Alopecurus Myosuroides Blackgrass ( ) and Silky Windgrass (Apera Spica-Venti) at Wheat Harvest

Weed Science Seed production and retention at maturity of Alopecurus myosuroides www.cambridge.org/wsc blackgrass ( ) and silky windgrass (Apera spica-venti) at wheat harvest

1 2 Research Article Zahra Bitarafan and Christian Andreasen

1 Cite this article: Bitarafan Z and Andreasen C Research Assistant, Department of Plant and Environmental Sciences, Faculty of Science, University of 2 (2020) Seed production and retention at Copenhagen, DK-2630 Taastrup, Denmark and Associate Professor, Department of Plant and Environmental maturity of blackgrass (Alopecurus Sciences, Faculty of Science, University of Copenhagen, DK-2630 Taastrup, Denmark myosuroides) and silky windgrass (Apera spica- venti ) at wheat harvest. Weed Sci. doi: 10.1017/ Abstract wsc.2020.7 Blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) Received: 6 August 2019 P. Beauv.] are becoming a significant problem in Europe. Due to the development of herbi- Revised: 20 November 2019 Accepted: 3 January 2020 cide-resistant biotypes and unwanted side effects of herbicides, there is a need for new integrated weed management strategies to control weeds. Therefore, reducing weed infestations Associate Editor: by targeting seed production during crop harvest should be considered. In 2017 and 2018, we Prashant Jha, Iowa State University estimated the fraction of the total seed production of A. myosuroides and A. spica-venti in a Keywords: field that potentially could be collected by a grain harvester during winter wheat (Triticum Autumn-sown crop; grass weeds; aestivum L.) harvest. Twenty plants of each species were surrounded by a porous net before seed-shedding pattern; soil seedbank; flowering to trap shed seeds during reproductive development. Seeds were collected and weed seed production; weed management counted weekly up until and immediately before wheat harvest, and the ratio of harvestable seeds to shed seeds during the growing season was determined. Alopecurus myosuroides Author for correspondence: −1 −1 Christian Andreasen, Department of Plant and produced on average 953 seeds plant in 2017 and 3,337 seeds plant in 2018. In 2017 Environmental Sciences, Faculty of Science, and 2018, 29% and 37% of the total A. myosuroides seeds produced, respectively, were University of Copenhagen, Højbakkegaard Allé retained on plants at maturity. Apera spica-venti produced on average 1,192 seeds plant−1 13, DK-2630 Taastrup, Denmark. in 2017 and 5,678 seeds plant−1 in 2018, and retained 53% and 16% of the seeds at harvest, Email: [email protected] respectively. If a grain harvester potentially collected approximately 30% of the total seed production of the two grass weeds and removed or killed them, it would reduce seed input to the soil seedbank. However, such methods cannot stand alone to reduce weed pressure.

Introduction During the last 30 yr, the frequency of autumn-sown crops in Denmark has increased almost 70% at the expense of annual spring crops and grass leys (Andreasen and Streibig 2011;Anonymous 1971, 2005). A shift from summer to winter annual crops favors winter annual weed species such as blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) P. Beauv.], which are now among the most common weeds across large areas of Europe (Aamisepp and Avholm 1970; Andreasen and Stryhn 2008; Melander et al. 2008;Naylor 1972). Both species are highly competitive weeds that can cause substantial yield reduction in winter wheat (Triticum aestivum L.) crops (Vizantinopoulos and Katranis 1998). In England, the economic threshold level for A. myosuroides was found to be only 12 plants m−2 (Moss 2013), while a density of 10 plants m−2 of A. spica-venti can lower grain yield in winter wheat by 17% in Denmark (Melander 1995). Apera spica-venti is one of the most abundant grass weeds in arable lands of Central and Eastern Europe (Massa and Gerhards 2011). Naylor (1972) reported that autumn-germinating A. myosuroides produced up to 8,000 seeds plant−1, while Holzner (1981) recorded 50 to 6,000 seeds plant−1.SeedsofA. spica-venti are tiny (1.6 by 0.4 by 0.5 mm) (Holm-Nielsen 1998) and are produced in large numbers per plant depending on the growing conditions (Warwick et al. 1985). Seed shed has been reported 1 to 2 wk before winter wheat harvest at the end of July in Germany (Kampe 1975;Koch1968). Apera spica-venti has been reported to produce up to 2,000 to 16,000 seeds plant−1 (Holzner et al. 1982;Melander1993). It has been reported that a density of 10 plants m−2 of A. spica-venti can lower grain yield in winter wheat by 17% in Denmark, and control of heavy A. myosuroides infestations in winter cereal fields can increase crop yield up to 30% (Melander 1995;Naylor1972). The control of A. myosuroides and A. spica-venti has mainly relied on spraying with acetyl © Weed Science Society of America, 2020. CoA carboxylase (ACCase) inhibitors and acetolactate synthase (ALS) inhibitors. Both species have been reported resistant to ACCase inhibitors and ALS inhibitors and are among the most widespread herbicide-resistant weeds in Europe (Keshtkar et al. 2015). Consequently, there is a need for an integrated weed management strategy that includes nonchemical weed control. Moreover, political initiatives to reduce unwanted side effects of pesticide use in Europe can result in further restrictions in chemical weed control (Anonymous 2009). Integrated weed

