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Summary Modelling weed seedling emergence pattern appears to be a promising approach in the development of effective weed management programmes based on the selection of optimal timing of control operations. Thermal and hydrothermal time models propose that seed germination rates are proportional to the amount by which temperature and water potential exceed threshold values for these environmental factors. Hence, base temperature for seed germination is a fundamental biological parameter for the prediction of weed emergence. A series of laboratory experiments were conducted to estimate base temperature in three weed species belonging to the Asteraceae family, predominant in conservation tillage fields in north-eastern Italy. The traditional method based on germination assays at constant temperatures was compared with a method based on assays at alternating temperatures. The latter might represent an alternative to the former for those species which do not germinate or only poorly under constant temperatures. Base temperature was estimated by regressing the reciprocal of the median germination time on temperature comparing two functions, a broken-stick and an exponential-type model. Both models showed good fit to all data in the whole temperature range and in almost all cases provided similar estimates of base temperature. The main result is that, for the weed species examined in this study, the use of alternating temperatures for base temperature estimation appears to be possible. However, further research is required to test if the use of germination assays performed at alternating temperatures can be a suitable method to estimate base temperature of species that have too low germination at constant temperatures.

Loddo D, Masin R, Otto S & Zanin G (2011). Estimation of base temperature for Sorghum halepense rhizome sprouting. Weed Research 52, 42–49. Summary Sorghum halepense is a rhizomatous perennial summer weed. It spreads by seeds and rhizomes that form ramets. The development of predictive models for ramet emergence (RE) from rhizomes may provide important information about their seasonal dynamics and consequently for the timing of control operations. The aim of this work was to analyse the effect of temperature on S. halepense rhizome sprouting (RS) and to estimate its base temperature, which is the first step for creating mathematical models to predict RE. Rhizomes collected from two North Italian populations were incubated at several constant temperatures. The total number of ramets, sprouted rhizomes and their ratio (ramet/sprouted rhizome) were calculated. The influence of temperature on sprouting performances was analysed. Base temperature was calculated using two methods: the reciprocal time of 50% RS (method) and RE (method). Confidence limits (at 0.95 level) were defined for each estimated base temperature using a bootstrap method. Base temperatures were compared to verify whether there were differences between populations and methods. Results indicated a significant stimulating effect of temperature on S. halepense rhizome performances. Estimated base temperatures did not differ between populations, nor between methods within a population (Padova RS 9.7 ± 1.25°C (confidence limits), RE 10.0 ± 1.28°C, Mantova RS 8.0 ± 1.89°C and RE 9.7 ± 1.23°C). The same thresholds may consequently be adopted for thermal time models for the two populations. These results also suggest that both methods (RE and RS) can be used without distinction to estimate the rhizome base temperature.

Summary 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) belowground 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

Otto S, Loddo D & Zanin G (2010). Weed-poplar competition dynamics and yield loss in Italian short-rotation forestry. Weed Research50, 153–162. Summary In recent years there has been increasing interest in short-rotation poplar plantations for biomass production and cropping techniques and weed control strategies are being developed. Slow initial poplar growth can favour weed infestation and so there is a need for appropriate timing of weed control, based on an understanding of the competitive relationship and dynamics between poplar and weeds. A field experiment with annual and biennial crop cycles was conducted over two years. A 35 cm wide within-row weedy strip was allowed to develop as the basis for competition. Yield data were fitted with sigmoidal equations, in order to find the critical point (CP) and critical period of weed control (CPWC), using thermal time as the independent variable. Results showed that poplar is very sensitive to weed competition, especially in the first growing season after planting or cutting, and that competition can cause important yield losses. In the annual cycle, the CP corresponds to a yield loss of 26% and 8% in the first and second growing season respectively; in the biennial cycle the CP corresponds to a yield loss of 29%. Furthermore, the CPWC is long. For example, in the first year, based on a 5% yield loss, it lasts from 30 to 84 days after planting. This makes effective weed control difficult to achieve only using a pre-emergence herbicide, and thus necessitates a post-emergence treatment, either with herbicides or inter-row cultivation. These results, together with the inability of the crop to recover from damage, mean that resources must be invested in weed control soon after the beginning of the cropping cycle.

