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Remotely sensed infrared canopy temperatures provide an efficient method for rapid, non‐destructive monitoring of whole‐plant response to water stress. Field studies were conducted in 1992 and 1993 to evaluate the potential for using canopy temperatures to screen for drought tolerance in wheat. In both years, 12 spring wheat (Triticum aestivum L.) genotypes were grown under two irrigation levels (well‐watered and moisture‐stressed) imposed between tillering and anthesis with a line‐source sprinkler irrigation system. Canopy temperature measurements were taken in well‐watered and moisture‐stressed plots between 1330 and 1430 h (MDT) on five clear days in 1992 and seven clear days in 1993 during the late vegetative and early reproductive growth periods following closure of the plant canopy. Genotypes exhibited differences in mean canopy temperatures across the two irrigation levels and two years. Klasic consistently had the highest canopy temperature under moisture‐stressed conditions, while Bannock and Pondera had the lowest. Bannock, Yecora Rojo and Klasic had the warmest canopies under well‐watered conditions, while Vandal, Amidon and Rick had the coolest. Plot‐to‐plot variation in canopy temperature under water stress conditions was evident for differences in grain yield. Significant correlations between canopy temperature and yield under moisture‐stress conditions and drought susceptibility index values indicated the potential for screening wheat genotypes for drought response.

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Emex spinosa and Emex australis are invasive dicotyledonous weeds. The effects of various environmental factors on the germination of these weeds were investigated under laboratory and glasshouse conditions. Germination response of both species was lower at warmer temperature, and maximum germination was recorded at 20/12°C (day/night). Light stimulated germination in both species, but considerable germination also occurred under darkness. More than 80% of E. spinosa seeds germinated at pH between 6 and 9, whereas E. australis seeds germination was considerably decreased at pH 9. Emex spinosa was fairly tolerant to salinity as compared with E. australis and germination (21%) of E. spinosa occurred even at 200 mM NaCl. Both species were sensitive to osmotic stress, but E. spinosa tolerated more osmotic stress than E. australis. Temperature above 20/12°C (day/ night) and low osmotic potential increased time to start germination and mean germination time (MGT), as well as decreased germination index (GI) of both species. Darkness resulted in increased MGT and decreased GI in both species when compared with 10 h photoperiod. Salt stress strongly increased time to obtain 50% germination and reduced GI of both species. In both species, an increasing burial depth decreased emergence percentage and emergence index and increased time to start emergence, although some seed emerged even at 10 cm burial depth. It was concluded that both species can germinate over a wide range of environmental conditions. However, E. australis was more sensitive under adverse environmental conditions compared with E. spinosa. This information on germination ecology may aid in developing tools and strategies for management.

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Little seed canary grass (LCG) is a pernicious weed of wheat crop causing enormous yield losses. Information on the interference and economic threshold (ET) level of LCG is of prime significance to rationalize the use of herbicide for its effective management in wheat fields. The present study was conducted to quantify interference and ET density of LCG in mid-sown (20 November) and late-sown (10 December) wheat. Experiment was triplicated in randomized split-plot design with sowing dates as the main plots and LCG densities (10, 20, 30, and 40 plants m(-2)) as the subplots. Plots with two natural infestations of weeds including and excluding LCG were maintained for comparing its interference in pure stands with designated densities. A season-long weed-free treatment was also run. Results indicated that composite stand of weeds, including LCG, and density of 40 LCG plants m(-2) were more competitive with wheat, especially when crop was sown late in season. Maximum weed dry biomass was attained by composite stand of weeds including LCG followed by 40 LCG plants m(-2) under both sowing dates. Significant variations in wheat growth and yield were observed under the influence of different LCG densities as well as sowing dates. Presence of 40 LCG plants m(-2) reduced wheat yield by 28 and 34% in mid- and late-sown wheat crop, respectively. These losses were much greater than those for infestation of all weeds, excluding LCG. Linear regression model was effective in simulating wheat yield losses over a wide range of LCG densities, and the regression equations showed good fit to observed data. The ET levels of LCG were 6-7 and 2.2-3.3 plants m(-2) in mid- and late-sown wheat crop, respectively. Herbicide should be applied in cases when LCG density exceeds these levels under respective sowing dates.

-An understanding of seed germination ecology of weeds can assist in predicting their potential distribution and developing effective management strategies. Influence of environmental factors and seed size on germination and seedling emergence of Convolvulus arvensis (field bindweed) was studied in laboratory and greenhouse conditions. Germination occurred over a wide range of constant temperatures, between 15 and 40

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