Vol. 51—1997 - NorthEastern Weed Science Society

34
EVAL ATION OF HERBICIDE PROGRAMS FOR MUGWORT CONTROL IN CORN
M.Y. Day, B.S. Hagood, Jr., and S.M. Johnson'
ABSTRACT
Fie d experimentswere conducted in 1995 and 1996 in Westmoreland County, Virginiato
evaluate h rbicide programs for the control of mugwort (Artemisia vulgaris L.) in field com (Zea
mays L.). I experiments were conducted using a randomized complete block design with four
replicatio on a Leaf silt loam soil of pH 6.2 and 1.5% organic matter content. Com ('Pioneer
3163') was planted in 76-cm rows at approximately48,900 seeds/ha on May 8, 1995 and May 25,
1996.Indi dual plots consisted of 4 com rows 7.6 m in length, where the inner two rows received
treatment d the outer rows served as borders. Herbicide applications were made with a CO 2 ­
pressurize backpack sprayer delivering210 llha of water at 220 kPa using flat fan spray tips. In
both exp . ents, the effects of two primary independent variables, herbicide treatment and
applicatio timing, were evaluated. Herbicide applicationtimings included preemergenceto com,
earlyposte ergence (5-6 leaf com), and late postemergence (10-15 leaf com). Mugwort heights in
1995 and 1996 were 5-15 and 5-10 em, 20-25 and 15-20 em, and 30-45 and 20-25 em for
preemerg ce, early postemergence, and late postemergence application timings, respectively.
Herbicide eatmentsincluded2,4-D, clopyralid,flumetsulamplus clopyralid,2,4-D plus clopyralid,
and 2,4-D plus clopyralid plus flumetsulam.One rate of 2,4-D was used, while varying rates of
clopyralid dlor flumetsulamwere evaluated.Dependentvariablesevaluatedincluded crop response,
mugwort ontrol, and com yield. All data were subjected to appropriate analysisof variance and
mean sep ation at the 0.05 significancelevel.
No herbicide treatment caused a significantreduction in com vigor in either 1995 or 1996.
Mugwort ontrol was highlydependent on herbicidetreatment, rate, and timingof application.No
treatment hichdidnot containclopyralidaffordedgreaterthan 58% mugwort control in either year.
Amongcl yralidcontainingtreatments,mugwort control varied as a functionof clopyralidrate and
timingof plication. Neither the addition of2,4-D nor flumetsulamto clopyralidprovided greater
mugwort ntrolthanthe controlobservedwith clopyralidalone. In 1995, applicationsof clopyralid
madeat th earlypostemergencetimingprovidedsignificantlygreater control than applicationsmade
at the earli or later timing,where the 0.15 kg/ha rate afforded approximately70% control and the
0.30 kglh rate approximately 85% control. In 1996, clopyralid applications made at the late
postemerg ce timingprovidedsignificantlygreater mugwort control than that observed with earlier
applicatio , where rates of 0.15 and 0.30 kglha again provided approximately70 and 85% control,
respectivel . In both studies,the timingof optimumsusceptibilityoccurred when mugwort was 20-25
em in hei 1.No significanteffects of herbicidetreatments on com stand were observed, and com
yield varie as a function of mugwort control.
Grad.Res. Asst,Professor, and WestmorelandCo. Ext. Agent, Dept. of Plant Pathol., Physiol.and
Weed Sci. VPI+SU, Blacksburg, Va 24061.