Corn plantations are the major technical field crops in the Republic of Moldova, advantaged in agro-ecological and productive aspects, which annually are invaded by the attack of harmful organisms with considerable parasitic impact. Phytosanitary monitoring of plantations is an essential condition in establishing the most effective methods of control of harmful organisms in corn in vegetation period, motivations for the development and application of some remedies to regulate the parasitic impact with the host plant. The results of the phytosanitary control carried out annually in corn crops, note a significant diversity of 7 key diseases (common and dusty tall, forms of rottenness, fusariosis, helmintosporiosis, nigrosporiosis, diplodiosis) caused by 20 pathogens with significant and optional pathological specialization and 17 species of harmful nematodes of order Tylenchida, corn specific ecto-endoparasitic and sedentary forms with trophic specialization as well as for other corns and technical crops invasive of major agronomical importance. The diseases structure and diversity of pathogens responsible for triggering corn diseases and associated harmful nematodes invasive complex have been estimated, with the determination of the impact of plant protection index, such as: Density (D.n.), Attack frequency (F.%), Attack intensity (I%), estimation scales used to determine the impact after corn reaction to attack of parasite organisms.