Question: apple tree fruit disease
some productions of green apples, have diffuse yellowish spots commonly called bitter maculations, what they really are and what is the correct name, thanks
Answer: apple tree fruit disease
bitter pitting, or blotchiness, of the apple tree is a disease that is not caused by a parasite, bacterium or virus; in fact it is instead a problem of nutritional deficiencies, and the common name is the one you indicated, sometimes translated into English "bitter pit".
This problem, characterized by small dark spots in the fruits, which occur at harvest, but often even after a few weeks (therefore in the fruits already harvested, and stored for storage); these spots are slightly depressed, and in the center there is a little pulp with a rotting and mushy appearance. often, the bitter maculation (which sometimes manifests itself late) is associated with chlorotic trees, with yellowish foliage and not very luxuriant development. This pathology develops when calcium is deficient in fruits.
Generally in Italy the soil is rich in calcium, and therefore the lack of calcium in the fruits is not always due to an actual lack of calcium in the soil: limestone, generally present in the soil or in the water used for irrigation, is commonly absorbed from plants throughout their development.
However, it happens, in rare cases, that the soil is very acidic, or contains small amounts of limestone, and therefore a simple autumn fertilization with calcium chloride-based products solves the problem for the following year's harvest. This event occurs in areas with poorly calcareous soil, or in land that is very exploited from an agricultural point of view.
However, sometimes the bitter maculation also occurs in apple trees grown in soils rich in calcium; in this case, the calcium deficiency is due to long periods of drought, which occurred when the plant already presents the fruits (the leaves draw water from the other tissues, and also from the fruits, and together with the water deprive the fruits also of calcium) . This pathology also develops when the fruits tend to develop excessively fast, due to excess nitrogen in the soil, or the plant is unable to absorb calcium from the soil, because it is excessively rich in manganese or potassium ions.
So, if you live in an area with poorly calcareous soil, before the plant sheds its leaves, apply foliar fertilization with calcium-based products, and possibly also use a fertilizer product next spring that also contains calcium (you often find rich fertilizers calcium among vegetable products specific for tomatoes); If, on the other hand, you live in an area with calcareous and calcium-rich soil, then keep the crop care more regular, and therefore water the sapling regularly in dry periods, and avoid excess fertilizer, especially nitrogen. Even a light green pruning of the tree, in spring, can help.
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