Vol. 51—1997 - NorthEastern Weed Science Society

113
Fall V rsus Early SummerApplicationsfor Controlof Hemp Dogbanein Corn
W. S. Curran, E. L. Werner, and P. H. Craig)
ABSTRACT
Hempdogbane( pocynumcannabinumL.) is an herbaceouscreepingperennialthat is nativeto
NorthAmerica. t is foundthroughoutCanada.the UnitedStates,andespeciallythe mid-Atlantic
region. Hempd gbaneis a seriousproblemweedin bothcultivatedand noncultivatedfieldsin
many parts of Pe sylvania. Althoughcrop reductiondue to hempdogbanevaries,someresearch
from Nebraska s owed a 15%reductionin com, 32% loss in sorghum,and 37% loss in soybean
grainyield from controlledinfestations. In conventionaltillagesystems.hempdogbaneis rarely
a seriousweed p oblem. However,with the increasein conservationtillagesystemsandlack of
effectiveselecti herbicides,hempdogbanehasquicklybecomea seriousproblem.
In the fall of I , 1994,and 1995,experimentswereestablishedin DauphinCounty.
Pennsylvaniato omparefall applicationof one or moresystemicherbicidesto postemergence
applicationsin c rn. Previousto the fall treatments,the hempdogbanewas allowedto regrow
followingeither heat harvest in early July or in a fallowfield. All fieldlocationshad a historyof
no-tillage. Fall bicidetreatmentsin 1993and 1994includedglyphosateat I and 21b ailA,
dicambaat 0.5 d l lb aeIA, dicambaplus 2,4-DLVE at 0.5 lb aeIA each, andglyphosateplus
2,4-DLVBor di ba at l lb plus 0.5 IblA. Herbicideswereappliedat two applicationtimings
eitherin early S temberor in early October. In 1995,only a singletimingof glyphosatewas
appliedin late ptember, Corn was plantedno-till the followingspring. Both years,a bumdown
herbicideplus a oil residualgrass plus broadleafprogramwas appliedprior to corn planting.
Postemergence rbicidetreatmentsin corn includeddicambaor 2,4-Damineat 0.51blAand
primisulfuronpl s dicamba at 0.0181bai plus0.251b/A. Onlydicambaplus primisulfuronwas
comparedin the 995 experiment Allherbicidetreatmentsincludeda nonionicsurfactantat 0.25%
v/v in the spray ixture. In addition.the 1995experimentcomparedthe performanceof the
herbicidetreatm nts in no-tilland minimum-till(springchiselplow)corn. Weed control
evaluationsincl ded visualestimatesof percentcontrol(0 to 100scale),weeddensity,and weed
biomass.
The hempdogb e infestationwas severethroughoutmost of the corn in 1994and 1996and more
variablein 1995 The treatmentsthat includedfall appliedglyphosatewereclearlyvisiblein early
summershowin good control (>85%)of hempdogbaneand severalother perennialweeds
presentin the fi d. However.the emergenceof newshootsin sometreatmentsthroughoutthe
summerredu the performanceratingsby August The additionof dicambaor 2,4-Dto
glyphosatedid n t improveoverallperformanceon hempdogbanein 1994or 1995.although
including2,4-D id improvethe controlof dandelion. In general,dicambaand 2,4-Dperformance
was lesseffecti thanglyphosateand increasingglyphosateratedid not improvecontrol The
Septemberand tober timingsproducedsimilarresults,althoughthe Septembertimingmayhave
had a slightadv tage in 1994becauseof cold weatherand a lightfrostjust priorto the October I
application. In eneral,the post applicationsin com wereequalor lesseffectivethanthe fall
applications.In 996, althoughcontrolwith primisulfuronplus dicambawas equalto fall applied I
glyphosate(>85 control),root bud growthwas observedon the post corn treatedhempdogbane.
Tillagedid not i uencethe levelof controlin 1996,althoughmorehempdogbaneshootswere I
observedin som chiseltreatmentsin the mid-summer evaluation. The fall treatmentfollowedby
an additionalpo t corn treatmentprovidedsome of the bestcontrol(> 90%)of hempdogbaneand
shouldallowfo better controlof a numberof perennialweeds.
) Assoc. Prof. red Sci., Res. Tech., Dept. of Agron., and Ext. Agent. DauphinCo., The
PennsylvaniaS te University,UniversityPark. PA 16802.