Knowing which are the main viruses is useful: recognizing them in fact allows us to react promptly removing the plant, and to avoid wasting time in unnecessary treatments. We therefore list some typical viral diseases of the vegetable garden and orchard.
Common cucumber mosaic virus (CMV)
The common mosaic virus which is indicated by the initials CMV (from the English Cucumber mosaic virus) is attributed to the cucumber, even if it is a pathology capable of spreading a lot and for this particular attention must be paid.
In addition to cucumber, among the cucurbits affects mainly zucchini and squash, but in reality it is a virus capable of infecting many other horticultural species: pepper, aubergine, tomato, spinach, celery, pea and others. Among the ornamental we can find it on dahlias, asters and gladioli, as well as on wild herbs.
The leaf limb of infected plants appears bullous, malformed and thickened, and the typical mosaic discoloration is noted.
Zucchini yellow mosaic virus (ZYMV)
This virus is referred to as ZYMV (Zucchini yellow mosaic virus). The leaves take on a yellow mosaic pattern, they curl up strongly at the edges and the plants strongly reduce their development. On the fruit of the courgette there are longitudinal cracks, while on the melon there are cracks and mosaics in the skin and pulp of the hardened masses and small and deformed seeds. It is a virus transmitted by Bemisia tabaci, which is why the fight against this insect is important.
Lettuce mosaic virus (LMV)
This virosis, denoted by LMV (Lettuce mosaic virus) is a typical salad problem. You notice one yellow mosaic on the leaf limb and necrosis in the midrib. In the cap varieties, the tuft cannot form well.
Potato Y Virus (PVY)
The most frequent virosis of potatoes is the virus Y or PVY (Potato virus Y). It is present in various strains, and when this disease occurs, it can be dangerous, so much so as to reduce the production of potatoes in half or more.
The greatest damage occurs when planting already infected tubers, and for this reason one must be very careful when reusing part of the crop as a seed tuber: for this purpose it is good practice to practice the pre-sprouting, with which we can distinguish healthy tubers from shorter and stockier shoots, from those affected by viruses, which instead show thin and elongated shoots. The leaves of virus-affected potato plants remain small and wrinkled, and then wither. Again, aphids can act as vectors.
Spotted Artichoke Curl (AMCV)
AMCV (Artichoke mottled crinkle virus) is a virus that we often find on artichokes. This pathology causes blistering, yellowing of the leaves and malformations of the flower head (the part of the artichoke that is collected).
In the artichoke field the diseases are particularly serious, being a perennial crop. The spotted curl is transmitted a lot, as well as from already infected plants, even from the remains left to decompose on the ground, which must instead be promptly removed.
Sadness of citrus fruits
The orchard can also be affected by viral diseases. A known virosis in the citrus field is Tristeza, a very harmful disease when it occurs, because it can lead to the desiccation of many specimens of orange, lemon or other citrus fruit.
Plants affected initially slow down their development, the leaves then turn yellow and detach, and if the virus hits the root system, the plant's ability to absorb water is compromised. Disease transmission is caused by aphids.
Golden flavor of the vine
The golden flavescence of the vine would not really be a virosis: it is a pathology caused by phytoplasmas, organisms once confused with viruses but which are actually microorganisms similar to bacteria. Like viruses, they too can survive inside other living beings, and specifically inside the lymphatic vessels (phloem).
This disease, which in the vine causes yellowing, leaf curling and difficulties in the lignification of the branches, is transmitted by another insect, the leafhopper Scaphoideus titanus, for which compulsory fighting is foreseen.