Hemp dogbane is a tallgrowing, perennial broadleaf weed often mistaken for common milkweed. It spreads by seed and overwintering rootstock. In Ohio, hemp dogbane tends to appear in areas that have not been tilled for a number of years.
Noncrop/Fallow Areas. Glyphosate (3 lbs ae/A or 2% solution for spot treatment) or glyphosate + 2,4D (1.13 lb ae/A + 1 pint/A) can be applied when dogbane are in the latebud to flower stage of growth. Treatments following crop harvest or mowing should be delayed until weeds regrow to a mature stage. These treatments provide only partial control, but are currently the most effective treatments available. Growers should take advantage of any periods when fields are not planted with a crop to try to control dogbane.
Corn. Glyphosate (Roundup Ready corn) applied at 0.75 lb ae/A will suppress or control dogbane, but a second application may be necessary. Postemergence application of Exceed (1 ounce/A), Spirit (1 ounce/A), or Beacon (3/4 ounce/A) plus 1/2 pint/A of 2,4-D will provide the most effective suppression/control of dogbane in corn. Other postemergence treatments with activity include combinations of dicamba (1/4 to 1/2 pint/A) with Exceed, Spirit, Beacon, Permit (2/3 ounce/A), or Accent (2/3 ounce/A). Dicamba (1/2 to 1 pint/A) applied alone will suppress dogbane, with best results if dogbane plants are at least 8 inches tall. If corn is less than 8 inches tall, the higher rate can be applied. If corn is more than 6 to 8 inches tall, the use of drop nozzles is suggested to avoid corn injury. A second application may be necessary to control regrowth; apply when regrowth reaches a height of 8 inches.
Soybeans. Application of glyphosate (Roundup Ready soybeans) applied at higher labeled rates is the only effective postemergence treatment. A second application may be necessary. Late postemergence applications, when plants are in the bud to flower stage, will provide the most complete control of underground plant parts. For lateseason control in soybeans without tolerance to glyphosate, a ropewick or sponge applicator can be used to apply glyphosate when weeds are sufficiently taller than soybeans (weeds usually 3 to 4 feet tall). Wipe dogbane plants twice in opposite directions for best results.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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