Bedstraw weed seed

Catchweed Bedstraw, Galium aparine

Catchweed Bedstraw, Galium aparine
Galium aparine is a distinctive herbaceous annual weed with a number of common names including cleavers, bedstraw, catchweed bedstraw, grip grass, stickywilly, and others. This fast-growing plant in the madder famliy (Rubiaceae), native to the northern hemisphere (North America and Eurasia), occurs in all US states except Hawaii, and in most provinces of Canada and northern Mexico. It can grow in a variety of habitats, including forests and woodlands, meadows, prairies, disturbed areas, and cultivated crops. It is commonly found in low shrubby vegetation, arable fields, and in gardens with moist soils. It causes problems in crops during harvesting when bedstraw becomes tangled with the crop or equipment.
This plant supposedly has many medicinal uses. The dried and roasted fruits can used to make a coffee substitute (this plant is in the same family as coffee, Coffea spp.). The young leaves can be eaten raw or cooked.
The leaves of catchweed bedstraw are arranged in whorls
The leaves and stems of G. aparine have fine hook-like hairs (similar to Velcro ® ) that readily adhere to clothing and animal fur, giving rise to some of its common names. Because they cling to each other, the plants don’t mat down easily when used as a mattress filling, giving rise to the name bedstraw. The scratchy hairs can be mildly irritating to those with sensitive skin. The simple linear leaves are borne in whorls of six to eight along the square stems with few branches. The tip of each leaf has a sharp firm point.
Plants often can’t stand up on their own, so sprawl onto others for support.
Seeds germinate very early in the spring, to produce a gangly plant with long stems. Plants can grow up to 6 feet but can’t stand up on their own, so they often use other upright species for support, clambering over the other vegetation with the aid of hooked bristles at the stem angles. Left on their own, they remain low and sprawling, forming dense tangles only a foot or so in height, shading out any smaller plants they grow over. In some areas, this species grows as a winter annual, germinating in the fall, and overwinter as a small plant, to grow quickly in spring.
The tiny white or pale green flowers are born terminally or in leaf axils.
In early spring to summer, tiny, inconspicuous pale green or white flowers are borne in the leaf axils or terminally. Each inflorescence (a cyme) has 3 to 5 flowers. Each flower is only 2-3 mm across, with four petals. Once pollinated by flies or beetles, spherical fruits of two nearly round halves are produced. Each fruit half contains a single small, spherical, oval or kidney shaped seed. The gray to brown seeds are 1-4 mm in diameter and are covered with small tubercles. The hooked bristles create a burr, which is easily dispersed on animal fur or clothing. Individual plants produce 300-400 seeds, although some specimens will produce many more.
Hooked bristles on the seed capsule create a burr, which easily sticks to animal fur.
Seeds remain viable in the soil for only a couple of years. They survive passage through the digestive tracts of cattle, horses, pigs, goats, and birds, so bringing uncomposted manure into a garden may inadvertently introduce this weed.
Catchweed bedstraw is best controlled while still small.
This weed is not difficult to control if pulled or hoed out while small, before flowering and seed production commences. G. aparine has a shallow root system, with a branching taproot. However, it is weakly connected to the stem so that when weeding, the roots often remain behind (and can grow again) when the tops are pulled. The brittle stems break easily, so it is difficult to remove an entire plant intact. Nearby fragile plants may be damaged as it is pulled if its leaves or stems stick to the tender plants.
– Susan Mahr, University of Wisconsin – Madison

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Weed Seed: Galium verrucosum (Warty bedstraw)

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

Distribution

Canadian: Not present in Canada (Brouillet et al. 2016 Footnote 1 ).

Worldwide: Native to southern Europe and the Mediterranean (Tutin et al. 1976 Footnote 2 , Hanf 1983 Footnote 3 ). Naturalized in central Europe (Tutin et al. 1976 Footnote 2 ) and in North America, it has been introduced in Michigan (USDA-NRCS 2016 Footnote 4 ).

Duration of life cycle

Seed or fruit type

Schizocarp, divided into 2 fruits

Identification features

  • Fruit diameter: 2.0 – 3.0 mm

Shape

  • Fruit is spherical, slightly compressed dorsiventrally

Surface Texture

  • Fruit surface is densely covered with tubercles

Colour

  • Fruit is pale green to straw yellow

Other Features

  • Hilum is located on the ventral side, and is marked by a small knot of tissue

Habitat and Crop Association

Cultivated fields, in scrub and degraded grassland (Hanf 1983 Footnote 3 ).

