plants Review Biology and Management of Vulpia myuros— An Emerging Weed Problem in No-Till Cropping Systems in Europe Muhammad Javaid Akhter , Peter Kryger Jensen, Solvejg Kopp Mathiassen , Bo Melander and Per Kudsk * Department of Agroecology, Aarhus University, DK-4200 Slagelse, Denmark; [email protected] (M.J.A.); [email protected] (P.K.J.); [email protected] (S.K.M.); [email protected] (B.M.) * Correspondence: [email protected] Received: 6 May 2020; Accepted: 2 June 2020; Published: 3 June 2020 Abstract: Recently, Vulpia myuros has become a problematic grass weed species in parts of Europe. It is most common in no-till cropping systems. The inherent tolerance to several selective grass weed herbicides is of serious concern to the successful management of V. myuros in arable farming. Here, we reviewed the available knowledge about the biology of V. myuros to identify knowledge gaps and assess management efforts to identify best practices for control. V. myuros is a winter-annual species producing seeds with a short dormancy that can germinate at a wide range of conditions. Seed longevity in the soil is short. Little information is available on the influence of V. myuros on crop yield but some results suggest that yield losses can be significant. The findings provide a better understanding of the weedy characteristics of V. myuros and highlight that management strategies in Europe need to be diversified and integrate preventive and cultural control methods. Finally, we identify some of the management tools that should be considered to minimize the impact of V. myuros on European farming and future needs for research to develop sustainable integrated weed management strategies. Keywords: life cycle; vernalization; seed dormancy; seed germination; seed longevity; cultural weed control; non-chemical weed control; chemical control; integrated weed management 1. Introduction The genus Vulpia comprises more than 20 species [1], of which several are considered to be weeds of agricultural crops. Vulpia spp. are C3 plants and are native to Central and Southern Europe and the Mediterranean area [2], but are widespread and have been reported on most continents. Vulpia myuros (L) Gmelin, known as rat’s-tail fescue, and Vulpia bromoides (L) Gmelin, known as barren or brome fescue, are the most common weeds in the genus and will be referred to collectively as Vulpia spp. The two species are impossible to distinguish at the early growth stages but, as they develop, they can be separated morphologically by differences in panicle and lower glume structure (Figure1). Only V. myuros has been reported as a weed problem in Europe and therefore the focus of this review will be on this species. Plants 2020, 9, 715; doi:10.3390/plants9060715 www.mdpi.com/journal/plants PlantsPlants2020 2020, 9, 715, 9, 715 2 of 214 of 14 (a) (b) FigureFigure 1. 1.Panicle Panicle and and spikelet spikelet of ( a)) V. myuros andand (b (b) )V.V. bromoides. bromoides . Initially,Initially,V. myurosV. myuroswas was not not reported reported as as a a problematic problematic weed in in field field crops, crops, but but its its abundance abundance has has increasedincreased in in cereal cereal crops, crops, particularly particularly in in North North America America and and Australia, Australia, following following the adoption the adoption of no‐ of no-tilltill cropping systems systems [2,3]. [2,3]. In In Europe, Europe, V.V. myuros myuros isis a arecent recent weed weed problem. problem. The The first first occurrence occurrence in in agriculturalagricultural fields fields in in Denmark Denmark was was reported reported in in redred fescue ( FestucaFestuca rubra rubra L.)L.) for for seed seed production production in the in the latelate 1990s 1990s [4]. [4]. A A recent recent survey survey of of grass grass weeds weeds inin grass seed seed crops crops revealed revealed that that V.V. myuros myuros hashas become become commoncommon in somein some regions regions of Denmarkof Denmark [5], [5], and and within within the the last last five five years, years, it has it has also also been been reported reported more 2 frequentlymore frequently in winter in cereals winter in cereals Denmark in Denmark and often and at densities often at densities of several of hundred several hundred plants/m 2plants/m[Melander, pers.[Melander, com.]. V. pers. myuros com.].is V. also myuros reported is also frequently reported frequently in winter in cereals winter in cereals France in [Bonin,France [Bonin, pers. comm.].pers. comm.]