Common weed seed size

Weed Seed: Ambrosia artemisiifolia (Common ragweed)

Secondary Noxious, Class 3 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs across Canada except in NU and YT (Brouillet et al. 2016 Footnote 1 ).

Worldwide: Native to North and South America, and widely introduced elsewhere including Europe, Africa, temperate and tropical Asia, Australasia and the Pacific Islands (USDA -ARS 2016 Footnote 2 ). Widely distributed in North America with both native and introduced populations present in the U.S. and Canada (Brouillet et al. 2016 Footnote 1 , USDA -NRCS 2016 Footnote 3 ).

Duration of life cycle

Seed or fruit type

Achene within a bur

Identification features

  • Bur length: 1.9 – 3.7 mm
  • Bur width: 1.5 – 2.8 mm
  • Achene length: 1.5 – 3.0 mm
  • Achene width: 1.5 mm

Shape

  • Bur and achene are obovate

Surface Texture

  • Bur is dull, woody

Colour

  • Bur is dark grey with purple streaks
  • Achene is brown

Other Features

  • Bur has a ring of several spines near top approximately 0.5 mm long and an apical spine approximately 1.5 mm long

Habitat and Crop Association

Cultivated fields, fencerows, pastures, shores, canals, quarries, railway lines, roadsides, wasteland and disturbed areas (FNA 1993+ Footnote 4 , Darbyshire 2003 Footnote 5 , CABI 2016 Footnote 6 ). Found in a range of both agronomic and horticultural crops, particularly in cereals and cultivated row crops (Basset and Crompton 1975 Footnote 7 , CABI 2016 Footnote 6 ). Often present as a dominant species in early succession of uncultivated areas (CABI 2016 Footnote 6 ).

General Information

Seeds of common ragweed are commonly found in stored and transported grains, and have been dispersed around the world as contaminants in seed and grain crops, including cereals, oilseeds and bird seed.

A single plant typically produces 3,000 – 4000 seeds, although up to 32,000 seeds per plant have been reported. Seeds remain viable for up to 40 years (CABI 2016 Footnote 6 ).

Similar species

Perennial ragweed (Ambrosia psilostachya)

  • Perennial ragweed burs are a similar size, obovate shape and grey colour as common ragweed.
  • Perennial ragweed burs have smaller spines, or only an apical spine that may be broken off, and may lack the purple streaks of common ragweed burs.
  • If the burs are removed, it is difficult to distinguish between common and perennial ragweed achenes.

Photos

Common ragweed (Ambrosia artemisiifolia) burs Common ragweed (Ambrosia artemisiifolia) burs and one achene Common ragweed (Ambrosia artemisiifolia) bur Common ragweed (Ambrosia artemisiifolia) burs

Similar species

Similar species: Perennial ragweed (Ambrosia psilostachya) burs Similar species: Perennial ragweed (Ambrosia psilostachya) bur Similar species: Perennial ragweed (Ambrosia psilostachya) bur wall partially removed showing achene

Footnotes

Brouillet, L., Coursol, F., Favreau, M. and Anions, M. 2016. VASCAN, the database vascular plants of Canada, http://data.canadensys.net/vascan/ [2016, May 30].

Darbyshire, S. J. 2003. Inventory of Canadian Agricultural Weeds. Agriculture and Agri-Food Canada, Research Branch. Ottawa, ON .

Bassett, I. J. and Crompton, C. W. 1975. The biology of Canadian weeds. 11. Ambrosia artemisiifolia L. and A. psilostachya DC. Canadian Journal of Plant Science 55: 463-476.

