The effect of chaff collection on the combine harvester dispersal of wild oat (Avena fatua L.)
Shirtliffe, Steven J.
With herbicide resistant wild oat increasing in frequency, new weed management techniques must be explored which modify ecological processes to manage weed populations. The first objective of this research was to determine if chaff collection will reduce the dispersal of wild oat. Seed shed from wild oat was measured and the effect of chaff collection and seed shed was determined using a computer simulation model. Chaff collection results in a significant reduction in the dispersal distance of weed seeds by combine harvesters. Without chaff collection, combine harvesters can disperse wild oat seeds approximately 150 m. However, with chaff collection the dispersal is reduced to approximately 30 m. Wild oat and wheat display similar phenotypic development. The phyllochron interval is similar within locations. Plant development as measured by Zadoks plant development scale was different between wild oat and wheat but this difference was constant between years and locations. Seed shed occurs in wild oat during the ripening process of wheat. In an early harvest of wheat most of the weed seeds would still remain on the plant. A computer simulation model of harvest dispersal revealed that timing of harvest is the most important variable in wild oat patch expansion. A delayed harvest would occur when most of the weed seeds have been shed by the plant. Chaff collection and delayed harvest result in the least amount of wild oat patch expansion as determined through computer simulations. By delaying harvest most of the wild oat seeds would fall to the ground in the original patch and would not be available to be taken into the combine and dispersed. An early harvest which attempts to maximize harvest export of wild oat seed is the most best strategy to manage a spatially uniform wild oat wild distribution. The second objective was to determine if a wild oat patch displays fractal geometry. A portion of a wild oat patch was determined to be highly fractal. This supports a fractal theory of dispersal which explains how a weed can be both highly dispersed and patchy.