Issue No. 10, Article 6/May 28, 2004
Pokeweed Biology and Control in Corn and Soybean
Common pokeweed (Phytolacca americana) is a perennial weed that has become more prevalent across Illinois in recent years. Pokeweed, also called pokeberry, pigeonberry, crowberry, and inkberry, is the only member of the pokeweed (Phytolaccaceae) family in the continental United States. It is native to the eastern U.S. The plant is rarely found in areas where temperatures fall below 5°F but thrives where they reach more than 68°F in summer. Distribution appears to be widespread, and common pokeweed is continuing to invade reduced-tillage fields. It prefers loamy soils and can easily be found in pastures, roadsides, fencerows, open woods, and wood borders.
Pokeweed has a large, fleshy root that when established makes control of the plant difficult. The stem and petioles of pokeweed are reddish colored. Leaves are green, quite large (up to 10 inches long), alternate, and smooth. Plants can reach heights of 2 to 8 feet freestanding but may extend taller if a supportive structure exists. The smooth, fleshy stems die back during the winter. Flowers are white or green and arranged in an elongated cluster (racemes). Pokeweed fruits are berrylike and black when mature. Birds eat the berries and then scatter the seeds, which explains why pokeweed is commonly found along fence lines and under trees where birds have roosted. Birds are also the culprits for introducing pokeweed into previously uninfested areas. Pokeweed seeds, which can remain viable for up to 40 years, accumulate in the soil until optimal germination conditions occur. Seedlings emerge in late spring to early summer, while perennial shoots emerge in early spring.
Pokeweed is considered a poisonous plant, but birds are immune to the poison. The poison found in pokeweed is concentrated in the leaves, berries, and roots. Young shoots contain a very low dosage of this poison and can be stripped of leaves and outside cuticle, then prepared similar to asparagus.
Pokeweed, like many plants that form taproots, generally does not tolerate intensive tillage practices. Common pokeweed is thus generally not a problem in crop fields exposed to tillage. In fact, one of the most effective ways to combat pokeweed is with mechanical controls, such as moldboard plowing and disking. However, with the increasing popularity of reduced- and no-tillage production practices, controlling pokeweed often requires using herbicides. Several soil-applied herbicides provide adequate control of pokeweed emerging as seedlings. However, there may not be enough residual herbicide activity to control established perennial plants; this leaves postemergence applications to control pokeweed. Table 3 lists postemergence herbicide options for control or suppression of common pokeweed in corn and soybean.
Keep in mind that it is often very difficult to achieve complete control of established (i.e., perennial) pokeweed plants with a single herbicide application. If pokeweed continues to be a management problem in the treated areas, intensive mechanical control methods may be necessary to get it under control.-- Dawn Nordby