Hophornbeam copperleaf is a summer annual weed in the Euphorbiaceae, or spurge, family. Hophornbeam copperleaf is also less commonly known as "three-seeded mercury" because the seed pod is divided into three chambers. Hophornbeam copperleaf may grow to as much as 40 inches in height and has distinctly toothed leaves. Hophornbeam copperleaf is primarily a weed of agronomic crops but can also occur along fencerows, in landscapes and in nursery crops.
Hophornbeam copperleaf seedlings have two round cotyledons that are slightly hairy (Figure 1). Hophornbeam copperleaf seedlings are often mistaken for velvetleaf or prickly sida (also called teaweed), but both velvetleaf and prickly sida have seedlings with one round and one heart-shaped cotyledon.
Mature hophornbeam copperleaf plants have leaves that are alternate, egg- or diamond-shaped, with finely toothed margins. Although many members of the spurge family emit a milky sap when broken, hophornbeam copperleaf does not. Mature hophornbeam copperleaf plants are sometimes confused with prickly sida but the leaves of hophornbeam copperleaf are usually much wider than those of prickly sida, and this species does not have small stipules (spines) in the leaf axils like prickly sida (Figure 2).
Hophornbeam copperleaf is monoecious, which means that male and female flowers occur on the same plant. All flowers are relatively inconspicuous. The male flowers occur on axillary spikes while the female flowers are most noticeable and occur on a long, terminal spike (Figure 3). As mentioned previously, hophornbeam copperleaf has seed pods that are divided into three chambers, and these pods split open at maturity. Hophornbeam copperleaf seed are only slighter more than 1 mm in diameter, pear-shaped, and have "dimples" on both surfaces (Figure 4). In research conducted by Horak et al., hophornbeam copperleaf growing alone could produce as many as 12,510 seeds per plant, while plants growing in competition with soybean produced 980 seeds per plant.
Hophornbeam copperleaf emergence can begin in late May to early June and can continue throughout most of the growing season. I believe one of the reasons we have seen an increase in the number of hophornbeam copperleaf infestations in Missouri over the past five years is its ability to germinate late in the season, sometimes well into August. This allows it to escape most herbicide applications completely or often the plants are so small at the time of the postemergence herbicide application that the spray droplets never come in contact with them.
Most of the available research conducted on the management of hophornbeam copperleaf in soybean has revealed that Authority First and other Authority products, FirstRate, and Boundary will provide good preemergence control while glyphosate, Cobra/Phoenix, and Flexstar are effective postemergence products. In corn, atrazine will provide a period of residual control but due to the extended germination potential, season-long control with a preemergence application of atrazine alone is unlikely. Postemergence applications of atrazine and crop oil, 2,4-D, Clarity, Distinct, or Status can also provide good control of hophornbeam copperleaf in corn.
REVISED: March 29, 2016