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The effects of long term (established in 2008) five-field crop rotation (barley (Hordeum vulgare L.) with undersown red clover (Trifoium pratense L.), red clover, winter wheat (Triticum aestivum L.), pea (Pisum sativum L.), potato (Solanum tuberosum L.)) on the biomass, abundance and diversity (Shannon-Wiener index) of weeds in three organic (Org) and two conventional (Conv) systems after the second rotation were investigated. The results include data from the second rotation in 2013 – 2017. The control system (Org 0) followed only the crop rotation. In the organic systems Org I and Org II winter cover crops were used. In Org II system composted cattle manure was also applied. The conventional cropping systems were treated with herbicides and fungicides and system Conv 0 acted as control (no fertilizer use). Mineral fertilizer was used in Conv II. In general, the significant differences were evident between conventional and organic cropping systems. There were also some differences depending on the crop. The weed biomass was the lowest in barley and potato plots, with significantly higher values in organic than in conventional systems. In clover plots the highest biomass of weeds occurred in Conv II whilst the lowest in Org I. In winter wheat plots the biomass of weeds was significantly lower in conventional systems than in any of the organic systems. Pea plots had the highest biomass, abundance and diversity of weeds in all systems within all rotational crops. Slight tendencies showed the decrease of weed abundance and diversity at the end of the rotation in systems with cover crops (Org I and Org II). This could be explained by better growing conditions due to higher microbial activity and organic carbon content in the soil of organic systems. [ABSTRACT FROM AUTHOR]

In the long term five field crop rotation experiments of organic and conventional growing systems on potato plots the phenology and formation of local-population of Colorado potato beetles were monitored from 2008 to 2013. The beetles started to colonize the field from the establishment of the experiment. The initial population density of beetles was low in both, conventional and organic plots because various cereals and rape had been cultivated on the field and in the vicinity for many years previously. The number of beetles and damage level increased year after year because the potato field remained at the same block, the suitable overwintering places were nearby and the winter mortality was low. As a result of coincidence of several favourable factors like constantly high temperatures, optimal precipitation and availability of fresh food until the late autumn, the second generation of beetles developed in 2010 in Estonia for the first time. This year the number of pest increased sharply when the summer beetle's offspring reach the adult stage and started to reproduce. The unprotected plots were entirely defoliated, in the conventional plots application of Fastac 50 killed the larvae and therefore the plants had less damage. As the spraying did not destroy the adults and the eggs, the new larvae hatched soon. Early spring and warm summer promoted fast emergence of beetles and enabled development of two generation also in 2013 for the second time. During the observation period the numerous vital local Colorado potato beetles population has been developed in this area. This was facilitated by the neighbouring position of organic and conventional plots as the organic plot acted as a reservoir of the pest and the conventional plot as a food reserve. [ABSTRACT FROM AUTHOR]