Fertilizers apply to orchids only if the corresponding light is ensured, as well as heat and water at the level required by the species. When flowers start blooming for the plant, it is better to decrease the level of azoth as compared to phosphorus and potassium, because when exceeding, it can inhibit the process of flower formation.
In certain orchids, one can notice the phenomenon of blackening of the growth tips of the young leaves, which advance to the plant's stalk, and in very grievous cases, it can advance to young pseudo bulbs. This implies calcium deficiency which can be manifested during the hot season when the plant is in full growth, and can be solved by giving it calcium.
When deep yellow spots that later on become black appear on the leaves, it is a sign of too cold nights or of cold water used for watering. This may occur especially in winter. When their leaves turn red, this means they have excessive light or they didn't get enough azoth fertilization.
The yellowing, necrosis and falling of the flower buttons can be a consequence of excessive heat or of intoxication with the ethylene emitted by the surrounding plants which have lost their freshness. Wrinkles on pseudo bulbs can be a sign of insufficient water or of the necrosis on the roots' surface.
Viruses can get manifested under the form of irregular spots or stripes, yellow at first, evolving towards necrosis; to prevent viruses, the recommendation would be to destroy all insects which are the vectors of the disease and sterilizing the tools that are being used with a natural solution of trisodium phosphate or lime water with a very high Ph level.
Black rots are largely spread. These symptoms may appear at the plant's base or on the roots, the attacked parts turning black, and often presenting with a yellow margin; cutting out the attacked parts and treating them with fungicides are absolutely necessary in this special case.