Studies were carried out in an experimental orchard established on the area of Agricultural and Pomicultural Experimental Farm in Przybroda belonging to the Agricultural University in Poznań. The establishing of an orchard in the place of a previously existing one exerted an influence on the tree growth impediment and increased the number of tree losses. Poor growth decreased both the individual yield from one tree and the yielding from the area unit. Irrigation as well as fertilization had an effect on the occurrence of soil fatigue phenomenon. Increased irrigation intensity and low fertilization doses increased the results of replantation disease. The least effects of soil fatigue were found in case of no additional irrigation and an increased dose of tree fertilization. Experimental conditions did not exert any effect on fruit quality.

In the years 2003–2005 studies were conducted in the area of Lublin the aim of which was to study the population dynamics of aphids colonizing the trees of Juglans regia L. in the street and the park sites against the course of weather conditions. The weather in spring probably had no effect on the date of hatching of the larva of fundatrix, which was usually observed in the third 10-days’ period of May. On the other hand, the dry period, heat waves (above 30°C) and stormy rainfalls affected the break in the aphid population observed in July and August. The maximum population of P. juglandis was found in the second 10-days’ period of June, while that of Ch. juglandicola – at he turn of June and July. The highest number of P. juglandis was observed in 2004, while that of Ch. juglandicola in 2003. In 2003 the dominating species in both sites was Ch. juglandicola, while in the other years of studies it was P. juglandis.

In the years 2004–2006 on American ginseng plantation covered with the mineral mulch Agran, located in Krasnystaw (the Lublin region) there were compared the effects of five methods of plant protection. Each year 5 plants showing disease symptoms were sampled from particular experimental combination in order to perform the mycological analysis. The results of the analysis showed that in particular years of the experiment the quantitative and qualitative composition of pathogenic fungi isolated from the examined ginseng parts was differentiated. There was proved that fungi from the genera of Altenaria, Fusarium, Cylindrocarpon, Phytophthora and Pythium irregulare, Rhizoctonia solani Botrytis cinerea create a considerable danger for the ginseng plants.