Is tilling an effective way of controlling noxious weeds?

Not unless you have annual or bi-annual seed producing plants, and till before they produce seeds.  Tilling can actually profoundly increase the size and density of weeds if used on root spreading plants like Canada thistle and Leafy spurge because the individual root segments will grow into separate plants.  Tilling the soil can also invert the topsoil with sub soils, which may be of lesser quality soil.