Combined applications of insecticides and fungicides may result either in synergism or antagonism between them. Synergism is produced when the association of fungicides with insecticides leads to a joint action that is superior to the arithmetical sum of actions exercised by the single fungicide or insecticide. Ali and Singh (2003) showed synergism of mancozeb + endosulfan mixture which resulted in increased efficacy of fungicide against

cercospora leaf spot of sesamum. Antagonism is the condition found when the efficacy of the association is below the arithmetical sum of actions expressed by the single fungicide or insecticide. The combination of monocrotophos with mancozeb showed decreased insecticidal activity against red cotton bug (Lakshminarayana and Subbaratnam, 2000).

When the pesticide mixture yields neither increased nor decreased effect to the arithmetical sum of actions expressed by themselves when used alone, such condition is said to be showing independent effect upon mixing. Peshney (1990) reported no change in the activity of resultant pesticide mixture, carbendazim and carbaryl when used against Myrothecium roridum compared to their affects when used alone.

As most of the pesticides are specifically toxic either to insect pest or disease causing pathogen, management of both with any single pesticide is not practicable. Therefore it is necessary to mix an insecticide with the fungicide and apply on a crop. Application of two or more chemicals can save time, labour, energy and equipment cost provided there are no adverse effects on the plant, non target organisms and on the efficacy of the chemicals in combating the problems.