Hemp Dogbane (Apocynum cannabinum L.)
Hemp dogbane is a perennial. Seedlings become perennial 5 to 6 weeks after emergence. The perennial creeping rootstocks persist many years in the soil.
Hemp dogbane seed germination is later than that of common lambsquarters and common ragweed, but new shoots develop from the rootstocks and begin emerging in April.
Seedlings emerge from 1" or less in fine-textured soils and less than 2" in coarse-textured soils. Shoots from root buds, however, can emerge from much deeper in the soil profile.
Production Average: Hemp dogbane plants produce from 800-12,000 seeds per plant. Each plant usually has 10 to 60 seed pods and each pod contains between 80-200 seeds.
Dispersal Mechanisms: Seeds are dispersed over long distances by wind. Creeping rootstocks are fragmented by tillage and are spread through the field.
Longevity: The seed of hemp dogbane is not persistent and survives less than 6 months in the soil. The rootstocks are very persistent in the soil because, in one growing season, they will grow a depth of 6 feet and spread up to 10 feet.
Dormancy: There is very little seed dormancy. More than 75% of the seeds germinate the year they are produced.
Hemp dogbane is very competitive. It has been shown to reduce corn yields 8-10% and soybean yields up to 40%.
Preferred Soil / Field Conditions:
This weed prefers low-lying wet area, but can grow in dry upland soils.
No information is available at this time.
Tillage: Uprooting, chopping, and burying the hemp dogbane rhizomes will control this weed. This is why it is less of a problem in tilled cropping systems.
Rotary hoeing: Rotary hoeing is not effective on perennial hemp dogbane. It is, however, very effective on new seedlings less than 1/4" in height.
Flaming: This is not an effective means of controlling perennial hemp dogbane plants.
Crop rotation: Repeated mowing suppresses hemp dogbane. Therefore, including a forage in the rotation helps with control. Small grains reduce the competitiveness of hemp dogbane, though patches of this weed will grow. Combine around patches then either till or treat with herbicide in August or September.
Planting date: Planting date has no effect on managing hemp dogbane.
Application timing and effectiveness: Many herbicides control hemp dogbane in the seedling stage, but few are effective on it once it becomes a perennial. Timing of application is important for control.
For more specific information regarding control with herbicides go to the Hemp dogbane section of the MSU Weed Guide for Field Crops in the Publications section.