Chitosan, (Biochikol 020 PC) a potential elicitor of plant defence and also an active inhibitor of fungal growth was used in experiments. The compound was used at concentrations 0.01 to 0.2% as a plant spray for rose protection against Sphaerotheca pannosa var. rosae, Peronospora sparsa and Diplocarpon rosae, Oidium chrysanthemi and Puccinia horiana on chrysanthemum, against Melampsora epitea on willow. Myrothecium roridum on dieffenbachia and against Lophodermium spp on Scots pine. Effectiveness of this product, applied curatively 2-times at 7-day-intervals after appearance of rose powdery mildew symptoms on most of plant parts, was about 32%. When compound was applied just after the first disease symptoms appearance, after 2-week-protection its effectiveness was about 43-60%. After 4 weeks, effectiveness of chitosan (Biochikol 020 PC) increased and ranged from 67 to 77%. In the control of P. sparsa on rose shrubs, growing in plastic tunnel, chitosan at conc. 0.025% was applied 4 times at weekly intervals. Effectiveness of chitosan against this pathogen was over 72%, similar as standard fungicide. Increase of chitosan (Biochikol 020 PC) concentration resulted in decrease of its effectiveness. In case of D. rosae control, chitosan used 9 times at weekly intervals was applied after first disease symptoms. After 3-week-protection effectiveness of the compound varied from 18 to 60% according to used concentration. After 9 weeks of protection effectiveness of tested product ranged from 16 to 23% and was connected with used concentration. Increase of chitosan concentration resulted in better protection of rose shrubs. Effectiveness of chitosan (Biochikol 020 PC) used 4-times at conc. 0.01 to 0.05% as chrysanthemum spray in the control of Oidium chrysanthemi ranged from 69 to 79%, whereas against Puccinia horiana from 54-97%. Two-time-spraying of willow with rust symptoms (Melampsora epitea) with chitosan at conc. 01-0.04% caused decrease of disease severity from 26 to 47%. Additionally about 10 to 25% of uredinia were dried up. Chitosan (Biochikol 020 PC) applied for leaf spraying inhibited the development of Myrothecium leaf spot on dieffenbachia more than 85%. Curative application of the compound controlled Myrotecium leaf spot at about 40%. Chitosan efficacy was also tested against one-year-old Pinus sylvestris seedlings growing in field conditions. Plants were sprayed fortnightly 14-times (long programme) or 5-times (short programme) against Lophodermium spp. Observations made during next spring showed that effectiveness of chitosan (Biochikol 020 PC) was more than 50% (long programme) and below 50% (short programme).