Downloaded from https://www.cambridge.org/core. Copenhagen University Library, on 02 Mar 2020 at 09:49:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/wsc.2020.7 2 Bitarafan and Andreasen: Seed production and retention

control that combines multiple strategies will be a necessity to find a compromise between crop production, crop protection, and agricultural biodiversity in the future (Andreasen and Streibig 2011; Anonymous 2018). Alopecurus myosuroides and A. spica-venti are solely propa- gated by seeds, and their long-term control is dependent upon minimizing seed production (Moss 1983; Szekeres 1991). A major factor in weed seedbank replenishment is the dispersal of weed seeds by grain harvesters (Walsh et al. 2013). During grain harvesting, separation of harvested material takes place directly on the grain harvester. Grains are separated and often collected in a grain tank. Straw is separated and chopped or placed in a row behind the grain harvester, and the chaff fraction, which consists of the remaining harvested material, is spread across the field (Glasner et al. 2018). Weed seeds also enter the front of the grain harvester at harvest, exit the machine in the chaff fraction, get redistributed evenly across the field, and contribute to weed prob- lems in subsequent crops (Broster et al. 2016; Glasner et al. 2018). Therefore, grain harvest provides an opportunity to collect and destroy weed seeds by targeting the weed seed–bearing chaff fraction. In Australia, several approaches to managing this chaff material have been developed in harvest weed seed control (HWSC) systems. These include collection in chaff carts for live- stock feed or burning, confinement with straw in narrow windrows (50 to 60 cm) that are burnt, direct baling with straw during harvest, placement in a narrow (20 to 30 cm) row or rows on dedicated wheel tracks, or processing by chaff-processing impact mills Figure 1. Seed nets in a wheat field in (A) late May and (B) mid July (2018). attached to the harvester (Walsh et al. 2013; 2018b). At the moment, a new system using the heat source from the exhaust 18, 2017, with the cultivar ‘KWS Cleveland’ at a seeding rate of gas of the combine harvester to kill weed seeds is under consider- 180 kg ha−1 and harvested on July 31, 2018. Both fields were clay ation (Jakobsen et al. 2019). The intention is to bring the chaff soils, and crops were grown without pesticides. Before the weeds fraction and contained weed seeds into contact with hot exhaust started to flourish, 20 plants of each species were selected randomly gases to kill the weed seeds before returning this material to the and surrounded by a seed trap comprising a porous net (precision- field (Andreasen et al. 2018; Glasner et al. 2018; Jakobsen et al. woven open-mesh fabrics SEFAR NITEX 06-475/56, Sefar, 2019). The critical question is how much of the total weed seed pro- Germany; mesh opening: 475 μm; opening area: 56%) (Figures 1 duction in a growing season is retained on the weed plants at crop and 2) covering an area of approximate 710 cm2. The nets sur- harvest. If a large fraction of the total seed production could be rounded the plant at the soil surface to make it possible to collect collected and removed from the field or destroyed at crop harvest, the seeds. If there were other plants inside the net, they were this could contribute significantly to reduce the soil seedbank removed. Twenty other plants of each species without seed nets and hence the weed infestation of these two aggressive weed were followed during the growing season to compare the develop- species. In this study, we recorded the seed-shattering pattern of ment of plants inside and outside the nets. All selected plants A. myosuroides and A. spica-venti and estimated how much of survived until harvest. Nets were checked each week to record the total seed production the plants retained at wheat harvest to the start time of seed shattering. Thereafter, seeds were collected get an indication of the potential for HWSC. Our hypothesis is that by a portable vacuum cleaner every 6 to 8 d depending on the a large fraction of the seeds is retained on the weed plants at crop weather conditions and stored in paper bags. Seeds were collected harvest, and consequently there is potential to collect or destroy and counted until wheat harvest (Figures 1 and 2). At harvest time, the seeds with a combine harvester to reduce weed infestation in weed plants were cut 15 cm above the soil surface, as no plants set the following years. seeds below this height; also, a height of 15 cm reflects practical harvest height for the growers. The number of seeds remaining on the weed plants before crop harvest was counted. For both spe- Materials and Methods cies, the number of seeds retained on the plants at wheat harvest Methods and the number of seeds shed before the wheat harvest were determined. The last weed seed collection took place at the first We recorded the seed production and seed shed of A. myosuroides opportunity for wheat harvest. At crop harvest, the weed plants and A. spica-venti during two growing seasons in two winter wheat were cut at the soil surface, dried in a drying cabinet at 80 C for fields located in Taastrup (55.63°N, 12.28°E), Denmark. One field 24 h, and weighed. was sown on September 27, 2016, with the cultivar ‘Elixer’ at a seeding rate of 210 kg ha−1 and harvested on August 15, 2017. − Weather Conditions The field was fertilized with 150 kg ha 1 of NPKS (22-3-8-3) on September 27, 2016, 500 kg ha−1 of NPKS (22-3-10-2) on Weather data came from a weather station in the area (55.67°N, March 16, 2017, and 250 kg ha−1 NPKS (33-3-10-2) on April 12.30°E) (Figure 3). Daily rainfall, wind speed, and the daily maxi- 25, 2017. The other field was unfertilized and sown on October mum and minimum temperature were collected. The mean daily

