my sage is suffering in the foliage at the bottom is gray and dry and seems to have a fungus and the leaves roll up in themselves. Some leaves are eaten by ...? I don't know what insect. I would like to have suggestions.
sage is a perennial herbaceous plant of Mediterranean origin, which has a semi-shrubby development, therefore it forms dense tufts, with woody and semi-woody branches, and leaves of an almost gray color. The color of the leaves is due to the fact that they have adapted to live even in hot and dry conditions, such as happens for lavender leaves. Even if a sage plant can easily survive outdoors in Italy, both in summer and in winter, completely exposed to direct sunlight, it is actually quite useful to shade it in the hottest periods of the year, and especially during the central hours of day. This is because the intense heat and the dry air favor the development of a series of insects, against which the plant has no chance of defense. In general, the symptoms you indicated, that is, leaves that turn yellow and curl up, then dry out, are due to the mites (also commonly called red spiders); these are tiny insects, generally not visible to the naked eye, which feed on the leaf's sap, piercing it and causing death. Against these insects, special acaricides are used, but since it is an aromatic plant, which therefore also enters your kitchen, perhaps it would be appropriate to use some completely organic methods, so as not to introduce any chemical residue into your diet. Against mites you can first of all remove the damaged leaves, and then spray a mixture of water and soft soap on all the foliage; It is a sort of creamy soap, which you can find in specialized shops, which is used as an insecticide and acaricide, as it is based on potassium and not sodium as is the common soap.
Not seeing a picture of your sage is difficult, however, to make a diagnosis; in summer, the main causes of yellowing are related to heat; but the sages tend to suffer even when they are watered excessively, and when they are cultivated in an always damp ground; if this is your case, then you will simply have to learn to wait until the soil is dry before watering your sage again, as these plants fear water stagnation, and strong soil moisture.