Considerable variation was observed among four fungi, involved in damping-off of cotton seedling, as to their response to the application of Atriplex nummularia (AT) ground seeds to the growth medium. Rhizoctonia solani was resistant to the applied concentrations of AT. Contrary to the inhibitory effect on Macrophomina phaseolina and Sclerotium rolfsii, AT stimulated growth of Fusarium oxysporum. Analysis of variance for effects of different concentrations of AT on pathogenicity of the fungi indicated highly significant effects of concentrations, fungi, and their interaction. Due to the highly significant interaction between concentrations and fungi, an interaction least significant difference was calculated to compare between concentration means within each fungus. These comparisons showed that the fungi responded differently to the applied concentrations. The application of AT, as a seed treatment, at a rate as low as 3 g/kg seeds significantly decreased damping-off caused by any individual fungus, while the increase of application rate to 6 and 9 g/kg seeds did not significantly improve the efficiency of AT in controlling the disease. Moreover, in case of fungal mixture, the increase of application rate to 6 and 9 g/kg seeds resulted in significant reduction in efficiency of At compared to the rate of 3 g/kg seeds. Effect of AT on linear growth of the fungi under pure culture conditions was not related to its effect on pathogenicity of the fungi under greenhouse conditions. Twelve field trials were conducted in Sakha, El-Gemmeiza, Sirs El-Lian and Mallawy in 1999 (three planting dates in each location) to evaluate the effectiveness of treating seeds with AT in suppressing cotton seedling damping-off under field conditions. AT was effective in controlling damping-off only in Sirs El-Lian, where it significantly reduced it by 33.33, 33.76, and 39.55% in the first, second, and third planting dates, respectively. In this site, AT was as effective as the standard fungicide Monceren in controlling the disease. AT also significantly increased seedcotton yield in Sirs El-Lian by 35.65 and 38.42% in the second and third planting dates, respectively. In Sakha, AT significantly increased seedcotton yield by 15.38% in the third planting date. Seedcotton yield of all the other experiments was not affected by the application of AT.