Seed Shedding during the Wheat Growing Season In 2017, the mature seeds of A. myosuroides started shattering between July 4 and 11, corresponding to 1,978 and 2,089 GDD, respectively (Figure 4A). There was a significant difference between the weekly numbers of seeds shed during the 6 wk before wheat harvest (P ≤ 0.001). The greatest number of seeds dropped between July 31 and August 7, corresponding to 2,416 and 2,536 GDD, respectively, and the least between July 4 and 11 (Figure 4A). In 2018, seed shattering started between June 13 and 20 (corresponding to 1,561 and 1,678 GDD) (Figure 4B). There was a significant difference between the weekly numbers of shattered seeds during the 7 wk before wheat harvest (P ≤ 0.001). The highest and lowest number of seeds shed happened between July 24 and 30 (corresponding to 2,318 and 2,461 GDD) and between July 4 and 10 (corresponding to 1,926 and 2,033 GDD), respectively (Figure 4B). The average plant dry weight at crop harvest varied significantly between the 2 yr (1.98 g in 2017; 6.17 g in 2018; P ≤ 0.001), as the wheat suffered from drought in 2018. In 2017, mature seeds of A. spica-venti started shattering Figure 2. Maturing plants of Alopecurus myosuroides in nets in late May (A.1) and mid between July 19 and 26 (corresponding to 2,212 and 2,331 July (B.1). Maturing plants of Apera spica-venti in nets in late May (A.2) and mid July GDD) (Figure 5A). There was a significant difference between (B.2). the weekly numbers of seed shed during the 4 wk before the wheat harvest (P ≤ 0.001). The greatest number of shattered seeds occurred between August 1 and 8 (corresponding to 2,434 and temperature was calculated as a mean of the daily maximum and 2,555 GDD), and the least number was shed between July 19 minimum temperature, which was used to calculate the growing and 26 (Figure 5A). degree days (GDD) for the growing seasons (Equation 1). In 2018, seed shattering started between July 4 and 11 (corresponding to 1,926 and 2,052 GDD) (Figure 5B). There was a XS 2 significant difference between the weekly numbers of seed shed GDD ¼ ðÞT b [1] m 0 during the 4 wk before wheat harvest (P ≤ 0.001). The greatest S 1 amount of seed shattering took place between July 11 and 18 (cor- where T represents the mean daily temperature, b represents the responding to 2,052 and 2,195 GDD), and the least between July 24 m 0 and 30, respectively (corresponding to 2,318 and 2,461 GDD) base temperature (0 C), S1 is the sowing date, and S2 is the harvest date. (Figure 5B). The average plant dry weight varied significantly between the 2 yr (0.69 g in 2017; 4.59 g in 2018; P ≤ 0.001). The seed-shattering pattern of the two grass species varied Data Analysis between the 2 yr (Figures 4 and 5). In the dry and warm weather The difference in weekly seed shed of weed species during the in 2018, weeds and crop plants matured much earlier than in the growing season of wheat was evaluated using a method for cold and wet year of 2017, resulting in an earlier crop harvest. repeated measurement in R v. 3.6.1 (R Foundation for Statistical Walsh et al. (2018a) reported that early seed shedding reduced Computing, Vienna, Austria, http://R-project.org). The analyses the proportion of seeds retained above the harvest height at crop were done using the extension packages LME4 (Bates et al. 2015) maturity. The same was found for A. spica-venti but not for and MULTCOMP (Hothorn et al. 2008). Each weed species was ana- A. myosuroides. Apera spica-venti shed 46.8% of the total number lyzed separately. The difference in plant dry weight at harvest in the of produced seeds before harvest in 2017 but 83.3 % in 2018 two seasons was also evaluated using ANOVA. (Figure 6A and B). Alopecurus myosuroides shattered 70.7% of the total number of seeds before harvest in 2017 and 63% in 2018. Moss (1983) reported that A. myosuroides seeds were shed Results and Discussion during a period from about late June to late August in the south Midlands of England. As winter wheat in this part of England is Seed production depends on many factors such as soil fertility and usually harvested after mid-August, most seeds are likely to be weather conditions as well as competition from other plants shed before harvest. Secondary heads are sometimes formed in (Raymond 2011). Very different weather conditions characterized late July or August from stem nodes, but they are not normally the two growing seasons. In 2017, the summer in Denmark was important in the production of seeds (Moss 1983). Secondary cold, wet, and cloudy with no days with temperatures >30 C. In heads were also observed in some of the plants in the second year contrast, the weather in 2018 was unusually dry, warm, and sunny but not in the first year. It was observed that early-shed seeds tend with many days with temperatures >30 C. It was the warmest to be derived from seeds near the apex of the heads and late-shed summer since 1874 (Figure 3) (Danmarks Meteorologiske seeds from the base of the heads. Institut 2018). Consequently, the weather resulted in a substantial difference between the 2 yr in terms of seed production and seed- The Percentages of Weed Seeds Retained at Wheat Harvest shattering patterns of the two weed species. However, the wind speed, which also affects seed shattering, did not differ much In 2017, A. myosuroides retained 29.3% of the seeds produced in between the summers. the season at harvest, and 38.9% in 2018 (Figure 6A). For

