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According to Grime's model, velvetleaf can be classified as a competitive-ruderal species. Its biological and ecological characteristics make it particularly competitive and persistent in cultivated fields. Herbicide control is difficult and, once established, it is almost impossible to avoid seed production. The economic threshold, on a single year basis, varies between 0.3 and 1.7 plants m–2. When the competitive relationships and their effects are evaluated, it is very difficult to apply a weed management system based on a single-season threshold. When one considers the agronomic implications of the ecological characteristics of velvetleaf over a longer period, it can be concluded that the use of a single-season economic threshold is probably not the best management strategy.

Predicting weed emergence dynamics can help farmers to plan more effective weed control. The hydrothermal time concept has been used to model emergence as a function of temperature and water potential. Application of this concept is possible if the specific biological thresholds are known. This article provides a data set of base temperature and water potential of eight maize weeds (velvetleaf, redroot pigweed, common lambsquarters, large crabgrass, barnyardgrass, yellow foxtail, green foxtail, and johnsongrass). For five of these species, two ecotypes from two extreme regions of the predominant maize-growing area in Italy (Veneto and Tuscany), were collected and compared to check possible differences that may arise from using the same thresholds for different populations. Seedling emergence of velvetleaf and johnsongrass were modeled using three different approaches: (1) thermal time calculated assuming 5 C as base temperature for both species; (2) thermal time using the specific estimated base temperatures; and (3) hydrothermal time using the specific, estimated base temperatures and water potentials. All the species had base temperatures greater than 10 C, with the exception of velvetleaf (3.9 to 4.4 C) and common lambsquarters (2.0 to 2.6 C). All species showed a calculated base-water potential equal or up to 21.00 MPa. The thresholds of the two ecotypes were similar for all the studied species, with the exception of redroot pigweed, for which the Veneto ecotype showed a water potential lower than 20.41 MPa, whereas it was 20.62 MPa for the Tuscany ecotype. Similar thresholds have been found to be useful in hydrothermal time models covering two climatic regions where maize is grown in Italy. Furthermore, a comparison between the use of specific, estimated, and common thresholds for modeling weed emergence showed that, for a better determination of weed control timing, it is often necessary to estimate the specific thresholds

We reviewed studies aimed at understanding functional relationships between weeds and arthropods in agroecosystems as influenced by biodiversity at different scales, with the main goal of highlighting gaps in knowledge, research methods and approaches. We first addressed: (i) the regulation of arthropod communities by weed diversity at genetic, species and habitat levels, (ii) the regulation of weed communities by arthropods through seed predation and dispersal and (iii) below-ground weed-insect interactions. We then focussed on methodologies to study weed-arthropod interactions in agricultural landscapes and discuss techniques potentially available for data analysis and the importance of joint weed-arthropod trend detection. Lastly, we discuss the implications of research findings for biodiversity conservation policies (agri-environmental schemes) and suggest some priorities for future work. Results showed that to date research has largely ignored weed-arthropod interactions in agricultural landscapes. No information is available on the role of weed genetic diversity as driver of weed-arthropod interactions, whereas studies on effects of species and habitat diversity often lack a functional perspective and/or a spatial component. Also, information on how management of the wider agricultural biotope might express positive weed-arthropod functional interactions is scarce. Another area worth being explored is the relationship between weed-leaf/root herbivores and beneficial arthropods. Tools for spatial data analysis might be useful for elucidating weed-arthropod interactions in agricultural landscapes, but some methodological aspects, e.g. the definition of the most appropriate experimental design and sampling scale/frequency, must be refined. New studies on weed-arthropod interactions should encompass an explicit spatial component; this knowledge is particularly important for improving IPM/IWM systems and designing more targeted agri-environmental schemes