wick et al., 1983). Living plants do not actively release high amounts of ITCs (Bö rner, 1961), because glucosi-The allelopathic potential of isothiocyanates (ITC) released by nolates are located in the vacuole and myrosinase is turnip-rape mulch [Brassica rapa (Rapifera Group)-Brassica napus L.] was evaluated. Six different ITCs were identified from chopped bound to the cell wall (Bjö rkman, 1976). As long as this turnip-rape by HPLC-DAD/HPLC-MS. All plant parts contained separation exists, there is only a low ITC content in the 2-phenylethyl-ITC. In the shoot n-butyl and 3-butenyl-ITC domicells (Tang, 1971). Larger amounts of ITCs can only nated. Younger leaves, flowers, and buds also contained small amounts be released by the breakdown of the cells, e.g., during of benzyl and allyl-ITC. Furthermore, marginal amounts of 4-pendecomposition of dead plant material (Bell and Muller, tenyl-ITC were detected. In the soil, where turnip-rape mulch was 1973), or even faster by incorporating green plant mateincorporated, only low amounts of ITCs were detected. It was shown rial into the soil. If Brassica spp. plant tissues are incorthat the DT 50 of ITCs in soil are very short. Germination tests with porated into the soil, it is possible to control weeds in weed seeds in aqueous ITC solutions showed, that aryl-ITCs were the following crop by ITCs released from the mulch the most suppressive compounds. Within the alkyl-ITCs, the activity decreased with increasing molecular mass. The susceptibility of differ- (Brown and Morra, 1995; Boydston and Hang, 1995; ent weed species to ITCs mainly depended on seed size. Smaller seeds Al-Katib et al., 1997). This might be a chance to reduce tended to be more sensitive. Further studies demonstrated a high the use of herbicides and could be an additional tool to biological activity of ITCs in the vapor phase. n-Butyl-ITC was more control herbicide-resistant weeds. suppressive in the vapor phase than in aqueous solution, while 2-The objectives of this study were to evaluate the allelphenylethyl-ITC showed the opposite effect. Results demonstrated opathic potential of ITCs released by turnip-rape that weed suppression observed in the field was probably due to the mulch. Therefore, the content of ITCs in different parts high amounts of ITCs identified in turnip-rape mulch. Isothiocyanates of turnip-rape, and in the soil after incorporation was were strong suppressants of germination on tested species-spiny determined, and the phytotoxicity of different ITCs on sowthistle [Sonchus asper (L.) Hill], scentless mayweed (Matricaria inodora L.), smooth pigweed (Amaranthus hybridus L.), barn-several weed species-spiny sowthistle [Sonchus asper yardgrass [Echinochloa crusgalli (L.) Beauv.], blackgrass (Alopec-(L.) Hill], scentless mayweed (Matricaria inodora L.), urus myosuroides Huds.), and wheat (Triticum aestivum L.)-and smooth pigweed (Amaranthus hybridus L.), barnprobably interact with weed seeds in the soil solution and as vapor yardgrass [Echinochloa crusgalli (L.) Beauv.], blackin so...

The environmental situation and current yield performance of sugar beet production in Germany are described and compared to those in other European regions. A continuous increase in yield performance and enhanced technical quality have been achieved through progress in breeding and improvements in crop management systems. This rise in yield potential has been brought about not by increased production intensity, but by better use of natural resources and production factors. In Germany, legislation rules many environmental aspects of agricultural plant production, and special laws are in force concerning fertilizer use, soil protection, and pesticide use. In sugar beet, nitrogen fertilizer use has decreased greatly and may be reduced further in some regions. A further reduction of potassium and phosphorus fertilizer use does not seem to be appropriate. Conservation tillage contributes to soil protection and is already performed on > 100 000 ha of land growing sugar beet. Strategies of integrated production aim to reduce pesticide use to the bare minimum. Integrated pest management is effective to control insects, nematodes and leaf spot diseases. Pesticide use in sugar beet is dominated by herbicide application. The most promising strategy to reduce the amount of active ingredient seems to be the growing of genetically modified herbicide‐tolerant varieties. Possible directions for future research are discussed, and the prospects for sustainable development, in terms of economic, ecological and social factors, are considered.

