Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate


John O. Evans


To improve management and control of jointed goatgrass (Aegilops cylindrica Host.) on traditional winter wheat (Triticum aestivum L.) cropland, a better understanding of the effects spring crop and wheat planting date have on weed populations and wheat yield is needed. A study of the effects of safflower (a spring crop) and wheat planting dates (early vs late) was conducted over a 2-yr period. Long term effects will be examined over a 5-yr period. The effects these treatments had on yield, weed seed contamination, jointed goatgrass population density, and soil seedbank concentration were measured. Two identical experiments were initiated, the first beginning in 1996, the second in 1997.

In experiment one, initial plant counts showed similar numbers of jointed goatgrass plants in all treatments. In experiment two, initial spring plant counts showed increased numbers of jointed goatgrass in unplanted plots prior to planting safflower, and slightly reduced population densities in October-planted wheat when compared to September-planted wheat. Winter wheat yields were 25% and 35% higher in September-planted wheat than in October-planted wheat, in 1997 in experiment one, and1998 in experiment two, respectively. Crop contamination with jointed goatgrass propagules was four times higher in early vs late-planted wheat in 1997, and 36% higher in 1998. Jointed goatgrass plants in safflower were reduced 97% compared to preplan! counts in both experiments. In experiment one, 1998 fallow season plant counts showed 55% and 75% less jointed goatgrass in fallow safflower plots than in fallow plots of September- and October-planted wheat, respectively, with fallow plots of September-planted wheat having 46% less than fallow plots of October-planted wheat. Soil seed bank concentrations were highest at the 0-5 cm depth of October-planted wheat, which had nearly a 10-fold higher concentrations compared to safflower and September-planted wheat at this depth. There were no differences at depths below 5cm.

This study showed the use of safflower to be a very useful management tool for reducing jointed goatgrass populations. September-planted wheat, with similar jointed goatgrass populations, yielded higher, and had less contamination and was therefore more competitive with jointed goatgrass than wheat planted in October, observed through a reduction in jointed goatgrass propagule production. Planting wheat in October, for the purpose of controlling jointed goatgrass through additional tillage, proved ineffective. Jointed goatgrass population densities were not reduced in experiment one, and only slightly reduced in experiment two. The dramatic loss of yield, associated with the later plantings, far outweighs any benefits gained by delaying wheat planting.