We have previously described the biology and management options for several problematic weed species encountered by Illinois soybean and corn producers. The next weed species in this series is hophornbeam copperleaf (Acalypha ostryifolia). |
Hophornbeam copperleaf seedling.
Hophornbeam copperleaf is a summer annual species in the Euphorbiaceae family. This plant family, also referred to as the Spurge family, includes several other problematic weed species, many of which have a milky sap. Hophornbeam copperleaf, however, does not contain the characteristic milky sap of other Euphorbiaceae family members. It is indigenous to Illinois and most commonly found in the southern third of the state. Over the past 5 years, however, we have identified populations in cornfields and soybean fields progressively farther north in the state, and in 2000 we identified a population as far north as Tazewell County. Several other copperleaf species can be found in Illinois, and while most of these other species are not generally considered problematic in agronomic production systems, Virginia copperleaf (Acalypha virginica) can be a troublesome weed species in southern Illinois.
Hophornbeam Copperleaf Morphology and Biology
Hophornbeam copperleaf has pubescent cotyledons and true leaves with short hairs and finely toothed (serrated) margins.
Hophornbeam copperleaf seedling.
The leaves are simple and alternate and somewhat heart-shaped at the base. Additionally, a reddish coloration is often observed where the main leaf vein intersects the petiole.
Hophornbeam copperleaf vein coloration.
Hophornbeam copperleaf may sometimes be misidentified (especially during early vegetative development) as prickly sida (Sida spinosa). 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 and prickly sida.
Hophornbeam copperleaf is monoecious (male and female flowers on the same plant), with staminate (male) flowers produced on axillary spikes and pistillate (female) flowers produced on a long, terminal spike.
Hophornbeam copperleaf mature plants.
Seed pods of hophornbeam copperleaf are dehiscent (pods split open at maturity to release seed), and seeds appear to require warm temperatures for germination. A warm soil temperature germination requirement may suggest that this species is able to germinate and emerge later during the growing season. Emergence can begin in late May or early June and may continue for most of the remaining growing season. Additional flushes of hophornbeam copperleaf frequently appear following precipitation.
Hophornbeam copperleaf infestation.
A recently published experiment reported the average seed production of hophornbeam copperleaf plants growing alone (without competition) was approximately 12,518 seeds per plant, much greater than the average seed production (980 seeds per plant) when grown with soybean.
Hophornbeam Copperleaf Control
In general, DNA herbicides do not control hophornbeam copperleaf, and response to ALS-inhibiting herbicides is variable. We initiated a field research experiment in 2000 to evaluate several soil-applied and postemergence soybean herbicides for hophornbeam copperleaf control. Results from the experiment appear in Table 2 and Table 3. Six weeks after preemergence application, all rates of Authority, FirstRate, and Boundary provided good-to-excellent control, while most other soil-applied herbicides provided poor control (Table 2). Postemergence control was good to excellent with all rates of glyphosate and the high rate of Cobra and Flexstar (Table 3). Soybean injury can be a concern with Cobra, and loss of soybean leaves, coupled with precipitation and the later-emergence pattern of hophornbeam copperleaf, in some instances may allow additional hophornbeam copperleaf growth to occur.
Data on corn herbicides for hophornbeam copperleaf control are very limited. Atrazine, in previous work from Oklahoma State University in 1971, performed well, but present-day application rates may not provide sufficient residual control for a species that can emerge late in the growing season. Postemergence applications of atrazine and crop oil may also provide control, but again, application-timing restrictions may reduce the effectiveness of this treatment.
This season, we have again initiated field research to examine the effectiveness of several soybean and corn herbicides for hophornbeam copperleaf control. These experiments are located in Edgar, Macon, and Tazewell counties on producer fields with a history of hophornbeam copperleaf infestations. Preemergence and postemergence corn and soybean herbicide treatments will be evaluated to determine which of those products can provide effective hophornbeam copperleaf control. In addition to herbicide efficacy experiments, we also plan to conduct several biology/ecology experiments to help elucidate the growth characteristics of this species.--Aaron Hager and Christy Sprague