Effects of cyclohexylamine and norspermidine on powdery mildew infection of spring barley

The spermidine synthase inhibitor cyclohexylamine (CHA) and the spermidine analogue norspermidine were evaluated against powdery mildew infection of spring barley in field trials over a 2-year period. Both compounds reduced mildew infection as effectively as a commercial fungicide, a mixture of flutriafol and carbendazim. Percentage disease reduction afforded by CHA and norspermidine in year 1 ranged from 32% to 67% at the final assessment and from 52% to 77% in year 2 of the study, when compared with plants from untreated plots. No difference was observed in the disease control conferred by 1.0 mM concentrations of the compounds and 5.0 mM applications, the optimum dose being less than 5.0 mM. No significant differences in final yield were obtained, comparing the treated crop with the untreated control. Although reductions in disease were apparent, additional environmental factors may have prevented a subsequent crop yield response.