Convolvulus arvensis

Convolvulus arvensis can be confused with several other members of the Convolvulaceae (Morning-glory family). C. sepium is quite similar in appearance but can be distinguished by its larger leaves, flowers, and seeds, and by two large bracts inserted at the base of the flower. C. spithamaeus is shorter than C. arvensis and is erect with oval leaves. Several species of Ipomoea resemble C. arvensis, but they can be distinguished by their annual habit, capitate stigma, longer sepals, and blue or purple corolla. Polygonum convolvulus (Polygonaceae) can be confused with C. arvensis due to its arrow-shaped leaves and twining stems but is distinguished by its annual habit and clusters of small green flowers in the leaf axils.

Convolvulus arvensis is distributed throughout the world from latitude 60 degrees N to 45 degrees S and is found in temperate, tropical, and Mediterranean climates (Holm et al. 1977). It is found in dry to moderately moist soils and can survive long periods of drought. It grows best on fertile soils but persists on poor, rocky soils as well. It is a troublesome weed in cultivated fields, pastures, gardens, roadsides, and various native plant communities. It is found in large patches rather than as isolated plants and grows best in open communities in association with annual, biennial, and short-lived weeds (Weaver and Riley 1982).

The extensive root system of Convolvulus arvensis enables it to colonize new areas rapidly. The primary root is a taproot from which lateral roots develop. Most lateral roots die back each year, but some persist for several years, spreading horizontally. Buds arise on the lateral roots 50-100 cm from the parent taproot (Hickman and Swan 1983) and develop into rhizomes that have the potential to establish new crowns when they reach the surface (Weaver and Riley 1982). Excised root segments establish new roots and crowns more effectively than rhizome segments. The periods of best establishment are spring and late summer (Swan and Chancelor 1976), which coincide with the normal tillage period in agriculture. In general, root regeneration from vertical roots and rhizomes is probably more important than from lateral root segments.

Convolvulus arvensis has the potential for extensive lateral spread through regeneration from underground parts. Best (1963) found that a 5-cm section of a lateral root with buds could produce as many as 25 shoots four months after planting. Four months after transplanting, shoots can be produced up to 120 cm from the transplant. Shoots can be found nearly 300 cm away from the transplant after 15 months. Even young seedlings have the ability to resprout successfully. Swan (1983) cut bindweed seedlings 1 cm below the surface and studied subsequent regeneration. Regrowth occurred one to four weeks after plants were cut and was correlated more strongly with the age of the seedlings than with the aboveground biomass. All plants cut 44 days after emergence regenerated, but some plants cut only 20 days after emergence regenerated as well.

Convolvulus arvensis overwinters by means of its roots and rhizomes. Shoots are killed back to the crown by freezing temperatures, but hardened roots can withstand temperatures as low as -6 C (Weaver and Riley 1982). During the winter dormant period, food reserves in the plant remain stable as only a small amount is used in respiration. The reserves are gradually depleted during emergence and leaf development. Leaves return carbohydrates to the roots, but until the later growth stages, food is used faster than it is replaced (Swan 1980). The large carbohydrate reserve in roots contributes to the regenerative capacity of C. arvensis. Roots commonly grow to a depth of 2 m but have been found as deep as 9 m (Phillips 1978).

Natural variation in morphology and growth of Convolvulus arvensis is evidenced by different biotypes. Among biotypes are found differences in leaf morphology, floral characteristics, and biomass allocation to roots and shoots (DeGennaro and Weller 1982). Time of flowering can vary by as much as 23 days, with earliest flowering plants having 19 times more flowers per plant than the latest flowering plants. The number of root buds that develop into shoots can vary from 2% to 75% (Degennaro and Weller 1984b). Biotypes can also be distinguished by differences in resistance to herbicides. For a given rate of application of glyphosate, top kill can vary from 25% to 100%. Glyphosate application of 1.7 kg/ha killed 100% of a sensitive type, while an application of 3.4 kg/ha killed only 40% of a resistant type (DeGennaro and Weller 1984a). Biotypes appear to be self-incompatible, thereby insuring outcrossing and maximum genetic variability in the next generation.

Environmental conditions also affect the morphological and physiological characteristics of C. arvensis. Plants growing under low-moisture conditions have smaller leaves with more cuticular wax. Plants growing in semi-arid regions are usually more resistant to control than in humid regions because they have less leaf area, thicker cuticles, lower leaf-to-root ratios, and generally slower metabolic processes (Meyer 1978).

Seed production is variable and depends on environmental conditions. Seed set is usually greater in dry, warm weather and on dry, calcareous soils, and it is usually poor during rainy periods or in poorly drained soil (Whitesides 1979). Each seed weighs about 10 mg. The number of seeds produced per plant ranges from 25 to 300, although the spatial limit of a plant is sometimes difficult to determine (Weaver and Riley 1982). Seeds have a hard, impermeable seed coat. They generally fall near the parent plant but can be dispersed by mammals and birds after ingestion, by water, and as a contaminant in crop seeds (Holm et al. 1977).

Convolvulus arvensis seeds can remain viable in the soil for over 20 years (Timmons 1949). Seeds are able to germinate as soon as 15 days after pollination, and scarified seeds will germinate over a wide range of temperatures (Weaver and Riley 1982). Chilling greatly enhances germination by increasing seed coat porosity and enhancing for the exchange of gases and water. Seeds chilled at 5 C for 21 and 24 days had germination rates of 55% and 85%, respectively, as compared to 10% for unchilled seeds (Jordan and Jordan 1982).