General Information

Warty bedstraw seed has been introduced into Britain as a contaminant in imported caged bird food (Hanson and Mason 1985 Footnote 5 ). Historically, it was recorded to occur rarely in corn fields (Lindley 1835 Footnote 6 ).

Similar species

Cleavers (Galium aparine)

  • Cleavers are a similar size, a similar globose shape and bristles with an inflated base that appear similar to the rough surface of warty bedstraw.
  • Cleavers have tubercles that are white and translucent rather than the opaque yellowish tubercles of warty bedstraw. The hilum area is a deep hole rather than the tissue knot of warty bedstraw.

Photos

Warty bedstraw (Galium verrucosum) schizocarp and fruits Warty bedstraw (Galium verrucosum) fruit, inner side Warty bedstraw (Galium verrucosum) fruit, outer side

Similar species

Similar species: Cleavers (Galium aparine) fruits Similar species: Cleavers (Galium aparine) fruit Similar species: Cleavers (Galium aparine) fruit and tubercles

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].

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. and Webb, D. A. (eds.) 1976. Flora Europaea. Volume 4: Plantaginaceae to Compositae (and Rubiaceae). Cambridge University Press, Cambridge, UK .

Hanf, M. 1983. The Arable Weeds of Europe. BASF Aktiengessellschaft, Ludwigshafen, Germany.

Hanson, C. G. and Mason, J. L. 1985. Bird seed aliens in Britain. Walsonia 15: 237-252.

Lindley, J. 1835. A synopsis of the British flora: arranged according to natural orders. The second edition. Longman, Rees, Orme, Brown, Green, and Longman.

Catchweed bedstraw and false cleavers

Description: The two species are very similar in appearance. The seedling stem is green with purple or brown splotches. The first true leaves are elliptical or narrow, spine-tipped and arranged in spoke-like whorls of four or more. Cotyledons are egg shaped with notched tips and long stalks. The upper cotyledon surface is green and hairy. The leaf surface, margins and midvein on the underside have backwards curving, stiff hairs.

  • Catchweed bedstraw: Cotyledons are egg shaped, 0.24–1.25 inch long by 0.2–0.5 inch wide.
  • False cleavers: Cotyledons are 0.2–0.4 inch long by 0.08–0.16 inch wide.

Mature plants have four-sided, square, jointed stems that branch near the base and have backward curving bristles clustered near the leaf whorls that cause the weed to cling to neighboring objects. Leaves are in whorls of usually eight, but sometimes six. Leaves have a strong central vein and an indistinct stalk. Leaf edges and midveins are rough, and leaf tips are prickly. Roots are fibrous.

  • Catchweed bedstraw: Plants form loose, sprawling mats. Stems grow up to 5 feet long. The base of the stem bristles is round. Leaves are green, oval to lanceolate and 0.5–3 inches long by 0.1 inch wide.
  • False cleavers: Plants are stiffer, rougher and more branched than catchweed bedstraw and have stems up to 6.6 feet long. The base of the stem bristles is flattened. Leaves are linear, yellowish and are 0.5–2.6 inches long by 0.1–0.24 inch wide.

Individually stalked flowers are grouped in clusters arising from leaf axils. Flowers are four-petaled. Fruits are split into two identical parts, each containing one seed. The dry fruit (the apparent seed) is gray-brown, a rounded kidney shape and usually covered in short hooked hairs that cling to clothing and fur.

  • Catchweed bedstraw: Flowers are white and 0.08 inch in diameter. Seeds are 0.08–0.16 inch long.
  • False cleavers: Flowers are pale yellow to yellow-green but occasionally white and are 0.04–0.06 inch in diameter. Seeds are 0.1 inch long.

Similar species: Smooth bedstraw (Galium mollugo L.) is a rhizomatous perennial weed that largely lacks hairs except for the rough leaf margins. It has smaller leaves (0.4–1.1 inch long by 0.08–0.16 inch wide) than catchweed bedstraw. Many other, non-weedy species of bedstraw are present in most regions of North America. Carpetweed (Mollugo verticillata L.) has smooth leaves and stems, lacks square stems and has leaves that vary in size and shape within each whorl.

Taxonomic note: These two species are difficult to distinguish, and their weedy behavior is considered similar by farmers and weed professionals. However, there are sufficient differences in flower and fruit size, chromosome numbers and molecular markers to justify classification as separate species. Most of the research that supports the descriptions presented in this chapter was conducted on catchweed bedstraw and will be identified as such, but it should be understood as generally applicable to false cleavers as well. Where research specifically distinguished between these species, this will be noted explicitly in the specific section under discussion.

