Wild Four-O'Clock (Mirabilis nyctaginea) - J. Doll

Wild Four-O’Clock (Mirabilis nyctaginea) Jerry Doll Wild four-o’clock is a vigorous perennial weed that is becoming more common in cropped land in several states. There are more than 300 species in the Four-O-clock plant family with most found in the tropical Americas. In the tropics and Orient, other members of this family are used for medicinal uses, and as a cosmetic or jelly dye, but any economic uses of wild four-o’clock are lost or remain to be discovered (Kantrud 1995). Wild four-o’clock is native to North America and its original area of distribution was from Texas to Saskatchewan, Canada (Kantrud 1995). It is now found to the east coast of the USA. The genus name is from the Latin word for “wonderful” and the species name is from the Greek word nyct for “night.” This species is called “wild” four-o’clock to distinguish it from the ornamental species of four-o’clocks that have larger flowers. Habitat/Spread Wild four-o’clock is common along roadsides and railroad embankments and in fence rows, prairies, meadows, pastures and waste areas. Plants seem to thrive in grazed areas of North Dakota rangeland because seedlings establish where wildlife and livestock have trampled or animals have burrowed. Its movement from the western plains eastward was tracked in an interesting fashion: by observing the distribution of an insect that feeds only on wild four-o’clock: the coreid (Catorhintha mendica Stal) (Hoebeke and Wheeler 1982). The insect moved steadily eastward as wild four-o’clock became established along railroad right-of-ways in the 1880s and early 1900s. Wild four-o’clock spread eastward as a result of the shipment of agricultural products to eastern cities via the newly complete rail system in the 1850s. Wild four-o’clock grows readily on railroad right-of-ways while many species do not so there was little competition to slow the growth and spread of this invasive species. The insect’s arrival in Wisconsin and Minnesota is documented to be as early as 1910 (Hoebeke and Wheeler 1982). It has now found from Lake Eire and on to the Atlantic coast. This is consistent with the observation of wild four-o’clock along the interstate system of Wisconsin and probably other states as well. Description Once established, wild four-o’clock has a very large taproot that is often 3 inches or more in diameter (Figure 1). Weed books describe the root as fleshy but it seems to be somewhat woody under Wisconsin conditions. Leaves are opposite, simple, heart-shaped (resemble a lilac leaf), 1 to 3 inches long and usually with a pointed tip (Figure 2). Plants grow 2 to over 3 feet tall and have erect, branched stems with conspicuous nodes that are particularly evident after leaf drop (Figure 3). Stems are often 4-sided but are not as square as those of plants in the mint family. Leaves are widely separated on the stem and have a short petiole. The inflorescence is an umbel of terminal clusters, each cluster with 1 to 5 flowers (Figure 4).
Figure 1: Roots of an old wild four o'clock plant	Figure 2: View of alternate leaves and stem of wild four o'clock

Figure 3: Stems of wild four o'clock after leaf drop showing swollen nodes	Figure 4: Inflorescense and individual flowers of wild four o'clock
Individual flowers are perfect, have no petals and are bell-shaped with pink to reddish purple sepals (calyx). Seeds are oblong, grayish-brown to yellow, warty or wrinkled with 5 ribs that are about 3/16 of an inch long. Wild four-o’clock is easily distinguished by the large, tough taproot; the opposite lilac-like leaves; branched, squarish stems; and the pink to reddish flowers that open in the late afternoon and close in the late morning. Biology Seeds are highly viable and most germinate near the parent plant. Young taproots look much like miniature carrot roots. The root becomes large and well entrenched as plants age. Plants resume growth each spring from crown buds. Stems branch after plants are 1 to 2 feet tall and plants flower from June to September. Wild four-o’clock is named because the flowers open in late afternoon. An Iowa study found that indeed most flowers open between 3:30 and 4:00 p.m. (CST) (Cruden 1973). Flowers begin to emit a faint, sweet odor at twilight that attracts insects (Cruden 1973). Pollination is often done by nocturnal insects but self-pollination also occurs. Pollinated flowers close by 7:30 a.m. and non-pollinated ones by 11:00 a.m. This forces bees and other insects that visit flowers in the morning to visit those that are not yet pollinated. Single flowers produce only one seed but 65% of the flowers examined in Iowa had seeds (Cruden 1973). In the early summer, flowers are normal in the way they develop and pollinate; later in the season the flowers are smaller and do not open so that self-pollination is the only way seeds are formed. New plants arise primarily from seed but propagation from root segments is also possible. Management Moldboard plowing kills nearly all established plants and most wild four-o’clock infestations are in fields where this tool has not been used for many years. Thus it is very likely that the adoption of conservation and no-tillage systems is a major reason wild four-o’clock has become more common in field crops. Thus growing grain crops and using conventional tillage often kills established plants. As with nearly all taprooted perennials, repeated mowing not only prevents seed production but should weaken plants sufficiently so that many die during the winter months. No information on the activity of soil applied herbicides on germinating seeds of wild four-o’clock nor of postemergence herbicide activity on established plants of this weed was found. It is common experience that wild four-o’clock is not controlled by 2,4-D and is suppressed by chlorimuron (Classic) in soybeans. Research at the Univ. of Wisconsin found that dicamba (alone or with diflufenzopyr) provides reasonable wild four-o’clock suppression in corn. Our research found that wild four-o’clock plants can be effectively controlled in glyphosate resistant crops. The ideal system is to plant a glyphosate resistant soybean variety or corn hybrid in a no-till system, use a reduced rate of a soil-active herbicide along with the burndown herbicide, and apply 0.75 lb ae/A of glyphosate when wild four-o’clock plants are in the early flower growth stage. There is no need for higher glyphosate rates, a second herbicide nor a second application. However, a followup row cultivation could be done 7 to 14 days after application if desired. References Cruden, R,.W. 1973. Reproductive biology of weedy and cultivated Mirabilis (Nytaginaceae). Amer. J. Botany 60:802-809. Hoebeke, E.R. and A.G. Wheeler, Jr. 1982. Catorhintha mendica, a Great Plains coreid now established on the Atlantic Coast. Entomological News 93:29-31. Kantrud, H.A. 1995. Wild Four-O’clock. Native Wildflowers of the North Dakota Grasslands. Jamestown, ND: Northern Prairie Wildlife Research Center Home Page. http://www.npwrc.usgs.gov/resource/literatr/wildflwr/wildflwr.htm (Version 02DEC97). Stubbendieck, J., G.Y. Friisoe, and M.R. Bolick. 1994. Wild four-o’clock. pp. 368-9 in: Weeds of Nebraska and the Great Plains. Neb. Dept. Agric. Lincoln, NE. 590 p.


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