Triadimenol seed treatment was evaluated for control of early infections of spring wheat ( Triticum aestivum L. cultivars Max and Sinton) by Pyrenophora tritici-repentis (causal fungus of tan spot), Erysaphe graminis f. sp. tritici (causal fungus of powdery mildew), Leptosphaeria nodorum (causal fungus of Septoria nodorum spot), and Cochliobolus sativus (causal fungus of spot blotch). In controlled environment studies, triadimenol seed treatment controlled both tan spot and powdery mildew up to 20–30 days and 40–50 days after sowing, respectively. However, triadimenol seed treatment provided no control of early infection by airborne inoculum of L. nodorum and C. sativus. Powdery mildew-resistant cv. Max was completely free of symptoms or signs of E. graminis f. sp. tritici. In field experiments, triadimenol seed treatment controlled early development of tan spot and powdery mildew for 5 and 10 days longer, respectively, than in controlled environment studies. Control of both diseases in cv. Sinton and tan spot control in cv. Max resulted in yield increases of approximately 20% and 15%, respectively, at two different field locations.