In the years 1999–2001 studies were conducted on the field belonging to the Experimental Station at Czesławice. The field contained naturally accumulated infection material. The subject of the studies was soybean, Poland cv. and chitosan in the form of micro-crystalline gel containing 2.76 of the pure compound. Water solution of this compound with 0.1% chitosan was used in the experiment. Two combinations were considered using chitosan for spraying the seedlings and the plants at the initial stage of anthesis, and the control without any treatments. In each year, field observations were performed which considered the number and healthiness of seedlings and plants at anthesis. After the harvest, the size and quality of the soybean seeds yield were also determined. In the course of field observations the infected seedlings as well as the infected plants at anthesis were taken for laboratory mycological analysis. The studies found out differentiated emergencies and healthiness of plants in particular experimental combinations. Chitosan used for spraying the plants at anthesis slightly improved the healthiness of plants and seeds and contributed to an increase of the yielding as compared to the combination where it was used for the spraying of four weeks old seedlings, and also in comparison to the control. Soybean seedlings were infected by F. solani and R. solani most frequently. On the other hand, plants at anthesis were mostly infected by F. oxysporum f. sp. glycines. The following were isolated from the infected soybean seeds: Phomopsis sojae, Phoma exigua var. exigua, F. oxysporum, R, solani, A. alternata, B. cinerea and S. sclerotiorum.

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