Models of interference in monocultures and mixtures of wheat (Triticum aestivum L.) and quackgrass (Elytrigia repens (L.) Nevski.).

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Wilcox, Douglas Howard
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Quackgrass is the most serious perennial grassy weed of wheat in Manitoba. Field experiments and surveys investigating the nature and extent of interference in monocultures and mixtures of quackgrass and wheat were conducted over the years 1987 to 1989 at Portage La Prairie, Manitoba, Canada. Intraspecific and interspecific interference between spring wheat and quackgrass was investigated in the field using an additive series design consisting of five replacement series proportions at total stand densities of 75, 150, and 300 plants sqM. A revised synthetic no-interaction analysis determined that wheat was superior to quackgrass in both intraspecific and interpecific interference and that niche dedifferentiation was large. Quackgrass reproductive variable were less sensitive to interspecific interference than were vegetative variables. Surveys of commercial fields of spring wheat infested with quackgrass were conducted using a dynamic stratified random sampling design in which systematic samples were taken at approximately 30, 60 and 93 days after planting. Wheat yield loss, as a percentage of weed-free yield, (Yw%) was related to spring quackgrass shoot counts/m-2 (Qs) by a rectangular hyperbolic model of the form Yw% = 98.7(1-0.433(Qs)/100(1+(0.433(Qs)/193.7))). Wheat kernel weight was the wheat yield component most influenced by quackgrass infestation. In quackgrass populations the majority of new rhizome production occurred during wheat senescence and biomass partitioning to heads increased as quackgrass infestation increased. Allometric models of the relationship between quackgrass parts were site specific and generally became more accurate the later the sampling date. A set of models relating spring quackgrass infestation to yield losses in hard red spring wheat, flax, and polish canola were combined with allometric models in a multi-year spreadsheet (Lotus 1-2-3, v 3.1) model. Simulations run using the multi-year model demonstrated the potential of a spreadsheet model of assisting in weed control decisions.
quackgrass, wheat, interference, competition, mixture, replacement, survey, weed, allometry, model, Elytrigia, Triticum, Agropyron, repens
Wilcox, Douglas Howard, Ph.D., The University of Manitoba, February 1995, Models of Interference in Monocultures and Mixtures of Wheat (Triticum aestivum L.) and Quackgrass (Elytrigia repens (L.) Nevski.). 265 pgs.