. Recently, V. myuros was also reported to be an upcoming weed problem in Romania in direct Recently, V. myuros was also reported to be an upcoming weed problem in Romania in direct seeded seeded winter oilseed rape [6], while in other countries, for example the UK, V. myuros is still winter oilseed rape [6], while in other countries, for example the UK, V. myuros is still considered a considered a minor weed problem [7]. minor weed problem [7]. In recent years, the area under no‐till cropping systems has increased throughout Europe [8]. This,In recent in combination years, the with area an under inherent no-till tolerance cropping to some systems of the most has increased widely used throughout graminicides Europe [9], is [ 8]. This,likely in combination the cause of with increasing an inherent problems tolerance in both to Denmark some of theand most Romania widely [6,8]. used The graminicides inconsistent [ 9], is likelyperformance the cause of herbicides, of increasing which problems provide consistent in both Denmark control of andother Romania important [6 grass,8]. The weed inconsistent species, performancemeans that ofpreventive herbicides, and which non‐chemical provide control consistent methods control will have of other to be important applied to grassprevent weed V. myuros species, meansfrom that infesting preventive fields. and non-chemical control methods will have to be applied to prevent V. myuros from infestingThe most fields. recent reviews on Vulpia spp. date back to the 1990s [2,10]. Recent problems with V. myurosThe most in parts recent of Europe reviews call on forVulpia an updatedspp. date review back summarizing to the 1990s the [2 ,10new]. Recentinformation problems that has with V. myurosbecomein available parts of about Europe this call grass for weed an updated species. The review objective summarizing of this review the is new to provide information insight that into has becomethe biology available and ecology about this of V. grass myuros weed, including species. the Theimpact objective on crop ofyield this and review quality, is toavailable provide control insight intomethods, the biology and andto translate ecology this of V. information myuros, including into sustainable the impact management on crop yield strategies and quality, for European available controlconditions. methods, We and also to suggest translate directions this information for future into research sustainable on the management biology and strategies management for European of V. conditions.myuros needed We also to suggestrefine management directions for strategies. future research The review on thealso biology includes and results management from studies of V.on myuros the closely related V. bromoides whenever relevant. In some countries, e.g., Australia, the two species often needed to refine management strategies. The review also includes results from studies on the closely occur together [11], and when this is the case, the term Vulpia spp. will be used. related V. bromoides whenever relevant. In some countries, e.g., Australia, the two species often occur together2. Biology [11], and when this is the case, the term Vulpia spp. will be used. 2. Biology 2.1. Botanical Description 2.1. BotanicalV. myuros Description has a hexaploid genome with 42 chromosomes [1]. Vulpia species were previously classified under the genus Festuca, but moved to a genus of their own because their cleistogamous V. myuros has a hexaploid genome with 42 chromosomes [1]. Vulpia species were previously flowers, long‐awned lemmas and annual growth habit contrasted with the typical Festuca attributes classified under the genus Festuca, but moved to a genus of their own because their cleistogamous of chasmogamous florets, lemmas with short awns and a perennial growth habit [1]. Festuca flowers,Stem long-awned length of lemmas V. myuros and varies annual considerably growth habit from contrasted 5 and up to with 75 cm the depending typical on theattributes growing of chasmogamousconditions. Leaf florets, sheaths lemmas are overlapping with short and awns slightly and hairy. a perennial Dense stands growth at habitearly growth [1]. stages have a tuftedStem appearance length of V.with myuros slender,varies erect, considerably and finely pointed from leaves, 5 and with up to visible 75 cm veins depending on the upper on the side. growing Leaf conditions.sheaths of Leaf V. myuros sheaths are are split overlapping with few hairs. and Inflorescences slightly hairy. of DenseV. myuros stands are 5 at to early 35 cm growth long, dense stages with have a tufted appearance with slender, erect, and finely pointed leaves, with visible veins on the upper side. Leaf sheaths of V. myuros are split with few hairs. Inflorescences of V. myuros are 5 to 35 cm Plants 2020, 9, 715 3 of 14 long, dense with green–purple color and 5 to 12 mm long spikelets with multiple florets per spikelet with 1 or 2 self-fertile stamens [1]. Seeds of V. myuros are 3.5 to 4.5 mm in length and 0.5 to 0.6 mg in weight [2,12,13]. Seeds of V. myuros attach easily to clothing, animal fur, wool and hairs [2,12,14]. The panicles are generally very narrow, slightly secondly positioned, partially enclosed in the leaf sheath and 5–35 cm long. The lower glume is 0.4–2.5 mm long, and is one tenth to two fifths the length of the upper glume.