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Crop loss due to drought is a complex issue, because it changes according to the drought intensity and duration, and the developmental stage of the plants when drought occurs. In order to assess the drought-induced decline in crop harvest, drought variability and the yield sensitivity of winter wheat, maize, sugar beet, and sunflower to drought during their growing seasons is investigated in the Republic of Moldova. This is then used as an example of the response of non-irrigated crops to increasing drought tendency in south-eastern Europe. The quantification of drought was done by using the standardized precipitation evapotranspiration index (SPEI) at 1-to 12-month lags during the period from 1951 to 2012. The relationship between drought at various time scales and the standardized yield residuals series (SYRS) for individual crops over the country and the Balti chernozem steppe of Moldova (represented by Balti experimental site) for the 1962-2012 farming years were investigated. In order to detect the trends and the shifts in the SPEI time series over 62 years, the non-parametric, Mann-Kendall and Pettitt tests were used for each month of the year to cover the main life cycle of the crops. The trend analysis of agricultural drought emphasizes an increasing trend from June to October, and becomes significant in the southern region at the 95% level during July to September. The SPEI highlights the main periods of dry/wet persistence and the regional characteristics of drought which are present in the Southern region, and make this region more prone to severe drought persistence, mostly during the last decade. Drought during the plant reproductive stages may significantly reduce grain yield potential, the relation between the SYRS and the SPEI explaining up to 62% of the low-yield variability.

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This study presents a detailed analysis on the role of snow cover during the cold season (October-March) on soil moisture deficit and drought development during the growing season (April-September) in the lowland and highland sites in the Czech Republic. Besides daily, weekly and seasonal series of basic snow-cover characteristics [the first day and the last day of snow cover, the number of days with snow cover (DSC), snow depth and snow water equivalent (SWE)] and soil water content measurements, six drought indices have been used in this study to quantify drought. Accumulations of years with significantly below average DSC/SWE were recorded in the early 1960s, mid-1980s, late 1990s and most of the 2000s. The trend towards an earlier end date of snow cover is found in both lowland and highland sites. However, the most significant shift in the dates of early end of snow cover has been identified to occur mostly in the hilly areas while in the lowland areas, these changes are not that evident. Liquid precipitation more than solid precipitation (snowfall) during the cold season lead to weakening correlation between SWE/DSC and the subsequent early summer (April-May-June, AMJ) soil moisture. Snow-cover characteristics can significantly influence soil water saturation during the first part of the growing season, while seasonal amount of SWE can explain up to 45% of soil moisture variability during AMJ season. More than 52% of dry AMJ followed after cold seasons with poor snow, and 42% of wet AMJ season followed after cold seasons with abundant snow. The strength of correlation between drought indices and soil moisture anomalies is higher in later summer. The negative anomalous snow characteristics in conjunction with winter and AMJ drought amplify lingering impact on the depletion of soil moisture in the later summer.KEY WORDS anomalous snow seasons; snow-cover depth; snow water equivalent; snow phenology; soil moisture; drought indices (SPI, SPEI, PDSI, scPDSI, Z-index, scZ-index)

BACKGROUND Intensive application of acetolactate synthase (ALS)‐inhibiting herbicides has resulted in herbicide‐resistance in many weeds, including Bromus sterilis. The present study was conducted to identify the mechanisms conferring resistance to ALS‐inhibiting herbicides in a Bromus sterilis biotype. RESULTS Dose–response studies revealed the resistant biotype to be 288 times less sensitive to pyroxsulam than the susceptible biotype. Furthermore, experiment with a single‐dose, proved this biotype was also cross‐resistant to propoxycarbazone, iodosulfuron plus mesosulfuron and sulfosulfuron. Prior treatment with malathion, a known inhibitor of cytochrome P450s, reduced the level of resistance to pyroxsulam. No mutations were detected from the partial ALS gene sequencing. Flow cytometry and chromosome counting rejected ploidy level variation between the susceptible and resistant biotypes. Relative copy number variation ruled out gene amplification. Quantitative real‐time polymerase chain reaction (PCR) detected a significant difference in ALS gene expression between the susceptible and resistant biotypes. CONCLUSIONS Target gene overexpression and enhanced metabolism by cytochrome P450s are likely mechanisms of resistance to pyroxsulam in Bromus sterilis. The current findings highlight the need to monitor additional brome populations for herbicide resistance in Europe and endorse the need for alternate herbicides in integrated weed management to delay the possible evolution of herbicide resistance in these species. © 2020 Society of Chemical Industry