Management

Deep moldboard plowing (8–10 inches) can help suppress populations of these species. After plowing, seeds will be buried too deeply to emerge during the current season, and since the seeds usually die off quickly, most will be gone before they return to the surface with subsequent tillage. If you wish to avoid annual moldboard plowing, use this practice to bury seeds the spring after years with heavy seed production; then use conservation tillage practices in following years. This will allow extra years for the buried seeds to die. Because the seeds do not survive long in the soil, rotation into a hay crop like alfalfa can also greatly decrease seed populations.

Since catchweed bedstraw responds strongly to P, avoid accumulating excessively high P levels in the soil. If P levels are higher than necessary for good crop production due to regular use of manure or compost as an N source, increase use of legume cover crops for N and decrease applications of compost or manure.

Cultivation with a harrow or tine cultivator tends to increase germination of both species and can be used to help flush out seedlings that are then killed during preparation of a seedbed. Because seedlings often emerge from two or more inches, rotary hoeing is relatively ineffective, and tine weeding should be aimed at burial of seedlings just after emergence. In cereal grains a tine weeder can be used to comb these weeds out of the crop just prior to when grain stems elongate. When soil is dry, set the weeder to just graze the soil surface; although much of the plant will be left, the practice can shift the competitive balance in favor of the crop.

Since most seeds are retained on the plant at harvest of spring-planted crops, equipment designed to harvest and destroy weed seeds during crop harvesting operations would be effective at reducing populations of these species.

Ecology

Origin and distribution: Although catchweed bedstraw is native to coastal areas of eastern and western North America to the Aleutian Islands, the weedy races in agricultural fields appear to have been introduced from Europe. It presently occurs in most of the United States and southern Canada. It also is native to Eurasia and has been introduced into temperate areas worldwide. False cleavers is native to Europe and is widespread in Asia, Africa and North America. In North America, it occurs throughout the United States, southern Canada and into Alaska. Molecular analysis revealed that the predominant Galium species found in west Canadian fields is false cleavers and that these populations are closely related to each other and to European populations of the same species.

Seed weight: Mean population seed weights of catchweed bedstraw range from 3.7–16.9 mg. Mean population seed weights of false cleavers range from 1.6–2.8 mg.

Dormancy and germination: Germination behavior varies greatly depending on the local race, habitat and time of year the seeds are produced. Many, and sometimes all, of the seeds produced in agricultural fields are capable of germination immediately after falling from the plant. Seeds germinated in darkness just as well as in alternating light/dark conditions. Unlike most weeds, light inhibits germination and exposure to light induces dormancy. In some races, drying leads to dormancy. In others, dry seeds lose dormancy with time. Cold wet conditions will break dormancy, as will nitrates. Optimum temperature for germination of catchweed bedstraw varies considerably with country of origin, from 33–68°F. Catchweed bedstraw seeds produced in agricultural settings in Great Britain germinated at temperatures of 41–59°F, with optimum germination at 48–54°F. False cleavers has a slightly higher optimum temperature requirement of either a constant 72°F or alternating daily temperatures between 50°F–75°F. Germination of catchweed bedstraw was optimum at 40–60% soil moisture holding capacity, whereas false cleavers required a slightly higher optimum of 50–80%.

Seed longevity: Few seeds of catchweed bedstraw last longer than two years in the soil. In two six-year experiments in tilled grain fields, catchweed bedstraw seeds declined at 51% and 65% per year. In France, the annual mortality rate was 41% in untilled soil. One study showed the usual pattern of increasing survival with depth.

Season of emergence: Catchweed bedstraw exhibits a wide range of potential emergence periods, primarily in the fall and spring but sometimes also in summer, and in mid-winter in warmer regions. A dry autumn can delay peak emergence until spring. Seeds from two populations were collected in Turkey. In one population, seeds were collected in June, and seedlings from these seeds had two peak emergence periods per year in November and in April to June. Seeds from the second population were collected in September, and seedlings from these had one peak emergence period in June to August. Emergence patterns of false cleavers is generally similar to that of catchweed bedstraw, except that false cleavers is more sensitive to dry soil conditions than catchweed bedstraw, which is adapted to a wider window of soil moisture conditions. Once emerged, early growth rate of several populations of both species responded similarly to temperature and moisture conditions.

