Jursík M., Soukup J., Holec J., Andr J., Hamouzová K. (2015): Efficacy and selectivity of pre-emergent sunflower herbicides under different soil moisture conditions. Plant Protect. Sci., 51: 214-222.We ranked the most frequently used pre-emergent herbicides in sunflower (Helianthus annuus) according to their efficacy and selectivity under different soil moisture conditions within 2008-2011. The efficacy of oxyfluorfen, aclonifen, acetochlor, dimethenamid, and propisochlor on the majority of weeds (Chenopodium album, Echinochloa crus-galli, Amaranthus retroflexus, Mercurialis annua, and Solanum physalifolium) was only slightly affected by the soil moisture and these herbicides can be used in arid and semiarid regions. The efficacy of linuron, prosulfocarb, and pethoxamid was strongly affected by soil moisture and was insufficient under dry conditions. The majority of herbicides showed good selectivity for sunflower. Crop injury rate of 5-15% was recorded after application of flurochloridone and acetochlor. For flurochloridone, the phytotoxicity increased due to irrigation after herbicide application. The highest sunflower injury rate (27-35%) was recorded after application of oxyfluorfen.

Small plot trials were carried out in years [2001][2002][2003] with sugar beet. In the treatment without weed control, dry weight of sugar beet top and LAI of sugar beet were very low (approx. 50 g/m 2 and 0.5 m 2 /m 2 , respectively). Yield loss of sugar beet was 80-93%. Dominant weeds were Chenopodium album, Fumaria officinalis and Galium aparine. In the treatments where weeds were removed (by hand) until 4 leaf stage of sugar beet, dry weight of sugar beet top and LAI of sugar beet at first increased normally, but were markedly decreased from the half of the vegetation period. Yield loss of sugar beet was 54-28%. Dominant weed in this treatment was Amaranthus retroflexus. The development of sugar beet top dry weight and LAI of sugar beet was practically identical in the treatments where weeds were removed until 8-10 leaf stage of the crop and in those where weeds were removed during the whole vegetation period (500-900 g/m 2 , or 4-7 m 2 /m 2 , respectively). No yield loss of sugar beet was recorded. Dry weight of weeds did not exceed 30 g/m 2 and LAI 0.1 m 2 /m 2 . A. retroflexus and Mercurialis annua were the most frequent weeds in this treatment.

Laboratory experiments were carried out with seeds of Galinsoga ciliata and Chenopodium album in 1998, 2000 and 2001. The study involved germination of non-dormant seeds in the light and the dark at 5-30°C, the germination energy at 15, 24, and 33°C, and the primary dormancy of seeds matured during the period from July to October. Both weeds germinated better in the light compared to the dark. Seeds of G. ciliata germinated at 10-33°C. Germination exceeding 85% was recorded at 12-28°C. Ch. album germinated in a wider temperature interval (5-33°C). Maximum germination (75%) was obtained at 18°C. A very high germination energy of G. ciliata seeds was found at 24°C. At this temperature, 89% of seeds germinated during the second and third day of the germination test. Seeds of Ch. album had a low germination energy at 15 and 24°C. The germination energy was high only at 33°C, however, the total germination reached at this temperature was only 26.5%. Both G. ciliata and Ch. album formed primary dormant seeds during all three testing years. The length of primary dormancy varied from 10 to 100 days depending on the date of ripening and on the year. The longest primary dormancy was found with early ripened seeds (July and August).

Four efficacy and selectivity small plot field trials were carried out in four sunflower hybrids at two localities in Middle Bohemia during 2008 and 2009 with herbicides containing the active ingredients flumioxazin and fluorochloridone. For Chenopodium album, an efficacy of 97% was found after pre-emergent application of fluorochloridone + acetochlor; the efficacy of oxyfluorfen was 88-95%; the efficacy of flumioxazin was below 50% at both tested application rates (30 and 60 g/ha) and application timings (2 sunflower leaves and 4 to 6 sunflower leaves); efficacy of flumioxazin increased to 67% and 69%, when surfactants were added (isodecyl alcohol ethoxylate and heptamethyltrisiloxan). Full control of Amaranthus retroflexus was found after all pre-emergent and early post-emergent herbicide treatments; efficacy of late post-emergent herbicide treatments was below 93%. Full control of Mercurialis annua was found only after application of oxyfluorfen. Thlaspi arvense was fully controlled by fluorochloridone + acetochlor (pre-emergent) and oxyfluorfen (in both application terms). Selectivity of the four tested sunflower hybrids to fluorochloridone + acetochlor, bifenox and flumioxazin was acceptable (phytotoxicity 6 to 27%). Higher phytotoxicity (23-45%) was recorded when surfactants were added to flumioxazin. The highest phytotoxicity (68-81%) was recorded after the application of oxyfluorfen.

