Vol. 54—2000 - NorthEastern Weed Science Society

COMPARISON OF WEED CONTROL SYSTEMS WITII HERBICIDE RESISTANT CORN
Q.R. Johnson, MJ. VanGessel, and S.K. Rick'
ABSTRACT
CropProtectioncompaniesarenow promotingweed controlsystemsthatarebuiltaround
herbicideresistantcom (Zea mays L.) hybrids. Sincethesetechnologiesarerelativelynew, little
is knownabouthow these systemscomparein termsof efficacy,yield, andrelativecost.
In 1999 a field experiment was established at the University of Delaware's Research and
Education Center to evaluate weed control systems that are being promoted by DuPont,
Monsanto, AgrEvo, and Cyanamid. For each company a preemergence (PRE) followed by midpostemergence
(MPOST) system (pRE fb POST) and a total early-postemergence (EPOST)
system were evaluated. Additionally,forMonsantoandAgrEvototalMPOSTsystemswere
included. The DuPont systems utilized a conventional com hybrid (Pioneer 3394, IIOcrm);
Monsanto systems utilized a glyphosate-resistant com hybrid (Dekalb DK589RR, 108crm);
AgrEvo systems utilized a glufosinate-resistant com hybrid (pioneer 34A55LL, llOcrm); and
Cyanamid systems utilized an imidazolmone-resistant com hybrid (Pioneer 33951R, II0crm).
Controlof common lambsquarters(Chenopodium Album L.), commonragweed(Ambrosia
artemisiijolia L.), large crabgrass (Digitaria sangutnalis (L.) Scop.), and ivyleaf momingglory
(Ipomoea hederacea (L.) Jacq)wereevaluatedvisually.Com yields andrelativesystem costs
were also compared.
AJI of the systems provided excellent common lambsquarters control (>93%). All of the systems
providedexcellent commonragweedcontrol(>91%)exceptCyanamidsystemsat both PREtb
POST (86%) and EPOST (76%). All of the systems provided very good to excellent control of
large crabgrass (>87%) except the DuPont system at EPOST (75%) and AgrEvo systems at both
EPOST (79%) and MPOST (65%). Many of the systems provided very good control of ivyleaf
momingglory(>84%). However,the DuPont,Monsanto,andAgrEvoEPOSTsystems provided
72%, 80%, and 79% ivyleaf momingglory control, respectively.
Yield reductionsattributedto reducedweed controlwere observedin the CyanamidPRE fb
POST system, EPOST systems from DuPont, AgrEvo, and Cyanamid, and the AgrEvo MPOST
system. Loweryields in all of the Monsantosystemswereattributedto com hybrid. This
hybrid'smaturityappearedto beshorterin thistest thanrelativematurityratingswould suggest,
andit was moreproneto lodging. Calculatednet returnswere lowerwiththe CyanamidPREfb
POST system, the DuPont and Cyanamid EPOST systems, and the AgrEvo MPOST system.
lExt. Assoc. andAssoc. Prof., Dept.PlantandSoil Sci., Universityof Delaware, Res. and
Educ. Ctr., Georgetown, DE 19947; and DuPont Agricultura1 Products
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