Pests and Diseases of Plant

Pests are living things whose existence is disturbing crops, causing economic losses. Some scientists explain the meaning of pests, almost all explanations about pests are living things that cause economic loss.
In the agriculture, when pests attack crops, pests will leave a mark. Mark is a guide that can be observed on a plant to identify the pest. Every pest has a specific host plants according to nutritional needs. Almost every pest has a major host plant and alternative hosts. 

examples:

Valanga Nigricornis have primary host is the leaves of corn and rice leaves are alternate hosts. Signs crop pests are leaf shreds erratically and sometimes leaving only the veins.

Valanga Nigricornis

While the disease is a deviation from normal behavior, causing the plants or plant parts can not be normal activity. The plant can be known by the symptoms. Symptoms are changes in the plant which is a reaction to the influx of foreign plants just as bacteria, viruses, and others. Agrios explained that the disease will occur if three conditions fulfilled from the disease triangle. The following is the disease triangle:

disease triangle

Disease will occur at a time and place for three terms, namely, (1) if the plants are vulnerable / susceptible to disease, (2) capable of infecting pathogens (virulent), and (3) a supportive environment or appropriate. disease will not occur if one of the conditions above not fulfilled, although two other conditions fulfilled.
Examples of pathogens that attack the plant:
Gleousporium Frugtigenum disease in apples caused by fungi. characteristics of this disease include: patches on the outside of the apple, the patches are get into the meat, and potholes.

Gleousporium Frugtigenum