Search

Climate change is predicted to result in rising temperatures which directly influence weed growth. Moreover, alterations in farming practice and variations in the timing of maize sowing affect weeds also indirectly. The main objective of this study was to establish the methodological concept of time-for-climate substitution for use in applied research. For this purpose, a semi-field experiment was conducted with the three important maize weeds Amaranthus retroflexus, Echinochloa crus-galli and Setaria viridis, which were cropped together with maize. In four treatments sowing of weeds was delayed in order to use naturally raising temperatures. This study focusses on late weed growth properties such as tillers, panicles, seeds and biomass as they allow important demographic conclusions for long-term weed population development. Over the season, temperature was continuously monitored with data loggers and growing degree days were calculated in order to relate the late growth properties to the climatic conditions the weeds experienced during early growth in the four treatments. The results from this study suggest that the tested weeds may benefit in two ways: (1) From warmer conditions during seedling emergence and early growth with enhanced vegetative growth and seed set; (2) from more growing degree days available as a result of earlier maize sowing and related extended cropping seasons. We conclude that our methodology is suitable to investigate climate change effects on weeds for applied questions. In order to limit weed growth and weed seed set under future conditions, management measures such as herbicide treatments at later growth stages and earlier harvest of maize should be explored. Furthermore, we suggest that functional relationships between late weed growth properties such as fecundity and different climatic conditions can be used to improve the accuracy of demographic and bioclimatic models.

Data on weed species currently found in winter oilseed rape, the extent of their occurrence and regional distinctions were collected in autumn 2005, 2006 and 2007 from a total of 1463 oilseed rape (OSR) fields throughout Germany. Investigations took place in untreated parts of OSR fields at the four to six leaf stage of rape. Weed frequencies and densities were determined by randomly placing a 0.1 m2 square frame ten times in each plot, identifying and counting all plants within the frame. Results presented here mainly focus the distribution of important weed species and differences in their frequencies and densities between German Federal states. The majority of weed species occurring in winter oilseed rape is not evenly spread over Germany. There are weed species with a limited distribution which can be frequently found in some regions but are absent in others. Sisymbrium officinale, Descurainia sophia, Centaurea cyanus, Anchusa spp., Sonchus spp., Rumex spp. or Euphorbia spp. are some weed species with mainly regional importance. Several ubiquitous weed species show regional differences in their densities. Capsella bursa-pastoris, Chenopodium album, Galium aparine, Lamium spp., Matricaria spp., Stellaria media, Thlaspi arvense, Veronica spp. and Viola arvensis were among the most frequent weed species in OSR in all German federal states though sometimes differing significantly in regional densities. Recent field observations reporting an increased spreading of Geranium spp., Sisymbrium spp. or Anchusa arvensis in intense OSR cropping areas are verified by these results.

Anaerobic digestion in biogas reactors generates a semi-solid leftover, the digestate, which is frequently used as a crop fertiliser. If weed seeds in the maize biomass that is used for feedstock survive the process of anaerobic digestion, the use of digestate could contribute to the spread of weeds. We investigated here the probability that weeds enter the biogas production chain via maize biomass. Five organic and four conventional maize fields were sampled to determine the identity, density and biomass of the weeds present, and the number and viability of seeds produced. This was done separately for plant parts below and above the anticipated cutting height of the maize crop, close to the anticipated harvest date. Weed density varied from 56 to 568 weeds m−2 and weed seed production from 886 to 229 256 seeds m−2. Conventional fields tended to have lower weed biomass, lower seed production, and lower proportion of the seeds above the cutting height of maize, with lower seed viability. The main weeds were Chenopodium album and Echinochloa crus-galli. In general, either weed plants were small and produced few seeds that were largely found below the cutting height of maize, or they were tall and produced numerous seeds that were largely found well above the cutting height. Given the numbers of weed seeds produced per hectare in this study, it is likely that some will survive anaerobic digestion in biogas plants, although in low numbers, as seed survival during anaerobic digestion tends to be low.

The influence of potato cultivar (Solanum tuberosum L. cvs. Albatros, Borwina, Fasan, Kormoran, Pirol, Salome, Romanze and Terrana) and leaf zone on the reproduction rate of green peach aphid, Myzus persicae (Sulzer) and potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae), was assessed in glasshouse experiments. Aphids were caged in five leaf zones of each cultivar. M. persicae prefers senescent leaves. Fecundity and reproductive rate of M. persicae were greater on the lower leaves than on upper leaves (P< 0.001). The total fecundity and reproduction rate of M. euphorbiae were greater on the upper leaves than on lower leaves (P< 0.001). The results showed that the reproduction rate of M. persicae and M. euphorbiae differed significantly (P< 0.05) among cultivars.