Downloaded from https://www.cambridge.org/core. Copenhagen University Library, on 02 Mar 2020 at 09:49:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/wsc.2020.7 4 Bitarafan and Andreasen: Seed production and retention

A B C 6 2016 4 2016 2016 2017 2017 25 2017 3.5 2018 5 2018 2018 20 3 4 2.5 15 3 2

10 Wind (m/s) 1.5 2 Precipitation (mm) 1

Temperature (°C) 5 1 0.5

0 0 0 123456789101112 123456789101112 123456789101112 Month Month Month –5

Figure 3. Weather data for 2016, 2017, and 2018. (A) monthly average air temperature, (B) precipitation, and (C) wind speed. Temperature, precipitation, and wind speed were measured at 2, 1.5, and 2 m above ground level, respectively.

Figure 4. Average number of seeds shed from Alopecurus myosuroides each week and the cumulative number of seeds shattered during the growing season of winter wheat in (A) 2017 and (B) 2018. Growing degree days (GDD) = sum of daily mean temperatures above 0 C from the date the wheat was sown.

Figure 5. Average number of seeds shed of Apera spica-venti each week and the cumulative number of seeds shattered during the growing season of winter wheat in (A) 2017 and (B) 2018. Growing degree days (GDD) = sum of daily mean temperatures above 0 from the date the wheat was sown.

A. spica-venti, the corresponding numbers were 53.2% (2017) and competitive ability of the wheat, resulting in large growth and a 16.7% (2018) (Figure 6B). dense wheat stand. In 2018, the wheat plants became drought Shirtliffe et al. (2000) and Taghizadeh et al. (2012) also found stressed, resulting in less growth and a thinner wheat stand to cre- that weed seed retention varied according to climatic conditions, ate more space and light for the weeds, resulting in a higher weed and it would most likely also vary across different agro-ecosystems seed production. Zerner et al. (2008) found a similar relationship (Walsh and Powles 2007). The rainy conditions in 2017 favored the between wheat and weed biomass production. Weeds in annual

Figure 6. The total number of seeds produced in the season illustrated as the sum of retained seeds on the plants at wheat harvest and the seeds shed before wheat harvest for (A) Alopecurus myosuroides and (B) Apera spica-venti during the growing season of winter wheat. Standard error bars of the total seed productions are shown.

