Five different biocontrol preparations and the commercial bioagent Plant guard varied in their effects in controlling powdery mildew of grapes, incited by Uncinula necator (Schw.) Burr. A mixture of Trichoderma harzianum isolate number 5 and isolate number 28 with T. hamatum isolate number 17 proved to be more effective than the single isolates and even was the most potent of the tested bioagents. However, the least potentiality was recorded with Bacillus subtilis application. Number of sprays increased the disease control up to three sprays, whereas the fourth spray did not increase the efficiency of the bioagent. Concerning with the bioagent concentrations, five various doses had been tested and the most effective was 250 ml of the bioagent preparation in 100 liter of water. No great differences were obtained if the concentration was increased to 350 ml/100 L water. Two different scales had been applied for disease detection; disease incidence and disease severity. The latter scale was more reliable. In general, all the bioagent treatments gave similar or near similar potentiality while great differences occurred with the disease incidence.