There are many diseases that can afflict plants. Some of these diseases produce symptoms that are clearly visible. Other diseases are more insidious and attack the plant from within. In this way they sap the strength of the plant and by the time the disease is discovered it is too late to save the plant.

These insidious diseases are the most difficult to study because it is most difficult to study because it is practically impossible to see or know what is going on inside the plant. In some cases the disease is the result of different factors, each of which combines to cause several changes to take place.

In the practice, some cures are more expensive than the plant itself and it is cheaper simply to let the plant die.

It is easier to tackle plant diseases when these have been caused by external factors. For example, there are many insects and other small creatures that bring about certain changes in plants. Once these changes are recognized, the disease can be treated by chemical and other means. Today helicopters and aeroplanes are used to spray insect-killing chemicals on crops which have been attacked by pests and parasites.

It is important to know the cause of the disease so that the cure can be found. Fortunately, modern botanists are helped by chemists using the most advanced forms of technology.

Probably the best control is provided by the use of disease resistant plants and expensive efforts are being made to develop such varieties.