Cucumber is one of the most popular and favorite vegetable crops cultivated under greenhouse in Egypt. A greenhouse experiment was carried out to reduce cucumber transplants root rot. Soaking cucumber seeds before sowing in different concentrations of micronutrients, antioxidants, and their combinations were evaluated for controlling Rhizoctonia solani root rot. The results indicated that the highest seedling stand 73.4% after 12 days was recorded after soaking cucumber seeds in sodium selenium solution at 1 ppm. In artificially infested pots with R. solani seed treated with potassium tartrate and boric acid had the highest seedling stands with a clear increase in total phenol contents. Potassium tartrate combined with boric acid showed the highest reduction in radial growth of R. solani by 88.9%. The highest reduction of oxalic acid produced by R. solani on PDA medium supplemented with boric acid were measured using high performance liquid chromatography. Our findings demonstrated an effective approach for inducing resistance in cucumber transplants to Rhizoctonia root rot utilizing micronutrients and free radical scavengers.