Emergence depth: Seedlings emerge best from anywhere in the top 2.4 inches of soil, but many can emerge from 4 inches or more. Emergence from a depth of 0.8–2.4 inches was higher than from the soil surface, partly because emergence of both species is enhanced by uniform soil moisture and declines with intermittent drying conditions as occurs at the soil surface.

Photosynthetic pathway: C3

Sensitivity to frost: Before flowering begins, the plants are very cold hardy. One study showed that they tolerate temperatures of at least -13°F, though another showed severe damage or death at 14°F or lower. The threshold temperature for frost tolerance appears to fluctuate with season, decreasing from 19°F in October to 1°F in December and then increasing to 28°F by April. After flowering begins, the plants are killed by a hard frost.

Drought tolerance: Catchweed bedstraw thrives in moist habitats and is not drought tolerant. One report indicated that false cleavers plants are more drought tolerant than catchweed bedstraw, but both species are rare in areas with low summer rainfall.

Mycorrhiza: Both presence and absence of mycorrhiza have been reported.

Response to fertility: Catchweed bedstraw is highly responsive to both N and P, and its dry matter production continues to increase with added P even at very high levels of P fertility. It responds most, however, when N and P are both applied. Increasing N fertility rates increases this weed’s competitiveness with wheat. It grows best at pH from 5.5–8.

Soil physical requirements: Both species thrive in a wide range of soil textures but prefer moist, fertile soils.

Response to shade: Catchweed bedstraw grows best in open conditions but can survive and reproduce in woodland habitats. It scrambles up onto crops by means of the prickles on the stems and leaves, thereby avoiding shade. This weed is highly adaptable to shade conditions by lowering respiration sufficiently to maintain a positive carbon balance. Plants produce more leaves at the expense of root production under shade conditions. Shade of an individual branch leads to death of the shaded branch with little shift in the growth pattern of other branches.

Sensitivity to disturbance: Uprooted plants readily reroot on moist soil. Little regrowth or seed production occurs if stems are removed during or after flowering.

Time from emergence to reproduction: Plants establishing in late summer and fall overwinter and flower from May to September and set seed from June to October. Plants establishing in the spring begin flowering about six weeks later. Generally, as the combination of temperature and day length increase, the number of days between emergence and flowering decreases. Seeds mature about one month after the flower opens.

Pollination: The flower structure normally ensures self-pollination, but a wide variety of insects visit the flowers, and occasional cross pollination may occur.

Reproduction: Plants typically produce 300–400 seeds but under favorable conditions may produce more than 1,500 seeds. When subject to competition from a vigorous grain crop, seed production is as low as nine seeds per plant in one study. Seed retention at spring wheat harvest in western Canada was variable, ranging from 62% to 95%, and 90% of seeds were situated at a height on the plant that could be harvested by combine.

Dispersal: The hooked hairs on the fruit coat help the seeds disperse on fur and clothing. Seeds are a persistent contaminant of crop seed, particularly canola in the Canadian prairies, and have been spread by humans worldwide. These species also commonly move in straw from infested crops and in combines. The fruits float and disperse along streams and irrigation canals. The seeds pass through livestock without loss of viability and are dispersed in droppings and with the spread of manure.

Common natural enemies: Larvae of the sawfly Halidamia affinis, the mirids Criocoris piceicornis, Polymerus nigritus, and P. unifasciatus, and the gall forming aphids Aphis galiiscabri and Galiomum langei are restricted to Galium species. Harvester ants (Messor barbarus) consumed 49% of catchweed bedstraw seeds on the soil surface between grain harvest and fall in Spain, but the rate of seed predation in North American fields is unknown.

Palatability: Although catchweed bedstraw has been used as a pot herb, it is also considered to be poisonous and unsuitable for people or livestock. The plant is very coarse, and consumption can cause a low-level poisoning. It is preferred by geese and can be used as a poultry feed. A coffee substitute can be made from seeds.

Weed Characteristics Summary Table

Catchweed bedstraw
Growth habit Seed weight (mg) Seed dormancy at shedding Factors breaking dormancy Optimum temperature for germination (F) Seed mortality in untilled soil (%/year) Seed mortality in tilled soil (%/year) Typical emergence season Optimum emergence depth (inches)
sprawling 4–17 No cms, ni 33–72 41 51–65 fall and spring 0.8–2.4
Photosynthesis type Frost tolerance Drought tolerance Mycorrhiza Response to nutrients Emergence to flowering (weeks) Flowering to viable seed (weeks) Pollination Typical & high seed production (seeds per plant)
C3 high low unclear high 6–10 4 self, can cross 350 & 1,500

Table Key

General: The designation “–” signifies that data is not available or the category is not applicable.

