A study has been carried out in the greenhouse in order to establish correlations between seed and field infection intensities and to determine disease tolerance limits. It was observed that the pre- and post-emergence mortality of seedlings increased as the seed infection increased. On the other hand, yield and seed mass decreased with the increase in seed infection. Seed infection levels of 5 to 10 percent due to M. phaseolina and A. alternata showed no significant effect on yield performance in relation to the control (healthy seeds). It was concluded that with infection levels from 10 to 5 percent due to A. alternata and M. phaseolina, sunflower seed can be sown safely without seed treatment. This finding may be helpful in reducing the cost of seed and health hazards involved in indiscriminate use of chemicals.