Competitive ability of six summer catch crops (Brassica napus, Lolium multiflorum, Lolium perenne, Phacelia tanacetifolia, Sinapis alba and Trifolium incarnatum) in volunteer winter wheat based on field trials was experimentally tested during the years 2004-2007 in central Bohemia (Czech Republic). The production of aboveground biomass and plant cover of sown catch crops, volunteers and weeds was assessed on experimental plots. General linear models revealed significant influence of catch crops, year and their interaction on dry-mass of the volunteers. The lowest average values of volunteer biomass at the end of growing season (average from [2004][2005][2006][2007] were recorded on plots sown with S. alba (124.7 kg/ha) and P. tanacetifolia (186.3 kg/ha). The average biomass of volunteer plants in stands of S. alba was significantly lower than the biomass of volunteers in stands of L. perenne, L. multiflorum and T. incarnatum. The lowest average biomass of weeds was recorded also in S. alba stands. In the context of our study, catch crop is a crop sown between seasons of regular plantings to make use of temporary idleness of the soil.

There is much documentation in the scientific literature (e.g. Clay et al. 1999, Hamouz et al. 2006, Gerhards et al. 2012) that weeds are distributed in a patchy manner throughout agricultural fields. An aggregated distribution pattern of weed populations provides opportunity to reduce the herbicide application if site-specific weed management is adopted. Gerhards et al. (2002) achieved herbicide savings of 60% and 92% for dicotyledonous and monocotyledonous weeds, respectively, in spring barley (Hordeum vulgare L.) cultivation, and savings of 11% and 81% were achieved for the same weed groups for maize (Zea mays L.). In two winter wheat fields, Häusler et al. (1998) found that herbicide applications were necessary for 24% and 35% of the area for Galium aparine L., for 25% and 31% for other dicotyledonous weeds and for 55% and 7.5% for grasses. Using a simulation, Christensen and Heisel (1998) estimated a 40% reduction of herbicide consumption, and Nordmeyer and Häusler (2000) calculated the need for herbicide application from 7% to 64% of the total area in various fields.Site-specific weed management is based on the threshold concept: the aim is to adjust the intensity of management practices to the actual degree of weed infestation, with only those areas having a weed density exceeding the predefined control threshold typically being treated. However, sitespecific weed management requires the precise setting of control thresholds for effectiveness and reliability. Furthermore, both areas that are treated superfluously and unsprayed areas that will show increases in weed infestation should be Impact of site-specific weed management on herbicide savings and winter wheat yield P. Hamouz, K. Hamouzová, J. Holec, L. Tyšer Department of Agroecology and Biometeorology, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Prague, Czech Republic ABSTRACTAn aggregated distribution pattern of weed populations provides opportunity to reduce the herbicide application if site-specific weed management is adopted. This work is focused on the practical testing of site-specific weed management in a winter wheat and the optimisation of the control thresholds. Patch spraying was applied to an experimental field in Central Bohemia. Total numbers of 512 application cells were arranged into 16 blocks, which allowed the randomisation of four treatments in four replications. Treatment 1 represented blanket spraying and the other treatments differed by the herbicide application thresholds. The weed infestation was estimated immediately before the post-emergence herbicide application. Treatment maps for every weed group were created based on the weed abundance data and relevant treatment thresholds. The herbicides were applied using a sprayer equipped with boom section control. The herbicide savings were calculated for every treatment and the differences in the grain yield between the treatments were tested using the analysis of variance. The site-specific applications provided herbicide savings ...

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Velvetleaf is one of the most significant and fastest spreading alien weeds in Europe, and it is a difficult weed to control in conventional sugarbeet. Laboratory experiments were carried out in 2007 and 2008 and field experiments were carried out in 2006, 2007, and 2008 with the aim of finding effective herbicide combinations and optimum timing of control. Herbicides containing the active ingredients phenmedipham, desmedipham, ethofumesate, clopyralid, and triflusulfuron were all tested at different timings. Phenmedipham + desmedipham + ethofumesate gave 87% velvetleaf control in pot experiments when applied at the growth stages of velvetleaf cotyledons and one true leaf, but only 27 to 42% control in field trials. Triflusulfuron gave 76% control in pot experiments and 83 to 88% control in field experiments. The timing of the first and second herbicide applications was very important: the first application of herbicides must be at the cotyledon stage of velvetleaf. A 1-wk delay in first application reduced herbicide efficacy by 8%. A 5-d period between the first and second treatments gave 93% control, while a 10-d period between the first and second treatments gave only 77% control. Sugarbeet yield decreased by 60 to 86% due to competition with velvetleaf when a standard herbicide combination (phenmedipham + desmedipham + ethofumesate) was used, and the velvetleaf produced between 6,700 and 14,800 seeds m−2. Inclusion of triflusulfuron in the herbicide treatment significantly reduced velvetleaf seed production to between 200 and 4,700 seeds m−2. In most cases, inclusion of triflusulfuron increased sugarbeet yield. Better velvetleaf control occurred in years when the sugarbeet canopy developed early and the index of leaf area of sugarbeet was higher.