Cover crop seed preference of four common weed seed predators

Invertebrate seed predators (ISPs) are an important component of agroecosystems that help regulate weed populations. Previous research has shown that ISPs’ seed preference depends on the plant and ISP species. Although numerous studies have quantified weed seed losses from ISPs, limited research has been conducted on the potential for ISPs to consume cover crop seeds. Cover crops are sometimes broadcast seeded, and because seeds are left on the soil surface, they are susceptible to ISPs. We hypothesized that (1) ISPs will consume cover crop seeds to the same extent as weed seeds, (2) seed preference will vary by plant and ISP species, and (3) seed consumption will be influenced by seed morphology and nutritional characteristics. We conducted seed preference trials with four common ISPs [Pennsylvania dingy ground beetle ( Harpalus pensylvanicus ), common black ground beetle ( Pterostichus melanarius ), Allard’s ground cricket ( Allonemobius allardi ) and fall field cricket ( Gryllus pennsylvanicus )] in laboratory no choice and choice feeding assays. We compared seed predation of ten commonly used cover crop species [barley ( Hordeum vulgare ), annual ryegrass ( Lolium multiflorum ), pearl millet ( Pennisetum glaucum ), forage radish ( Raphanus sativus ), cereal rye ( Secale cereale ), white mustard ( Sinapis alba ), crimson clover ( Trifolium incarnatum ), red clover ( Trifolium pratense ), triticale (× Triticosecale ) and hairy vetch ( Vicia villosa )] and three weed species [velvetleaf ( Abutilon theophrasti ), common ragweed ( Ambrosia artemisiifolia ) and giant foxtail ( Setaria faberi )]. All four ISPs readily consumed cover crop seeds ( P < 0.05), but cover crops with hard seed coats and seed hulls such as hairy vetch and barley were less preferred. Our results suggest that farmers should select cover crop species that are avoided by ISPs if they plan on broadcasting the seed, such as with aerial interseeding.

Keywords

This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction

Invertebrate seed predators (ISPs) such as carabid beetles (Coleoptera: Carabidae) and crickets (Orthoptera: Gryllidae) are key drivers of weed seed destruction (Westerman et al., Reference Westerman, Wes, Kropff and Van der Werf 2003; Kulkarni et al., Reference Kulkarni, Dosdall, Spence and Willenborg 2015a) and the subsequent reduction of weed emergence (White et al., Reference White, Renner, Menalled and Landis 2007; Kulkarni et al., Reference Kulkarni, Dosdall and Willenborg 2015b). ISPs can consume seeds before seed dispersal (pre-dispersal predation) or once the seeds have been shed and are on the soil surface (post-dispersal). Multiple generalist seed predators contribute to post-dispersal predation, which is a form of biological control that can reduce weed populations (Crawley, Reference Crawley and Fenner 1992). Previous research has shown that landscape context (e.g., proximity to field edge) and farm-management practices (e.g., reduced tillage practices) both influence ISP activity density and weed seed predation rates (Trichard et al., Reference Trichard, Alignier, Biju-Duval and Petit 2013; Petit et al., Reference Petit, Trichard, Biju-Duval, McLaughlin and Bohan 2017).

In addition to field research, laboratory feeding assays have been used to determine weed seed preference by ISPs, and results determined in the laboratory often translate directly to field preference (Honek et al., Reference Honek, Saska and Martinkova 2006; Petit et al., Reference Petit, Boursault and Bohan 2014; Ward et al., Reference Ward, Ryan, Curran and Law 2014). In general, constraints such as ISP body size and mouthpart strength determine which seeds can be consumed (Honek et al., Reference Honek, Martinkova, Saska and Pekar 2007; Lundgren, Reference Lundgren 2009). Several species of carabid beetles such as Amara aenea DeGeer (Ward et al., Reference Ward, Ryan, Curran, Barbercheck and Mortensen 2011), Anisodactylus sanctaecrucis Fabricius (White et al., Reference White, Renner, Menalled and Landis 2007), Harpalus affinis Schrankl (Honek et al., Reference Honek, Saska and Martinkova 2006) and crickets such as Gryllus pennsylvanicus Burmeister (Carmona et al., Reference Carmona, Menalled and Landis 1999) and Teleogryllus emma Ohmachi and Matsuura (Ichihara et al., Reference Ichihara, Inagaki, Matsuno, Saiki, Yamashita and Sawada 2012) have been evaluated for seed preference. However, the Pennsylvania dingy ground beetle (Harpalus pensylvanicus DeGeer) has been the model ISP species for seed preference work. Lundgren and Rosentrater ( Reference Lundgren and Rosentrater 2007) found H. pensylvanicus preferred species with small, dense seeds with hard seed coats [e.g., redroot pigweed (Amaranthus retroflexus L.); mass ~0.33 mg; seed coat strength ~47.81 MPa] compared with large seeds [e.g., ivyleaf morning glory (Ipomoea hederacea L.); mass ~24.65 mg; seed coat strength ~3.95 MPa]. Ward et al. ( Reference Ward, Ryan, Curran and Law 2014) found H. pensylvanicus consumed 71% of presented giant foxtail (Setaria faberi Herrm.) seeds compared with Abutilon theophrasti Medik) seeds.

