Pest, Disease Or Virus...?

Press, Volume CI, Issue 29797, 13 April 1962, Page 7

Pest, Disease Or Virus...?

There is much confusion over these three terms, and some persons regard them as being identical. Nothing could be further from the truth. A pest is an insect or other animal which feeds upon plants at one stage or another of its life history. Although a pest is usually mobile, there are a few pests which become immobile once they have found their host, living there for the rest of their lives. But pests are capable of movement from plant to plant at some stage of their existence.

It is this mobility—amongst other factors, as any schoolboy studying biology will quickly tell me—which distinguishes a pest from a disease. A disease is caused by the attack of a fungus upon a plant—and a fungus is basically a plant, too. It lives within the tissues, obtaining its nourishment from the plant cells themselves. Diseases spread by spores in the air or in water films. Not all diseases are caused by plants, however—some are caused by bacteria, creatures exhibiting both plant and animal characters. A virus—and this is a sadly misused term —is the simplest organism of all. Some biologists regard it as a “living chemical” for a virus is incapable of multiplication outside the tissues of the host. Since it lives within the plant cells, it cannot be attacked by any of the orthodox methods of pest and disease control. Viruses are commonly spread by insects, which absorb them into their body in the process of feeding, contaminating fresh plants when they transfer their attentions. The control of virus “carriers” is one method of controlling viruses.