Pest, disease or disorder?

Normal plant growth and general health can be affected by a wide variety of pests, diseases and disorders. But what is the difference between each of these?

Plant pests

Plant pests are living agents that cause problems for the host plant by feeding on it.

Most pests are parasites.

Examples of parasitic plant pests include:

• insects
• slugs
• snails
• nematodes

Plant diseases

Plant diseases are also living agents feeding on the plant. They interfere with and affect the normal functioning of the plant.

Diseases are usually parasites.

Some examples of plant diseases include:

• fungal diseases - ink spot, dieback
• viral and virus-like diseases - mosaic virus, ring spot
• bacterial diseases - canker, galls.

Plant disorders

Plant disorders are often caused by factors like:

• variations in temperature - particularly hot days or cold nights
• soil pollutants - toxic metals and salt in the soil
• air pollutants - chemicals from refineries or smelters
• air particulates - dust from mining operations blocking sunlight or clogging plant stomata.

Examples of plant disorders include leaf burn from excessive sunlight, waterlogging of roots from too much rain and wilting caused by high salt levels in the soil.