The breakdown is not due to decay, however, because rots usually spread down into the flesh in round or conical shapes, whereas ordinary scald is diffuse. Causal factors Ordinary scald, a physiological disorder of apples, is sufficiently complex that its true cause has never been definitely established. A number of factors affecting individual fruits, together with weather conditions during their growth, have a direct bearing on susceptibility to ordinary scald. The disease is usually worse in years when the weather is hot and dry during the last few weeks before harvest. Susceptibility varies greatly from season to season.
Ordinary scald is primarily a disease of immature fruits.
It is worse on apples from heavily irrigated trees than on those from trees receiving moderate irrigation. Disease development is favored by storage temperatures above tight packages. Stacking containers to allow good air circulation in the storage room reduces, but does not control, scald. Delaying storage may greatly increase the development of scald, especially if the fruits receive little ventilation during the delay. If immature fruits are adequately ventilated, however, a delay in storing sometimes reduces the development of scald.