JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. SUMMARY(1) The demography of the annual grass weed Avena sterilis ssp. ludoviciana was studied during three consecutive years on populations growing in winter wheat crops in central Spain. Seed banks were determined annually by soil sampling followed by wet sieving. Permanent quadrats were monitored periodically to obtain data on the periodicity of seedling emergence, the fates of seedlings and their reproductive performance.(2) Seedling emergence took place from mid-October to mid-April, with a peak in November-December. The progress of emergence was well described by a logistic model and it was closely related to the cumulative rainfall recorded during that period. Total seedling recruitment from the seed bank ranged from 31 to 46% during the three seasons.(3) Average seedling survivorship ranged from 31 to 81% during the three seasons. Within each season, survivorship was highly variable for the different cohorts. The major causes of mortality during the life-cycle were pre-planting tillage, frost and drought stress and inter-and intra-specific competition.(4) Average adult fecundity varied from thirteen to twenty-one seeds per plant. Within each season, fecundity was highly dependent on the age of the plant. The relationship between plant age and fecundity was well described by a negative exponential model.(5) Overall, the cohorts emerging soon after wheat planting were the most successful ones, having the largest contribution to the next generation.

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Summary A long‐term study was conducted during 4 consecutive years to determine the effects of herbicides on the major demographic parameters and on the dynamics of the populations of Avena sterith ssp. ludoviciana (Durieu) Nyman growing in winter wheat crops in Central Spain. The three herbicides tested bad different effects on the life cycle of the plant. Tri‐allate was moderately effective in reducing seedling recruitment and seedling survivorship, but it resulted in adult fecundities similar to or higher than, those of the check plots. Difenzoquat was highly effective in reducing plant survivorship and it consistently reduced the reproductive capacity of the survivors. Flamprop‐isopropyl L was not very effective in reducing plant survivorship, but it had the largest influence on adult fecundity. Overall, although the three herbicides were able to reduce substantially (59–95%) the production of new seeds, large numbers of seeds were returned annually to the soil in all the treatments. The annual application of any of the three compounds during 4 consecutive years had a marked effect on the long‐term evolution of the populations of buried seeds in the soil, emerged seedlings, mature plants and new seeds produced. Continuous herbicide application resulted in a gradual depletion of the seed bank of A. sterilis in the soil. At the end of the 4‐year period, buried seed populations in the herbicide‐treated plots were (61–81%). lower than those at the beginning of the experiment, and 92–95% lower than those of the check plots at the same lime. However, the seed reserves present in the treated plots were Mill high enough to require some type of control programme.

Aim of study: A predictive model of the seedling emergence pattern of Phalaris brachystachys Link (short-spiked canary grass) was developed, aimed to contribute to support a more efficient management of this troublesome, competitive weed in winter cereal crops around its native Mediterranean range and in different areas of the world where it is introduced. Area of study: Southern (Andalusia) and northern Spain (Navarra). Material and methods: A model describing the emergence pattern of P. brachystachys in cereal fields based on accumulation of hydrothermal time in soil was developed and validated. For model development, cumulative emergence data were obtained in an experimental field, while an independent validation of the model was conducted with data collected in two commercial wheat fields from climatically contrasting regions of Spain. Main results: The relationship between cumulative emergence and cumulative hydrothermal time (CHT) was well described by a Logistic model. According to model predictions, 50% and 95% seedling emergence takes place at 108 and 160 CHT above base water potential for seed germination, respectively. The model accurately predicted the seedling emergence time course of P. brachystachys in the two commercial wheat fields (R2 ≥ 0.92). Research highlights: This model is a new tool that may be useful to improve the timing of control measures to maximize efficiency in reducing P. brachystachys infestations in cereal crops.