Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations [0, 0.5, 1, 2.5, 5, 7.5 and 10% (w/v)] of Brassicaceae CCs (Sinapis alba, Raphanus sativus, Camellina sativa) and of the CCs Fagopyrum esculentum and Guizotia abyssinica on germination and early growth of Ambrosia artemisiifolia L. The allelopathic effects were species and concentration-dependent. C. sativa, for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas S. alba and R. sativus inhibited germination and early growth of A. artemisiifolia only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of F. escultneum and G. abyssinica were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in C. sativa. Our results suggest that C. sativa is the most allelopathic CCs and that the fruits of C. sativa are the plant organs richest in allelochemicals.

Effective weed management depends on correct control timing, which depends on seedling emergence dynamics. Since soil temperature and soil moisture are the two main factors that determine weed germination, the hydrothermal time model can be used to predict their emergence. The aim of this study was to estimate the base temperature (T_b) and base water potential (Ψ_b) for the germination of Chenopodium album, Amaranthus retroflexus, Setaria pumila, and Panicum capillare collected from fields in continental Croatia and then to compare these values with those of Italian populations embedded in the AlertInf model. Germination tests were performed at seven constant temperatures (ranging from 4 to 27 °C) and eight water potentials (0.00–1.00 MPa). The estimated T_b and Ψ_b were 3.4 °C and −1.38 MPa for C. album, 13.9 °C and −0.36 MPa for A. retroflexus, 6.6 °C and −0.71 MPa for S. pumila, and 11.0 °C and −0.87 MPa for P. capillare, respectively. According to the criterion of overlap of the 95% confidence intervals, only the T_b of C. album and the Ψ_b of A. retroflexus of the Croatian and Italian populations were similar. Further field experiments should be conducted to monitor the weed emergence patterns of C. album and calibrate the AlerInf equation parameters.

The efficacy of weed management depends on the correct control timing according to the seedling emergence dynamics. Since soil temperature and soil moisture are two main factors that determine weed germination, the hydrothermal time model can be used to predict their emergence. The aim of this study was to estimate the base temperature (Tb) and base water potential (Ψb) for germination of Chenopodium album, Amaranthus retroflexus, Setaria pumila and Panicum capillare collected from fields in continental Croatia and then to compare these values with those of Italian populations embedded in the AlertInf model. Germination tests were performed at seven constant temperatures (ranging from 4 to 27°C) and eight water potentials (0.00 to - 1.00 MPa). Estimated Tb and Ψb were 3.4°C, -1.38 MPa for C. album, 13.9°C, -0.36 MPa for A. retroflexus, 6.6°C, -0.71 MPa for S. pumila and 11.0°C, -0.87 MPa for P. capillare, respectively. According to the criterion of overlap of the 95% confidence intervals, only Tb of C. album, and Ψb of A. retroflexus were similar between Croatian and Italian populations. Further field experiments should be conducted in the Croatian field to monitor weed emergence patterns of C. album and to calibrate the AlerInf equation parameters.