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Question: apple fruit disease
some productions of green apples, have widespread yellowish patches commonly called bitter maculations, what they really are and what is the correct name, thanks
Answer: apple fruit disease
the bitter pitting, or maculation of the apple tree is a disease that is not caused by a parasite, a bacterium or a virus; in fact it is instead a problem of nutritional deficiencies, and the widespread name is precisely that indicated by you, sometimes translated into English as “bitter pit”.
This problem, characterized by small dark spots in the fruits, which occur at harvest, but often even after a few weeks (ie in fruits already collected, and stored for storage); these spots are slightly depressed, and in the center there is a little pulp with a decaying and musty appearance. often, with the bitter maculatura (which sometimes occurs late) chlorotic trees are associated, with yellowish foliage and a little luxuriant growth. This pathology develops when calcium is lacking 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: the limestone, usually present in the soil or in the water of the watering, is commonly absorbed from plants for all their development.
However it happens, in rare cases, that the soil is very acidic, or that it contains small amounts of limestone, and therefore a simple autumn fertilization with products based on calcium chloride, solves the problem for the following year's harvest. This event occurs in areas with poorly calcareous soil, or in lands that are heavily exploited from an agricultural point of view.
Sometimes the bitter spotting occurs also in apple trees grown in calcium-rich soils; in this case, the lack of calcium is due to long periods of drought, occurring 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 they also deprive the fruits of calcium) . This disease also develops when the fruits tend to develop excessively fast, due to excess nitrogen in the soil, or even the plant is unable to absorb calcium from the ground, because this is excessively rich in manganese or potassium ions.
So, if you live in an area with poorly calcareous soil, before the plant loses its leaves, apply foliar fertilization with calcium-based products, and eventually use a fertilizer product that also contains calcium next spring (often find rich fertilizers of calcium from the vegetable garden specific products for tomatoes); if instead you live in an area with calcareous soil and rich in calcium, then keep the cultivation treatments more regular, and then water the tree regularly in dry periods, and avoid excess fertilizer, especially nitrogen. Even a light green pruning of the tree, in spring, can help.