In this review results are summarized regarding the effect of virus infection on the physiological processes of weeds. Through several host-virus model relations the biomass and seed production, seed viability and germination, nutrient uptake, drought-resistance and photosynthetic pigment content of healthy and virus infected plants were compared. Because of their broad host range and high genetic variability viruses cannot be used for biological weed control. It was concluded that viruses unfavourably can influence physiological processes of weeds. Therefore, they may contribute indirectly to the reduction of competitive ability and population of weeds.