Introduction

Convolvulus arvensis, commonly known as Field Bindweed, is a well-known plant that has been recognized as being invasive in North America for more than 100 years already. This is because of its detrimental effects on agriculture, which led to its early recognition as an invasive weed. Once established, Field Bindweed is notoriously difficult to eradicate. Instead, most removal programs should focus on control rather than eradication. It is already a significant part of North American ecology, so we will never rid ourselves of this weed. However, new patches can be eradicated before they become too well-established. Any growth in natural areas, particularly nature reserves and parkland, should be eradicated where possible in order to preserve the native species also growing there. Agricultural lands, on the other hand, can focus on controlling this invasive pest to mitigate the damage they are causing.

Description of Convolvulus arvensis

Leaves & Stems

Convolvulus arvensis is a herbaceous perennial trailing or climbing vine. It grows from a very deep persistent root system that develops shoots from buds on the roots down to depths of 1 m. It has a main tap root that can grow from 0.5 – 3 m long. Other vertical roots from the main root may penetrate from 5 – 9 m deep, depending on the soil and site conditions. The roots also spread laterally in all directions from the main tap root allowing it to spread adventitiously throughout all of its length. Lateral roots are shallower and generally only penetrate down to 30 cm deep.

The stems are slender and grow from 20 cm to 2 m long and are either hairless or finely pubescent. Stems twine anticlockwise allowing them to climb over structures and other plants.

Leaves are alternate, have a petiole (leaf stalk), and vary significantly in shape and size. They may be lanceolate, ovate, or narrow-oblong and range in size from 1 – 10 cm long and 0.3 – 6 cm wide. The tips are acute, and the leaves themselves may be entire or hastate–sagittate (arrow-shaped) at the base and may be hairless or lightly pubescent.

Flowers & Fruits

Flowers of Convolvulus arvensis are axillary and may be solitary or found in cymes of 2-3 flowers on peduncles (flower stalks). They are subtended by bracteoles 2-4 mm long. The flowers have sepals that are free and obtuse in shape and 2.5 – 4.5 mm long. It has a funnel-shaped corolla with 5 radial pubescent bands. The corolla is entire and not divided into individual lobes, 1 – 2.5 cm in diameter and 1 – 2.5 cm long, and may be found in white or pink varieties. It has 5 stamens that are inserted in the corolla tube and a single style with 2 oblong stigmas.

Field Bindweed produces a capsular fruit that is globular or ovoid with a persistent style at the base. It breaks open irregularly and releases four seeds that are 3 – 5 mm in diameter, dark brown or black, with a granular testa (outer coating).

Toxicity

Convolvulus arvensis is considered mildly toxic. It contains tropane alkaloids that can have toxic effects on the autonomic nervous system and have been found to cause intestinal fibrosis in horses. The seeds are especially toxic compared to the rest of the plant.

Similar Species Frequently Confused With

Many, many plants are often confused with Convolvulus arvensis. By far, most of them belong to the Convolvulaceae family and have similar bell-shaped flowers. Occasionally people mistake the unrelated Oenothera speciosa or Evening Primrose for Field Bindweed with its pink flowers. However, this can easily be differentiated by the fact that its corolla actually has 5 overlapping petals and is not at all entire like Convolvulus arvensis. The other non-related plant that is sometimes confused with it is Fallopia convolvulus Black-bindweed or Wild Buckwheat of the Polygonaceae with similar leaves but reddish stems and small lobed flowers. The more closely related and similar-looking species can be differentiated as follows:

