Abstract: Efficiency of compounds of both synthetic and biological origin on powdery mildew(Blumeria graminis f.sp. tritici) severity was tested on wheat cultivar Kanzler (susceptiblestandard) under field conditions in small plot experiments in 2004-2008. Plants were sprayed byextracts of several plants, with possible biological effect – oak bark (OB), curcuma (CU), ginger(GI), giant knotweed (RS), glycine betaine (GB), and known resistance inducers –benzothiadiazole (BTH) and salicylic acid (SA). Untreated Kanzler was used as a control (CO).In the year 2004 disease severity of powdery mildew was the highest, and in other years waschanging. Untreated control demonstrated much more disease severity than the same cultivartreated by individual inducers. Disease severity after treatment with inducers was the lowest onBTH- and GI-treated and the highest on SA- and OB-treated plants. In 2008, when the diseaseincidence was extremely low, application of inducers resulted in diverse results. Preponderanceof application dates except the first treatment by GB produced lower disease severity than CO.The earlier treatment by CU induced the lowest disease severity in comparison with othertreatments. In general, the experiments showed long-term suppression of the powdery mildewseverity on wheat.