cropping systems are generally not very shade tolerant, and the 2018. Walsh et al. (2018a) also found that seed production of growth and development of A. myosuroides and A. spica-venti L. rigidum was reduced when it grew in competition with a higher are restricted under low light conditions (Gommers et al. 2013; biomass–yielding wheat crop. Increased crop competition will both Yasin et al. 2017). A typical response to crop-canopy shading increase HWSC efficiency and reduce weed seed production, because by shade-intolerant species is a more erect growth habit weed plants surviving the increased competition from the crop (Vandenbussche et al. 2005; Yasin et al. 2017). Therefore, the weed usually become taller, and therefore their seeds will be easier to seed heads will be produced higher in the crop canopy and are eas- harvest (Yasin et al. 2017). Zimdahl (2004) also reported that weed ier to collect during crop harvesting (Walsh et al. 2018a). However, growth and weed seed production were positively affected by dry in our experiments, all seed heads were above 15 cm in both years, conditions and reduced competition from moisture-stressed crops. which may make it possible for a grain harvester to collect the Alopecurus myosuroides and A. spica-venti produced 3.5 and 4.7 seeds, but it is likely that some seeds may be spread and fall to times more seeds, respectively, in the dry season compared with the soil surface during the harvesting process. The number of the rainy season in our experiment. GDD to seed shattering varied between the 2 yr, showing that other The plants of A. myosuroides and A. spica-venti produced seeds factors like drought influence the physiological maturation of the on upright shoots, making it possible to collect most of the seeds plants (Figures 4 and 5). retained on the plants at harvest with a grain harvester. The average The fraction of the total seed production retained on number of seeds per plant produced in the growing season was A. myosuroides and A. spica-venti was 29.3% and 53.2% in 2017 2,145 and 3,435 for A. myosuroides and A. spica-venti, respectively. and 37.9% and 16.7% in 2018, respectively. For rigid ryegrass The average percentage of seeds retained on the plant was 33.6% (Lolium rigidum Gaudin), 80% and 96% seed retention at wheat and 34.9%, respectively. If a grain harvester removed or killed harvest have been reported in Australia (Walsh and Powles 2007) approximately 30% of the total seed production of these two and Spain (Blanco-Moreno et al. 2004), respectively. The level of aggressive grass weeds, it could contribute to reducing seed input wild oat (Avena fatua L.) seed retention has been reported to be to the soil seedbank. However, such methods cannot stand alone between 20% and 50% in Canada (Feldman and Reed 1974; and need to be combined with other weed control methods to Shirtliffe et al. 2000) and about 20% in the United Kingdom reduce weed pressure. A long-term investigation of the impact (Barroso et al. 1994). The level of seed retention for ripgut brome of collecting the seeds on weed infestation is required to assess (Bromus diandrus Roth) and wild radish (Raphanus raphanistrum L.) the effect of the HWSC technique for these grass species. Such was reported to be 40% to 50% in the United Kingdom (Howard research would enlighten us as to whether the seed shed before har- et al. 1991) and Italy (Balsari et al. 1994). In 2014, the seed retention vest would still produce a high infestation level in the fields in the in more than 100 fields in the United Kingdom infested with long term. A. myosuroides was studied during 4 wk before crop harvest. The study indicated that about 80% to 90% of the seeds were shed by Acknowledgments. This work was a part of the project 105 SWEEDHART— the commencement of the harvest of winter wheat, while seed reten- Separation of Weeds during Harvesting and Hygienisation to Enhance Crop tion was approximately 40% to 50% at the usual harvest time for Productivity in the Long Term. The activity was conducted under the Joint winter barley (Hordeum vulgare L.) and canola (Brassica napus L.) European Research Projects in the Field of Sustainable and Resilient in late July (Walsh et al. 2018b). The seed-shedding pattern of A. myo- Agriculture under ERA-NET Cofund FACCE SURPLUS 2015. We thank suroides indicates that HWSC systems will potentially have a greater Innovation Fund Denmark for financial support. No conflicts of interest have impact during canola and barley crop harvest than winter wheat har- been declared. vest. Naylor (1972) and Budd and Shildrick (1968) found that the growth and seed production of A. myosuroides were reduced more by the presence of wheat plants than by the same number of References A. myosuroides plants. We observed less biomass and seed produc- Aamisepp A, Avholm K (1970) Apera spica-venti in Sweden: occurrence, tion of A. myosuroides and A. spica-venti in 2017 than in 2018, biology and control. Pages 50–55 in Proceedings of the 10th British Weed indicating the positive effect of lower wheat crop competition in Control Conference. Brighton, UK: British Crop Protection Council

Downloaded from https://www.cambridge.org/core. Copenhagen University Library, on 02 Mar 2020 at 09:49:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/wsc.2020.7 6 Bitarafan and Andreasen: Seed production and retention