• Calystegia sepium (sometimes as Convolvulus sepium) Hedge Bindweed of the Convolvulaceae family, has a sub cosmopolitan distribution with several subspecies native throughout North America. It has pale matt green sagittate leaves that are arranged spirally rather than alternately on the stem. When in bud, the flowers are surrounded by green bracts that are tinged with crimson, and its flowers, when open, are much larger, from 3 – 7 cm in diameter. Its fruit is an almost spherical capsule.
• Calystegia subacaulis of the Convolvulaceae family is a narrow-range species endemic to the North and Central California Coast Ranges and the San Francisco Bay Area, where it is found in woodland and chaparral scrub habitat. In its range, it can be differentiated by its hairy stems and leaves and its short stems that grow no more than 20 cm long.
• Calystegia macrostegia Bellflower of the Convolvulaceae family also has a narrow range found along the Pacific coasts of southern California and western Mexico. Its leaves are large and triangular and are often more than 10 cm wide. It also produces longer stems to 9 m in length and larger flowers 2 – 6 cm in diameter.
• Calystegia spithamaea of the Convolvulaceae family is native to eastern North America, primarily the northeastern USA. Its stems are mostly erect rather than trailing or twining, its light green leaves are quite hairy, and its flowers are not entire and instead have 5 shallow lobes.
• Convolvulus equitans the Wounded Bellflower is native to the southern US and northern Mexico. It can be differentiated by its usually lobed rather than entire leaves and its corolla of similar size but with 5 distinct though shallow lobes, each with a very distinctly acute apex. The flower also has a distinct pink or purple throat giving it the common name of Wounded Bellflower.
• Calystegia silvatica Greater Bindweed is native to Europe but has been introduced to the eastern and western US and Canada. It can easily be differentiated by its larger leaves that are arrow-shaped and its very large flowers up to 9 cm in diameter that are always white and never pink.
• Calystegia purpurata Pacific False Bindweed is a narrow endemic found along the Pacific coast of California. It has lobed leaves that are triangular in shape and larger flowers up to 5 cm in diameter that vary in color from white to pink to purple or cream and often have purple stripes.
• Evolvulus sericeus Silver Dwarf Morning Glory of the Convolvulaceae family is native to the southern USA, Mexico, and parts of tropical Americas. It can easily be differentiated by its very small size, only about 30 cm tall, and the fact that it grows erect rather than a vine. It also has linear to narrowly lanceolate light green or gray-green leaves that are generally hairy.
• Calystegia soldanella the Dunebell is native to beaches of western North America, Europe, and East Asia. It is found growing only on beach sand dunes making it easy to differentiate by its location. Its leaves are also very thick, glossy, and fleshy, producing large singular pink flowers.
• Calystegia occidentalis Chaparral False Bindweed is native to California and Oregon, where it grows in foothills and montane habitats. It has small leaves up to 4 cm that are typically hairy, lobed, and arrow-shaped. It produces 1-4 flowers on a single stalk, and each flower is fairly large, from 2 – 5 cm in diameter, and is white, cream, or yellow in color but never pink.
• Bouchetia erecta of the closely related Solanaceae family is native to the gulf coast of the US. It is a much smaller plant, never more than 30 cm tall, and it has lanceolate leaves and lobed corollas containing bright yellow stamens.
• Ipomoea imperati  Beach Snowdrop of the Convolvulaceae family is native to the Americas but is restricted to beach sand dunes. Its white flowers are similar in shape but are usually larger and may be tinged with blue. Its leaves are highly variable in shape but are glossy and fleshy.
• Ipomoea lacunosa  Snowdrop of the Convolvulaceae family is native to eastern North America, mostly in the USA. It has a much smaller taproot, but the vines can grow to similar lengths, 2 m long. Its leaves are always large (8 – 9 c long) and are ovate when young but become cordate (heart-shaped) when mature, and they are always on long petioles (leaf stalks) at least 3 cm long. The similar-sized, usually white but occasionally pink flowers may or may not be shallowly lobed. It has distinctive pinkish or purple anthers on white filaments, and it produces large seed capsules that are spherical and hairy.

Native Distribution of Convolvulus arvensis

Field Bindweed is native throughout much of Europe and Asia in temperate, tropical, and Mediterranean regions.

Habitat Types Where Field Bindweed is Found

Convolvulus arvensis grows successfully in a wide range of temperate, tropical, and Mediterranean climates. It is very problematic for agriculture in the temperate zones between 60°N to 45°S latitude, though it also grows in tropical regions as well. It is a serious pest in wheat, barley, corn, legume, and sugar beet fields as well as vineyards and tree crops.