Summary Seventeen Italian experiments relating to maize, soyabean and durum wheat were used to analyse the variability of duration of tolerated competition (DTC) and weed-free period (WFP) curves across reasonably homogeneous areas. The data sets were analysed by regression analysis using four models relating yield loss to weed density, time of emergence and removal. These models differ in the way they account for the effect of time of weed removal on potential competitiveness. A sigmoidal relationship between these two variables appears necessary. The model with the best overall performance was then used to test the stability of the parameters that give the shape of the curve in relation to time of emergence and removal. This was done by comparing a full model with shape parameters specific to each experiment and a reduced model with a common set of parameters for all the experiments referring to a specific crop. For all three crops, the residual sum of squares of the reduced model did not increase significantly, indicating that, across tested environments, the yield loss caused by mixed weed infestations can be expressed by a single set of parameters relating weed competitivity to time of emergence and removal. For a given area, it should therefore be possible to predict yield loss on the basis of a quite limited set of experiments, thus greatly simplifying the development and use of decision support systems (DSS).

Summary Digitaria sanguinalis, Eleusine indica, Setaria glauca and S. viridis are troublesome summer annual weeds in turf. For taking rational decisions on the necessity for the level and type of weed management, it is important to know when weeds are ready to emerge (dormancy status) and also how long weed seeds can survive in the soil. Seeds of these four species were buried 4.0–4.5 cm deep in steel mesh net bags placed under permanent turf and periodically exhumed for 3 years to evaluate viability and determine the dormancy/non-dormancy cycle. D. sanguinalis, S. glauca and S. viridis showed the typical dormancy cycle of summer annual species, and their seed viability declined completely after 3 years of burial. In contrast, E. indica demonstrated unusual behaviour, with long persistence and no dormancy.

The mechanisms of herbicide resistance were investigated in two diclofop-methyl-resistant Lolium spp. populations from central Italy, Roma ’94 and Tuscania ’97. These two populations were compared with two susceptible Italian populations (Vetralla ’94, Tarquinia ’97) and a resistant and a susceptible population from Australia, SLR31 and VLR1. The activity of acetyl Co-A carboxylase (ACCase) extracted from susceptible (S) or resistant (R) individuals from the Italian populations was inhibited by both aryloxyphenoxypropanoate (diclofop acid and fluazifop acid) and cyclohexanedione (sethoxydim) herbicides. Diclofop-methyl was rapidly de-esterified to diclofop acid at a similar rate in both R and S populations. In all populations, diclofop acid was subsequently degraded to other metabolites. The rate of degradation of diclofop acid was not significantly faster in R than in S populations; however, diclofop acid was degraded more completely in Roma ’94 and Tuscania ’97 compared with the S populations. Application of the mixed-function oxidase inhibitor 1-aminobenzotriazole (ABT) significantly enhanced diclofop-methyl toxicity towards both R populations, but not in S populations. However, enhanced herbicide metabolism does not completely account for the measured resistance level. A mechanism other than an altered ACCase and enhanced herbicide metabolism appears to be responsible for resistance to diclofop-methyl in Roma ’94 and Tuscania ’97.

Populations of Lolium spp. collected in central Italy were screened for resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides and compared with known susceptible and resistant Lolium rigidum (Gaud.) populations from Australia. Populations Roma’94 and Tuscania’97 were up to 8- and 7.5-fold more resistant to diclofop-methyl, respectively, than susceptible populations in pot experiments. However, populations Tarquinia’97 and Vetralla’94 were not resistant. Diclofop-methyl resistance levels in the Italian populations were lower than in the Australian populations SLR31 and WLR96 (16.5 and > 64 times more resistant than S respectively). In an agar germination test, Tuscania’97 showed low levels of cross-resistance to fluazifop-p-butyl, whereas no cross-resistance was found in the Roma’94 population.

Floral surveys were carried out on a field of 28 m x 100 m on the nodes of a regular 2 m x 2 m grid, using a rectangular sampling area of 25 cm x 30 cm. In total, 765 units were sampled, each one characterized by the spatial co-ordinates and the number of seedlings of different weed species. The spatial representation of the weeds was obtained with kriging. Simulations were carried out for Amaranthus spp., which had the highest frequency and density (221 plants m -2 ), and Portulaca oleracea L., a species that combined a more aggregated distribution with a medium-high density (27 plants m -2 ). The results obtained clearly indicated that the usefulness of geostatistical procedures depends on the type of question posed by the user. If the goal is to estimate weed density and, consequently, crop yield loss, kriging appears to overburden the decision-making process, without improving the estimates obtained. This procedure becomes useful for obtaining weed infestation maps to be used for intermittent spraying applications. The reliability of these maps increases with the number of samples used for kriging. With the more aggregated species, at least 50 samples are required to obtain an infestation map. The reduction in the area to be treated depends on the threshold level adopted and on the number of samples used for kriging. With a threshold around the break-even point for most post-emergence treatments, this reduction varies from 10% to 40% with maps obtained from 50 and 175 samples respectively. The usefulness of infestation maps obtained with kriging for improving the decision-making process is strictly dependent on the weed patch dynamics : if these patches remain relatively stable over time, kriging can be carried out periodically without overburdening the decision-making process, whereas, if they are not stable, maps need to be drawn up each year, with a significant increase in costs.