Though the material properties of seeds play a large role in determining seed preference, nutrient regulation has been proposed as another major factor of insect food selectivity (Behmer, Reference Behmer 2009). When multiple food sources are available, insects select those that optimize ratios of macronutrients such as lipids, carbohydrates and proteins. These nutrient ratios determine the health, development and evolutionary fitness of individual insects (Simpson et al., Reference Simpson, Clissold, Lihoreau, Ponton, Wilder and Raubenheimer 2015). Jensen et al. ( Reference Jensen, Mayntz, Toft, Clissold, Hunt, Raubenheimer and Simpson 2012) determined that the predatory carabid Anchomenus dorsalis (Pontoppidan) selected food to optimize a lipid-to-protein ratio of 0.36, which maximized the number of eggs a female could lay. Likewise, Harrison et al. ( Reference Harrison, Raubenheimer, Simpson, Godin and Bertram 2014) found that spring field crickets (Gryllus veletis Alexander and Bigelow) consume food sources that give a protein-to-carbohydrate ratio of 1 to 4.1 for males and 1 to 2.3 for females. Previous research has also shown how insects can maintain their required nutrient ratios by switching between nutritionally suboptimal but complementary foods (Behmer, Reference Behmer 2009).

Laboratory seed preference of ISPs is generally studied in no choice and choice trials, but quantified in many different ways. In no choice trials, seed from a single plant species is offered to a captive insect, whereas seed from multiple plant species is offered in choice trials. In no choice trials, Lundgren and Rosentrater ( Reference Lundgren and Rosentrater 2007) presented 0.25 g of seed for each plant species they tested, whereas Ward et al. ( Reference Ward, Ryan, Curran and Law 2014) presented nine seeds regardless of seed size. In their choice trials, Honek et al. ( Reference Honek, Martinkova, Saska and Pekar 2007) presented 15 seeds of large-seeded species [e.g., great burdock (Arctium lappa L.)] and 30 seeds of small-seeded species [e.g., common lambsquarters (Chenopodium album L.)], while Ward et al. ( Reference Ward, Ryan, Curran and Law 2014) standardized by seed number in their choice trials and offered three seeds each of velvetleaf, giant foxtail and common lambsquarters. Quantifying consumed seeds is also variable among researchers. Some authors consider a seed consumed when >50% has been destroyed (e.g., Honek et al., Reference Honek, Martinkova, Saska and Pekar 2007), and others consider a seed consumed if the seed coat is cracked and part of the endosperm is damaged (e.g., Carmona et al., Reference Carmona, Menalled and Landis 1999). Although methods vary in the literature, most ISP research has focused on assessing the ecosystem service of weed seed destruction and characterizing ISP ecology (Kulkarni et al., Reference Kulkarni, Dosdall, Spence and Willenborg 2015a).

