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Moria of the pear tree
The death of the pear tree is caused by a unicellular organism genetically correlated with the phytoplasmas that cause the brooms of the apple tree and the yellowness of the stone fruit. This phytoplasma occurs in the phloem tubes, infecting also the body of the psyches, or the insects that live on the leaves and on the buds of the pear. The activity of the phytoplasma is harmful because it causes the substances processed in the leaves to stagnate and prevents their transfer to the roots: this causes the degeneration of the vital tissues and the progressive desiccation of the plant. Contamination of other plants occurs through psyches: in this way, the disease is transmitted to the entire orchard and can cause the death of thousands of trees, as happened in Trentino Alto Adige in the 1940s. On that occasion, the phytoplasma of the disease caused the death of 50,000 pear trees. In addition to the various species of Pyrus, mortality can also affect other shrubs, such as quince and nashi.
How it manifests itself
This pathology appears above all in the autumn season, manifesting itself through three different syndromes: rapid decay, slow decay and leaf curl. In rapid decay, leaves and fruit wither a few days after the appearance of the first symptoms: the dried parts remain attached to the plant that dies quickly. The slow decay is manifested by a reddening of the leaves, followed by sprouts, flowers and scarce and small fruits: the roots and branches dry slowly until the death of the tree. In leaf curling, the foliage gradually changes appearance: the leaves, in fact, redden and wrap themselves. This last variant of the syndrome can be resolved with definitive healing or pave the way for more serious forms of the disease.
How to identify the pathology
The death of the pear tree is revealed through a precise symptomatology that mainly concerns the color and morphology of the leaves. The phytoplasma attack hinders the absorption and transmission of nutrients in the various parts of the plant, which then undergo a process of desiccation and early death: the first symptom, in this regard, is represented by the reddening of the leaf blade , which progressively tends to roll up and curl up to dry out completely. If fruits are present on the tree, they wilt within a few days, while remaining attached to the branch. In spring, the pear tree affected by die-off develops a very weak vegetation, with sparse and stunted foliage and buds. The often fulminant course of the disease, which can kill the plant a few weeks after the appearance of the first symptoms, makes it necessary to adopt timely and targeted strategies.
The fight against illness
To combat the disease, one of the most effective strategies is the containment of psyches: these phytophagous insects, in fact, are the first vehicle of transmission of the disease. The first precautionary measure to be taken to avoid the proliferation of phytoplasmas is therefore the drastic reduction of phytophagous, obtainable through the use of products based on azadiractin or with the use of antagonist insects (such as anticorids). To prevent mortality the pruning of the thinning is very useful, which has the effect of airing the plant avoiding the stagnation of humidity that favor the appearance of parasites. A treatment with nitrogen-based fertilizers can help the plant strengthen its defenses and overcome the infection more easily. Plants that are very suffering and suffering from an already very advanced stage of the disease must be destroyed in order to reduce the sources of inoculation for vector insects.