Pesticide is a collective term for chemical pest control agents. They are applied as a spray or as a powder dust. Depending on the pest group controlled, they are called herbicides, which act against weeds (e.g. quitch), fungicides, which act against fungi (e.g.. mildew), insecticides, which act against insects, acaricides which act against mites (e.g. spider mites) and nematicides, which control plant parasitic nematodes.