Growth habit: A two-word description; the first word indicates relative height (tall, medium, short, prostrate) and second word indicates degree of branching (erect, branching, vining).

Seed weight: Range of reported values in units of “mg per seed.”

Seed dormancy at shedding: “Yes” if most seeds are dormant when shed, “Variable” if dormancy is highly variable, “No” if most seeds are not dormant.

Factors breaking dormancy: The principle factors that are reported to break dormancy and facilitate germination. The order of listing does not imply order of importance. Abbreviations are:

scd = seed coat deterioration

cms = a period subjected to cold, moist soil conditions

wst = warm soil temperatures

at = alternating day-night temperatures

Optimum temperature range for germination: Temperature (Fahrenheit) range that provides for optimum germination of non-dormant seeds. Germination at lower percentages can occur outside of this range. The dash refers to temperature range, and the slash refers to alternating day/night temperature amplitudes.

Seed mortality in untilled soil: Range of mortality estimates (percentage of seed mortality in one year) for buried seeds in untilled soil. Values were chosen where possible for seeds placed at depths below the emergence depth for the species and left undisturbed until assessment. Mortality primarily represents seed deterioration in soil.

Seed mortality in tilled soil: Range of mortality estimates (percentage of seed mortality in one year) for seeds in tilled soil. Values were chosen for seeds placed within the tillage depth and subjected to at least annual tillage events. Seed losses are the result of dormancy-breaking cues induced by tillage, germination and deterioration of un-germinated seeds.

Typical emergence season: Time of year when most emergence occurs in the typical regions of occurrence for each weed. Some emergence may occur outside of this range.

Optimum emergence depth: Soil depths (in inches below the soil surface) from which most seedlings emerge. Lower rates of emergence usually will occur at depths just above or just below this range.

Photosynthesis type: Codes “C3” or “C4” refer to the metabolic pathway for fixing carbon dioxide during photosynthesis. Generally, C3 plants function better in cooler seasons or environments and C4 plants function better in warmer seasons or environments.

Frost tolerance: Relative tolerance of plants to freezing temperatures (high, moderate, low).

Drought tolerance: Relative tolerance of plants to drought (high, moderate, low).

Mycorrhiza: Presence of mycorrhizal fungi. “Yes” if present; “no” if documented not to be present, “unclear” if there are reports of both presence and absence; “variable” if the weed can function either with or without, depending on the soil environment.

Response to nutrients: Relative plant growth response to the nutrient content of soil, primarily N, P, K (high, moderate, low).

Emergence to flowering: Length of time (weeks) after emergence for plants to begin flowering given typical emergence in the region of occurrence. For species emerging in fall, “emergence to flowering” means time from resumption of growth in spring to first flowering.

Flowering to viable seed: Length of time (weeks) after flowering for seeds to become viable.

Pollination: “Self” refers to species that exclusively self-pollinate, “cross” refers to species that exclusively cross-pollinate, “self, can cross” refer to species that primarily self-pollinate, but also cross-pollinate at a low rate, and “both” refers to species that both self-pollinate and cross-pollinate at relatively similar rates.

Typical and high seed production potential: The first value is seed production (seeds per plant) under typical conditions with crop and weed competition. The second value, high seed production, refers to conditions of low density without crop competition. Numbers are rounded off to a magnitude that is representative of often highly variable reported values.

Further Reading

Defelice, M.S. 2002. Catchweed bedstraw or cleavers, Galium aparine L.—A very “sticky” subject. Weed Technology 16: 467–472.

Malik, N. and W.H. Vanden Born. 1988. The biology of Canadian weeds. 86. Galium aparine L and Galium spurium L. Canadian Journal of Plant Science 68: 481–499.

Taylor, K. 1999. Biological Flora of the British Isles. No. 207. Galium aparine L. Journal of Ecology 87: 713–730.

Tidemann, B.D., L.M. Hall, K.N. Harker, H.J. Beckie, E.N. Johnson and F.C. Stevenson. 2017. Suitability of wild oat (Avena fatua), false cleavers (Galium spurium), and volunteer canola (Brassica napus) for harvest weed seed control in western Canada. Weed Science 65: 769–777.

Wilson, B.J., K.J. Wright and R.C. Butler. 1993. The effect of different frequencies of harrowing in the autumn and spring on winter wheat, and on control of Stellaria media (L.) vill., Galium aparine L. and Brassica napus L. Weed Research 33: 501–506.

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