Posted: 22/04/2012 at 10:49
Thanks for your comments, much appreciated.
The actual tan coloured spots look to have a 'hard matt' finish and yes I did give the plants a foliage feed with a soluble fertiliser. I wonder if these spots are the result of undisolved particles landing and sitting on the leaf - or as suggested, sun scorch caused by the droplets? I will leave one leave with mark on and watch it and report back.
Thanks for helping.