Chemical damage to plants may arise in three major ways:

1. Careless application of a chemical.
2. Using the wrong chemicals for a particular problem or plant.
3. Applying the right chemicals, but at the wrong rate or interval.

Contact weedkiller damage can affect plants that have been inadvertently sprayed with weedkiller, either through careless application or by spray drift in windy conditions. Contamination may also occur if equipment used for weedkiller is then used to water plants. Bleached patches appear on the affected foliage, which may then turn brown. If the plant has been severely contaminated, its growth may be affected and it could even die. Use a watering can or dribble bar applicator instead of a sprayer and keep all equipment for use with weedkillers separate.

Plants may also be damaged by applications of fungicides or insecticides if they are applied at the wrong rate or during hot, sunny conditions. Never treat plants in bright sunlight as this may lead to scorching, and ensure that the manufacturer's guidelines for application rates are followed carefully. Young plants, and those that are under stress are much more vulnerable to damage, and may be injured by the application of some chemical treatments.

There are a number of plants that are particularly sensitive to certain fungicides and insecticides. This is known as phytotoxicity, and may lead to discoloured foliage, stunted growth and even plant death. The manufacturer's instructions will often list those species that should not be treated; however, if in any doubt, test the fungicide or pesticide on a small area of the plant before using.