Corn poppy (Papaver rhoeas), the most problematic broadleaf weed in winter cereals in Southern Europe, has developed resistance to the widely-used herbicide, 2,4-D. The first reported resistance mechanism in this species to 2,4-D was reduced translocation from treated leaves to the rest of the plant. However, the presence of other non-target site resistance (NTSR) mechanisms has not been investigated up to date. Therefore, the main objective of this research was to reveal if enhanced 2,4-D metabolism is also present in two Spanish resistant (R) populations to synthetic auxins. With this aim, HPLC experiments at two 2,4-D rates (600 and 2400 g ai ha-1) were conducted to identify and quantify the metabolites produced and evaluate possible differences in 2,4-D degradation between resistant (R) and susceptible (S) plants. Secondarily, to determine the role of cytochrome P450 in the resistance response, dose-response experiments were performed using malathion as its inhibitor. Three populations were used: S, only 2,4-D R (R-703) and multiple R to 2,4-D and ALS inhibitors (R-213). HPLC studies indicated the presence of two hydroxy metabolites in these R populations in shoots and roots, which were not detected in S plants, at both rates. Therefore, enhanced metabolism becomes a new NTSR mechanism in these two P. rhoeas populations from Spain. Results from the dose-response experiments also showed that pre-treatment of R plants with the cytochrome P450 (P450) inhibitor malathion reversed the phenotype to 2,4-D from resistant to susceptible in both R populations. Therefore, it could be hypothesized that a malathion inhibited P450 is responsible of the formation of the hydroxy metabolites detected in the metabolism studies. This and previous research indicate that two resistant mechanisms to 2,4-D could be present in populations R-703 and R-213: reduced translocation and enhanced metabolism. Future experiments are required to confirm these hypotheses, understand the role of P450, and the relationship between both NTSR mechanisms. On this basis, selection pressure with synthetic auxins bears the risk of promoting the evolution enhanced metabolism in Papaver rhoeas.

Many weed species are becoming rare due to intense agricultural management, which leads to a decrease of biodiversity in agroecosystems. Cultivating some of these species for their oilseed content may help preserve them while profiting agronomically. Thlaspi arvense is one of these species with potential as an industrial crop. The aim of this work was to develop a model to describe the emergence of this species, and that can help to make decisions for its management, whether for conservation or production purposes. The emergence of two accessions of T. arvense, one from Spain and the other from USA, sown in Spain (Almenar) and USA (Morris), over two seasons (2011–12 and 2012–13) and in Riga (Latvia) over one season (2012), was followed to compare patterns and extent, as well as to develop emergence prediction models based on hydrothermal time (HTT) and photohydrothermal time (PhHTT). For the USA accession, the percentage of seeds that emerged was significantly higher than that of the Spanish accession. Both accessions presented two emergence peaks (autumn–winter and spring) in both localities, but while these peaks could be considered as two different flushes in Almenar – for both accessions –, they appeared to be a single flush disrupted by low winter temperatures in Morris. An HTT-based model was applicable for both accessions with less precision than the PhHTT-based one, which was more accurate in most cases but failed in certain circumstances for the USA accession. The differences in emergence percentage among accessions suggest that some accessions might be more amenable to being used as a crop. The two models developed in this work predicted the emergence of both accessions of T. arvense quite accurately. The inclusion of photoperiod in the hydrothermal time equation, creating a new unit that we have called photohydrothermal time, offers a possibility to obtain more accurate models.This work was supported by the Ministerio de Educación y Cienciade España (AGL2010-22084-C02-01). We thank the Botanical Garden of the University of Latvia for letting us set the experiment in their court. The group from Lleida thanks Núria Moix, Ana Isábal, Jordi Rey-Ana Baños and Eva Edo for their help in the field. We also thank Joe Boots for his expert field assistance at the Morris, Minnesota field site. Finally, we thank Dr Frank Forcella for his valuable suggestions to improve this manuscript

Multiyear field data from Spain were used to model seedling emergence for three bedstraw species (Galium) that can coexist in winter cereal fields. The relationships between cumulative emergence and both growing degree days (GDD) and hydrothermal time (HTT) in soil were analyzed as sigmoid growth functions (Weibull). Iterations of base temperature and base water potential were used to optimize the HTT scale. All species were well described with Weibull functions. Both GDD and HTT models provided good descriptions of catchweed bedstraw emergence, as its seedlings have less dependence on soil water potential than false cleavers and threehorn bedstraw, which were described best with HTT. The HTT model for catchweed bedstraw was validated successfully with independent data from the United Kingdom. The models may be useful for predicting bedstraw emergence in semiarid Mediterranean regions and elsewhere.

Crop rotation in winter cereals in semiarid Mediterranean climates is highly desirable to prevent weed infestations, but the climatic conditions make it difficult to implement alternative crops to winter cereals. Camelina (Camelina sativa (L.) Crantz) is an interesting option, as it is able to produce profitable yields thanks to its tolerance to cold and drought. In this work, three autumn–winter sowing dates (SD1, October; SD2, December; SD3, January) and two sowing rates (R1, 8 kg ha⁻¹; R2, 11 kg ha⁻¹) were chosen to evaluate the effectiveness of these cultural methods to control weeds over three seasons, and to determine effects on camelina seed yield. Results showed that a significant reduction of weed coverage was obtained by delaying the sowing date. Sowing rates did not show differences in weed coverage. In contrast, no apparent yield penalty was observed among sowing dates and rates. These results show that the introduction of camelina as a rotational crop in semiarid Mediterranean climates is a feasible option for helping to suppress winter weeds, as well as to provide productive seed yield in these climatic conditions.