Relatively little research has been conducted on the negative effects of weed seed predators such as carabid beetles and crickets on crop seeds. One group of crops for which seed predation might be particularly relevant is cover crops. Cover crops are increasingly used in the USA to improve soil health, suppress weeds and provide other ecosystem services (Singer, Reference Singer 2008; Schipanski et al., Reference Schipanski, Barbercheck, Douglas, Finney, Haider, Kaye and White 2014; SARE, 2016; Wayman et al., Reference Wayman, Kissing Kucek, Mirsky, Ackroyd, Cordeau and Ryan 2016). In the Northeast USA, a large portion, if not most, of the land that is cover cropped is in a crop rotation with corn and soybean and the cover crops are seeded after corn and soybean are harvested in the fall. However, cover crops are also used extensively in small grain, forage and specialty crop production. For example, some farmers ‘frost seed’ red clover into wheat in early spring, while other farmers seed sudangrass and buckwheat in mid-summer between early and late season vegetables (Mohler and Johnson, Reference Mohler and Johnson 2009). Interseeding cover crops into corn and soybean in mid- to late summer is also becoming more popular (Belfry and Van Eerd, Reference Belfry and Van Eerd 2016; Blanco-Canqui et al., Reference Blanco-Canqui, Sindelar, Wortmann and Kreikemeier 2017; Curran et al., Reference Curran, Hoover, Mirsky, Roth, Ryan, Ackroyd, Wallace, Dempsey and Pelzer 2018; Youngerman et al., Reference Youngerman, DiTommaso, Curran, Mirsky and Ryan 2018). In addition to drill seeding, cover crops are seeded by broadcasting with a fertilizer spreader or by aerial seeding with airplanes (Fisher et al., Reference Fisher, Momen and Kratochvil 2011; SARE 2016). The method used by farmers often varies with farming system (e.g., drill seeding is more common in grain production whereas broadcast seeding is more common in vegetable production) and farm type (e.g., aerial seeding is more common on larger compared with smaller farms). Seeds on the soil surface are much more likely to be consumed by ISPs (White et al., Reference White, Renner, Menalled and Landis 2007; Kulkarni et al., Reference Kulkarni, Dosdall and Willenborg 2015b), so cover crop seeds may be susceptible to ISP predation when they are broadcast. Wilson et al. ( Reference Wilson, Allan and Baker 2014) reported losses of 48–98% of aerially seeded cover crop seeds 1 week after seeding and hypothesized that seed predators (e.g., by insects, rodents and birds) were responsible for these losses.

Beyond seed placement (e.g., in furrow covered with soil compared with on the soil surface), the level of seed predation of cover crops will likely vary depending on a number of factors including the presence of seed predators, their activity levels and their seed consumption preferences. Given that ISP seed preference is likely based on seed size and seed coat strength, cover crops that are similar to preferred weed seeds could also be consumed. The goal of this study was to assess ISP seed preference for common cover crop species, and to compare their relative preference to common weeds that are known targets of ISPs. To quantify ISP preferences, a series of no choice and choice laboratory seed preference trials were conducted. We hypothesized that (1) ISPs will consume cover crop seeds to the same extent as weed seeds, (2) seed preference will vary by plant and ISP species, and (3) seed consumption will be influenced by seed morphology and nutritional characteristics.

Materials and methods

Laboratory experiments

Ten cover crop species and three weed species were used to test seed preference of four weed seed predators (Table 1). These plant species were selected because: (1) the cover crop species are used by farmers and the weed species commonly occur in cropping systems in the Northeast, and (2) they vary in several key seed traits including weight, size, compressive yield strength and oil and protein content. Weed seeds were collected from the Musgrave Research Farm in Aurora, NY (42°73′N, 76°63′W) in the fall of 2015 and kept in cold storage for the winter. Cover crop seeds were purchased from several seed companies including King’s ArgiSeeds (Lancaster, PA, USA) and Lakeview Organic Grain (Penn Yan, NY, USA). Germination of cover crop and weed seeds was tested prior to the preference trial to verify their viability, and all plant species had at least 60% germination. Dry seeds were used in all trials. Because size can influence seed viability in some species (Stanton, Reference Stanton 1984), which may affect ISP preference (Ward et al., Reference Ward, Ryan, Curran and Law 2014), within-species seed sizes were kept as similar as possible through visual inspection and careful seed selection for each experiment.

Table 1. Seed trait values for species included in preference trials

Seed length and width were determined by the average measurements of 50 seeds. Seed volume was estimated as the volume of a cylinder using: volume = π × length × (0.5 × width) 2 . Strength is the compressive yield strength (i.e., the amount of force per unit area required to break the seed), and was estimated from the literature (references below); strength for references 1–3 was reported in Newtons and converted to MPa based on our area measurements for each seed. Oil and protein are expressed as the % total seed weight. O:P is the oil-to-protein ratio of each seed species.

Common weed seed size

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