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dc.contributor.authorEberwine, John Wrighten_US
dc.date.accessioned2014-03-14T21:20:18Z
dc.date.available2014-03-14T21:20:18Z
dc.date.issued1996-04-05en_US
dc.identifier.otheretd-10042006-143905en_US
dc.identifier.urihttp://hdl.handle.net/10919/39614
dc.description.abstractIn the summers of 1989 and 1990, researchers in Va. and Md. began to observe lateseason reductions in com vigor in areas treated with nicosulfuron or primisulfuron for postemergence johnsongrass control. Symptoms observed included chlorosis, reddening of the leaves and shortening of the internodes. The nature and time of symptom expression were consistent with those caused by maize chlorotic dwarfvirus (MCDV) and maize dwarf mosaic virus (MDMV) infection of com. It was hypothesized that postemergence johnsongrass control increased the incidence and severity of MCDV and MDMV in virus-susceptible corn hybrids due to increased feeding by vectors of these viruses on treated corn. Field experiments were conducted in 1991 and 1992 to evaluate the effect of postemergence johnsongrass control with broad casted nicosulfuron, postemergence directed imazethapyr, mechanical control and no control on virus disease incidence and severity in a virus-susceptible ('Southern States 565') and a virus-tolerant ('Southern States 844) corn hybrid. Visual injury evaluations taken 10 weeks after treatment showed that the virus-susceptible com hybrid sustained significantly more injury, averaged across johnsongrass control methods, than did the virus-tolerant corn hybrid. Within the virus-susceptible com hybrid, where johnsongrass was controlled, regardless of method, significantly more injury was observed relative to the nontreated check. Further, averaged across johnsongrass control treatments, the virus-tolerant corn hybrid yielded significantly higher compared to the virus-susceptible com hybrid. Experiments conducted in 1993 and 1994 utilized cages as a means of preventing insect movement from the infected johnsongrass to the crop. Blackfaced leafhopper evaluations suggested that the cages significantly reduced leafhopper movement from the infected johnsongrass to the corn, however complete exclusion was not achieved. Results of corn tissue assays showed that MCDV and MDMV were being transmitted, however no treatment differences were detected. Two experiments were conducted in 1994 to analytically test the hypothesis and to determine the time course of MCDV and MDMV double infection of corn tissue. Johnsongrass control treatments evaluated included broadcast nicosulfuron and no treatment. Postemergence johnsongrass control increased MCDV and MDMV incidence 9 to 21 days after treatment. Further, significantly more double infections of MCDV and MDMV were observed 14 to 21 days after treatment in experimental units receiving the nicosulfuron application.en_US
dc.format.mediumBTDen_US
dc.publisherVirginia Techen_US
dc.relation.haspartLD5655.V856_1996.E247.pdfen_US
dc.subjectnicosulfuronen_US
dc.subject(MDMV)en_US
dc.subjectmaize dwarf mosaic virisen_US
dc.subjectjohnsongrassen_US
dc.subject.lccLD5655.V856 1996.E247en_US
dc.titleEffect of postemergence johnsongrass control on MCDV and MDMV incidence and severity in field cornen_US
dc.typeDissertationen_US
dc.contributor.departmentWeed Scienceen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineWeed Scienceen_US
dc.contributor.committeechairHagood, Edward Scott Jr.en_US
dc.contributor.committeememberBrann, Daniel E.en_US
dc.contributor.committeememberStromberg, Erik L.en_US
dc.contributor.committeememberTolin, Sue A.en_US
dc.contributor.committeememberWilson, Henry P.en_US
dc.contributor.committeememberYoungman, Roger R.en_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-10042006-143905/en_US
dc.date.sdate2006-10-04en_US
dc.date.rdate2006-10-04
dc.date.adate2006-10-04en_US


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