Sugar cane, a C4 plant is an ideal candidate for yield estimates (correlations) via NDVI. However it is important to consider the correct timing. Evidence shows that 2 months preceding the beginning of harvest is the ideal time (beginning of March in Northern Australia).
Skyspec can assist you to develop long term data for your farm. Not just yield estimates that can assist with harvest planning, but plant heath surveys that can assist with improving of soils, improving drainage and improving irrigation, as well as precision application of nutrients and ameliorates.
See case studies links below
Cutting-edge agriculture research confirms that multispectral drone imagery is being used to optimize harvest yields for crops. https://www.pix4d.com/blog/optimizing-harvest-schedules-sugarcane