Andreasen C, Bitarafan Z, Fenselau J, Glasner C (2018) Exploiting waste heat Howard CL, Mortimer AM, Gould P, Putwain PD, Cousens R, Cussens GW from combine harvesters to damage harvested weed seeds and reduce weed (1991) The dispersal of weeds—seed movement in arable agriculture. Infestation. Agriculture 8:42 Pages 461–490 in Proceedings of the Brighton Crop Protection Andreasen C, Streibig JC (2011) Evaluation of changes in weed flora in arable Conference—Weeds. Lavenham, UK: British Crop Protection Council fields of Nordic countries based on Danish long-term surveys. Weed Res Jakobsen K, Jensen JA, Bitarafan Z, Andreasen C (2019) Killing weed seeds with 51:214–226 exhaust gas from a combine harvester. Agronomy 9:544 Andreasen C, Stryhn H (2008) Increasing weed flora in Danish arable fields and Kampe W (1975) The emergence dynamics of black grass (Alopecurus myosur- its importance for biodiversity. Weed Res 48:1–9 oides) and silky apera (Apera spica-venti) in the Palatinate in 1970 to 1974. Anonymous (1971) Landbrugsstatistik 1970 herunder gartneri og skovbrug. Gesunde Pflanz 27:133–138 Copenhagen, Denmark: Danmarks Statistik. 247 p Keshtkar E, Mathiassen SK, Moss SR, Kudsk P (2015) Resistance profile of her- Anonymous (2005) Landbrug 2004, Statistik om Landbrug, gartneri og bicide-resistant Alopecurus myosuroides (black-grass) populations in skovbrug. Copenhagen, Denmark: Danmarks Statistik. 251 p Denmark. Crop Prot 69:83–89 Anonymous (2009) Directive 2009/128/EC of the European Parliament and of the Koch W (1968) Environmental factors effecting the germination of some annual Council of 21 October 2009 establishing a framework for Community action to grasses. Pages 14–19 in Proceedings of the 9th British Weed Control achieve the sustainable use of pesticides. https://eur-lex.europa.eu/legal-content/ Conference. Brighton, UK: British Crop Protection Council EN/ALL/?uri=celex%3A32009L0128. Accessed: October 31, 2019 Massa D, Gerhards R (2011) Investigation on herbicide resistance in European Anonymous (2018) European Parliament resolution of 13 September 2018 on silky bent grass (Apera spica-venti) populations. J Plant Dis Prot 118: the implementation of the Plant Protection Products Regulation (EC) No 31–39 1107/2009 (2017/2128(INI)) http://www.europarl.europa.eu/sides/getDoc. Melander B (1993) Population dynamics of Apera spica-venti as influenced by cul- do?pubRef=-//EP//TEXTþTAþP8-TA-2018-0356þ0þDOCþXMLþV0// tural methods. Pages 107–112 in Proceedings of the Brighton Crop Protection EN. Accessed: December 13, 2018 Conference—Weeds. Brighton, UK: British Crop Protection Council Balsari P, Finassi A, Airoldi G (1994) Development of a device to separate weed Melander B (1995) Impact of drilling date on Apera spica-venti L. and seeds