Vol. 54—2000 - NorthEastern Weed Science Society

DOUBLE CROP CORN WEED CONTROL IN VIRGINIA
S. R. King, E.S. Hagood, and C.C. Kenley'
ABSTRACT
Double crop production of com (Zea ~s) for grain following the harvest of a
small grain is not currently practiced in Virginia Historical precipitation and
evapotransportation data indicate that delayed com planting could result in a higher
probability of moisture during critical periods of crop development. Double crop com
may also reduceeconomicriskas two cropswould beharvestedin thesame year. Field
experiments were conducted in three Virginia locations in 1998 and 1999 to determine
the herbicideinputsrequiredfordoublecropcom productionrelativeto those requiredin
full season no-till com production. Experiments were conducted in a split-plot,
randomized complete block design with cropping system as the main plot and herbicide
treatmentas the subplot. Herbicidetreatmentsincluded combinationsof nonselective
herbicides for no-till establishment and/or preemergence residual herbicides and/or
selective postemergenceherbicidesinbothproductionsystems. Glyphosatetolerantcom
was planted in all experiments and postemergence glyphosate treatments were also
evaluated. In each experiment,dependentvariablesincluded weed control by species
evaluatedthroughoutthe season,as well as weed biomassandcom yield evaluatedat the
end of the growing season. Generally.nonselectiveherbicideswere not requiredin the
double crop system where atrazinewas appliedas a preemergencetreatment,or where
selective postemergencetreatmentswere applied.Wherea significantproportionof the
infestationwas comprisedof perennialspecies, however, atrazinetreatmentswere not
sufficient in the double crop system. Postemergenceglyphosate treatmentsprovided
excellent broad spectrum weed control in this situation. In heavy annual grass
infestations, postemergenceglyphosate treatmentsprovided superiorweed control to
preemergencetreatmentsalone,andequivalentweed controlto treatmentsin which both
preemergenceand postemergenceherbicideswere applied Com yield responseto weed
control and cropping system variables varied significantly between the 1998 and 1999
growingseasons.Whereadequatelateseasonrainfallwas received,economicreturnfrom
small grain and com crops in the doublecrop system was higherthanthe returnin the
full-season system, particularlyin infestationswhere the double-eropsystem allowed
significantreductionin herbicideinput.
, 'Grad. Res. Asst., Prof., and Res. Spee. Sr., Dept, of Plant Path., Phys., and Weed
Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
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