Hemp Dogbane

Abstracts:

• Effect of Tillage System and Herbicide Application Timing on Hemp Dogbane Control in Corn. William S. Curran, Dwight D. Lingenfelter, and Edward L. Werner. 1998. Proc. NCWSS 53:75.
• Fall Versus Early Summer Applications for Control of Hemp Dogbane in Corn. W. S. Curran, E. L. Werner, and P. H. Craig. 1997. Proc. NEWSS 51:113.

Effect of Tillage System and Herbicide Application Timing on Hemp Dogbane Control in Corn. William S. Curran, Dwight D. Lingenfelter, and Edward L. Werner, 1998. Proc. NCWSS 53:75.

Hemp dogbane (Apocynum cannabinum L.) is a herbaceous perennial that frequently infests agronomic crops throughout the middle and eastern corn belt. The objectives of this research were to 1.) compare the effect of fall, spring, and no tillage on the control of hemp dogbane in corn and 2.) compare fall applied glyphosate to a postemergence herbicide application in corn for control of hemp dogbane. Three herbicide treatments and two or three tillage treatments were evaluated at a farm in central Pennsylvania having a long history of no-till and a severe infestation of hemp dogbane. The trial area was in wheat the previous year. The herbicide treatments included a.) glyphosate applied at 1.0 lb ai/A to hemp dogbane up to 40 inches tall in the vegetative stage of development in mid to late September, b.) primisulfuron plus dicamba (0.036 + 0.25 lb/A) applied in early June in corn to hemp dogbane up to 35 inches tall in the early to late bud stage of development, and c.) a sequential treatment of the previous two treatments (fall glyphosate followed by June primisulfuron plus dicamba). All treatments included a nonionic surfactant at the appropriate concentration. All herbicide treatments were applied with a ATV mounted CO2 sprayer at 10 gpa carrier and 40 psi. The tillage treatments included fall chisel plowing in late October followed by spring disking, spring chisel plowing in mid March followed by disking, and no tillage. The fall tillage treatment was not included the first year of the study. Hemp dogbane control was estimated using visual estimates of control, weed density, and weed biomass for a 12 to 16 week period following the June application. The experiment was repeated over time.

Hemp dogbane control ranged from 50 to 98% depending on treatment and year. Fall chisel plowing improved early season control in one of two years, but did not impact late season control of hemp dogbane. Spring chisel plowing increased hemp dogbane biomass in the absence of an effective herbicide in one of two years. Spring chisel plowing also reduced glyphosate performance in one year and primisulfuron plus dicamba performance in another. Spring chisel plowing plus primisulfuron and dicamba was the least effective treatment in one of two years, providing only 50% control. Glyphosate was more consistent than the early summer application across years and appeared to provide better control of perennial vegetative structures. The combination of fall glyphosate followed by primisulfuron plus dicamba in corn always provided greater than 90% control regardless of tillage system.

Fall Versus Early Summer Applications for Control of Hemp Dogbane in Corn. W. S. Curran, E. L. Werner, and P. H. Craig, 1997. Proc. NEWSS 51:113.

Hemp dogbane (Apocynum cannabinum L.) is an herbaceous creeping perennial that is native to North America. It is found throughout Canada, the United States, and especially the mid-Atlantic region. Hemp dogbane is a serious problem weed in both cultivated and noncultivated fields in many parts of Pennsylvania. Although crop reduction due to hemp dogbane varies, some research from Nebraska showed a 15% reduction in corn, 32% loss in sorghum, and 37% loss in soybean grain yield from uncontrolled infestations. In conventional tillage systems, hemp dogbane is rarely a serious weed problem. However, with the increase in conservation tillage systems and lack of effective selective herbicides, hemp dogbane has quickly become a serious problem.

In the fall of 1993, 1994, and 1995, experiments were established in Dauphin County, Pennsylvania to compare fall application of one or more systemic herbicides to postemergence applications in corn. Previous to the fall treatments, the hemp dogbane was allowed to regrow following either wheat harvest in early July or in a fallow field. All field locations had a history of no-tillage. Fall herbicide treatments in 1993 and 1994 included glyphosate at 1 and 2 lb ai/A, dicamba at 0.5 and 1 lb ae/A, dicamba plus 2,4-DLVE at 0.5 lb ae/A each, and glyphosate plus 2,4-DLVE or dicamba at 1 lb plus 0.5 lb/A. Herbicides were applied at two application timings either in early September or in early October. In 1995, only a single timing of glyphosate was applied in late September. Corn was planted no-till the following spring. Both years, a burndown herbicide plus a soil residual grass plus broadleaf program was applied prior to corn planting. Postemergence herbicide treatments in corn included dicamba or 2,4-D amine at 0.5 lb/A and primisulfuron plus dicamba at 0.018 lb ai plus 0.25 lb/A. Only dicamba plus primisulfuron was compared in the 1995 experiment. All herbicide treatments included a nonionic surfactant at 0.25% v/v in the spray mixture. In addition, the 1995 experiment compared the performance of the herbicide treatments in no-till and minimum-till (spring chisel plow) corn. Weed control evaluations included visual estimates of percent control (0 to 100 scale), weed density, and weed biomass.

The hemp dogbane infestation was severe throughout most of the corn in 1994 and 1996 and more variable in 1995. The treatments that included fall applied glyphosate were clearly visible in early summer showing good control (>85%) of hemp dogbane and several other perennial weeds present in the field. However, the emergence of new shoots in some treatments throughout the summer reduced the performance ratings by August. The addition of dicamba or 2,4-D to glyphosate did not improve overall performance on hemp dogbane in 1994 or 1995, although including 2,4-D did improve the control of dandelion. In general, dicamba and 2,4-D performance was less effective than glyphosate and increasing glyphosate rate did not improve control. The September and October timings produced similar results, although the September timing may have had a slight advantage in 1994 because of cold weather and a light frost just prior to the October application. In general, the post applications in corn were equal or less effective than the fall applications. In 1996, although control with primisulfuron plus dicamba was equal to fall applied glyphosate (>85% control), root bud growth was observed on the post corn treated hemp dogbane. Tillage did not influence the level of control in 1996, although more hemp dogbane shoots were observed in some chisel treatments in the mid-summer evaluation. The fall treatment followed by an additional post corn treatment provided some of the best control (> 90%) of hemp dogbane and should allow for better control of a number of perennial weeds.