While it is known mostly as an agricultural weed, it also is frequently found in natural areas, particularly in riparian habitats and open communities such as meadows and grassland. They thrive in areas with cleared and disturbed ground, such as agricultural areas and fallow fields, as well as new construction, land clearing, roadsides, and waste areas.

Human Uses of Field Bindweed

Convolvulus arvensis has a number of medicinal properties. A decoction of the root may act as a diuretic and a laxative. Tea from the flowers and or the leaves has been used to treat fevers and wounds. Caution should be used, however, as taking too much or for too long could potentially cause blood in the urine and toxic effects on the autonomic nervous system. In small doses over short periods of time, it is considered safe.

The stems are sometimes used as twine for tying up plants and other things. While it works well as twine, its usefulness is short-lived, so it should not be used for long-term storage of things, for example. A green dye is sometimes made from the whole plant.

Distribution of Convolvulus arvensis in North America

The species was first brought to the US likely as a contaminant in seed though it was also intentionally planted in baskets. It was first reported in the wild in Virginia in 1739 and, by the 1800s, had already spread throughout the eastern seaboard. By 1838 it had made its way west to California.

In Canada, Convolvulus arvensis has been recorded throughout the southern provinces of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, and Prince Edward Island. So far, it has not been reported in Newfoundland or the northern territories.

In the USA, Field Bindweed is even more widespread. It has been reported in every state in the continental USA as well as in Hawaii. It is absent only in Alaska.

In Mexico, Convolvulus arvensis so far has been reported in Baja California Norte, Baja California Sur, Sonora, Sinaloa, Chihuahua, Coahuila, Nuevo Leon, Durango, Tamaulipas, San Luis Potosi, Jalisco, Zacatecas, Aguascalientes, Guanajuato, Queretaro, Hidalgo, Michoacan, Mexico State, Mexico City, and Puebla. Given that the climate is suitable for it in many other states on the Caribbean side and in the south, it is likely that its range is still spreading.

Eurasian Bindweed has been introduced on every continent except Antarctica.

How Field Bindweed Spreads

Convolvulus arvensis was first introduced to the Americas by accidental introduction as a contaminant in other seeds. It may have also been intentionally planted in flower baskets. Since it spread as a contaminant early in the days of European settlement, it has already invaded much of the habitable zones in North America suitable to its growth.

Short-distance dispersal occurs through contamination of its seeds in other plant materials, where it grows as a weed in fields with agricultural crops. Short-distance dispersal of seeds can also occur via water, clothing, animals, vehicles, and machinery.

Birds can also disperse the seeds short and long distances because the seeds can remain viable in the digestive tract for up to 144 hours making migratory birds an important source of long-distance dispersal.

Dispersal also occurs with poorly disposed of yard waste debris filled with seeds or simply cut plants and roots that can regenerate via fragments. Solarization of removed plant matter is critical to prevent further spread this way.

Habitats at Risk of Invasion in North America

Most habitats in North America at risk of invasion have already been invaded. These include any disturbed areas such as agricultural fields, pastures, roadsides, and waste areas. Its range in North America will likely continue to spread in parts of Mexico where it has not yet reached its potential or has not yet been accurately reported as already being there. As climate change continues its warming trend in northern latitudes, it seems likely that it will continue to spread northwards in the southern provinces of Canada and may, in some locations, particularly near the coast, even reach the southern parts of the Northern Territories.

Impacts of Invasion

Field Bindweed threatens agricultural crops where it has been found to compete for water and nutrients, resulting in reductions in yields anywhere in the range of 0 – 100%. While only studied in crops, it is logical to assume a similar threat to native plant communities. In addition to competition for water and nutrients, it is an aggressive grower and climbs over other vegetation, physically smothering it and reducing biodiversity in that way as well.

It has been reported to be mildly toxic to some grazing animals, horses in particular. However, sheep, pigs, and goats seem more resistant to the toxic effects.

