EN
This paper presents the results of research carried out by the Agronomy Department of Poznań Life Science University, at the Experimental Station Swadzim in 2009–2010. The aim of research was to evaluate the effects of maize plants density on the occurrence of European corn borer (Ostrinia nubilalis Hbn.), frit fly (Oscinella frit L.) and maize common smut (Ustilago zeae Unger.) on plants of four maize hybrids characterized by different length of ripening period. The level of damage caused both by the European corn borer and frit fly was comparable for all individual maize hybrids. It was also stated that medium – late cultivars showed a higher level of common smut as compared to early ones. The lower percentage of maize plants damaged by European corn borer and frit fly was related to a higher maize plant density. In contrast to pest infestation the intensity of occurrence of maize common smut increased with a higher plant density, especially in case of early hybrids.