The affix ṭhañ comes optionally comes in the remaining senses after the word śarad when expressing illness or heat.,
Thus शारदिको रोगः 'the autumnal disease', शारदिक आतपः 'the autumnal heat or sunshine'.
Why do we say \when denoting sickness or heat\? Observe, शारदं दधि 'the autumnal curd'. This ठञ् debars the ऋतु अण् 4.3.16.,