Potential Benefits of Invasion

It does not supply any significant nutritional food sources for native or domestic species and threatens species richness. There are no potential benefits of its invasion.

Methods to Remove Field Bindweed

As always, prevention of invasive species introductions is the preferred method. However, in the case of Convolvulus arvensis it has already been well established throughout North America, so control becomes the next best option. Control, however, is made particularly challenging due to both the longevity of the seeds in the soil seed bank (20 or more years) and the ability of the plant to regenerate via fragmentation of the stems or roots.

Fortunately, no one appears to be selling Convolvulus arvensis, so deliberate introductions of new plants are not likely to happen. Sadly this is not the case with many invasive species. Perhaps because Field Bindweed is such a well-known pest plant and has been known as such for well over 100 years now, people have actually stopped intentionally planting it.

Physical Control of Convolvulus arvensis

Once already established, physical control is always the most effective means. Physical control is labor-intensive and time-consuming, but it usually causes the least amount of environmental damage. Eradication of Field Bindweed once well established is difficult to impossible, but control and mitigation can be achieved.

Physical methods to remove Field Bindweed generally involve removing mature individuals before they go to seed to reduce the amount of seed in the soil. Since seeds are resilient enough to last more than 20 years in the soil, this makes control particularly challenging. Each year ongoing monitoring will be needed to remove any new seedlings as they generate from the soil seed bank.

The other added factors that make the control of this plant particularly challenging are its ability to resprout after being cut down, as well as its ability to generate new plants via fragmentation. When mature individuals are removed, try to pull out as much of their extensive root system as possible. This includes their very long and deep taproot as well as the lateral roots it produces that generally remain in the top 30 cm of the soil. Use a weed puller or a shovel to dig the taproot. For lateral roots, try to trace them from the main taproot along the soil. Heavy or compacted soils make this challenging, but the more root you remove, the better.

Since it can resprout from any remaining fragments, this absolutely must be followed with ongoing monitoring several times throughout the growing season. This can be done via the cutting of new sprouts or the cultivation method. To use the cutting method, simply cut any shoots that are regenerating, being sure to cut about 8 cm below the soil surface and repeat this for several years. Eventually, fewer and fewer sprouts will regenerate until the food reserves in the root system are completely depleted, and they can no longer regenerate. The more frequent the cutting, the less the root system has a chance to restore any energy stores, and the less treatment time is required. At a minimum, 2-3 years of extensive treatments will be required.

Frequent cultivation is a popular method to deal with resprouting mature plants and new seedlings. If the area is cultivated with a hoe or using agricultural equipment every 14 days throughout the growing season, the Field Bindweed can sometimes be controlled in as little as 2 years. It is critical to return to the patch and cultivate every 14 days, however. If left too long, the new green leaves will supply more energy to the extensive root system and prolong the necessary treatment time.

Solarization of large patches is a less labor-intensive method, and it will both deplete the root reserves and destroy any new seedlings as they try to emerge. Cover the area with a large black or other dark tarp and weigh the tarp down, leaving it there for 3 – 5 years. With many invasive plants, 2 years is sufficient, but due to the extensive root systems of Convolvulus arvensis, a minimum of 3 years is absolutely necessary. Prematurely removing the plastic mulch will no doubt result in re-infestation. The area should also still be monitored around the tarp edges throughout the growing season to look for lateral roots that try to sprout new plants outside of the tarped area.

Disposal of Convolvulus arvensis Once Removed

All plant material, whether it has seeds or not, must either be burned or solarized. Even without seeds, Convolvulus arvensis can generate new plants via root and stem fragmentation, so all plant material must be destroyed before disposal to prevent new infestations from carelessly discarded plant waste. Burning is a quick and effective method to dispose of the waste. However, it is not allowed in all areas and certainly not in all seasons. The other option is to solarize the material. To solarize, put the shrubs under a thick black tarp or into thick black garbage bags and leave them in the full sun for a good 8 weeks at least to be sure that all seeds and fragments are no longer viable. Some sources recommend shorter solarization periods, but this varies with latitude, aspect, cloud cover, etc, so leaving as long as possible ensures complete sterilization of the plant debris. Once properly solarized, the material can then be discarded at your local dump but do still inform them of what the material is so that they can properly dispose of it.