harvested by a combine and reduce their degree of germination. Report Alopecurus myosuroides Huds. in winter cereals. Weed Res 35:157–166 No. 94-D-062. Pages 562−573 in Proceedings of the 12th World Congress of Melander B, Holst N, Jensen PK, Hansen EM, Olsen JE (2008) Apera spica-venti the International Commission of Agricultural Engineers. Milan, Italy: population dynamics and impact on crop yield as affected by tillage, crop International Commission of Agricultural Engineers rotation, location and herbicide programmes. Weed Res 48:48–57 Barroso J, Navarrete L, Sanchez Del Arco MJ, Fernandez-Quintanilla C, Lutman Moss SR (2013) Black-grass (Alopecurus myosuroides): everything you really PJW, Perry NH, Hull RI (1994) Dispersal of Avena fatua and Avena sterilis wanted to know about black-grass but didn’t know who to ask. A patches by natural dissemination, soil tillage and combine harvesters. Weed Rothamsted Technical Publication. Harpenden, Hertfordshire, UK: Res 46:118–128 Rothamsted Research. 4 p Bates D, Maechler M, Bolker B, Walker S (2015) Fitting linear mixed-effects Moss SR (1983) The production and shedding of Alopecurus myosuroides Huds. models using lme4. J Stat Softw 67:1–48 seeds in winter cereals crop. Weed Res 23:45–51 Blanco-Moreno JM, Chamorro L, Masalles RM, Recasens J, Sans FX (2004) Naylor REL (1972) Aspects of the population dynamics of the weed Alopecurus Spatial distribution of Lolium rigidum seedling following seed dispersal by myosuroides Huds. in winter cereal crops. J Appl Ecol 9:127–139 combine harvesters. Weed Res 44:375–387 Raymond ATG (2011) Agricultural Seed Production. Cambridge, MA: CABI. Broster JC, Walsh MJ, Chambers AJ (2016) Harvest weed seed control: the 216 p influence of harvester set up and speed on efficiency on south-eastern Shirtliffe SJ, Entz MH, Van Acker RC (2000) Avena fatua development and seed Australia wheat crops. Pages 38–41 in Proceedings of the 20th shatter as related to thermal time. Weed Sci 48:555–560 Australasian Weeds Conference. Perth, Western Australia: Weed Society Szekeres F (1991) The development of Apera spica-venti. Bot Kozlemenyek of Western Australia 78:113–125 Budd EG, Shildrick JP (1968) Preliminary observations of competition between Taghizadeh MS, Nicolas MA, Cousens RD (2012) Effects of relative emergence Alopecurus myosuroides and grass seed crops. Pages 9–13 in Proceedings of time and water deficit on the timing of fruit dispersal in Raphanus raphanis- the 9th British Weed Control Conference. Brighton, UK: British Crop trum L. Crop Pasture Sci 63:1018–1025 Protection Council Vandenbussche F, Pierik R, Millenaar FF, Voesenek LACJ, Van Der Straeten D [DMI] Danmarks Meteorologiske Institut (2018) Vejr, klima og hav. https:// (2005) Reaching out of the shade. Curr