Weed of the Month: Hophornbeam Copperleaf

Published: July 7, 2011

Hophornbeam copperleaf (Acalypha ostryifolia Riddell), also known as three-seeded mercury, is a summer annual that may grow to as much as 40-inches in height with distinctly toothed leaves. Hophornbeam copperleaf is primarily a weed of agronomic crops, but can also occur along fencerows, pastures, wastelands, roadsides, and landscapes or nursery crops. Hophornbeam copperleaf is a herbaceous dicot plant in the Euphorbiaceae, or spurge, family but lacks the milky sap that is characteristic of most members of this family.

Figure 1: Hophornbeam copperleaf seedling.

Hophornbeam copperleaf seedlings have two round cotyledons that are slightly hairy (Figure 1). Seedlings are often mistaken for prickly sida (or teaweed), but prickly sida has one round and one heart-shaped cotyledon. The leaf margins of prickly sida are more coarsely serrated than those of hophornbeam copperleaf, and hophornbeam copperleaf does not have the small stipules (spines) in the leaf axils like prickly sida. Hophornbeam copperleaf emergence can typically occur anywhere from late-May through the rest of the summer months until the first frost.

Mature hophornbeam copperleaf plants have leaves that are arranged alternately along the stem, are egg- or diamond-shaped, and have finely toothed margins (Figure 2). Hophornbeam is monoecious, which means both male and female flowers occur on the same plant.

Flowers are inconspicuous but male flowers are found on axillary spikes while female flowers are observed on a long terminal spike. This weed is also known as three-seeded mercury because the seed pod is divided into three chambers which split open at maturity. Seed pods contain many seeds, with some studies reporting as many as 12,518 seeds produced per plant when grown alone and 980 seeds per plant when grown in competition with soybeans.

Figure 2: Mature hophornbeam copperleaf plant.

Hophornbeam copperleaf seems to be an increasing weed problem in Missouri, especially in soybean production fields throughout the state. Since this weed is capable of germinating throughout the summer, we often see infestations of this weed develop after post-emergence applications of non-residual herbicides like glyphosate have been made. On the other hand, even if this weed is emerged at the time of the post-emergence herbicide application, it may be so low in the canopy at the time of application that we fail to get adequate herbicide coverage on the leaf surfaces. For these reasons, an effective management program must consider the late-emerging tendency of this species.

Residual, soil-applied herbicides that include sulfentrazone (in Authority products), cloransulam (FirstRate, in AuthorityFirst, in Sonic), flumioxazin (in Valor products, in Envive) or metribuzin (Sencor, in Boundary, in Authority MTZ, etc.) have been shown to provide good to excellent control of hophornbeam copperleaf in soybeans. Post-emergence herbicides that should provide good control of emerged plants include fomesafen (Flexstar, Dawn, etc.), lactofen (Cobra, Phoenix), acifluorfen (Ultra Blazer), glyphosate (Roundup, etc.) or glufosinate (Ignite for use only in LibertyLink soybeans).