Summary: Resume: Zusammenfassung A method to evaluate potential crop damage from multi-species weed infestations is presented. The method is based on the hyperbolic relationships between density of a single weed species and crop yield loss. When considering a mixed weed population, the density of each species is transformed into a Density Equivalent, defined as the density that is equal to the density of a reference species giving the same yield loss. A hypothetical species with i and a parameters both equal to 100 was adopted to describe the relationship between yield and reference density. The method has been evaluated with data from a 2-year experiment on soybean (Glycine max (L.) Merril) grown in mixtures with Xanthium strumarium L. subsp. italicum, Polygonum persi-caria L. and Panicum miliaceum L. The mixtures included seven weed densities with different proportions of the three weed species. The model described the data well, but it showed an average 7–5% overestimation of crop damage. The reasons for this overestimation and the utility of the model in weed management is discussed. La densiteequivalente: une methode pour predire les penes de rendement causees par des populations melangees de mauvaises herbes Une methode est presentee qui permet d'evaluer le dommage potentiel causea une culture par des infestations multi-specifiques de mauvaises herbes. Elle est basee sur les relations hyperboliques entre la densite d'une mauvaise herbe donnee et la perte de rendement de la culture. Quand on considere une population de mauvaises herbes melangees, la densite de chaque espece est con-vertie en une DensiteEquivalente, definie comme la densiteegale a la ensite de la mauvaise herbe de relerence qui occasionne la meme perte de rendement. Une espece hypothetique avec des parametres 'i' et 'a' tous deux egaux a 100 a ete definie pour decrire la relation entre le rendement et la densite de reference. La methode a eteevaluee avec des donnees tirees d'une experimentation de deux ans sur soja (Glycine max. (L.) Merril) en cultures melangees avec Xanthium strumarium L. subsp. italicum, Polygonum persicaria L. et Panicum miliaceum L. Les melanges comprenaient 7 densites de mauvaises herbes avec des proportions differen-tes des trois especes. Le modele decrivait bien les donnees mais il surestimait d'environ 7.5% le dommage a la culture. Les raisons de cette sures-timation et 1'utilite du modele dans la lutte centre les mauvaises herbes sont discutees. Eine Methode zur Vorhersage von Ertragsver-lusten durch Unkrautmischbestande mil Hilfe des Dichte-Aquivalents Die Methode zur Bestimmung moglicher Ertragsverluste durch Verunkrautungen mil mehreren Arten basiert auf dem hyperbolischen Verhaltnis zwischen der Dichte einer einzelnen Unkrautart und dem Ertragsverlust. Bei Unkrautbestanden mil mehreren Arten wird die Dichte jeder einzelnen Artinein Dichte-Aquiva-lent transformiert, das als die Dichte definiert ist, die der Dichte einer Referenz-Art gleich ist, die zu demselben Ertragsverlust fuhrt. Es wurde eine hypothetische Art mit den Parametern ‘i’ und ‘a’, beide gleich 100, angenommen, um die Beziehung zwischen Ertrag und Referenz-Dichte zu beschreiben. Die Methode wurde anhand von Daten aus einem 2 ahrigen Versuch in Sojabohne (Glycine max (L.) Merril) und Mischbestanden mit Xanthium strumarium L. ssp. italicum, Polygonwn persicaria L. und Panicum miliaceum L. uberpruft. Mit den 3 Unkrautarten wurden durch verschiedene Anteile 7 Unkrautdichtungen in den Mischungen eingestellt. Mit dem Model] konnten die Daten gut beschrieben werden, doch wurden die Ertragsverluste im Durchschnitt um 7.5 %uberbewertet. Die Grunde fur dies uberbewertung und die Brauchbarkeit des Modells fur die Unkrautbekampfung werden diskutiert.

(…) Dans les 186 series de donnees considerees, on n'a jamais observe de distribution normale. Les especes presentant les moyennes les plus basses (