Field bindweed, Convolvulus arvensis, is a native of Eurasia and was first documented in California in 1884 when it was collected in San Diego. By the first quarter of the twentieth century, field bindweed was proclaimed the worst weed in California and many of the western states. It most likely arrived in the United States as a contaminant in farm and garden seeds. However, because of its flowers and climbing nature, some seeds were probably planted as ornamentals, either aas a ground cover, in hanging baskets, or on trellises. Field bindweed has been given many names including perennial morningglory, creeping jenny, bellbine, sheep-bine, and corn-bind.
The first two leaves (cotyledons) of a field bindweed seedling are nearly square with a shallow notch at the tip. Plants that arise from rhizomes (underground stems) lack seed leaves. The first true leaves are arrowhead shaped and have petioles (leaf stems) that are flattened and grooved on the upper surface.
Mature field bindweed plants have aarrowhead-shaped leaves that can be between 1/2 to 2 inches long, depending on environmental conditions. Mature leaves at the base of the stem are larger than the young leaves at the stem terminal. The flowers are trumpet shaped, white to ppink in color, and 1 to 1-1/2 inches wide. Field bindweed is a prostrate plant unless it climbs on an object for support. It is often found growing on upright plants, such as shrubs or grape vines, with its stems and leaves entwined throughout the plant and the flowers exposed to the light. Under warm, moist conditions, leaves are larger and vines more robust than under drought conditions. The root system has both deep vertical and shallow horizontal lateral roots. The vertical roots can reach depths of 20 feet or more. However, 70% of the total mass of the root structure occupies the top 2 feet of soil. Most of these lateral roots are no deeper than 1 foot. Experiments oon bindweed have shown that its root and rhizome growth can reach 2-1/2 to 5 tons per acre.
In contrast to field bindweed, the ornamental annual morningglory has a larger (2 inches wide), more showy flower that may be white to blue or purple in color, a thicker stem that is sometimes hairy, and heart-shaped leaves that are 1-1/2 inches wide and 2 inches or more long. The two species are easy to distinguish from each other.
Field bindweed is a hhardy perennial found throughout California below 5,000 feet elevation. It spreads from an extensive rootstock as well as from seed. Most parts of the bindweed roots and rhizomes can produce adventitious buds, which can create new roots and shoots. Roots capable of budding are found to depths of 14 feet. Fragments of vertical roots and rhizomes that are as short as 2 inches can form new plants. Lateral roots serve another important function. At about 15 to 30 inches from the parent plant, a lateral often turns downward, becoming a secondary vertical root, and sends out both roots and shoots from the turning point. By this means a single field bindweed plant can spread radially more than 10 feet in a growing season. This extensive underground network allows for overwintering without foliage, and it can persist for many years in the soil.
One to four dark brown seeds are produced in round, smooth, 1/4-inch capsules. An average plant produces about 550 seeds. Within 1 month after forming, the seed coat matures and becomes impervious to water. Seed that is 60 years old has been found to be alive, and the seed are commonly found in the soil seedbank. Once the seed ccoat is weakened, seed will germinate at temperatures of 41° to 104°F.
Drought tolerance is a characteristic of field bindweed. In California, it seems to prefer heavy clay soils rather than sandy soils. When water is withheld, bindweed competes better than most other plants. If an area is well watered, ornamentals may compete better than the bindweed. In the landscape, field bindweed will survive with sprinkler or drip irrigation. If there is no summer water, the plant reduces its seed production first and then reduces growth and leaf size, but some flowers and seed are still produced.
Field bindweed is one of the most persistent and difficult-to-control weeds in ornamentals, orchard and vine crops, and field crops. It has a vigorous root and rhizome system that makes it almost impossible to control with cultivation. Its seed has a long dormancy and may last in soil for up to 60 years. It has a climbing habit that allows the plant to grow through mulches. Field bindweed is also very drought tolerant and once established is almost impossible to control with herbicides.
If field bindweed is present, agricultural land is devalued and the weed precludes planting of certain crops such as onions, melons, aand tomatoes.
Control of field bindweed is not easy, and it cannot be accomplished with a single treatment or in a single season. Effective control requires prevention of seed production, reduction of stored carbohydrates by deep tillage of the root system, competition for light from other plants, and constant vigilance in removing top growth.
There are three practices that can reduce the possibility of introducing field bindweed. Purchase and plant clean seed and ornamental stock; remove any seedlings before they become perennial plants; and prevent any plants from producing seed. If topsoil is introduced to a site, it should be free of propagules and seeds. It is important to control new infestations when they are small, because spot control is least expensive and the most effective.
Experiments in some annual and perennial crops have demonstrated the effect of shade on bindweed growth. In these studies alfalfa, cereal grains, and corn reduced bindweed growth. Shrubs and trees should also reduce growth, especially if there is another planting under the trees and the bindweed is not allowed to climb above the foliage of these plants.
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