Chemical Control of Field Bindweed

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species. Furthermore, it is often difficult to keep the chemical control method contained so that it does not directly affect any native species that are there during the application process itself. As a result, plots where chemical control is used usually show a decrease in species richness. On the other hand, in plots where only physical control is used, species riches significantly increases.

Furthermore, there are no chemical control methods that effectively target only Field Bindweed. Also, Field Bindweed has been shown to become herbicide-resistant in some cases after repeated application. Due to the physical nature of Field Bindweed, multiple applications are always needed.

Chemical control is not recommended.

Biological Control of Convolvulus arvensis

Biological control involves the use of a predator, herbivore, disease, or some other agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to only the target organism before releasing it into the environment. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day, there are still rats in Hawaii, but the mongoose has helped to decimate many native bird populations.

Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study. The use of biological control methods can never be used alone. They must be part of an integrated pest management approach.

Since we have so many native Convolvulus species in North America, and some of them narrow endemic species such as those in California in particular, biological control is not an option. Multiple biological control agents have been tested for Convolvulus arvensis, but so far, all of them have also impacted our native species.

Grazing can help control Field Bindweed, but cattle will not eat it, and horses should not eat it. Sheep and goats will eat it but prefer other plants, including native species. Pigs, however, seem to love the entire plant and will eat both the above-ground plant matter and the roots if given the time. If you have an area that needs to be controlled, build a fence around it. Then allow the pigs to graze unchecked for 2 years, and they should destroy all of the Convolvulus arvensis growing there. Using goats or sheep in a similar manner can also be effective. However, since sheep and goats do not eat the roots, they would need to remain fenced in the patch for 3-4 years instead of 2.

Integrated Pest Management & Ongoing Monitoring

Integrated management is always the best approach. In its simplest, most effective, and least impactful form, this involves physical removal methods, possibly biological control methods, replanting, and ongoing monitoring. Integrated management is required because the area needs to be monitored for returning sprouts or seedlings; otherwise, all the hard work done in removal could be wasted if the invasive species is allowed to regrow.

Replanting With Native Species is Crucial

In all cases of large patch removal, the site will need to be replanted immediately because the bare soil will allow the seed bank of Field Bindweed and other invasives in the soil to germinate and reinvade the patch they were removed from. A replanting program should already be planned and ready to implement immediately upon successful removal of Convolvulus arvensis. If you are just removing an isolated individual replanting with native species is generally not necessary as the native species around it will simply fill in the spot left behind.

Ongoing Monitoring is Essential

In all cases of invasive Field Bindweed removal, ongoing monitoring is absolutely essential. Regular monitoring programs should be put in place to ensure that any surviving individuals are removed so that the population is not able to recover. In the first 3 years, monitoring should be done every 2 weeks to ensure that resprouting plants are destroyed to deplete the energy reserves of their extensive root systems. After the first 3 years, monitoring can be cut down to 2-3 times per growing season to remove any seedlings that germinate or any rootstock still attempting to recover.

Monitoring is required whether the area is replanted or not. Do not assume that once replanted, Convolvulus arvensis will not still try to grow. Field Bindweed is aggressive and prolific and will outcompete planted vegetation if yearly monitoring is not put in place to remove young native plants before they have a chance to become established. Once the area is well established with mature native plants, a simple once-a-year monitoring program is sufficient to root out any new individuals that may try to pop up. And you get to view the successful rewards of your hard work!

References and Resources

CABI on Convolvulus arvensis https://www.cabi.org/isc/datasheet/15101

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

Fire Effects Information System on Field Bindweed https://www.fs.fed.us/database/feis/plants/vine/conarv/all.html

iNaturalist Plant Search https://www.inaturalist.org/home

USDA Plants Database https://plants.sc.egov.usda.gov/home

Willis, Lyrae (Unpublished).  Plant Families of North America.

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