Opin Plant Biol 8:462–468 www.dmi.dk/vejr/arkiver/maanedsaesonaar. Accessed: January 14, 2019 Vizantinopoulos S, Katranis N (1998) Management of blackgrass (Alopecurus Feldman M, Reed WB (1974) Distribution of wild oat seeds during cereal crop myosuroides) in winter wheat in Greece. Weed Technol 12:484–490 swathing and combining. Proceedings of the 1974 Annual Meeting of Walsh M, Newman P, Powles S (2013) Targeting weed seeds in-crop: a new Canadian Society of Agricultural Engineering. Laval University, Sainte- weed control paradigm for global agriculture. Weed Technol 27:431–436 Foy, Quebec, August 4−8, 1974 Walsh MJ, Broster JC, Aves C, Powles SB (2018a) Influence of crop competition Glasner C, Andreasen C, Vieregge C, Dikiy A, Fenselau J, Bitarafan Z, Shumilina and harvest weed seed control on rigid ryegrass (Lolium rigidum) seed reten- E (2018) Adaptations of harvesting methods and concepts in order to reduce tion height in wheat crop canopies. Weed Sci 66:627–633 weeds on agricultural fields and to gain potentially a so far unexploited bio- Walsh MJ, Broster JC, Schwartz-Lazaro LM, Norsworthy JK, Davis AS, mass feedstock. Pages 64–71 in Proceedings of the 26th European Biomass Tidemann BD, Beckie HJ, Lyon DJ, Soni N, Neve P, Bagavathiannan MV Conference and Exhibition. Copenhagen, Denmark: European Biomass (2018b) Opportunities and challenges for harvest weed seed control in global Conference and Exhibition cropping systems. Pest Manag Sci 74:2235–2245 Gommers CMM, Visser EJW, Onge KRS, Voesenek LACJ, Pierik R (2013) Shade Walsh MJ, Powles SB (2007) Management strategies for herbicide-resistant tolerance: when growing tall is not an option. Trends Plant Sci 18:65–71 weed populations in Australian dryland crop production systems. Weed Holm-Nielsen C (1998) Frø fra det dyrkede land. Forskningscenter Flakkebjerg. Technol 21:331–338 Copenhagen: Ministeriet for Fødevare, Landbrug or Fiskeri. 178 p Warwick SI, Black LD, Zilkey BF (1985) Biology of Canadian weeds. 72. Apera Holzner W, ed (1981) Ackerunkruter: Bestimmung, Verbreitung, Biologie und spica-venti. Can J Plant Sci 65:711–721 Ecologie. Graz, Stuttgart: Leopold Stocker. 175 p Yasin M, Rosenqvist E, Andreasen C (2017) The effect of reduced light intensity Holzner W, Hayashi I, Glauninger J (1982) Reproductive strategy of annual on grass weeds. Weed Sci 65:603–613 agrestals. Pp 111–121 in Holzner W, Numata MW, eds. Biology and Zerner MC, Gill GC, Vandeleur RK (2008) Effect of height on the competitive Ecology of Weeds. The Haque: Junk Publishers ability of wheat with oats. Agron J 100:1729–1734 Hothorn T, Bretz B, Westfall P (2008) Simultaneous inference in general Zimdahl RL, ed (2004) Weed–Crop Competition: A Review. Ames, IA: parametric models. Biom J 50:346–363 Blackwell. 198 p