Under ®eld conditions the ecacy of glufosinate-ammonium on Galium aparine L. is quite often variable. Experiments under controlled conditions with G. aparine and the more susceptible species Brassica rapa L. showed that especially low relative humidity (r.h.) and low light intensity reduced the accumulation of ammonia in the plants and glufosinate-ammonium performance. As the light intensity under ®eld conditions always exceeds the intensities applied in the experiments this parameter may not be of practical importance. In contrast, low r.h. often occurs under ®eld conditions and could explain the variable G. aparine control. A retention study showed that retention on G. aparine was signi®cantly higher than on B. rapa but ammonia accumulation in the plants indicated that glufosinate-ammonium uptake by G. aparine was lower than that by B. rapa. Glufosinate-ammonium performance was improved on both species by adding ammonium sulphate to the spray solution; however, the increase in ecacy by ammonium sulphate was two times higher for G. aparine than for B. rapa. Ammonia accumulation in untreated plant parts after glufosinate-ammonium application indicated some translocation of glufosinate-ammonium in B. rapa but none in G. aparine.

Alopecurus myosuroides is one of the most important grass weeds on arable land in Germany. For many years, it has developed herbicide-resistant populations. ACCase-and ALS-inhibiting herbicides, in particular, have lost significant efficacy. Two different mechanisms are commonly known to confer resistance to herbicides: target-site resistance (TSR) and non-target-site resistance (NTSR). In Germany, only approximately 5 to 10% of the herbicide-resistant black-grass populations have been reported to show TSR so far. To quantify the status and the distribution of TSR in Germany, 653 black-grass samples were collected between 2004 and 2012 all over the country. The samples were tested by bioassays and genetic analysis. Averaged over all tested samples, ACCase-TSR increased from 5.0% in 2004 to 54.3% in 2011. In 2012, the proportion of ACCase-TSR was lower than the previous years (38.5%). Similarly, ALS-TSR rose from 0.8% in 2007 to 13.9% in 2012. Regions with a high density of resistant black-grass samples were identified in the north and south of Germany. The data suggest a rapidly working selection of herbicide-resistant populations which may be due to current agricultural practices and the increasing use of herbicides acting on a single site.

The aim of this study was to evaluate new options for sugar beet mulch systems, using a glyphosate-resistant hybrid. In four field trials -conducted in 2002 and 2003 at two sites in a major sugar beet-growing region in the central Germany -three different mulch systems (straw, non-winterhardy and winterhardy cover crop) and an alternative seedbed preparation method (rotary band tillage) have been tested in comparison with a control treatment (plough, no mulch, broadcast seedbed preparation) representing the common German practice. In all systems, a set of eight different weed control programmes, including two reference treatments, one with selective conventional herbicides and five exclusively using glyphosate, has been evaluated for efficacy. It could be shown that the integration of winterhardy cover crops into sugar beet mulch systems reduced the risk of nitrogen loss by leaching. The changes in the nitrogen dynamics neither influence the yield nor the technical quality of the sugar beet. The field emergence of sugar beet decreased while using a winterhardy cover crop, but was not altered by the seedbed preparation method. Compared with the conventional broadcast seedbed preparation, the rotary band tillage did reduce the weed density. The lowest weed density was observed in the straw mulch system. It was not possible to control the remaining plants of the winterhardy cover crops completely with selective herbicides. If glyphosate was used until the four-leaf stage of the sugar beet, a regulation of the winterhardy cover crop was achievable. With glyphosate it was also feasible to control older weeds together with the newly emerging ones with post-emergence applications only. For most of the mulch systems tested, the sugar beet was very sensitive to weed competition between the four-and 10-leaf stage. If the weeds within the sugar beet rows were controlled during this sensitive period with an early glyphosate band application, the remaining weeds between the rows could be left uncontrolled until the 10-leaf stage of the sugar beet without any yield loss. Only in the combination of winterhardy cover crop · rotary band seedbed preparation, the weeds and cover crop had to be controlled directly after emergence of the sugar beet.