Weed of the Month: Asiatic Dayflower

Published: May 17, 2010

Asiatic dayflower (Commelina communis) is an annual monocot but has a growth habit and flower that more closely resembles that of a dicot plant. Asiatic dayflower is a native of Asia that was introduced into the U.S. as an ornamental and has escaped cultivation to become a weed of no-till agronomic crops, landscapes, and other horticultural crops.

Figure 1. Asiatic dayflower seedlings are often mistaken as a grass soon after emergence but have much wider leaves with distinct parallel veins.

Figure 2. Asiatic dayflower in a no-till corn field.

Asiatic dayflower can have an erect growth habit but more commonly creeps along the ground and is capable of rooting at the nodes. The leaves occur alternately along the creeping stem and are ovate to lanceolate in outline, as much as 5 inches long and 2 inches wide. All leaves and stems are hairless, and ach leaf has a membranous sheath which encircles the base of the leaf and stem. The flowers of Asiatic dayflower consist of two, very distinctive large blue petals with one white petal below (Figure 3). Asiatic dayflower generally blooms from mid- to late-summer in Missouri, with each flower blooming for a single day (thus the name). Several authors have found that the seed of Asiatic dayflower are capable of germinating throughout the growing season and that the seed can also remain viable in the soil for more than 4 ½ years.

Figure 3. Asiatic dayflower flowers. Notice the two blue petals above and one white petal below.

Asiatic dayflower has become more noticeable in recent years in no-till fields throughout Missouri. It forms dense colonies that can cause severe yield losses in both corn and soybean. Few herbicides provide acceptable control of Asiatic dayflower in soybeans. Recently, weed scientists at Iowa State University have conducted a number of trials to identify treatments for the management of this species. This research has revealed that in soybeans, Firstrate, Sencor, and the Authority products are some of the only herbicides that will provide acceptable Asiatic dayflower control when applied as a preemergence treatment. Similarly, Firstrate or Cobra are some of the only conventional herbicides that will provide acceptable control of this species when applied as a postemergence treatment in soybeans, but applications must be made before this species reaches six inches in height. Glyphosate at standard rates in Roundup Ready soybeans or corn will usually only provide a minor degree of suppression.